Camshaft Shims

[Frazier]

Hi Everyone,
I am working on setting the depth on my cams and I would like to know if there any shims made that are .25mm, Wayne states in his book that the shims are .25mm but I have found them to be .50mm. If the variance is .25mm I would think someone has made them thinner. Any thoughts...

Thanks,
Neil

[john walker's workshop]

never seen any. you don't want anything that thin anyway.

[Wayne 962]

Typo in the book. Please see the updated list of corrections to the book prior to starting a rebuild:

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

-Wayne

[dtw]

Yup - you don't need .25mm shims. Think about it- you need to get within .25mm +/-; that's a total of .50mm to play with. You should be able to add or subtract .50mm shims until you strike a measurement within .25mm of zero offset on either side. In other words, you'll end up less than .25mm too close or .25mm too far away.

[Frazier]

Thank you for the responses. I just put all new gears and chains. I am .17 and .2 That is the best I could get. I still wonder why not .25 shims, the base gaskets for the cylinders are .25. Thanks again...

[aigel]

I guess the allowed tolerance is large, so why make flimsy .25 shims if you don't have to? 250 microns, that's getting to the foil type thickness. And the base gaskets, they are in a location where you need more accurate adjustabillity, IMHO.

G

[kclem19]

So i'm encountering the same "issue". I got one of my sprockets to 0.02mm offset but the other is at 0.27mm. If I add a shim, i'll be at 0.23mm offset which will be allowable but i feel like there is a lot of room for error in the measurement to begin with so i'd like to be closer to zero offset.

What if I wet sand 0.25mm off of the back of the "gear" (not sure what its called, the piece that keys to the camshaft via woodruff key) that sandwhiches the shims? I have a nice, true piece of granite made for doing such things. Another possibility would be to take it to a machine shop and have them do it. Thoughts?

Thanks,
Kelly

[KTL]

Don't let the recommended tolerance make you feel like it's a super precise fitment we're trying to achieve. If you want to reduce the thickness of a shim or sand the base of the toothed hub, by all means go for it. But aiming for zero difference is not necessary IMO.

Reason I say this is because I once found a cam sprocket installed backwards on the 4-5-6 bank of cylinders. Recall that one sprocket is installed dish facing in, the other facing out. The engine didn't show any major wear on the sides of the sprocket and didn't have excessive chain slack due to the apparent chain misalignment/poor parallelism. The same chain and sprocket are still in that engine operating just fine. I think what happened is the previous wrencher properly calculated the shim count and then upon final assembly mistakenly flipped the sprocket? Because when I measured for the shims, the number of shims I used for the proper installation/orientation was the same count for the sprocket installed backwards.

I'm not saying that we should just slap the sprockets in place with little regard for calculating the shim count. Just saying that if you're on the fat end of the recommended tolerance, you're still going to be fine.

By the way the fan pulley shims are generally the same dimensions as the cam shims. So you can use a fan shim in a pinch if need be.

[kclem19]

Thanks for the reply. I agree with you. I guess the problem is that I have so much money wrapped up in the project I'd hate to have an engine failure after rebuild due to something I could have prevented. However, I understand there is also a risk a creating a problem when one doesn't really exist. After all, we are talking about being 1 thousandth off of center. I should probably leave it alone!

[KTL]

Nothing wrong with getting things dead nuts perfect. Just wanted to point out that in the case of the chain parallelism issue, it's not super critical.

That said, make sure what you're measuring is accurate/repeatable. A lot of guys scoff at the fancy tool by Stomski (and copied by GSF) for measuring the chain sprocket depth because it costs real money. Well, making a tool that lets you measure all by yourself (no second set of hands required) and also provides repeatable, accurate results takes some $. If you're only planning on building one of these engines just this one time, and you don't foresee anybody else you know getting some use out of it, yeah it's hard to justify buying the tool. I bought it because I knew somebody else in my group of guys would end up benefiting from it someday. It's come in handy a number of times building my engines and a few friends' engines. I'm sure it'll get more use in the near future.

[kclem19]

After battling some other issues, I'm back to shimming the camshafts. Is there a "maximum" amount of shims that you don't want to go over due to reducing the contact between the camshaft and the gear? I have 6 shims on the left of the engine and 2 shims on the right of the engine to get the measurement within the +/- 0.25mm spec. I'm just wondering if needing 6 shims is a problem and is it common/uncommon to require that many?

Thanks,
Kelly

[prschmn]

I would take a very good look at the face of the crankcase where you're setting the straightedge.
Six shims is very odd. Remember that any deviation at the crankcase is magnified out at the cam gear.

[kclem19]

Prschmn, Note that I am mixing a set of camshafts from a 1975 S with my 1973 heads. Not sure if that could have any impact?

So I have the stomski tool to check for this alignment; however, when i put the flat bar directly against my case, there seems to be a bit of a wobble (if i had to guess i could get a 10 to 15 thousandths feeler gauge under one end while pressing down the other end). Maybe this is where my error is coming from? I have a granite slab that I could potentially use to wet sand the front of the case, but I don't know how i'll know if i'm keeping it true or making it worse. Any advice?

[prschmn]

Mixing cams won't affect the alignment since that's controlled by geometry between
the case cylinders and heads. But you're right about the "wobble" being a problem when
you're measuring. You may want to try your wet sanding method to see if you've got a high or low spot. I'd say give that a try. The "ribs" where the mount attaches should keep the case and mainline perpendicular to the surface plate and let you see where any low spots are.

[prschmn]

Got your phone message but have been at the track for a few--anyway I'm wondering if you have looked at how much wear you have on the thrust plates? And have you tried sliding the cam towards the pulley end? And you do have the triangle gasket installed right?