Need some help with adjusting valves and setting cam timing...

[Jim_0068]

I am finishing up a top end rebuild on my brother's 1973 911T and have an easy quick question:

In my 911 project book, before you adjust the cams it says to adjust the valves. It says to bring #1 to TDC and adjust the valves. Now but how do i do that if the cam timing isn't right? Wouldn't my valve adjustments be wrong them?

See the catch 22 situation here? i know i am just missing something easy so can any of you help me?

thanks

Jim


Also i have been doing a little searching and hearing that i should adjust the valves a little tight, i bought the feeler gauge tool from Pelican parts but i don't think it was a .004, will the pelican one work ok? Thanks

[Groesbeck Hurricane]

If memory serves, at TDC #1 cylinder is on the lobe.

[jgparker]

As long as both the cam and the crank are in the ball-park of TDC, you can safely adjust the valve lash, since the gap will be constant for just about the entire compression cycle. Just make sure you are not trying to adjust the valve lash at the TDC overlap point, since this will totally screw up you cam timing.

I hope this is helpful,

JP

[Jim_0068]

Hmm....ok.

So this is my current scenario:

Valves aren't adjusted....cam timing isn't set yet. Sprockets are on cams and chain is on them.

So i can just get #1 to TDC, adjust the valves, and then go back and set the cam timing?

Is the above correct? Now if i did everything right even after the cam timing i could get #1 to TDC again and check the lash and it should still be correct right?

thanks again

[ChrisBennet]

At TDC, the rockers for the cylinder in question will be riding on the base circle of the cam i.e. the no lift/non-lobe part of the cam. It's a large enough area that you don't have to be exactly at TDC. If you look at a cam you can see that most of the time the rocker is riding on the base circle.
-Chris

[Jim_0068]

Ok, i don't think i am asking my question right. I understand about lashing valves and where the cams have to be etc. I have built a lot of motors in my life just not porsche motors.

Here is my main question: Can i adjust the valve lash without having the cam timing set? The cams are in, the sprockets are on, the chain is on. The chain tensioners ARE NOT ON. So do i just throw the chain tensioners on, get #1 to TDC adjust the valves? Then when the valves are all adjusted i go back and set the timing?

Thanks a bunch

[ChrisBennet]

Originally posted by Jim_0068
Hmm....ok.

So this is my current scenario:

Valves aren't adjusted....cam timing isn't set yet. Sprockets are on cams and chain is on them.

So i can just get #1 to TDC, adjust the valves, and then go back and set the cam timing?

Is the above correct? Now if i did everything right even after the cam timing i could get #1 to TDC again and check the lash and it should still be correct right?

thanks again

No, you should set the valve lash for #1, then set the timing for #1. Repeat for the #4.
If you adjust the other valves the spring pressure will try to make the cam move one way or the the other.

Tip: Set up your dial indicator and then rotate the engine several times and check that you get the same value every time that cylinder is at TDC i.e every 720 degrees of crank rotation. If it isn't consistent, adjust your chain tensioning device or smooth out the lube on the cam lobe. If you put assembly lube on the cam lobe too thick it will squeeze out and change your readngs as you go along.
-Chris

[Wayne 962]

Just make sure that the cam isn't acting on the rockers and that they are completely closed. Then adjust the clearances. So the answer to your question is yes - the cam timing does not have to be set.

Do you have a copy of the Engine Rebuild Book? It goes over that detail...

-Wayne

[Jim_0068]

I'm not sure if i do or not, if i don't i think i'm just going to run and get it because i am still a little confused.

[Groesbeck Hurricane]

Another tip, order the book direct from Pelican. You will get a really neat CD that way with tons of great photos!!

[jgparker]

You do have to rough time the cams to start the process. Put the cranck at TDC then point the dots on the cams north (up). The last two engines I timed, I got the cam timed within spec just by eye-balling the cams carefully. However, you can be way off and still set the valve lash at TDC on #1.

Like everyone else said, you really need the book.

Good luck,

JP

[Jim_0068]

Ok, i'll buy the book. But jg you pretty much answered my question thanks