CAM TIMING? How precise?

OK I just re-read the post from JAndrews and am nervous.

I took my engine out in the fall and replaced the chain tensioners. When this happened the cam timing slipped on the right(passenger) side. I did not have the cams out of the engine it must have come lose

Anyways I adjusted the cams by eye. Ensuring that the sprocket was lined up correctly ( the holes) Then I re-adjusted the valves. I am getting ready to put it back in the car. but when I read the post from JAndrews I got nervous!

Am i just being paranoid or should I be doing something before I end up spending big $$$?

Thanks so much

Shawn

Shawn,

Cam timing is critical to engine performance along with the potential causing engine damage if it is not.

Setting your cam timing is easy once you understand how it's done. You need to have a mircometer to set it properly along with the specs for your particular engine.

The haynes manual explains the correct way to set it up and provides the specs. Don't try and put an eyeball on it and think it's ok. As you well know, P-engines have critical tolerances. There are some good posts on the BBS regarding cam timing, so do some reasearch and you shouldn't have any problems on how to do it.

Steve

Shawn,

Maybe I should have been a bit more clear in my update post. The cam timing on my car was off .007 between cylinder #1 and cylinder #4. The acceptable range of timing is .197" to .213", however it is critical that whatever timing you choose in that range, #1 and #4 need to be within .001" or .002" of that setting.

In other words, my number 4 cylinder was set at .199". Therefore my number 1 cylinder needs to be set at .197" to .201". In actuality, my #1 cylinder was set at .224". In fact, it was out of the acceptable range altogether.

So as you can see, even though the acceptable range is nearly 1/2mm, it is critical that #1 and #4 be within extremely close tolerances. I do not believe that can be done by eye. I would take the time now to verify your timing across cylinders #1 and #4. It will save you the grief of taking everything back apart to re-adjust later.

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John
70/73 RS Spec Coupe

Took my 72 and installed rs p\c's with mod t cams for auto xing. Took 3 tries get the cams degreed in right. Take it part, degree it, put back together, drive it and do it again. You have to get a dial indicator to get it right..

I guess I am still confused about how the cam timing could have gone off if nothing was taken apart. I know the chain was off but, I was hoping for better news than that. So now I have to take off the heads too? How far down do I have to tear the engine? I can get all the tools required I have a lot of friends who are mechanics or I'll buy if I have to. Anone know what link has the procedure i'll need?

Here we go, I'm glad I have this post and all you guys otherwise I would never be able to afford to drive

Shawn

you gotta give metric values. it's so much easier to not have to convert to inches. find your engine type #, get the cam timing spec. from an official spec book. set engine to #1 firing position (Z1 on pulley aligned with the split of the cases)snug up cam nut and adj. #1 intake to .10mm. set up a metric dial gauge on the valve spring retainer of #1 intake valve. preload it and set it to zero. rotate engine 360 degrees clockwise (Z1 to case split again). the dial gauge now reads how much the valve has opened. compare to factory spec, if it's within tolerance, tighten nut.then recheck your job by turning engine counter clockwise until the dial gauge returns to zero, and then clockwise to Z1 again. if it's not in spec, pull the cam gear pin and turn cam to the proper spec(on the dial gauge), reinsert pin in the hole with no interference, and tighten nut.(always recheck after tightening nut). repeat on #4 intake. easy. a special tool is req'd to hold cam from turning as you tighten the nut.

[This message has been edited by john walker's workshop (edited 03-19-2001).]

Can someone please explain to me what a cam IS? and then what cam timing is? Thanks.

I have some pics on my website when I did this to my motor, it might help clarify things.

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Mark
www.mark.hargett.com
mark@hargett.com

Thanks so much everyone.

I actually posted this same problem in Nov 2000. Orb told me that since I didn't tamper with the cam sprockets only way to lose timing was if it slipped a tooth. As long as I got it back on that tooth I would be 100%, and wouldn't have to go through the entire dial-in procedure? that makes sense to me, but is it right?

I don't want to get it back in the car and have to take it out again. You know do it right the first time. But I also don't want to do more than is necessary.

Thanks again for all your patience and help

Shawn

I reiterate this. If you were happy with your cam timing before you started changing the tensioners, and during the tensioner upgrade the chain slipped a tooth, you do not have to redo the whole timing thing. As long as you did not change the chain itself or mess with the sprocket you can put it back on the exact same tooth and your timing will be identical as before.

If you use logic and think about how that tensioning system works and how the cam timing is effected by each component, you will be able to see for yourself.

To help you visulize this, the cam timing is entirely affected by the tight end of the chain, not the slack end. On the tight end, the only factors that would influence the cam timing are the chain wear, sprocket wear, or the actual sprocket adjustment using the little dowel pin behind the outer sprocket. Other then that, the big sprocket teeth set the timing.

[This message has been edited by orbmedia (edited 03-20-2001).]