sprocket alignment questions.

whackit · 10-07-2008, 10:22 PM

Hi folks,

I've been aligning my sprockets and have a few questions.

1. There is a small amount of play in the sprockets eg they can be pushed or pulled in a small amount (a "click" i havent measured it in or away from cam). Do I measure the sprocket alignment with sprocket closest, furthest or in the middle of this. Again, it's a very small amount.

2. Is the correct tolerance .25mm? The shims are .5mm which makes it hard for me to nail a .25mm window on one side, I'm assuming that the shim size (listed at .25mm) in Waynes's book is a typo, I'm just wondering if the tolerance is too.

Thanks.

304065 · 10-08-2008, 05:54 AM

No typo. Factory shims are 0.25mm which is why the max misalignment is 0.25mm.

Have you tightened the nut down enough to seat the inner sprocket against the snout of the cam, enough so you can barely see the end of the woodruff key in the keyway? A slight tap with a hammer while holding the camshaft with your fingers will seat it and should remove most of the slop.

911 tweaks · 10-08-2008, 06:40 AM

just a conformation point... I believe part of the question raised is that you can move the cam shaft in and out of the tower by ~0.25mm-0.50mm, thus, I have herd and experienced, that it is important to make sure that the cam shafts are 'pushed in' all the way "in" their bores to allow proper shimming & alignment of the sprockets & timing chains.

John: can you please confirm!! Specifically, that the cams need to be fully inserted into the towers = (as you stand at the front of the engine where the timing chains are, you push ~ lightly tap with hard plastic hammer, the cams towards the back/oil cooler end of the engine) do this lightly tapping after all of the hdwr is on the cams... then you acuratly start to do your alignment measurements.
This is a key point to allow a proper alignment... please input here John !!

Thanks and a great thread here guys !! It is all of the fine points in work and life that separate an ok job done from a great job done!!
Bob

304065 · 10-08-2008, 08:00 AM

whackit · 05:51 AM

I ahve also heard that "bottoming out" the sprockets is the way to go when taking the measurements.

All of my shims are .5mm. I measured them. It was a typo in Wayne's book:

http://www.101projects.com/911-Rebuild/corrections.htm

Quote:

Page 159 - ... Also, the shim thickness is 0.50mm, not 0.25mm

Are there .25mm shims available?

nabilious · 06-03-2009, 01:14 PM

Hey Whackit!!
I'm struggling with the same question here! Those shims are .5mm as I've measured an assorted back of them. What did you end up doing here? how many shims were used in each cam? did giving them a whack help your measuring procedure?
Thanks,
Nabil

JFairman · 06-03-2009, 01:28 PM

Those shims are also used in the fan pulley only they get corroded there, and there is a little bevel on the inner edge of one side of the thrust plate #4.
I think the bevel is to hold oil.

Eagledriver · 06-04-2009, 08:36 PM

You can get within .25mm with .5mm shims. If the sproket is .3mm "high" then remove 1 shim and it will be .2mm "low".

The cam longitudinal movement is controlled by the aluminum plate in the diagram above. I don't know how much movement it allows but I don't think there is an adjustment for it. There also doesn't seem to be a way to know which way the cam will go when the engine is running so I'd just try to take an average of the positions.

-Andy