That's what I was hopefully thinking...thought that only a belt snap at rpms would do real damage. Good to confirm that.
Actually the reason for the 2 revs by hand is to double check timing after belt is back on and make sure the damper is fully extended to check final clearance.

 

the crank is locked, TB is off. I tried to rotate the cam (on driver side) only. It moved and then stopped (valves hitting pistons I assume) so I gave it a pull because it felt like I needed to get past the resistance.... same feeling when you turn the engine over by hand.

That's when I stopped. So if anyt damage was done it would have been more from me "pulling" not the actual impact.

It sounds like I should be ok. My scope has a little mirror that attaches to the end of it. If that fits into the spark plug hole, maybe I'll take another look.

Auditech, you're right. I think the 4.2 would be almost impossible to change the tensioner w/ the belt on the sprocket. Assuming I didn't bend the valves, I'll be glad I would up doing the whole TB job anyway

 

Please don't take offense at the following comments...esp since you seem to have completed the job successfully. But just wanted to point out a couple of things for future reference and others using this thread for info...I often refer to old threads for help completing a job.

You may have misinterpreted some of the Bentley info. Don't understand why you want to rotate the camshafts independently of the engine...Bentley never calls for this. It actually says to remove the crank lock after removing the timing belt and rotate the crank 45 degrees "counterclockwise" (this CAN be done safely when the valve train is not involved, since belt is removed) to insure that no pistons are at TDC...all this BEFORE you start to remove cams.
After the cam tensioner swap is complete, then the crank is to be rotated 45 degrees clockwise back to TDC and crank lock replaced, before the belt is reinstalled.
Only after the the belt is replaced and tensioned to specs, the entire engine should be rotated 2 full revs clockwise, by hand turning at the crank...this to listen and insure that all is correct and no valves are hitting pistons.

But at no point does Bentley say to rotate camshafts independently of the rest of the engine. Admittedly the installed cams can be rocked back and forth a few degrees at the cam belt pulley with no harm done. I always do this a little on any engine to facilitate getting the belt teeth back to the proper place on the gear, when I'm doing a T-belt change...since I do NOT remove cam gears for this job, in deference to using paint marks on belt and pulley instead. The cam gear can easily be turned (as you pointed out) clockwise to the point of piston contact (about 35 degrees?), which I've done before, but can be returned counterclockwise the same amount back to TDC without doing any harm...this much travel backwards will not bind against cam followers, since it should not have passed to the next cam lobe yet (this was an assumption on my part, since I've done it so many times with no sign of damage in the future).

I would have been scared to continue all the way around clockwise with the camshaft, having to force it past piston contact, not knowing (as it turns out) that this probably does no harm either.

Let us know how it runs and if code stays cleared.

Cheers,
Sam

 

nearly in the procedure (wish it would let you cut/paste).... it basically says, remove the Timing belt, remove the cam sprocket and disconnect the connectors. Obviously the crank and cams need to be locked in order to get the cam sprocket off.

Then it says "rotate crankshaft 45 degrees counterclockwise so that no pistons stand at TDC". Why do you need to do that? I never removed the crank pin so I did the whole job with the crank locked.

Towards the end of the procedure it says "rotate back 45 degrees and reinstall crank lock".

I suppose this would have prevented me from bottoming out the valves and I could have rotated just the camshaft even though it doesn't specifically call for that. I didn't force it past the rotation of the cam lobe. Once I hit the point where it "sprung" clockwise and stopped is when I tried to pull it farther. I gave it a pretty good pull but it never actually moved beyond that point.

Like I said, everything appears to be dead on. Since I didn't do the work with the crank rotated 45 degrees, does that cause another issue?

On the valves, I tried using my borescope with a mirror but you can't really see anything. Last question, it also says "Alignment bushings for bearing caps and camshaft adjuster must be installed in cylinder head".

Are those some sort of shims? I didn't see anything in the disassembly that match the description.

thanks,

Bob

 

Those would just be slightly protruding "sleeves" (in the threaded holes), likely on the head half of the bearing on the head, to insure the bearing caps align precisely when you reinstall them. Those should have stayed in place on the head, during disassembly. I think the note was referring to a complete new assembly with all new parts.

I really think you have no worries now. As long as you're timed correctly, all the original caps back in original spots and direction, the cams and lifters have to settle right back to where they were.

Sam

 

ok, now I know what those are, they did stay in the head.

I'm going to do a final check and then reinstall the valve cover and wait for the rest of the TB parts to arrive tomorrow.

Actually, maybe I'll put the cover on last so I can verify the marks on the cams after installing the new belt.

I've done a few of the 40v timing belt jobs before, one thing I never get used to is the initial dry start which sounds like all the valves getting bent. Couple that a new/dry cam tensioner and my SNAFU and it should be stress free 60 seconds

thanks for all your help, I'll post back when I'm done.

Bob


Update for future reading - I took my other old 40v head and held a piston up to the valves to try and get an idea where the point of impact would be. The 3 intake valves extend out the farthest at the height of cam rotation. The bad news is the high point is on the outside edge of the piston so I don't think you would "see" the impact looking through the plug hole with a scope.

It's just too far away from the middle of the piston.

 

Thank YOU Bob.
Thanks to you, I (we) have already learned much more than Bentley tells us.
And yes, I fully agree that you should save the valve cover for last...I would want to see those cam timing marks line up, for peace of mind. I'm meticulous that way and always fear worst case scenarios.
Cheers,
Sam

 

Yeah i see what you did, basically fubar'd the job. I don't blame you though, the bentley manual is very misleading. The bentley is basically a copy of Elsa, which is written by the Germans. If you know anything about the germans they would expect you to be an expert mechanic just to attempt doing anything to that engine, basically hoity toity BS.
No big deal though, in order to bend those valves you would need hit them with over 1,000 lbs of force (according to a hoity toity german engineer i used to talk to) which can only be developed by high engine speed since the clearances are as such.

Put it back together and it will run like a champ, guaranteed.
I should also note that the tensioner break in process can take up to 100 miles of driving, so you might hear it chatter for a while.

 

auditech, thanks for that reply - that's what I wanted to hear! I gave it a good pull but no way I'm generating 1,000 lbs. or even 1/2 that. Good feedback on the tensioner as well.

Definitely my fault but in re-reading that entire section it would have been nice if it said "remove crank locking plug" and rotate crank back 45 degrees. Kind of obvious you can't rotate the crank w/o removing it but that statement would have jumped out at me.

It would be great if you could add your own "notes" to the Bentley.

Do you think my mock up using the old head/piston is correct? Have you seen damage to the center of the piston after a belt breaks? Looking at the angle of the valves I can see why they bend easily (aside from the obvious impact). It looks like the piston would impact the outer edge of the valves and basically push them sideways.

 

I've taken apart many engines with snapped timing belts and bent valves, and they usually do take a huge chunk out of the top of the pistons at almost a 45* angle. Of course those usually hit at well over 1,000lbs of force too.

It will be easy to tell if you slightly bent a valve after its running, you should have a major misfire, and the compression on that cylinder should be nill. I give that about a 5% chance though.