How a simple valve adjust can ruin your whole day.

[zKars]

Hardway, so from what your saying, it seems then that there was no actual touching of the chain to the valve cover. You can confirm that there is no marks in the aluminum?

If thats the case, then the patterns we see are likely just "cleaning" of the previous dark varnish coating by oil spraying from the chain. Did you recently change to so some of that modern "detergent" oil?

[Pomorza]

Guys

I have a bit of a theory I want to run by you. For what I remember the chain in tensioned by oil pressure using the tensioner. When you're turning your engine with a remote start I don't believe enough pressure builds up to actually put any "tension" on the chain. I say this because the last time I did a valve adjustment on my brother's 620 (L20) I noted that the backside of the chain - being the right hand side looking at the front of the motor - was rather loose and floppy. Its a new chain and I know I installed it correctly as I did it twice (see above post). Could that and the "blue shop towel of doom" caused the chain to skip a tooth or five while you were not paying attention.

The other reason I bring this up as last time I started the Z in the winter and revved the motor too quickly - before oil pressure built - there was a nice chain rattle coming from my engine. The chain is new - installed about two years ago and I know I did this right as I took forever doing it - literally took me like 8 hours, took my sweet time.

Thanks

Jan

[240260280z]

Guys

the chain in tensioned by oil pressure using the tensioner. When you're turning your engine with a remote start I don't believe enough pressure builds up to actually put any "tension" on the chain.

Thanks

Jan

Absolutely correct but there is one more detail: the chain should initially be installed with 0 slack. the tensioner simply maintains a firm pressure and takes up slop over time as the guides wear and the chain stretches.

Here is the initial install with no slack:

Edited July 20, 2013 by Blue

[siteunseen]

I pulled the cover off my '77 that only has about 1500 miles on a newly rebuilt motor, also looked at the one I took off my 240 about a month ago. It has to be so close that the oil is slinging against the cover and making those footprints like Zkars says. I use VR1 and my valve cover didn't look like that when I put the motor together back in September '12.

Sorry about that Hardway.

[darom]

zKars, don't feel too bad - you were helping your friend out. We are all human and make mistakes.

It took me 2 days to figure out the no-start condition on my 76. When I replaced the intake's exhaust gasket, I stuffed paper towels to keep dirt out. After cleaning and putting the intake back, I couldn't figure out why even with the air/fuel/spark I couldn't start the damn thing. Of course, I had a bunch of paper inside the cyl. head! :-) It is funny now, but at that time I felt like hitting myself with the hammer on the head to teach a lesson to pay attention.

[Pomorza]

Absolutely correct but there is one more detail: the chain should initially be installed with 0 slack. the tensioner simply maintains a firm pressure and takes up slop over time as the guides wear and the chain stretches.

Here is the initial install with no slack:

Blue

I remember this fact also, but if someone was to install the chain improperly or due to age the chain had strecthed enough to not be at 0 slack couldn't be possible that enough slack was there that the motion of the remote start caused it to jump a tooth? It's just a thought.

Jan

Edited July 21, 2013 by Pomorza

[zKars]

More details now that I'm made some positive progress. The car is running and left for its new home last night. The original power-on ticking/clicking noise that caused the iniitial investigation is gone. Replace with much more satisfying and familiar cold clearance set valve train clatter.

Blue/Jan, you guys are spot on about new chain being tight ie no slack. I installed the "new" (to him) head and a new chain and guide,s and as usual, the chain is a VERY tight fit.

I got the chain on its correct clocking, then when re-installing the (curved) tensioner, I had to use a c clamp across the chainand guide in the center to lightly compress it to get the top bolt (slotted hole) in the tensioner. Same when re-installing the tensioner. Tight fit indeed.

I took a picture of the old and new chain on the bench to show the length difference (sorry will post it later). The old is clearly stretched, but not quite to the extent I expected. The old head had shims under the towers as well which I removed for the near-stock thickness N42 that took its place (used his towers/cam/rockers/lashies). Would have been impossible to get that chain on with those shims in there.

I looked at the valve cover and it looks exactly like the two shown above. Not a mark/gouge in the cover that I can feel with my nail or finger, just the cleaned paths made by fresh modern oil clearing away varnish.

And in general, with more thought about what caused the tooth skip to start with, I'm more and more skeptical about the rag having anything to do with it. I just can't believe the texture and material strength (or lack of it) of it would be able to create a wad that would have had sufficient compressive strength to cause this. The rag was well distributed around the gear when I stopped dug it out. No concentration in one spot. I'm now inclined to believe its a combination of the herky/jerky motion of using the remote crank switch and the very loose chain with no tensioner pressure that ate my lunch. Beware!

Another learning point to add to the conversation. When using the starter to rotate things, it's now very clear that it had no problem bending the valves as it rotated the engine without so much as a hiccup that might give you clue something bad was happening. At one point late in the process, (actually just before the realization of doom occured) I'de put a socket on the crank nut to move the engine to exact TDC to get things lined up for another timing check. The engine rotated smoothly then BANG, it stopped dead. When back the other way, smooth until, BANG, same thing. Dead stop. I put quite a bit of pull on the handle and couldn't budge it. So its clear that HAND rotation or maybe pushing the car in gear is the right technique, if you have ANY reason to suspect an old loose chain or you're working on a new motor and testing if you turns over. Sounds obvious now, doesn't it?

[zKars]

and here are some pics

[zKars]

Finally had a chance to remove the valves from the head.

Enjoy the painfull art!

[SteveJ]

Ouch.

[LeonV]

Ouch.

Ouch is right!

[Pomorza]

That's actually not as bad as I've seen. Still painful to look at but I've seen much worse.