Pls Help: Big Problem with Cam Chain

lr172 · 07-24-2009, 06:39 PM

I had a leak in the left Chain Case, so I removed the case to replace the gaskets and o-ring. I got everything reassembled and pulled the valve cover to check the cam timing.

Before I disassembled, I marked the position of the chain on the sprocket, as well as the location of the pin in both the sprocket and the small sprocket behind it. I reassembled it in the same way and never turned the cam or the crank while apart.

When I pulled the valve cover, I didn't realize there were washers under the nuts and they all fell to the floor. I recovered 5, but still have not found the 6th. I don't think it could have fallen into the valve area, but anything is possible. I'll look harder around the garage tomorrow with the sunlight.

Onto the problem... As I turn the crank, I get about 90-120 degrees of rotation and there is a hard stop. It is not a gradual tightening like rolling into a comression stroke. It stops abruptly and forces the chaing tensioner to compress. I can come back and forth up to this point repeatedly. I can go backwards to Z1 (comression for #1), where I started, and rotate about 45 degrees in reverse from Z1 and get the same resistance.

I assume from the tensioner tightening that the blockage is on the cam shaft and not the crank. I will tear everything apart tomorrow, but was hoping some of the experts may be able to shed some clues to look at.

Even if the washer fell in there, I don't see how it could cause this. I am assuming that it is in the cam/sprocket area where I did the repair. Are there common mistakes that can cause this?

Thanks a bunch for any assistance you can provide.

Larry

dtw · 07-24-2009, 08:02 PM

Sounds to me like your chain slipped the sprocket on the intermediate shaft. Let me guess, left side?

lr172 · 07-24-2009, 09:13 PM

It is the left side. What do you mean by splipped the intermediate sprocket? I thought about possbililty that a link got bunced up on that srpocket, but I figured the the tensioner would have been more comrpessed due to the shorter chain. This is not the case.

Could you explain a bilt more about this problem and possibly how to solve it?

Thanks,

Larry

lr172 · 07-24-2009, 09:31 PM

Ok. I did some research and now understand that the chain likely skipped to a different tooth on the intermediate sprocket, as I was not carefull to keep tension on the chain while slack. I will go back and do the base timing from the manual and then the dial indicator timing method.

Therefore, the tension was from the valve(s) hitting the piston. I was initially turning pretty hard on the crank. Hard enough to compress the tensioners and to actually tighten the alternator nut a bit. Do you think I could have bent a valve doing this? Also. so that I can test this via leak down method, do you have any idea which piston/valve combination would contact each other at a poition approximately 90+ degrees clockwise from TDC/Compression for #1?

THanks for the help.

Larry

Flat6pac · 07-25-2009, 03:52 AM

You need the dial indicator on it. There is no guarantee that there was 6 washers under the cam gears as there is a thrust measurement on the cam drive gear that needs to be done too. The depth measurment is done by stacking the washers for thickness and measuring the depth of the gear from the face of the engine.
Dial indicator tells you the valve opening of the valve on intake by the cam..very necessary to proper measure.
Bruce

lr172 · 07-25-2009, 06:10 AM

Thanks for your help. The washers I was referring to above were the washers under valve cover nuts and not the shims under the cam gear. I included this part of the story just in case it is possible that the binding was coming from the washer stuck somewhere in the valve train.

I am about to head out now re-do the initial timing and see if the binding clears and then do a leakdown test.

Quote:

Originally Posted by Flat6pac

You need the dial indicator on it. There is no guarantee that there was 6 washers under the cam gears as there is a thrust measurement on the cam drive gear that needs to be done too. The depth measurment is done by stacking the washers for thickness and measuring the depth of the gear from the face of the engine.
Dial indicator tells you the valve opening of the valve on intake by the cam..very necessary to proper measure.
Bruce

lr172 · 07-25-2009, 09:08 AM

Well, clearly something went wrong somewhere. I was quite a ways out of position. Following the Bentley manual for the intial timing setting (930 mark on cam at 12:00 position while at TDC/Z1) helped me out and it is now timed close to perfect (.052" @ Z1) and have no issues with rotation. Also did a leak down on #2 and #3 and both checked out ok, so I didn't bend a valve.

A BIG THANK YOU to DTW for pointing me in the right direction. You guys are great!

Larry

dtw · 07-26-2009, 09:13 AM

We aim to please and love a happy ending. Lesson: check timing w/a dial gauge even if nothing moved - the extra 10 minutes of work can save lots o' green.

One more tip: since you have re-timed the left side. It is worthwhile to now check the timing on the right side, and make sure the two sides are in the same ballpark as far as timing. If they are significantly different, it can possibly make proper tuning an impossibility.

I knew it was the left side...because every time I work on an engine, it seems that that is the side that likes to slip. The chain will either jump on the intermediate sprocket, or it will completely fall off. Sometimes it gets cocked and binds up on the sprocket, or comes halfway off (only one half of the duplex chain engaged on the sprocket teeth). Seems it always ends up with me fishing around in the crankcase with a long screwdriver, trying to get the chain situated correctly again.

Lately, I try to keep a mechanical tensioner on the chain at all times during assembly, to prevent these bonehead mistakes of mine...