My last cam timing question

75-911S · 12-07-2005, 12:45 PM

After carefully following Wayne's book and the many suggestions given to me on this forum and gleaned from the many previous threads, I was able to get my cams timed to the right settings. Feeling very pleased, I moved on to install my new chain tensioners (non hydraulic) and the rocker arms for cylinders #1 and #4. I dutifully went through the piston to valve clearance routine on those cylinders and then installed the remaining rockers and checked all the rest of the pistons for valve clearance. (A time consuming by reassuring process.)

Then, having read that using a vice grip clamping system to set cam timing might yield different readings for different tensions on the chain, I thought I'd go ahead and check the cam timing now that the tensioners are installed figuring that this will be the tension the chains will actually be subjected to. And to my horror I found that both of my carefully timed cams didn't show the proper reading on the dial indicator until about 15-18 degrees BEYOND Z1.

So, here's the question - should I go through the cam timing procedure again with the tensioners installed to get the .47mm reading I need at Z1?

I was wondering if the position of the distributor when it's installed will compensate for the "problem"?

Jack

Eagledriver · 12-07-2005, 02:45 PM

Either you did it wrong before or you're doing it wrong now. What are you doing different? In order to get 15-18 degrees at the pulley your cams have to have rotated 8-9 degrees different than before. Is there enough slack in the chain to rotate the cams 8 degrees? You can tell by putting a wrench on the cam nut and trying to turn the cam so as to tighten the chain.

The direction of the error also seems to be wrong. If there were slack in the chains now the cams should be advanced not retarded as your readings indicate.

-Andy

75-911S · 03:26 PM

The only thing that is different is that the initial cam timing was done with the idler arms squeezed toward the cam housing lips with padded vice grips - and the second time the readings were taken with the chain tensioners installed.

There was no slack in the chain either time.

The first time the .47mm readings for my engine/cams were set at Z1. The second time the readings came only AFTER Z1 (about 15 - 20 degrees past).

Jack

2.7RACER · 12-07-2005, 08:41 PM

Jack,
Am I missing something?

"I was able to get my cams timed to the right settings. Feeling very pleased, I moved on to install my new chain tensioners (non hydraulic) and the rocker arms for cylinders #1 and #4. I dutifully went through the piston to valve clearance routine on those cylinders and then installed the remaining rockers and checked all the rest of the pistons for valve clearance. (A time consuming by reassuring process.)"

Weren't your chain tensioners and rockers installed when you first timed the cams?

How did you clamp the chain with vice grips? It isn't necessary to have the cam chains "hard tight." Snug works fine.

I can't imagine how you clamped the chains and got the cams retarded 15 to 18 degrees. Are you turning the crank clockwise?

Ultimately, trust the readings you are getting with the rockers and tensioners in place.

Remember you'll get the .47mm at Z1 and 1.0mm at 6 degrees after Z1.

Let us know what you find.

75-911S · 12-08-2005, 04:02 AM

2.7 Racer Asked:

1. Weren't your chain tensioners and rockers installed when you first timed the cams?
No, I followed Wayne's book and clamped the chain tight with padded vice grips. (pic)

2 Are you turning the crank clockwise?
Yes, and once I had the dial indicator readings I needed (.47mm for my engine/cam) I pulled the pin in the cam sprocket, moved the crank to Z1, found a new hole for the cam sprocket pin, tightened everything up, rotated the crank 720 degrees and everything looked great.

3 Ultimately, trust the readings you are getting with the rockers and tensioners in place. Remember you'll get the .47mm at Z1 and 1.0mm at 6 degrees after Z1.
This is exactly what I had when I first set the cams. Not now.
I guess that means I should do it all again. That's what I figured -but I thought I might be missing something.

Thanks once again for your advice.

Jack

safe · safe's Garage

When I timed my chains I noticed the the amount of tension you put on the idler arm changed the timing.
Wayne says to keep maximum tension... I belive that is to simulate the tension the chain will have with the engine running.

I did not recheck timing with only the tensioners.

wilke3169 · 12-08-2005, 06:07 AM

I used much the same devices that Jack is using to time my cams after rebuild. I don't think the chains were "Hard tight" but plenty tight to prevent slippage. I recently removed my tensioners to replace old style idler sprocket supports. After reassembly I checked my timing with the tensioners in place. Both sides were dead on where I set them before. Not sure what all this means except to say the timing was the same with "Tools" in place and with hydraulic tensioners as well.