Cam timing mysteries - 3.6 engine

[ischmitz]

I finally got to the stage of timing my cams after some fellow board memebers went out of their way to help me with my rebuild. Without them I would be nowhere even close.

When I tried the factory timing method where you do the rough adjustment by getting the punch marks pointing up at Z1 and then do the fine adjustment by rotating engine until you get the specified lift at TDC overlap, remove the dowel pin - whoops there moves the cam when you pull the pin.

There is no way in hell that you can take the dowel pin out of the sprocket with the intake valve lifted (only intake #1 and #4 rockers installed) and not have the rocker rotate the cam out of position unless you use superglue!!!

With the mechanical chain tensioner adjusted tight the cam rotated even without the dowel pin in the sprocket when I rotated the crank. With loose tensioners the cam would slide out of position by the rocker acting on the lobe once I pulled the dowel pin.

The only way I got my timing done was to back away from TDC, make adjustments based on how far away Z1 was with the desired lift and then check with several rotations of the engine where I ended up. Once I got the hang of it the second side went much faster. One side ended up at 2.28mm and the other at 2.32mm lift at TDC overlap. Spec was 2.2 - 2.4mm

Next weekend is final assembly time and hopefully first light.
Cheers,
Ingo

[pete911]

If all the rockers are in the cam won't move.

Pete

[cstreit]

Pete is right...

...it will sometimes still move but not very often...

...and the factory cam holding tool will prevent it...

[Wayne 962]

Right - as Jerry Woods told me, it's nearly impossible to do the cam timing on these engines without using the factory camshaft holding tools.

Hmm, I guess I need to get started on that 3.6 supplement...

-Wayne

[ischmitz]

Wayne,

you are talking about the 993 cams here. How many 3.6's have you rebuild so far? That's another story altogether. On the 964 there is nothing where you can hold the left cam. The cam tower has a plug at the flwheel end.

It makes sense that the cam hardly moves with all rockers installed during timing since at overlap exhaust and intake rocker push into oposing directions onto the cam shaft.

Ingo

[Wayne 962]

As I said before, I'm going to be working on the 3.6 supplement in the future...

-Wayne

[ChrisBennet]

Originally posted by ischmitz
Wayne,

you are talking about the 993 cams here. How many 3.6's have you rebuild so far? That's another story altogether. On the 964 there is nothing where you can hold the left cam. The cam tower has a plug at the flwheel end.

It makes sense that the cam hardly moves with all rockers installed during timing since at overlap exhaust and intake rocker push into oposing directions onto the cam shaft.

Ingo

I think I'm missing something here. Am I having another "Senior Moment"? Why can't I hold the 964 cam still the same way I do for a 3.2? Except for the cars that had pump drives (930's, MFI, 3.6 w/pwr steering) cam towers are usually plugged at the flywheel end anyway.
-Chris

[ischmitz]

From what I know the 993 cam towers are open on both ends. The have a couple of threaded holes in the cams where the Porsche cam holding tool attaches.

The 964 with PS are open on the left side but the cams don't have the same threaded holes.

Ingo

[ChrisBennet]

Ingo,
I see the source of the confusion now. I'm not familiar with the 993 setup but it sounds different than the earlier motors. The late 3.0, 3.2 and 3.6 (964) cams have a bolt in the end of the cam that you can use to turn the cam, and the sprocket has holes that you can use to hold the sprocket with using the 9191 tool.
-Chris

[Bill Verburg]

Here's pic of how it was done on my 993 w/ backdated 964 cam sprockets


The hydraulic lifters require either the factory tools or temporary replacement of the hyd lifters on #1 w/ mechanicals for cam timing purposes.

[911s]

LOOK AT THE SIZE OF THOSE INTAKE PORTS! AWSOME! Also appears that each port requires 3 bolts to hold intake securely to them. Wonder what these heads would do with forced induction?

[cstreit]

You sure got a purty motor there.

I promise to take care of it for you Bill, I'll even pay 1/2 of shipping!

[Bill Verburg]

Yeah, the ports and valves are pretty big
The last thing a fly sees after it gets past a cone flter


The last thing super fly sees on his way back out