964 Cam Timing Questions...

mikedsilva · 06:42 PM

I know there are a few threads on this.. I even have the p fixit video...
But here is my problem...

I have both camshafts installed.
Both dots pointing upwards.
Rockers installed for cyl 1 & 4.

With Z1 showing on the flywheel.. I set valve clearance for cyl 1.

Turn flywheel watching the dial indicator.
Dial indicator gets to 1.26mm but my flywheel has turned a bit too far.

AT this point, my understand is to pull the pin out, then turn the crank till Z1 is centred again, then re-install the pin in new spot.

The problem I have, is as soon as I can pull the pin out, my crank spins.. I assume it is the spring of the valve, that has been pushed on by the rocker.. now the spring is pushing back against the cam...

Am I doing something wrong here?

Flat6pac · 09-26-2016, 03:48 AM

I load all my rockers because it aids stability, gust harder to turn.
Load a couple more rockers to aid stability
Bruce

mikedsilva · 09-26-2016, 04:08 AM

What I did instead, was to turn crank till the valve was closed again, then while there was no load on the cam, remove the pin, turn crank slightly then re-install pin in next hole...

Then check all over again. Is there anything fundamentally wrong with that method?
I am pretty sure I am getting the same result....

Flat6pac · 09-26-2016, 06:16 AM

Have you been able to prove to yourself that's it's right, once you load the rockers, if you're not sure, will be the time to check
Moving one hole on the alignment has always represented, to me, .15mm of change.
Optimum C-2 cam setting is 1.25
Bruce

mikedsilva · 09-26-2016, 11:38 AM

Bruce, when I get home after work, I will load the other rockers and see...I've found that the width of the mark on the crank pulley, allows for some variation in the result.

Also, how much tension should be on the chain? I am using a brake pad spreader to apply tension; if I turn the handle on the tensioner I can change the readout on the dial gauge..

'78 SC · '78 SC's Garage

".I've found that the width of the mark on the crank pulley, allows for some variation in the result."

Good point. I printed a grid on clear film to provide a finer TDC mark over the pulley. This made a big difference in getting repeatable timing measurements. Without this I would get a different measurement each time I rotated the crank even if I didn't change the cam setting.

Flat6pac · 09-27-2016, 03:34 AM

Mike, I load the tensioners and with tension the chain becomes tight. If you tighten it mechanically the tightness will never be duplicated.
I use a breaker bar to turn the crank giving me control of the rotation.
Stomski has the equipment for accuracy but lining the pulley has always worked.
Bruce

superninety · 09-27-2016, 05:16 PM

Quote:

Originally Posted by Flat6pac

Mike, I load the tensioners and with tension the chain becomes tight. If you tighten it mechanically the tightness will never be duplicated.

Can you elaborate on how you load the tensioners? The "factory tool" for this procedure is a mechanical method of doing this. Are we saying that is not really the preferred method? Or....are you saying you just re-install the engine's own tensioners?

Many thanks !!

R.

Flat6pac · 09-27-2016, 05:31 PM

Instal the tensioners, that's what holds the chain under running conditions.
A tight mechanical tensioner to do the settings, the tension will never be duplicated with a hydraulic unit.
Bruce

mikedsilva · 10-04-2016, 04:39 PM

Well, as you know, I found that adjusting the chain with my brake pad spreader, would give me variations in the cam position and hence timing. So I lashed out and bought Stomski SR9401.
Looking at the porsche service manuual, they use a tool that looks much the same.. it has a spring inside, and you apply tension by turning in the bolt.

I only have experience with the 964, and as you might have read, the length of the tensioner on the left side is longer than the tensioner on the right side. However, the SR9401 tool is the same for both left and right (when you order, you get 2 pieces).
This means that I cannot get the SR9401 to seat on the cam chain box mount. I've reached out the Steve Stomski to see what I am doing wrong.. with difference in time zones, I don't expect an answer for a little while.

On another note, when I went to reinstall my right side tensioner (before I had the stomski tool) it was also very reluctant to be compressed enough for the cover to be bolted down. I made sure that I had the shorter tensioner, which I did.. as I squeezed it down, it felt solid. Then after a little while, oil started oozing out drop by drop.. and now it seems to compress... is it faulty?

Flat6pac · 10-04-2016, 06:20 PM

Mike, there is oil inside the 964 tensioner along with the spring. You're applying pressure to get the tensioner to load, oil has to come out. Once the oil has dripped out the spring is the only support.
On the pre 90 tensioners, they have to be put in a vise and re pinned closed but then the piston is just supported by the spring until the engine starts and the oil pressure supports the idlers, like will be in the 964 when oil pressure is reapplied.
Bruce

mikedsilva · 12:33 PM

Here is a video showing what I think are "tight spots"...
https://www.youtube.com/watch?v=V2Sj6ppGjpY&feature=youtu.be

After this, I then removed the sprocket bolts and pins, and reset my timing AGAIN.
I thought that perhaps I should start from scratch, and insert the tensioners at correct tension first, then set timing...

I am yet to see if I have the same slop (forgot to check that) but then I ran into trouble with the right bank in that I cannot install the stomski tool...

mikedsilva · 10-05-2016, 01:20 PM

Does this look normal?

mikedsilva · 10-06-2016, 03:39 AM

Update..... I think it is all good.
Had a good long chat to a friend who suggested it is likely the spring pressure from the valves pushing back on the cam lobes, creating tight points during rotation. I should mention that in the video, ALL my rockers are installed and valve clearances set.

Tonight I just spent an hour re-checking sprocket parallelity and that is all good. Put my cam chain guides back in, they are all good. If I start the crank pully at Z1 (tdc for one of them I guess) and start rotating... at approx 20 degrees, the left bank gets tight and pops the tensioner out.. keep rotating and as it gets toward 60 degrees, it gets slack again... now rotate through 60 and when another 20 degrees passes, the right side gets tight.. and as approaching the 120 mark, it gets slack again.. and the process goes on.. so definately sounds like the valve springs doing this. In fact when rotating nice and slow, as it starts to get tight, it almost "snaps" and you can watch the cam sprocket snap too.. the fact it is the same process on both sides, every 60 degrees, should suggest it is normal.

Hopefully someone a LOT more knowledgeable than me, will chime in!