Dreaded Upper Cam Chain Guide Failure

[Great White]

Originally Posted by 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

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.