Cam timing changed ???
 

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 :confused: 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...

That's what you get for checking them again.

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

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

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

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.

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.

Wow, you actually know it takes 9 revolutions :eek: 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

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.

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