Cam timing changed ???

[hobieboy]

Hi,
So I rebuilt the top end of the engine & everyone seemed fine so far

After my 1st track event (& ~500 miles total driving), I drained my oil, re-checked valve clearance, etc. just to make sure everything is ok after the break in period.

While I'm at it, I re-checked my cam timing using the dial indicator. Because of location, I ended up checking cylinder #3 and #4.

And that's the surprise - the value changed... I re-checked my cam timing, must be at least 5 times before I put the engine back into the car. They were 1.575.

Now, #3 is at 1.31 and #4 is at 1.46 I supposed this can be due to chain slacks (when I checked/set timing, I used vise grip/tensioner per Wayne's book)? Just want to tap into the knowledgeable group here to see if this is normal & if my guess is right.

Thanks...

[Eagledriver]

That's what you get for checking them again.

[ChrisBennet]

I don't think the chain tensioners apply enough pressure to make an accurate measurement. Using a different valve than the one you originally timed it with (#3 vs #1) probably introduces a little more error as well.
-Chris

[Jeff Alton]

The tensioners do not apply enough pressure to the ilder arms. I just did this today. Timed cams in the morning and then tonite I figure I will check them one more time with only the tensioners in instead of a mechanical means to tighten the chains. Nearly crapped my shorts when my perfectly timed cams seemed to be out. Pulled a tensioner and went back to mechanical tensioning to check, and the timing is spot on!

Cheers, Jeff

[Wayne 962]

Originally posted by catca
The tensioners do not apply enough pressure to the ilder arms. I just did this today. Timed cams in the morning and then tonite I figure I will check them one more time with only the tensioners in instead of a mechanical means to tighten the chains. Nearly crapped my shorts when my perfectly timed cams seemed to be out. Pulled a tensioner and went back to mechanical tensioning to check, and the timing is spot on!

That's a good explanation. Also, the engine will settle after it's run in - I don't think it's unusual to see some variations in the cam timing. When you re-adjust the valves after a few hundred miles, they are typically out of adjustment too...

-Wayne

[hobieboy]

Thanks for the confirmation guys... kinda what I was thinking as well.

The good news is that all my intake valves don't need adjustments It would have been a royal PITA to adjust cylinder #1 (which is why I checked the cam timing off #3 instead). Will continue my mission with the exhaust valves tonight.

[RoninLB]

there is also some varation from the crank gear not comming around to the same chain link at every rotation when rechecking timing. it takes 9 revolutions to bring everything back to original start of gear and chain link.

[hobieboy]

Wow, you actually know it takes 9 revolutions Amazing!!!!

I did check the timing twice and they do change ever slightly each time (by ~.01mm). I thought that's operator's error but maybe its just the chain then...

At this point, I'm kinda taking the noted & understood attitude. After many moons, I want to drive the car unless its really really bad

[350HP930]

It helps to thouroughly oil your chain before starting the process since the chain length will noticibly change depending on if its a little dry or loaded with oil.

[aigel]

I think this is a good example why any spec comes with a tolerance. What's the tolerance on this? I would not worry about it unless it is far outside the tolerance....

George