Yup, it was the rings on the front bank.
03-20-2011, 07:49 AM
#1
Supporting Maxima.org Member
Thread Starter
iTrader: (29)
Join Date: Oct 2005
Location: Middleboro/Carver, Ma
Posts: 4,572
Yup, it was the rings on the front bank.
Figured I'd post up that I finally got a chance to pull apart a 3.5 that had bad oil consumption, the front pre-cat had been ruined so I kinda new but nonetheless it was still interesting to see how far out of spec it was........
I only measured one front & one rear cylinder, here's the specs:
Ring end gap service limit:
Top- 0.021"
Bottom- 0.031"
Rear bank:
Top- .018"
Bottom- .020"
Front bank:
Top- .055"
Bottom- .040"
It also needed a few valve seals, I beleive the car would occasional smoke on start-up but I'm not positive on that, I am positive that some of them were worn out- I could feel it when I pulled the valves from the head, not all but there was 3-4 that were definitely not right. Most of the oil consumption was from the rings though, as evidenced by all the blowby, it was quite a bit.
I still think Nissan bored the 3.5's out to much for a 4 bolt/cylinder head bolt pattern, I can see wear @ 4 corners on the liner that I've never seen on a 3.0. The walls were glazed to shlt as well. I didn't check the piston clearance, but I have no doubts that it was in spec.
If you own a 5.5 gen, rip the front pre-cat off ASAP. It's probably to late for most though, it was on my moms I35 @ 80K, I actually think it happened when it was brand new though. I broke it in myself, and for the first couple 100 miles that thing would occasionally make some ****ed up sounds, sounded like a mix between detonation/pinging & something pinging in the exhaust.
I only measured one front & one rear cylinder, here's the specs:
Ring end gap service limit:
Top- 0.021"
Bottom- 0.031"
Rear bank:
Top- .018"
Bottom- .020"
Front bank:
Top- .055"
Bottom- .040"
It also needed a few valve seals, I beleive the car would occasional smoke on start-up but I'm not positive on that, I am positive that some of them were worn out- I could feel it when I pulled the valves from the head, not all but there was 3-4 that were definitely not right. Most of the oil consumption was from the rings though, as evidenced by all the blowby, it was quite a bit.
I still think Nissan bored the 3.5's out to much for a 4 bolt/cylinder head bolt pattern, I can see wear @ 4 corners on the liner that I've never seen on a 3.0. The walls were glazed to shlt as well. I didn't check the piston clearance, but I have no doubts that it was in spec.
If you own a 5.5 gen, rip the front pre-cat off ASAP. It's probably to late for most though, it was on my moms I35 @ 80K, I actually think it happened when it was brand new though. I broke it in myself, and for the first couple 100 miles that thing would occasionally make some ****ed up sounds, sounded like a mix between detonation/pinging & something pinging in the exhaust.
Last edited by KRRZ350; 03-20-2011 at 07:56 AM.
03-20-2011, 09:24 AM
#3
Shame that apparently quality control early on with VQ35s wasn't up to Nissan's usual standards.
I had a Target-Master 350 installed in a Chevelle I used to have. This was a GM replacement 4 bolt main 350 engine with 8.2:1 compression that was built at the GM plant in Mexico in the early 80s. Started seriously modding it when the engine had about 30,000 miles (Headers, intake manifold, Holley) on it and then at around 55k miles after a cam change followed quickly by a head change (041 fuelie heads) which bumped the compression to about 9.5:1 I started taking it out to the drag strip every 2 weeks for a couple years. Even with hideous 2.56 gears, I was running 14.60s @ 100 (that's like starting off in 2nd gear in our cars) and thrashing my car regularly, including several 135+ mph top end pulls. I switched to a 3.08 rear end with posi, then quickly put 4.11s in and was running 14.0 @ 97-100 and a lot higher rpms on the freeway-3400 rpms at 60! When I made the switch to the 4.11s, I was still using the column shifter for a few weeks before I could put in a floor mounted ratchet shifter. Redline came up so much quicker with the new gears that I couldn't shift the column shifter fast enough and quickly found out the less than spectacular improvement at the strip was due to 5 broken compression rings.
Yet, when the engine was torn down with 96,000 miles on it, 40k of those were hard drag strip use and uh...other racing activities, all the cylinders needed was a clean-up hone, there wasn't even a ridge at the top of the cylinders. Everything thing in the engine was in spec for a new engine, other than the broken compression rings. The engine used absolutely no oil in between oil changes, plugs looked pristine. Pretty amazing for an engine built in the early 80s by GM in Mexico.
Kind of frustrating then that so many of us have had oil control issues with early VQ35s. My 4AT 5.5 gen used a quart every 1500-1800 miles and then down to 1200 miles when the valve covers (especially the front one) started leaking pretty badly. My 6MT 5.5 gen so far has used a half quart over 1800 miles, which for some cars would still be unusually high but for our engines, it is actually pretty decent.
Look on the bright side, now you can bore the engine and get a little more displacement before you put it back together.
I had a Target-Master 350 installed in a Chevelle I used to have. This was a GM replacement 4 bolt main 350 engine with 8.2:1 compression that was built at the GM plant in Mexico in the early 80s. Started seriously modding it when the engine had about 30,000 miles (Headers, intake manifold, Holley) on it and then at around 55k miles after a cam change followed quickly by a head change (041 fuelie heads) which bumped the compression to about 9.5:1 I started taking it out to the drag strip every 2 weeks for a couple years. Even with hideous 2.56 gears, I was running 14.60s @ 100 (that's like starting off in 2nd gear in our cars) and thrashing my car regularly, including several 135+ mph top end pulls. I switched to a 3.08 rear end with posi, then quickly put 4.11s in and was running 14.0 @ 97-100 and a lot higher rpms on the freeway-3400 rpms at 60! When I made the switch to the 4.11s, I was still using the column shifter for a few weeks before I could put in a floor mounted ratchet shifter. Redline came up so much quicker with the new gears that I couldn't shift the column shifter fast enough and quickly found out the less than spectacular improvement at the strip was due to 5 broken compression rings.
Yet, when the engine was torn down with 96,000 miles on it, 40k of those were hard drag strip use and uh...other racing activities, all the cylinders needed was a clean-up hone, there wasn't even a ridge at the top of the cylinders. Everything thing in the engine was in spec for a new engine, other than the broken compression rings. The engine used absolutely no oil in between oil changes, plugs looked pristine. Pretty amazing for an engine built in the early 80s by GM in Mexico.
Kind of frustrating then that so many of us have had oil control issues with early VQ35s. My 4AT 5.5 gen used a quart every 1500-1800 miles and then down to 1200 miles when the valve covers (especially the front one) started leaking pretty badly. My 6MT 5.5 gen so far has used a half quart over 1800 miles, which for some cars would still be unusually high but for our engines, it is actually pretty decent.
Look on the bright side, now you can bore the engine and get a little more displacement before you put it back together.
03-22-2011, 05:45 AM
#4
Supporting Maxima.org Member
Thread Starter
iTrader: (29)
Join Date: Oct 2005
Location: Middleboro/Carver, Ma
Posts: 4,572
haha, I don't think a 3.5 would even run with 5 broken compression rings, good story SW.
Yeah I got pics, crappy ones though.
Motor is getting melted down, it was disgusting inside, and I still never found where all the brass shavings in the oil-pan came from, I think it was inside one of the VTC sprockets to be honest, does anyone know if there is brass in there? The car had cold-start rattle like you wouldn't beleive, and threw a cam code, something along the lines of couldn't advance or over advanced, even after switching out the solenoids. The thrust bearings looked OK, there was a lot of brass in the oil.
Yeah I got pics, crappy ones though.
Motor is getting melted down, it was disgusting inside, and I still never found where all the brass shavings in the oil-pan came from, I think it was inside one of the VTC sprockets to be honest, does anyone know if there is brass in there? The car had cold-start rattle like you wouldn't beleive, and threw a cam code, something along the lines of couldn't advance or over advanced, even after switching out the solenoids. The thrust bearings looked OK, there was a lot of brass in the oil.
03-22-2011, 07:39 AM
#6
Wait, people still blame the pre-cats for breaking the rings and not that Nissan simply used garbage rings?
Please, pleeeeeeease explain to me how a catalytic converter can become so clogged that debris gets sucked into the engine, breaking the oil seal rings, after 30,000 miles and ~18 months of ownership!? Until you can explain why people were burning oil after 20,000 miles, or fewer, it's bloody obvious to me that the pre-cats are not to blame.
Do the pre-cats accelerate oil burning in older cars? I don't know. The answer seems to be "maybe," but the oil-burning levels in cars with 40 and 50 thousand miles matches what others are experiencing at 140 thousand miles, so...
Please, pleeeeeeease explain to me how a catalytic converter can become so clogged that debris gets sucked into the engine, breaking the oil seal rings, after 30,000 miles and ~18 months of ownership!? Until you can explain why people were burning oil after 20,000 miles, or fewer, it's bloody obvious to me that the pre-cats are not to blame.
Do the pre-cats accelerate oil burning in older cars? I don't know. The answer seems to be "maybe," but the oil-burning levels in cars with 40 and 50 thousand miles matches what others are experiencing at 140 thousand miles, so...
03-22-2011, 10:04 AM
#7
Would the general recommendation be to get a compression test completed in order to make some attempt to determine if indeed the rings are to blame, that it would be apparent from the compression test?
03-22-2011, 10:23 AM
#9
What happened in my case, car in park and rev the engine. When the rpms drop you'd hear a wobble sound. Definately not on the engine but the pre-cat at the firewall was all jacked up.
The honeycomb material was loose and rattling around in the cat.
If you can, pull and inspect.
The honeycomb material was loose and rattling around in the cat.
If you can, pull and inspect.
03-22-2011, 12:00 PM
#10
Supporting Maxima.org Member
Thread Starter
iTrader: (29)
Join Date: Oct 2005
Location: Middleboro/Carver, Ma
Posts: 4,572
Yeah the rear ones fail also, BUT I've never seen them do anything except rattle- ie it's still all togethor
Last edited by KRRZ350; 03-22-2011 at 12:04 PM.
03-22-2011, 12:03 PM
#11
Supporting Maxima.org Member
Thread Starter
iTrader: (29)
Join Date: Oct 2005
Location: Middleboro/Carver, Ma
Posts: 4,572
Wait, people still blame the pre-cats for breaking the rings and not that Nissan simply used garbage rings?
Please, pleeeeeeease explain to me how a catalytic converter can become so clogged that debris gets sucked into the engine, breaking the oil seal rings, after 30,000 miles and ~18 months of ownership!? Until you can explain why people were burning oil after 20,000 miles, or fewer, it's bloody obvious to me that the pre-cats are not to blame.
Do the pre-cats accelerate oil burning in older cars? I don't know. The answer seems to be "maybe," but the oil-burning levels in cars with 40 and 50 thousand miles matches what others are experiencing at 140 thousand miles, so...
Please, pleeeeeeease explain to me how a catalytic converter can become so clogged that debris gets sucked into the engine, breaking the oil seal rings, after 30,000 miles and ~18 months of ownership!? Until you can explain why people were burning oil after 20,000 miles, or fewer, it's bloody obvious to me that the pre-cats are not to blame.
Do the pre-cats accelerate oil burning in older cars? I don't know. The answer seems to be "maybe," but the oil-burning levels in cars with 40 and 50 thousand miles matches what others are experiencing at 140 thousand miles, so...
Last edited by KRRZ350; 03-22-2011 at 12:09 PM.
03-22-2011, 12:12 PM
#12
Supporting Maxima.org Member
Thread Starter
iTrader: (29)
Join Date: Oct 2005
Location: Middleboro/Carver, Ma
Posts: 4,572
I never did a compression test on THIS motor, only because it was being replaced anyways, it was fubar'd, but yes, a compression test will confirm, my gauge reads a little high but if I saw anything from 140-170 on a warm motor I would be concerned, if you check front to back & see the fronts lower as well it will give you an idea.
03-22-2011, 07:24 PM
#13
I'll gladly explain it, since it's bloody obvious you aren't informed here. Reversion, in a nutshell your engine will occasionally suck exhaust gasses back into the motor. The front pre-cat doesn't get clogged, it is made of a substrate that is way to brittle, you literally touch it and it crumbles to sandy little bits on your finger, yes merely from touching it. Well between that, and the process of reversion, some of that substrate makes its way back into the motor & wears the rings. It's what happens, end of story. Whether the rings are crap or not definitly helps, but I guarantee you those cars with 20K that are burning oil have missing pieces from the front cat.
03-24-2011, 03:40 AM
#14
I never did a compression test on THIS motor, only because it was being replaced anyways, it was fubar'd, but yes, a compression test will confirm, my gauge reads a little high but if I saw anything from 140-170 on a warm motor I would be concerned, if you check front to back & see the fronts lower as well it will give you an idea.
03-24-2011, 08:16 PM
#17
Reversion, in a nutshell your engine will occasionally suck exhaust gasses back into the motor.
Reversion occurs with the pulse of energy from the combustion process, not with the gases themselves. When the pulse hits an area of low-pressure, it bounces off it and travels back towards the exhaust valve, mingling with the exhaust gases along the way. The pulse will change the momentum of some of that gas, but not all of it. Because of that, only trace amounts of exhaust gas can re-enter the combustion chamber.
At high engine speeds, the reversion wave only serves to alter the pressure in the area immediately outside the exhaust valve, helping to suck exhaust gases out more effectively--ie, a tuned exhaust. No gases can enter the chamber because of the major difference in pressures from the intake and exhaust sides of the air system.
The front pre-cat doesn't get clogged, it is made of a substrate that is way to brittle, you literally touch it and it crumbles to sandy little bits on your finger, yes merely from touching it.
Well between that, and the process of reversion, some of that substrate makes its way back into the motor & wears the rings
It's what happens, end of story. Whether the rings are crap or not definitly helps, but I guarantee you those cars with 20K that are burning oil have missing pieces from the front cat.
and correlation.
Wikipedia has an entire article on the issue.
Causation: Causes something to happen ("The act or process of causing.")
Correlation: " a relation existing between phenomena or things or between mathematical or statistical variables which tend to vary, be associated, or occur together in a way not expected on the basis of chance alone"
"Correlation does not imply causation" (related to "ignoring a common cause" and questionable cause) is a phrase used in science and statistics to emphasize that correlation between two variables does not automatically imply that one causes the other (though correlation is necessary for linear causation in the absence of any third and countervailing causative variable, and can indicate possible causes or areas for further investigation; in other words, correlation can be a hint)"
The other big problem with this is that the oil-burning issue affects all VQ35s up to a certain, non-specific date. Clearly, the pre-cats in 5.5 gens, 6 gens, 350Zs, Muranos, G35s, and M35s are not all the same.
"Oh, but what if they are all made out of the same material," you say. Well, clearly, if pre-cats could do this, they would be doing it to all sorts of cars from all sorts of manufacturers, not to mention every vehicle Nissan made from 02 - ~05, if not an even greater range of years. The process of taming the harmful pollutants in exhaust gas varies very, very little from manufacturer to manufacturer. There are only so many different catalysts in existence, and only so many ways of securing that catalyst to an apparatus that pulls gas through it to collide the NOx and hydrocarbons with said catalyst.
This is not a closed issue and I still firmly believe that the entire idea of pre-cats causing oil rings to wear is sheerly nonsensical.
Any response you can offer to these points would be greatly appreciated. You yourself don't have to respond, naturally, if there is someone else advocating the idea.
Sources:
http://www.bigcitythunder.com/pages/...ng_exhaust.pdf
http://www.rewarderheaders.com/reversio.htm
http://www.custom-car.us/exhaust/header.aspx
03-25-2011, 02:08 AM
#19
Member
Join Date: Mar 2011
Location: SoCal
Posts: 242
Original link:
http://forums.maxima.org/2951562-post7.html
I don't know how bits of the precat can flow the wrong way, but Nissan actually issued a recall about it. Here's a short excerpt:
DATE: JULY 29, 2003
FROM : PARTS AND SERVICE OPERATIONS
SUBJECT: 2002-03 ALTIMA/2002-04 SENTRA 2.5 LITER ENG. EXHAUST CAMPAIGN
ATTENTION - DEALER PRINCIPALS, SALES, PARTS AND SERVICE MANAGERS
THIS IS AN UPDATE TO PREVIOUS COMMUNICATIONS RELATED TO THIS CAMPAIGN. ADDITIONAL VEHICLES HAVE BEEN ADDED TO THE CAMPAIGN AND THERE ARE NOW 5 PNC CODES RELATED TO THIS CAMPAIGN BASED ON MODEL, MODEL YEAR AND THE SPECIFIC REPAIR REQUIRED TO COMPLETE THE CAMPAIGN.
***** CONDITION/NISSAN ACTION *****
ON SOME 2002-2003 ALTIMA VEHICLES EQUIPPED WITH THE 2.5 LITER ENGINE, THERE IS A POSSIBILITY THE EXHAUST PIPE HANGER PIN MAY CATCH DEBRIS FROM THE ROAD THAT COULD BE IGNITED BY CONTACT WITH THE CATALYTIC CONVERTER AND CAUSE A FIRE. IN ADDITION, ON BOTH THE 2002-2003 ALTIMA AND THE 2002-2004 SENTRA EQUIPPED WITH THE 2.5 LITER ENGINE, THERE IS A POSSIBILITY THAT CERTAIN ENGINE OPERATING CONDITIONS MAY CAUSE DAMAGE TO THE PRE-CATALYST. MATERIAL FROM INSIDE A DAMAGED PRE-CATALYST COULD ENTER THE ENGINE AND RESULT IN INCREASED OIL CONSUMPTION. IF THE ENGINE OIL LEVEL IS NOT CHECKED ON A PERIODIC BASIS AND DROPS BELOW THE LOW LEVEL, AND THE DRIVER CONTINUES TO OPERATE THE VEHICLE IGNORING NOTICEABLE ENGINE NOISE, ENGINE DAMAGE MAY OCCUR WHICH COULD RESULT IN A FIRE.
*EDITED FOR THE 340980934th TIME*
The recall I'm quoting above is NOT for Maximas, by the way. It's for a similar precat disintegration problem in the QR25 engine in the Altima and Sentra SE-R. You should check to see if there is a similar recall out for the Maxima if you are having precat disintegration problems.
DATE: JULY 29, 2003
FROM : PARTS AND SERVICE OPERATIONS
SUBJECT: 2002-03 ALTIMA/2002-04 SENTRA 2.5 LITER ENG. EXHAUST CAMPAIGN
ATTENTION - DEALER PRINCIPALS, SALES, PARTS AND SERVICE MANAGERS
THIS IS AN UPDATE TO PREVIOUS COMMUNICATIONS RELATED TO THIS CAMPAIGN. ADDITIONAL VEHICLES HAVE BEEN ADDED TO THE CAMPAIGN AND THERE ARE NOW 5 PNC CODES RELATED TO THIS CAMPAIGN BASED ON MODEL, MODEL YEAR AND THE SPECIFIC REPAIR REQUIRED TO COMPLETE THE CAMPAIGN.
***** CONDITION/NISSAN ACTION *****
ON SOME 2002-2003 ALTIMA VEHICLES EQUIPPED WITH THE 2.5 LITER ENGINE, THERE IS A POSSIBILITY THE EXHAUST PIPE HANGER PIN MAY CATCH DEBRIS FROM THE ROAD THAT COULD BE IGNITED BY CONTACT WITH THE CATALYTIC CONVERTER AND CAUSE A FIRE. IN ADDITION, ON BOTH THE 2002-2003 ALTIMA AND THE 2002-2004 SENTRA EQUIPPED WITH THE 2.5 LITER ENGINE, THERE IS A POSSIBILITY THAT CERTAIN ENGINE OPERATING CONDITIONS MAY CAUSE DAMAGE TO THE PRE-CATALYST. MATERIAL FROM INSIDE A DAMAGED PRE-CATALYST COULD ENTER THE ENGINE AND RESULT IN INCREASED OIL CONSUMPTION. IF THE ENGINE OIL LEVEL IS NOT CHECKED ON A PERIODIC BASIS AND DROPS BELOW THE LOW LEVEL, AND THE DRIVER CONTINUES TO OPERATE THE VEHICLE IGNORING NOTICEABLE ENGINE NOISE, ENGINE DAMAGE MAY OCCUR WHICH COULD RESULT IN A FIRE.
*EDITED FOR THE 340980934th TIME*
The recall I'm quoting above is NOT for Maximas, by the way. It's for a similar precat disintegration problem in the QR25 engine in the Altima and Sentra SE-R. You should check to see if there is a similar recall out for the Maxima if you are having precat disintegration problems.
03-25-2011, 09:09 AM
#21
@Seedy: Others go on in that thread to explain that Nissan chose not to use traditional EGR in those two applications of their 2.5L engine and the timings they chose for the exhaust valves (to still remain within tolerable emission levels) were far too aggressive and allowed the issue at hand to occur. I don't think the same situation applies to our VQ35s.
What the "certain engine operating conditions" are that "can" cause pre-cat damages is beyond me, however.
+3 on an image resize.
What the "certain engine operating conditions" are that "can" cause pre-cat damages is beyond me, however.
+3 on an image resize.
03-25-2011, 10:01 AM
#22
Member
Join Date: Mar 2011
Location: SoCal
Posts: 242
Yeah, that's possible I'm just regurgitating what my own limited research has found. As someone who just bought a Max, the oil consumption issue has me a little concern.
As for the image resize comment, is my sig a bit too big? I thought the same at first but there's some huge ones here
As for the image resize comment, is my sig a bit too big? I thought the same at first but there's some huge ones here
03-25-2011, 10:15 AM
#23
Yeah, that's possible I'm just regurgitating what my own limited research has found. As someone who just bought a Max, the oil consumption issue has me a little concern.
As for the image resize comment, is my sig a bit too big? I thought the same at first but there's some huge ones here
As for the image resize comment, is my sig a bit too big? I thought the same at first but there's some huge ones here
From what informal averaging I've done reading the Org, your 5.5 gen has like a 20% - 40% shot of being an old-burner. It's pretty common. I go through 1/4 - 1/2 quart every 3000 miles, and consider myself lucky.
edit: I'm looking at your sig again. You know, if you have a driver's-side corner shot at eye height for the max, it would match the perspective nicely side-by-side with the z. Better yet, get an actual photo of the cars side-by-side. Damn it... now I'm jealous. LOL
Last edited by Rochester; 03-25-2011 at 10:20 AM.
03-25-2011, 10:51 AM
#24
Member
Join Date: Mar 2011
Location: SoCal
Posts: 242
Thanks Rochester for the info, I'll keep an eye on my oil levels. Also, I definitely plan to get some new pics for a sig since I've added tint and coilovers will be on soon. That angle is a good idea though getting both cars in one shot might be hard with the motor out on the Z 
03-26-2011, 07:51 AM
#25
Junior Member
Join Date: Jul 2007
Location: Indianapolis, IN
Posts: 87
Great info about the rings.
Resizing would not only make this thread easier to read, it would also make the pics easier to view.
I don't know how bad oil consumption can get, but I go through a qt every 800mi.
Resizing would not only make this thread easier to read, it would also make the pics easier to view.
I don't know how bad oil consumption can get, but I go through a qt every 800mi.
03-26-2011, 09:55 AM
#26
I think erik will change his mind when his motor pops from bad cats.
If you don't have experience with it, stfu.
I bought one with about 70k. It didn't burn a drop and was fine. At 75k the precats, unbeknown to me had fallen completely apart, ruined the engine and clogged the main cat within 1,000 miles (I had just changed the oil). It didn't even make any noises other than a rattle, which sounded like the heat shield rattles. It ran fine the morning it failed, but in the afternoon the precats must have just blew to pieces. The engine started losing power, then refused to run. It was done for. The shop got it to run after cleaning out the cat and adding oil, but it had a knock.
Take your theoretical bull**** and cram it up your ***.
If you don't have experience with it, stfu.
I bought one with about 70k. It didn't burn a drop and was fine. At 75k the precats, unbeknown to me had fallen completely apart, ruined the engine and clogged the main cat within 1,000 miles (I had just changed the oil). It didn't even make any noises other than a rattle, which sounded like the heat shield rattles. It ran fine the morning it failed, but in the afternoon the precats must have just blew to pieces. The engine started losing power, then refused to run. It was done for. The shop got it to run after cleaning out the cat and adding oil, but it had a knock.
Take your theoretical bull**** and cram it up your ***.
03-26-2011, 12:50 PM
#27
Looks like I lucked out with my current 6MT '02. 2300 miles, only used a half quart. That's compared to a full quart every 1500-1800 miles, dropping to every 1200 mile when the front valve cover started puking oil onto the bank 2 heat shield. 
03-26-2011, 02:08 PM
#28
The pre-cats killed your cat, your cat killed your engine. The pre-cats did not break your engine which broke your cat.
It ran fine the morning it failed, but in the afternoon the precats must have just blew to pieces. The engine started losing power, then refused to run. It was done for.
The shop got it to run after cleaning out the cat and adding oil, but it had a knock.
Take your theoretical bull**** and cram it up your ***.
The only way to prove that the pre-cats can dissolve, backwards, into the engine and ruin the rings would be for you to rig up an engine with a transparent block, transparent exhaust manifold, and transparent pre-cats and watch it happen. Until YOU can offer direct evidence, I suggest you refrain from ad hominem attacks.
03-26-2011, 03:16 PM
#30
Supporting Maxima.org Member
Thread Starter
iTrader: (29)
Join Date: Oct 2005
Location: Middleboro/Carver, Ma
Posts: 4,572
^^Yes! For those on a budget the front precat can be dropped gutted & reinstalled in no time flat. That's how the I35 is running right now, I just didn't catch it in time & the OC has gotten progressivly
Pics resized, might take some time till we see it
Lol Erik, go take a pre-cat down or a motor apart before you discredit someone who has. I love the part about the mass of my finger, but you forgot these cars are missing chunks long before they got pulled. Got a better theory on why only the front rings are worn way beyond spec & the rears are fine? (I only measured two but eyeballed all, it was clear as day) I'd love to hear it, just don't go trying to say it's related to oil supply though because the #5 valve shim/buckets always get smoked first
Pics resized, might take some time till we see it
Lol Erik, go take a pre-cat down or a motor apart before you discredit someone who has. I love the part about the mass of my finger, but you forgot these cars are missing chunks long before they got pulled. Got a better theory on why only the front rings are worn way beyond spec & the rears are fine? (I only measured two but eyeballed all, it was clear as day) I'd love to hear it, just don't go trying to say it's related to oil supply though because the #5 valve shim/buckets always get smoked first
Last edited by KRRZ350; 03-26-2011 at 03:18 PM.
03-26-2011, 05:47 PM
#32
Crappy rings! Again, if this was as simple as one easy-to-replace component being the culprit, why was Nissan replacing entire engines instead of just swapping out the pre-cats? Hmm, probably because they have nothing to do with the oil-consumption problem.
Why did the oil-burning problem go away sometime during the 6th generation of Maximas? Did they start using a different kind of pre-cat, or did they make an internal change in the rings after the oil-burning problem was known? Hmm... I'm only seeing one set of catalysts listed for the 6th gens on Courtesy's website...
The compression ratio on the 3.0 block is roughly 10.0:1, the compression ratio on ours is either 10.3 or 10.5:1, depending on your source. Nissan bored out the block and called it a day, not upgrading their piston oil rings until it became obvious that they were deteriorating in real-world conditions under the additional stress of the higher compression ratio.
This has already been talked to death, we all know its the rings, so why is it so hard to just admit that Nissan used crappy, crappy rings? Maybe it wasn't Nissan's fault, per se, maybe the supplier screwed up a few hundred thousand and those took a few years to use up. The details are uncertain, but it's obvious that the pre-cats have nothing to do with the bad rings. The "logic" connecting the pre-cats to the bad rings is flimsy at best and "insult my intelligence" wrong at worst.
Are you seriously telling me that the pre-cats on Maximas, G35s, 350Zs, Muranos, M35s, and FX35s WERE ALL THE SAME!? All made out of exactly the same materials, all made with the exact same bends and whatever else is needed to ensure that they all break exactly the same way? A far, far more logical explanation, ONE WE ALREADY KNOW, is that bad rings were shared between the engines in FWD and RWD VQ35 blocks.
Ice cream sales and drowning deaths, people. http://en.wikipedia.org/wiki/Correla...s_both_A_and_B
@OP: Yeah, because taking an engine apart means you know what caused the damage. Wrong! Taking an engine apart can certainly reveal the cause of damage in some scenarios (a hole in a cylinder wall, bad valves, etc), but there are also many other variables at play that can't be known by looking at a broken engine laying in pieces on your workbench. Why were only some of the rings in that engine bad? I don't know. Why don't all VQ35s burn oil?
Why did the oil-burning problem go away sometime during the 6th generation of Maximas? Did they start using a different kind of pre-cat, or did they make an internal change in the rings after the oil-burning problem was known? Hmm... I'm only seeing one set of catalysts listed for the 6th gens on Courtesy's website...
The compression ratio on the 3.0 block is roughly 10.0:1, the compression ratio on ours is either 10.3 or 10.5:1, depending on your source. Nissan bored out the block and called it a day, not upgrading their piston oil rings until it became obvious that they were deteriorating in real-world conditions under the additional stress of the higher compression ratio.
This has already been talked to death, we all know its the rings, so why is it so hard to just admit that Nissan used crappy, crappy rings? Maybe it wasn't Nissan's fault, per se, maybe the supplier screwed up a few hundred thousand and those took a few years to use up. The details are uncertain, but it's obvious that the pre-cats have nothing to do with the bad rings. The "logic" connecting the pre-cats to the bad rings is flimsy at best and "insult my intelligence" wrong at worst.
Are you seriously telling me that the pre-cats on Maximas, G35s, 350Zs, Muranos, M35s, and FX35s WERE ALL THE SAME!? All made out of exactly the same materials, all made with the exact same bends and whatever else is needed to ensure that they all break exactly the same way? A far, far more logical explanation, ONE WE ALREADY KNOW, is that bad rings were shared between the engines in FWD and RWD VQ35 blocks.
Ice cream sales and drowning deaths, people. http://en.wikipedia.org/wiki/Correla...s_both_A_and_B
@OP: Yeah, because taking an engine apart means you know what caused the damage. Wrong! Taking an engine apart can certainly reveal the cause of damage in some scenarios (a hole in a cylinder wall, bad valves, etc), but there are also many other variables at play that can't be known by looking at a broken engine laying in pieces on your workbench. Why were only some of the rings in that engine bad? I don't know. Why don't all VQ35s burn oil?
Last edited by Eirik; 03-26-2011 at 05:50 PM.
03-27-2011, 07:24 AM
#35
Supporting Maxima.org Member
Thread Starter
iTrader: (29)
Join Date: Oct 2005
Location: Middleboro/Carver, Ma
Posts: 4,572
Are you seriously trying to say that nissan put bad rings on only the front bank of this motor?
Did you ever think that maybe a weak ring design or material exacerbates the problem? Same deal with the increased compression & bore size (leading to distortion), because it's pretty cut & dry that in THIS case on THIS motor had the precat not failed the front rings would still have acceptable end-gap], I'm positive on this, end of discussion.
Did you ever think that maybe a weak ring design or material exacerbates the problem? Same deal with the increased compression & bore size (leading to distortion), because it's pretty cut & dry that in THIS case on THIS motor had the precat not failed the front rings would still have acceptable end-gap], I'm positive on this, end of discussion.
Last edited by KRRZ350; 03-27-2011 at 07:31 AM.
03-27-2011, 07:28 AM
#36
Supporting Maxima.org Member
Thread Starter
iTrader: (29)
Join Date: Oct 2005
Location: Middleboro/Carver, Ma
Posts: 4,572
Agreed. I have hated 3.5's for awhile now, the new motor that replaced this one was 3 years old & had under 40K on it........ thank god I found the plastic pieces in the oil pan, apparently some of the new(er) 3.5's used chainsaw blades for the secondaries 
03-27-2011, 07:52 AM
#37
Supporting Maxima.org Member
Thread Starter
iTrader: (29)
Join Date: Oct 2005
Location: Middleboro/Carver, Ma
Posts: 4,572
Also, reversion does not happen only from the waves, that's only a small part of it. When a piston travels downwards it creates suction. The exhaust valve doesn't close the instant the piston hits TDC. Learn a little more about the 4-stroke engine instead of "talking to technicians at work".
03-27-2011, 05:00 PM
#38
Revision can warp valves when you run a motor without any exhaust manifolds. Turn it off, sucks in a bit of cold air. Whether or not there is enough suction to suck up chunks of the pre-cat, I don't know. Guess it depends on the size of the pieces. However, even very small pieces can scar the cylinder walls.
I do agree that the primary cause of the oil control issues is the rings. Could be the pre-cats play a minor role in some cases.
I do agree that the primary cause of the oil control issues is the rings. Could be the pre-cats play a minor role in some cases.
03-27-2011, 05:29 PM
#39
Crappy rings! Again, if this was as simple as one easy-to-replace component being the culprit, why was Nissan replacing entire engines instead of just swapping out the pre-cats? Hmm, probably because they have nothing to do with the oil-consumption problem.
Why did the oil-burning problem go away sometime during the 6th generation of Maximas? Did they start using a different kind of pre-cat, or did they make an internal change in the rings after the oil-burning problem was known? Hmm... I'm only seeing one set of catalysts listed for the 6th gens on Courtesy's website...
The compression ratio on the 3.0 block is roughly 10.0:1, the compression ratio on ours is either 10.3 or 10.5:1, depending on your source. Nissan bored out the block and called it a day, not upgrading their piston oil rings until it became obvious that they were deteriorating in real-world conditions under the additional stress of the higher compression ratio.
This has already been talked to death, we all know its the rings, so why is it so hard to just admit that Nissan used crappy, crappy rings? Maybe it wasn't Nissan's fault, per se, maybe the supplier screwed up a few hundred thousand and those took a few years to use up. The details are uncertain, but it's obvious that the pre-cats have nothing to do with the bad rings. The "logic" connecting the pre-cats to the bad rings is flimsy at best and "insult my intelligence" wrong at worst.
Are you seriously telling me that the pre-cats on Maximas, G35s, 350Zs, Muranos, M35s, and FX35s WERE ALL THE SAME!? All made out of exactly the same materials, all made with the exact same bends and whatever else is needed to ensure that they all break exactly the same way? A far, far more logical explanation, ONE WE ALREADY KNOW, is that bad rings were shared between the engines in FWD and RWD VQ35 blocks.
Ice cream sales and drowning deaths, people. http://en.wikipedia.org/wiki/Correla...s_both_A_and_B
@OP: Yeah, because taking an engine apart means you know what caused the damage. Wrong! Taking an engine apart can certainly reveal the cause of damage in some scenarios (a hole in a cylinder wall, bad valves, etc), but there are also many other variables at play that can't be known by looking at a broken engine laying in pieces on your workbench. Why were only some of the rings in that engine bad? I don't know. Why don't all VQ35s burn oil?
Why did the oil-burning problem go away sometime during the 6th generation of Maximas? Did they start using a different kind of pre-cat, or did they make an internal change in the rings after the oil-burning problem was known? Hmm... I'm only seeing one set of catalysts listed for the 6th gens on Courtesy's website...
The compression ratio on the 3.0 block is roughly 10.0:1, the compression ratio on ours is either 10.3 or 10.5:1, depending on your source. Nissan bored out the block and called it a day, not upgrading their piston oil rings until it became obvious that they were deteriorating in real-world conditions under the additional stress of the higher compression ratio.
This has already been talked to death, we all know its the rings, so why is it so hard to just admit that Nissan used crappy, crappy rings? Maybe it wasn't Nissan's fault, per se, maybe the supplier screwed up a few hundred thousand and those took a few years to use up. The details are uncertain, but it's obvious that the pre-cats have nothing to do with the bad rings. The "logic" connecting the pre-cats to the bad rings is flimsy at best and "insult my intelligence" wrong at worst.
Are you seriously telling me that the pre-cats on Maximas, G35s, 350Zs, Muranos, M35s, and FX35s WERE ALL THE SAME!? All made out of exactly the same materials, all made with the exact same bends and whatever else is needed to ensure that they all break exactly the same way? A far, far more logical explanation, ONE WE ALREADY KNOW, is that bad rings were shared between the engines in FWD and RWD VQ35 blocks.
Ice cream sales and drowning deaths, people. http://en.wikipedia.org/wiki/Correla...s_both_A_and_B
@OP: Yeah, because taking an engine apart means you know what caused the damage. Wrong! Taking an engine apart can certainly reveal the cause of damage in some scenarios (a hole in a cylinder wall, bad valves, etc), but there are also many other variables at play that can't be known by looking at a broken engine laying in pieces on your workbench. Why were only some of the rings in that engine bad? I don't know. Why don't all VQ35s burn oil?
Pre cats and cats are always positioned at a certain distance from the motor. FWD or RWD its the same distance.
This actually makes alot of sense. Think about little piece of metal being sucked back into the combustion chamber, this small piece of metal tear up the piston rings and make scratches on the cylinder walls. To fix that problem you will need to either re-bore the pistons and that will mean replacing the pistons and finding Custom sized Pistons&rings, OR replace the sleeves, pistons, and rings.
Do you realize the amount of labor that will go into all of that? And also every car that went in for the recall will be different from the rest of the cars on the road. Its cheaper, easier, quicker to just replace the whole motor along with the faulty exhaust parts.
Its no secret that Nissan started to cheap out on alot of things in the later years, the biggest evidence of this is look at the paint on newer nissans compared to older ones. You can touch the paint wrong and cause a deep scratch.
QR25s had the same problem as the VQ35 with eating their pre-cats and causing all kinds of problems including burning off oil.
Last edited by Crusher103; 03-27-2011 at 05:34 PM.
03-27-2011, 06:53 PM
#40
KRRZ, you just don't get it, but that's whatever. Keep spreading misinformation! It's the internet, after all. Don't sweat all my questions you were unable to answer because your pet theory can't explain them. Just keep doin' your thing.
@Crusher: How large would the piece of metal have to be? Are we talking measurements on the scale of millimeters or micrometers? I'm not seeing how chunks of any considerable size could move back into the engine. Surely pieces of metal that measure .01 mm across would just incinerate before doing any damage. KKZ didn't mention scarring on the cylinder walls and I can't make much out of his pictures. Doesn't scoring happen from a ton of different reasons, though? How would you be able to determine it was the pre-cat? It leads to a chicken-and-egg thing: Did the pre-cat hurt the rings that led to low-oil conditions that caused scoring, or did low-oil conditions cause scoring that gets blamed on the pre-cat?
I don't remember people on here mentioning Nissan gave them new exhaust manifolds/pre-cats with the new engine. I assumed Nissan would replace the bare minimum, but you're saying that included new pre-cats?
@Scottwax: That's what I thought, until further research revealed the ludicrously tiny odds of a pre-cat being able to damage the oil rings.
Here's an interesting post I dug up on an MR2 Spyder forum:
Is the VVT in our engines aggressive enough to allow pre-cats to enter the engine? I don't think so--we don't drive sports cars. Also, those guys were saying they'd pulled pre-cats at 15K miles and they were heavily damaged, implying that you can't expect your engine to live past 60K miles without removing the pre-cats..! Obviously, our situation isn't the same.
@Crusher: How large would the piece of metal have to be? Are we talking measurements on the scale of millimeters or micrometers? I'm not seeing how chunks of any considerable size could move back into the engine. Surely pieces of metal that measure .01 mm across would just incinerate before doing any damage. KKZ didn't mention scarring on the cylinder walls and I can't make much out of his pictures. Doesn't scoring happen from a ton of different reasons, though? How would you be able to determine it was the pre-cat? It leads to a chicken-and-egg thing: Did the pre-cat hurt the rings that led to low-oil conditions that caused scoring, or did low-oil conditions cause scoring that gets blamed on the pre-cat?
I don't remember people on here mentioning Nissan gave them new exhaust manifolds/pre-cats with the new engine. I assumed Nissan would replace the bare minimum, but you're saying that included new pre-cats?
@Scottwax: That's what I thought, until further research revealed the ludicrously tiny odds of a pre-cat being able to damage the oil rings.
Here's an interesting post I dug up on an MR2 Spyder forum:
Woah, wait a minute! How can the pre-cat get back into the engine: Surely the exhaust flow pushes it all out?
True to a certain extent, but here's the clever bit…
The 1ZZ-FE engine (Toyota's designation for the engine inside the MR2 Roadster) is a very clever piece of kit, and arguably its main party piece is the VVTi, or Variable Valve Timing Intelligent. This increases engine response all over the rev range by altering the timing of the cams, allowing for differing amounts of valve overlap in order to give great low-down torque as well as good top-end power. The 1ZZ also uses it's VVT to perform EGR (Exhaust Gas Recirculation) functions without the aid of a specific valve like other cars. Under certain operating conditions (usually steady cruise) the cams are timed to scavenge some exhaust gas back into the cylinders, as a way of reducing the high hydrocarbon emissions that modern petrol engines generate at certain times.
Unfortunately, when you combine this with some very sharp ceramic pre-cat particles, you can imagine what happens: The pre-cats start breaking down, and get dropped into the main cat which then causes excessive pressure, leading to oil blow-by in the engine. When the VVTi kicks in, the pre-cats are sucked back in and scratch and score the cylinder walls, leading to more oil passing by the piston rings and being burnt off without you even realising it. No oil in an engine leads to massive failure as every moving part grinds against metal, and in short you end up with a practically useless engine. When this happens the situation is compounded by the fact that hot oil is now allowed to drip directly onto the pre-cats and break them down even quicker, which in turn allows large chunks to block the main cat even more, which then stops any smaller pre-cat material escaping at all and sucks even more back into the engine to cause even more damage… A vicious circle of the very worst kind.
Some common symptoms of pre-cat failure are extreme oil loss, very noticeable lack of power all the way through the rev range, and horrible noises coming from your engine bay. Essentially, if you've got any of these problems and they are directly related to pre-cat loss, then it's too late. Even the oil warning light won't save you here, as by the time it comes on there's almost zero oil left in the engine anyway.
But I've read elsewhere that the pre-cats themselves are fine, it the piston rings which are the weakness…
This is where we come across a real conundrum, and a question to which no-one has a definitive answer. It's true that on very early MK3s there was a known problem with the piston rings themselves on a 1ZZ, and Toyota issued a technical document to the dealers around the world stating as such. They also changed the design of the piston rings for the facelift version of the Roadster, which became available in 2003.
Now whether it's a case of the piston rings failing, oil dripping onto the pre-cats and breaking them up, or the pre-cats self destructing and taking the piston rings with them, we just don't know. All we do know for certain is that whilst you can't take the piston rings out of the engine, you can remove the pre-cats from the manifold. No pre-cats = Nothing to get sucked back into the engine.
True to a certain extent, but here's the clever bit…
The 1ZZ-FE engine (Toyota's designation for the engine inside the MR2 Roadster) is a very clever piece of kit, and arguably its main party piece is the VVTi, or Variable Valve Timing Intelligent. This increases engine response all over the rev range by altering the timing of the cams, allowing for differing amounts of valve overlap in order to give great low-down torque as well as good top-end power. The 1ZZ also uses it's VVT to perform EGR (Exhaust Gas Recirculation) functions without the aid of a specific valve like other cars. Under certain operating conditions (usually steady cruise) the cams are timed to scavenge some exhaust gas back into the cylinders, as a way of reducing the high hydrocarbon emissions that modern petrol engines generate at certain times.
Unfortunately, when you combine this with some very sharp ceramic pre-cat particles, you can imagine what happens: The pre-cats start breaking down, and get dropped into the main cat which then causes excessive pressure, leading to oil blow-by in the engine. When the VVTi kicks in, the pre-cats are sucked back in and scratch and score the cylinder walls, leading to more oil passing by the piston rings and being burnt off without you even realising it. No oil in an engine leads to massive failure as every moving part grinds against metal, and in short you end up with a practically useless engine. When this happens the situation is compounded by the fact that hot oil is now allowed to drip directly onto the pre-cats and break them down even quicker, which in turn allows large chunks to block the main cat even more, which then stops any smaller pre-cat material escaping at all and sucks even more back into the engine to cause even more damage… A vicious circle of the very worst kind.
Some common symptoms of pre-cat failure are extreme oil loss, very noticeable lack of power all the way through the rev range, and horrible noises coming from your engine bay. Essentially, if you've got any of these problems and they are directly related to pre-cat loss, then it's too late. Even the oil warning light won't save you here, as by the time it comes on there's almost zero oil left in the engine anyway.
But I've read elsewhere that the pre-cats themselves are fine, it the piston rings which are the weakness…
This is where we come across a real conundrum, and a question to which no-one has a definitive answer. It's true that on very early MK3s there was a known problem with the piston rings themselves on a 1ZZ, and Toyota issued a technical document to the dealers around the world stating as such. They also changed the design of the piston rings for the facelift version of the Roadster, which became available in 2003.
Now whether it's a case of the piston rings failing, oil dripping onto the pre-cats and breaking them up, or the pre-cats self destructing and taking the piston rings with them, we just don't know. All we do know for certain is that whilst you can't take the piston rings out of the engine, you can remove the pre-cats from the manifold. No pre-cats = Nothing to get sucked back into the engine.