MrGone

iTrader: (30)

Please let me know if there is any part that is confusing and I will try my best to clarify. There are pictures below.

So there is no confusion, I am going to label the parts of the VTC assembly to the best of my knowledge (I also do not have the VTC Rebuild TSB available at the moment).

I consider the top of the VTC assembly the portion where the cap sits, or the cap itself. When I say the bottom of the VTC assembly I am referring to the portion where the gear sprocket portion is. The front of the VTC assembly is the top, where the back of it is the bottom. I am calling the bottom of the inner most part of the VTC assembly the base, this is the part that actually makes contact with the camshaft.

When I refer to the spline direction it is looking at the VTC assembly from the front to the back. So a clockwise spline direction means as the spline goes front to back along the assembly it moves towards the right. Counter-clockwise means the spline is moving towards the left. The housing of the VTC is the part which you can see; it is smooth on the outside and has a clockwise spline direction in the inside. The middle of the VTC refers to the center portion which slides between the housing and the base. The middle piece has clockwise splines on the outside and counter-clockwise splines on the inside. The base has counter-clockwise splines on the outside and is smooth on the inside.

I have always understood why they fail and what happens, but I've never understood why Nissan dealerships have told us sometimes the assemblies are "too far gone" to rebuild. It didn’t make sense if you are simply replacing a cap, spring and seal.

For a while I thought maybe the problem lied in the base of the VTC. I have noticed a ring worn into the base where the spring sits. I considered the assemblies are such close tolerances a fraction of a millimeter may make a big difference in the strength/effectiveness of the spring.

I also wondered if maybe the spring was rattling around and if welding it to the base would fix this. I'm sure this would help prevent the wear rings, but I believe that is all it would accomplish.

The Engine naturally spins clockwise, as does the valve train. Within the VTC assembly, the outer housing is spinning clockwise with the crankshaft and everything else in the engine. This causes the middle portion to twist toward the front or top of the housing; consequently it causes the base to twist the opposite direction, downward.

Now with the middle piece pressed against the top of the VTC and the base pressed towards the bottom, the spring is doing nothing, you could remove the spring and it would function perfectly, well, until you bolt it to a cam shaft. Valve springs put pressure on the camshafts. The camshafts compress the valve springs and they are exerting that force back to the lobes on the camshaft. The valve springs don’t care which way the camshaft spins, they just want to release the tension. This is where the spring in the VTC comes into play. You see if the base of the VTC assembly spins counter clockwise then the middle portion of the VTC will move downward toward the base of the VTC assembly. There is a spring between the middle portion of the VTC assembly and the base to keep this from happening.

I believe the clacking noise you hear when a VTC assembly “fails” happens because the spring is no longer strong enough counteract the pressures exerted from the valve springs and the center section is moving downward then back up.

Now for the actual function of the VTC. When the oil galley is blocked, pressure builds in the area between the top and middle of the VTC assembly. The pressure forces the middle portion of the VTC assembly to twist downward effectively retarding intake camshaft timing. There are three seals within the VTC assembly. The first seal is located on the lower outside of middle piece of the VTC. The second seal is located on the lower outside portion of the base. The third seal is located in the VTC cap.

I believe what happens when a VTC assembly is “too far gone” to rebuild is the seals are no longer able to maintain the proper oil pressure to counteract the pressure from the camshafts. This means the VTC will no longer be able to retard the camshaft.

Nissan only includes the VTC cap seal in their rebuild kits, along with a new spring and cap. It would make more sense if Nissan included the other two seals with their rebuild kits. I believe this would greatly increase the success rate for rebuilding VTC assemblies.


Now a few things to note:
-When installing aftermarket camshafts/valve springs, it would be prudent to replace the VTC springs at the very least. I would recommend finding a stronger solution. Keep in mind if the spring too strong you could impede VTC performance.
-Grounding a VTC assembly forces it to be in the advanced position all the time. This means the spring is compressed all the time and they are holding back oil pressure all the time.
-If your VTCs are grounded and you hear clacking on cold engine starts this is because there is no oil pressure in the VTC assembly.
-If your VTCs are ungrounded and you hear clacking, when you lug the engine the VTC solenoids engage providing pressure. If they still make noise while the engine is lugging either your seals are unable to retain the oil pressure, or the VTC solenoids are not functioning.
-The louder the clacking the weaker the VTC springs are, this is because the middle portion is traveling father.


Pics: (if you need a bigger copy let me know, these are resized to <25% )

MrGone

iTrader: (30)

Greeny

iTrader: (43)

I will add the vtc tsb...

Greeny

iTrader: (43)

subs1000w

when the vtcs are at rest ie no oil pressure i assume they are in the retard posision

MrGone

iTrader: (30)

correct

bhunter

iTrader: (3)

How do you get them out of the engine to fix them? Isn't that the really tricky part or not?

Greenbuggy

So, the other day my maxi stopped running when I was going down the road, pulled off a valve cover after I realized that I had spark and fuel, only to find that one of the VTC covers had literally exploded in the valve cover, fortunately it looks like it hasn't damaged anything. Does anyone have a cover from a bad VTC they'd sell me so I can rebuild this one, or a set of new or rebuilt VTC's so I can get my maxima running again? I really need to get my car back on the road. PM me or shoot me an email kris (at) speedyoldtruck (dot) com, thanks

internetautomar

iTrader: (30)

this had better be stickied

Michael

iTrader: (21)

haha dream on. I imagine your motor is toast. If the cap comes off the VTC assm. slips off which causes the chain to slip off time...this causes piston to valve collision which causes the valves to be bent.

I have seen 2 motors do exactly what you described first hand (have one right now with that problem) and both are toast. I have also read a couple of other members on here with the same thing...also bad motor.

You may be able to get a head (or rebuild them with new valves) and put it on along with the VTCs but chances are that with the chain slipping it probably took both heads out.

505max94se

iTrader: (15)

Perfect timing for this information Shawn, thanks! I'm going to be rebuilding the rear(left) vtc and replacing the front (right vtc) here in a week or so. Maybe I'll take some pics and post them.

It's weird because my '94 maxima never had a vtc problem at 145,000 miles but my '92 sounds like a diesel at 85,000 (est.) miles on the engine. Supposedly nissan fixed the problem in '94 so maybe I'll take apart a vtc from my '94 and compare it to a vtc from my '92.

Cliff Clavin

iTrader: (11)

I think it depends more on how the car is driven and how well it was maintained. Plus, there might just be some luck in there.

My first Maxima I changed the oil religiously, usually less than 3k miles. I drove it to 160k with ZERO vtc ticking. I didn't even know about it the vtcs when I owned that car. I also drove a lot on wide open freeways for hours at a time, with the oil flowing constantly and at high temperature. I am just guessing, but I think that helped keep the oil galleys clear.

My current Maxima I bought from my brother, who was the second owner. He was very good about changing the oil, but at a little over 100k, it developed a little and progressively got worse. At 145k, the ticking was loud and virtually constant. The first owner (brother bought it at I think 40k or 50k) might not have been good about changes. Also, my brother commuted in heavy traffic and made a lot of short trips in the car.

Please let us know what might be different on the 94. I can't see what they can do, since it is kind of a flawed system.

92 Max

I've just pulled the front and rear VTC on my 92 SE. The front wasn't too bad but the rear was a fight to the finish. The coil tower is too close to the VTC bolt to remove it. After much cursing and swearing (MUCH) I managed to remove the VTC. The Timing chain jumped on the rear exhaust cam, but luckily I followed the TSB and marked the chain before I started. I hooked a small bungee on the chain but hooked it up to the hood and the ex. cam slipped. I should have hooked it forward to keep the chain on the Cam.
First I though there was supposed to be special links at the sprocket marks but didn't see any at TDC.
Second, any words of wisdom for when I have to wrestle this back on? How do you get the VTC sprocket on when you can't put the bolt on separately? Should I have removed the Chain Tensioner?

MrGone

iTrader: (30)

woah wtf are you doing? lol, that's a lot of work

LMK when, I'll try to come lend a hand if you want


(and by lend a hand, I mean point, laugh, and play with the stereo stuff )

MrGone

iTrader: (30)

yeah, they jump, it sucks. I used whiteout to mark all my stuff because it's easier to see and it's easy to clean off. Even after lining everything up the way it came off (lined up perfectly with the marks along with degreeing the cams) somehow one of the cams was still off a tooth (I have no idea how, it didn't make any sense at all, but it happened). I also had to remove the tensioners (there are hooks on them which hold them in position, once everything is installed you flip the hooks and they spring outward putting tension on the chain). For the strut tower/rear vtc bolt clearance, either lower the tranny or jack it up at the pulley. It doesn't take much to get you 'all the room in the world' for removing and reinstalling them.

For the rear one, you have to reinstall it with the bolt going throught the VTC. You can't just set the VTC on then try to get the bolt in, there isn't enough room with the engine still inside the engine bay.

For the marked links, they are only helpful with the engine at TDC.


If I had to do it again I'd just remove the engine from the engine bay. It's so much easier, and I don't think it would take *that* much more time and would be worth the headache it saves.

92 Max

THanks for the info. After cursing and sweating trying to remove the rear VTC, I finally took a wooden broom handle and slowly collapsed the rear tensioner and hooked it. Then I was able to just twist the VTC enough to pull it out. I realize now that I've got to remove the rear tensioner, like I did in front, to lift the chain enough to twist the VTC out of there. With the tight room in there I didn't want to remove any more than I had to, but there's no avoiding it. This rear VTC is like working on my old MR2 (akin to working on an engine through a mail slot). I hope I didn't bend the chain. WHat I've done is to use a large twist tie to keep the upper chains hooked to the lower drive sprocket. If that doesn't jump then I can get the upper chains back where they're supposed to be.
I noticed that the book says there are silver links in the timing chain, as opposed to the normal gold colored links, at the special places marked on the cam sprokets (Dimples in the sprockets just under the chain where they're hard to see). Sadly the oil residue makes all of the links the same color tan. I'm going to try and resurect the color differentiation by washing the links near where I suspect the silver one is with gasket remover (NAPA). I've noticed that this nasty witches brew of solvents rips through this oil residue like magic in about 5 minutes of soaking. NTB93-126 explains the timing procedure fairly well. I found it on the owens family site (http://maxima.theowensfamily.com/tsb/NTB93-126.pdf)

«§»Craig B«§»

iTrader: (5)

There are different colored links the in timing chain, but it's hard to tell after they've been in the engine for a while. Get a wire brush and start cleaning them and you should be able to see the difference. I think the FSM tells you how many links should be between the special links so you can find one and then do some counting.

To get the rear VTC out, it helps a lot to tilt the engine down towards the driver's side of the car. Do this by removing the tranny mounts over there and jack up the pass. side of the engine.

DanNY

iTrader: (14)

insert pic of bumper press FTW!!!1111

92 Max

Yes the above mentioned TSB quotes 12 ROLLERS between the marked teeth between the exhaust and the Intake (VTC) sprocket.
THanks for the info on tilting the engine. I may need this to get this stuff back in.

Grace_Imports

iTrader: (1)

Great write-up and I vote for a sticky too. A thought that I would add; I think that a very thin shim to go into the base of the VTC where the spring rides (and wears) could be a solution. It would provide a renewed surface for the spring to rest on and could possibly add a little more pre-load on the spring. I am looking into doing an exchange program for VTCs for folks that don't want to bother with pressing themselves.

Grace_Imports

iTrader: (1)

I wouldn't spend a lot of time trying to get the original marks on the chain to line with the dimples on the sprockets. The marks are intended for initial assembly. After one engine revolution the links do not fall back in the same place that they started out on and chances are they didn't line back up that way when you did your tear down. I suggest white-out or whatever to mark the links to the sprockets when you disassemble. Another thing; The intermediate shaft sprocket dots for the upper chains are pointed down. You will not really be able to see them with the lower cover in place. Make sure you are TDC and then count the links per the FSM and you should be in good shape.

92 Max

I cleaned the links Around where I thought were the key links and found them. The damn links are grey metal and the alignment links are silver (brillant). Even cleaned up they all look almost the same. Remember that these links are 12 rollers away from each other so you don't have to clean the whole chain. I started working on this with cylinder one on TDC of the compression stroke (an extension from a compression gauge works well to remotely sense the compression). It's slipped from there along with the cams as I've worked on it but it's still close. When I'm done and put the engine back to TDC #1 at compression these silver links and dimples on the cam sprockets should line up on top. We'll see if I slipped the lower sprocket. One suggestion is to try different lighting to see these special links. They seemed to be more visible with a fluorescent light.

Jeff92se

iTrader: (82)

I've torn down two engines. One of them, the links lined up. The other did not (even though both were at TDC). So since the engine ran fine before, I just marked the sprockets and chains and reinstalled them according to the marks I made.

92 Max

Did both of them come from the factory that way? Or was one worked on by someone else and the links not aligned afterward.
I'm a little worried, because the exhaust cam slipped on the rear bank and when I cleaned the links I found that the link I marked was one off the silver link. However I marked that link hanging upside down, with poor lighting, while looking in a mirror, because of the tight area and with the mirror I may have been off. This engine has never had the valvetrain worked on so it should be as it left the factory.

Jeff92se

iTrader: (82)

I suspect that one (the one that didn't line up) was worked on before. As I saw orange RTV on the timing covers. Nissan uses gray rtv from the factory.

Cliff Clavin

iTrader: (11)

I wonder if the first owner had some work done to it? I know who owned it from 1997 (<50k miles) until now.

I would think it is very rare to work on the timing anything on a VE with under 50k miles, unless it was done at a dealership.

92 Max

Looking at the disassembled VTC pictures above I see two "O" rings or seals inside. Are these rings rubber, and can they be replaced or are they some sort of fibrous material and can't be replaced? I've always been told never to reuse seals.

MrGone

iTrader: (30)

they are plastic like


they have a slit in them and you can easily remove them. I've been trying to think of ways to improve them. If you think about the close tolerances there are, then clean the seals out (bottom side tends to be black and have buildup).

If you just took a spare and cut a "filler" peice it would increse the inner diameter which would probably allow oil to escape. I haven't looked but I would be surprised if Nissan sold just those seals (I mean why wouldn't they put them in the rebuild kits?).

Michael

iTrader: (21)

wait which ones? I have had 4 rebuild kits and all of them have had the O ring and seal in them.

MrGone

iTrader: (30)

yeah, they all come with the top O ring and seal, but there are 2 other O rings in the VTC.

Michael

iTrader: (21)

O gotcha...its been a while since I had mine apart so I cant remember and just figured you were talking about the 2 that come with the kit.

92 Max

THe rebuild kits have an "O" ring and fibrous washer or seal with the spring and cover. These go under this cover. The seals we're discussing are the ones on the middle of the shaft and the outside bottom of the gear section in the VTC. If you look at the pictures above one of them looks redish and has a diagonal slash through it.

92 Max

I appologise if this appears twice. The VTC rebuild kit comes with an "O" ring & fibrous washer that go under the new cap. The seals we're talking about are the ones on the middle of the shaft and the bottom, outside of the gear.
One of them in the pictures above looks red and has a slash through it.

Michael

iTrader: (21)

yeah I gotcha...see post just above your first one.

Greenbuggy

I haven't checked valvetrain timing (just ordered up a new VTC yesterday...regardless of whether or not I need to rebuild the head assy, I need a new VTC in front and I'm going to try and rebuild the rear). My timing chain was still on the VTC assy gear so here's hoping for the best - if I understand your explanation, you are saying when the cap comes off, the chain slips on the base gear?

I work in a shop, so rebuilding the lil bastard isn't an issue, it's just come at a bad time (cause I don't have much money, driving my buddy's '97 Ram isn't helping that situation either, but at least it gets me to work). My motor made no "angry" noises (I've heard and fixed a lot of them on various vehicles) when it stopped running, nor when I tried to restart it after I coasted to a stop.

Correct me if I'm wrong, but I was under the impression that the upper timing chains are separate entities, separate per head at the dual idler pulleys (at least thats what the chiltons shows) - if a VTC fails, it *should* cause chain slippage at the intake/exhaust cam of its respective head, without one of the front/rear chains binding (and causing problems at the lower timing chain - my chains were all still in place on their respective VTC sproket, idler sproket and exhaust sproket) so I'm drawing a blank as to how damage at one head would cause damage at another *IF* the lower timing chain isn't disturbed in that process

Michael

iTrader: (21)

You are correct...I apologize because I wasnt even thinking about the seperate chains...I was thinking about the VG I repaired from a tbelt slipping...sorry about that...just wasnt thinking.

Heck maybe you got lucky and it didnt hurt anything but I dont see how it wouldnt...just have to check and see.

just for reference...they guy I got the GXE from that had the tbelt slip didnt hear anything either...it just quit running. Pulled it to my house and found it screwed up.

Pervis Anathema

iTrader: (8)

How much did a new VTC cost and from where did you order it?

Greenbuggy

My boss's cost (I work at a shop owned by the boss, gets a discount at nissan) $383 per VTC assy, had to be special ordered. Should be here tomorrow or friday, I'll probably take some pics and post em up here.

(I would have dumped or parted this car if it wasn't a 5-speed...I looked long and hard to find one)

Michael

iTrader: (21)

have you taken your valve cover off yet? I assume you did since you said the VTC slid off. Here is what I am wondering...I was rebuilding the VTCs on my good motor a little while ago and looked at it. There is no way for the VTC to slip off unless the cap explodes or the bolt breaks. In my case and the other case I have seen the cap exploded which caused the VTC to slip off and cause the motor to jump time and tear up the head.

Here is a picture of what mine looked like (from the car I bought because of this)
If you look at the end you will see the cap is gone...I found pieces of it in the chain cover.

I am just curious if that is the same thing that happened to yours because I honestly dont see how it can slip without the cap breaking since the bolt and washer is larger than the cap hole that goes on the shaft.

Greenbuggy

My caps did break, pulled off the intake and rear valve cover only to find that the front and rear caps had both come apart. I think the root cause (aside from metal fatique caused by the VTC's clacking for several thousand miles) is that it appears the front tensioner cracked apart, the retaining pin (the one the clasp slides over so you can adjust the upper timing chain in front) slid out so the tensioner might have become overextended. My front timing chain has a couple messed up links, I'm going to pull the heads and check out the valves, and pull the side cover to verify timing (just in case the lower chain slipped or got messed up in the process) before I put everything back together.

Anybody got a rebuilt or rebuildable VTC? I'm going to need another and I can't afford to drop another $383 (in addition to the new tensioner and upper timing chain I'll already need) on a second VTC right now.