A couple cam timing questions: - Page 2

Mike Juzenas · 04-24-2006, 07:52 PM

Quote:

Originally posted by bbh03
Thanks Doug!

I just installed the tensioners and remeasured. The right stayed put, but now the left is advanced a little out of range (moved about 1.5mm). I will have to retime them tomorrow. It appears the left can be timed with the tensioner in place. Will that provide enough tension for timing or should I put a clamp back in there?

Thanks,

Put the clamp back in...I don't think you will get consistant results with just the pressure of the tensioner...

Cheers,

Mike

2.7RACER · 08:15 PM

Brian,
"Will that provide enough tension for timing or should I put a clamp back in there?"
Yes. Don't need a clamp. Just get them as close as possible.
Have fun,

Mike Juzenas · 04-24-2006, 08:53 PM

That will set him straight!! ;-)

I thought the tensioners will not pressure the chain enough to simulate a running engine (or at least that is what Gerry Wood's told me during an engine rebuild course). Of course its a personal choice....

Cheers,

Mike

2.7RACER · 09:56 PM

Mike,
I agree with your thought about consistent readings when the chain is snugged up.
Brian reported the right stayed put and the left jumped 1.5mm. I'm taking that to mean it is 1.5mm from where it should be. Or is it 1.5mm rather than 1.33mm?
I suspect the left side was moved while tightening the cam nut.
As you know it is important to hold the flats of the cam so as to not pull against the timing chain when torqueing down the nut.
Things shouldn't slip but the chain can jump.
I believe if Brian gets the left side consistently back to .0543, then carefully retightens the cam nut while holding the flats of the cam and not exerting any pressure on the timing chain it will be proper.
As you brought up he can then apply some extra pressure to the idle side of the timing chains, Snug not tight, and verify the numbers.
The timing chains when running are not tight, they are snug. If they were to be run tight, as you can guess they would wear out, (stretch) prematurely.
So I find myself in agreement with your and Gerry Woods advice.

bbh03 · 04-25-2006, 03:49 AM

Yes, it moved 1.5mm from where I had it! Hopefully I can put this to rest tonight and move on - I will report later. Thanks all!

bbh03 · 05-03-2006, 04:25 PM

Well, finally found some time to do it. Got both to 0.053" (1.346 mm) give or take 0.0005" (0.013mm) after taking 4 to 5 measurements per side. Done and done. Right near the middle of the range prescribed by John for this set up (1.26 - 1.40 mm). Thanks for all the help everyone!

As for the piston/valve clearance check, Wayne mentions a shortcut of setting the valve about 2.0mm open and SLOWLY turning the crank looking for resistance. Does anyone believe this meathod is suspect? It is obviously 100x faster and allows you to do the check on each valve multiple times in minutes.

I don't expect any issues regardless because 1) these are 3.2 L JE pistons with healthy valve pockets 2) the cylinders are new 3) very little was fly cut from the heads 4) deck height was set toward the high side since 0.25mm less would have been too close to the low side. 5) 964 cams. But I have to check anyway

Thanks!

Eagledriver · 05-04-2006, 09:18 AM

I don't like to turn the engine to see if I can hit a valve with a piston. You could do it as an after check just to make sure but I wouldn't do it as my first check. To check the clearance what I do is stop the piston about 8 degrees BTDC on the overlap and then turn the exhaust valve in until it hits the piston or 2.5mm if it doesn't hit. Then I reset that valve and turn the engine to about 8 degrees ATDC and do the same for the intake valve. Note that a check at TDC will not tell you the closest value because the piston moves very little in the last few degrees while the valve moves alot. The 8 degrees is just an estimate on my part based on some measurements another engine builder did. I figure somewhere betwee 5 and 10 degrees is where the closest approach is.

-Andy