Dreaded Upper Cam Chain Guide Failure

[Great White]

Last time I did my yearly oil change (a couple months after the pandemic hit,) I discovered steel glitter in the oil. I parked the car, set it up for hibernation, and haven't driven it since (except two short drives to renew the registration :cry: )


Fast forward to now, I'm finally in a position to repair it. Without further ado, let's get into it.


The pictures below are of the passenger side upper chain guide backing plate, cam cover, and chain. I haven't removed the driver's side cam cover as of yet. My questions thus far are as follows:


Does anybody sell replacement backing plates?


If no, is the driver's side backing plate identical?


If no, does somebody have a print of one so I can get a head start on making one from scratch?


If no to all of the above, I can reverse engineer it from a new plastic guide myself, I was just looking for a faster, simpler solution.


Next question...


Does the chain look okay to you guys?


Last question:


What on earth do I do to gain access to all 4 of the nuts holding the brake booster to the firewall? I haven't found a combination of socket extensions that will allow me to get a grip on all 4 of them. Two of them are easy, but the other two are obscured by the steering column. I managed to remove the throttle pedal assembly to gain a little more room, but now I feel like that was an exercise in futility. I'm not as flexible as I used to be I guess.


Any help is appreciated. Can't wait to hang with you guys in May.

[WARP TEN]

Talk with Jerry at Jerry's Gaskets and Marc Haibeck at Haibeck Automotive. I am sure they can offer some good advice. --Bob.

[AndrewL]

Jerry sells the facings. https://www.jerrysgaskets.com/search.php?search_query=facing

I can't help with your other questions as I haven't done that job yet.

[A26B]

............................ My questions thus far are as follows:
Does anybody sell replacement backing plates?................................

I am making a run of the Cam Cover Secondary Chain Guides now. So they will be available shortly.

I have lots of inventory of all of the chain guide facings, having made those several years ago.

[A26B]

..............................
The pictures below are of the passenger side upper chain guide backing plate, cam cover, and chain. I haven't removed the driver's side cam cover as of yet.

My questions thus far are as follows:........................

Next question. Does the chain look okay to you guys?....................................

I think your first question should be what caused this?
The Secondary Cam Chains had to be running very loose and making some sort of racket. I think you are pretty fortunate that you didn't explode the engine. Had the cams jumped timing or broke, valves would have collided with pistons.

Describe how you discovered this in the first place.

[Great White]

There have been no unusual noises. I simply discovered the steel in the oil during a routine oil change. I know it sounds crazy, but there were zero "symptoms" leading up to this discovery.

[Great White]

I finally managed to get the driver's side cam cover off after removing the brake booster.

If anybody is curious, the solution to the brake booster removal was ultimately removing some of the insulation around it and using a 1/4" drive deep-well socket with a swivel and long extension. It took forever and I needed a chiropractor adjustment afterwards.

For posterity I will post pictures of the driver's side upper cam chain guide backing plate, but I can already say it definitely doesn't look any better than the passenger side one pictured above.

[Z51JEFF]

How many miles does the car have?

[Great White]

How many miles does the car have?


I've got the battery disconnected at the moment, but if memory serves correctly the odometer reads around 162,000 mi. A prior owner had the engine gone though by Marc at around 124,000 mi some time around 2008. The engine has his 500hp treatment. I don't know what the actual reason for the work initially was. I will see if I can dig up info on what was replaced in the documentation I have. If I recall correctly, Marc did a pretty extensive rebuild on it.


Since I bought it, I haven't put very many miles on it. I have replaced a lot of parts (injectors, coils, plug wires, starter, vacuum lines, water pump, radiator etc.) but this is my first time having any internal engine issues with it. I run Amsoil and a wix filter for every oil change and I'm easy on it until the oil is up to temp.

[A26B]

You can tell from the lack of response to the missing facings and extensive wear on the guides themselves, that this is an unusual failure, because no one has ventured to answer.

The fact that BOTH L&R guides are affected, is something more than a Secondary Chain Tensioner failure, which is not common, certainly not both of them.

Getting a look-see at the whole chain system would be nice, but requires engine removal. Dropping the pan may not tell you much that is not already known. I don't think an intact facing could make it into the pan unless chewed up in bits. For $25 or so, you could get a flexible endoscope for an Iphone, that might show you bits laying around behind the timing cover.

Here's a picture of the chain system for reference.
https://cdn10.bigcommerce.com/s-nkg90o/product_images/uploaded_images/chain-guides-smallsize.jpg

Something is not right with the chain tensioning system, which really needs to be resolved. Even if the facings broke or fell off, the chain just does not normally ride that high above the sprockets when properly tensioned. The cam-cover chain guide facings usually don't incur much wear.

Just carefully work your way through it until you find the answer.

[Great White]

You can tell from the lack of response to the missing facings and extensive wear on the guides themselves, that this is an unusual failure, because no one has ventured to answer.

The fact that BOTH L&R guides are affected, is something more than a Secondary Chain Tensioner failure, which is not common, certainly not both of them.

Getting a look-see at the whole chain system would be nice, but requires engine removal. Dropping the pan may not tell you much that is not already known. I don't think an intact facing could make it into the pan unless chewed up in bits. For $25 or so, you could get a flexible endoscope for an Iphone, that might show you bits laying around behind the timing cover.

Here's a picture of the chain system for reference.
https://cdn10.bigcommerce.com/s-nkg90o/product_images/uploaded_images/chain-guides-smallsize.jpg

Something is not right with the chain tensioning system, which really needs to be resolved. Even if the facings broke or fell off, the chain just does not normally ride that high above the sprockets when properly tensioned. The cam-cover chain guide facings usually don't incur much wear.

Just carefully work your way through it until you find the answer.


I do own a fairly decent flexible endoscope and I actually did find what I believe to be the largest pieces of both facings...


I discovered the drivers side facing was resting just under the fixed chain guide on the drivers side (PN 10122171 in the above pic.) I failed to retrieve it as every attempt I made to remove it resulted in it moving further down into darkness. After studying your pic above, I don't think that facing will ever be retrieved without first removing the front cover and the drivers side fixed guide, which I know involves engine removal and the disassembly of many other components first.


The passenger side is a similar story, except I needed the inspection camera to actually find it. It was resting on the casting to the rear of the passenger side pivot (PN 10122172 in the above pic.) I fiddled with trying to remove it as well but with similar results, except when I lost it I heard it tap against everything on it's way down. I believe if that one isn't in the pan, it must be close.


As far as seeing any other failed components while looking around in the front cover with the inspection camera, I didn't see anything obvious that jumped out at me. That being said, I don't really know exactly how much of the cam drive system I can see with just the inspection camera from the top side.


I can take videos of most of the components inside of the front cover and post them if you think that would be helpful, however I am somewhat limited because the 90* mirror attachment for my camera fell to pieces when I took it out of the package. I can basically only look "straight ahead" with the inspection camera. I may try to glue the mirror assembly back together but I don't want it coming apart inside the engine as that would just be one more thing to retrieve.

[Subfixer]

Since this seems to be related to the chain tensioning system, could the problem be low oil pressure or blocked oil passages?
I removed the cam covers from 90 #116, which was flooded, abused and overheated but the guides were untouched.

Sent from my Pixel 4a (5G) using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)

[Great White]

Since this seems to be related to the chain tensioning system, could the problem be low oil pressure or blocked oil passages?
I removed the cam covers from 90 #116, which was flooded, abused and overheated but the guides were untouched.

Sent from my Pixel 4a (5G) using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)


The only way I know to test oil pressure is to put the whole thing back together, hook a test gauge up, and start the engine. I'm not opposed to doing that but at this point it has been suggested to disassemble further...


The gauge in the cluster always showed decent pressure however I know they aren't accurate.


There seems to be no signs of oil starvation in the top end (aside from the missing upper guides.)


Is it possible that the hydraulic tensioners are faulty? Is there any way for me to remove them and inspect them for proper function without damaging anything?

[Marc Haibeck]

Here is some information about upper chain facings coming loose. Note that this article is from 2008. I have seen about four more failures since then. We have found them when we remove the cam the covers for service unrelated to any cam chain or drive problem.
http://www.zr1specialist.com/HAT%20Web/articles/upper%20wear%20strip.htm

[Great White]

Here is some information about upper chain facings coming loose. Note that this article is from 2008. I have seen about four more failures since then. We have found them when we remove the cam the covers for service unrelated to any cam chain or drive problem.
http://www.zr1specialist.com/HAT%20Web/articles/upper%20wear%20strip.htm


Thank you for your contributions. I have three questions:
If you don't mind me asking, what did you have the cam covers off for?
What do you think causes the wear strip to fail?
What is your repair procedure after such a discovery (provided the engine arrived in a still-operable state such as mine?)


Thanks to everyone who has commented on this thread this far. If there's anybody following along who has something to contribute, I encourage you to do so. I don't feel this is something that should go ignored, as despite my best efforts I have found very little info on the matter aside from what Marc, Jerry, and Dynomite have contributed.


Not to spread fear, but be aware there were zero notable symptoms leading up to this in my case. No noises, no misfires, no noticeable lack of power even. I simply looked in my oil drain pan with a flashlight and saw some glitter whilst doing a routine oil change.


It takes a few seconds to look inside your passenger side cam cover after removing the oil cap to see if there is still a passenger side wear strip in there.

[grahambehan]

My input would be:
I agree with Marc and Jerry that cam tensior failure is unlikely a root cause for this scenario.
Firstly if we look at how the tensioner works. There is a spring within the tensioner that causes it extend when the chain is slack which allows oil to be allowed into the internal chamber, when the chain load tries to compress the tensioner the check ball seals and the compression of thr tensioner is controlled by the leakage path between the inner and outer sleeves. The next time the chain goes slack-rinse and repeat.
How does the chain go slack?
This is caused by not only wear, but also the differences in torsional loading due to cam events, opening vs closing ramps. So through the cycle this happens several times.
This causes a slackness in the chain between the cam sprockets, hence the need for the top chain snubber. With this part failemd there is potentially enough motion in the chain to allow contact to the metal surface.
Failure of the plastic "snubber" are not commonplace but do occur.
In this instance since metal to metal contact between the chain and the metal mount plate has occurred i would recommend replacing the chains, since the chain is an interference fit pin and prestressed to impart compessive loads to prevent failure.
Graham

[Great White]

My input would be:
I agree with Marc and Jerry that cam tensior failure is unlikely a root cause for this scenario.
Firstly if we look at how the tensioner works. There is a spring within the tensioner that causes it extend when the chain is slack which allows oil to be allowed into the internal chamber, when the chain load tries to compress the tensioner the check ball seals and the compression of thr tensioner is controlled by the leakage path between the inner and outer sleeves. The next time the chain goes slack-rinse and repeat.
How does the chain go slack?
This is caused by not only wear, but also the differences in torsional loading due to cam events, opening vs closing ramps. So through the cycle this happens several times.
This causes a slackness in the chain between the cam sprockets, hence the need for the top chain snubber. With this part failemd there is potentially enough motion in the chain to allow contact to the metal surface.
Failure of the plastic "snubber" are not commonplace but do occur.
In this instance since metal to metal contact between the chain and the metal mount plate has occurred i would recommend replacing the chains, since the chain is an interference fit pin and prestressed to impart compessive loads to prevent failure.
Graham


Thank you for your input Graham! This info gives me a better understanding of the function of this system and a tighter focus on my next step in repair.

[grahambehan]

You are welcome.
Graham