endplay shims? why 3?

[jan72]

Does anyone know why vw engines use 3 endplay shims between the main bearing and the flywheel? Using two shims with a total appropriate thickness would destroy something?
Is this right that these shims appear only from '52 on? Did they notice a premature wear of the axial bearing, or what?

[Marc]

Does anyone know why?....

Apparently not, but there's some good discussion/debate of the subject here:
http://www.shoptalkforums.com/viewtopic.php?t=78617

Is this right that these shims appear only from '52 on? Did they notice a premature wear of the axial bearing, or what?

Dunno, never worked on anything earlier than `55. If early engines didn't have shims then they must've relied upon closer production tolerances to keep the endplay within range (or maybe they just had a wider acceptable range). Using shims makes it much easier to compensate for tolerance stack-up in the manufacture of the crank, flywheel, and thrust bearing.

[jan72]

I see. I have put together a wasserboxer from '83 with its' 3 shims and a 411 flywheel from '69 (appearantly very rare, 200 mm); the endplay is 0,07mm which is very good. If you can fabricate things that give 0,07mm play over the years (even on different car models), it means you can do it 0 mm too, doesn't it?
Also, what is an "air gap"? I'm not an english speaker at all (Europe, Romania); thanks.

[busman78]

Think of three shims as a bearing, each shim makes up a part, inner race, outer race and the center shim is the same as the bearings. The end play allows for oil to get between the shims and for each to spin, tight enough to avoid the crank pounding out the thrust bearing/case but no tight enough to restrict the shims from getting lubricated and burning or seizing up.

Look at .003 (three thousands) as a minimum, .006 thousand as a max. I have run as low a .002 thousand, not ideal but...................

Trying to run .000 would not be ideal due to heat buildup, the shims would get worn down and then the case and thrust bearing would take a pounding.

[Bugfuel]

yes, the 3 shims are a bearing, and there needs to be some free play for oil to get in between shims.

Jan

[Tom in PA]

Does anyone supply oversize shims? I had to have my flywheel nose machined because I didn't have enough end play to get 3 shims in. Well the machinist removed a few thousands more than I specified and now with the 3 largest shims I have (and I measured probably 50-75 or more of them), I still have 0.0055. I'd really like to get it down to 0.004. The 3 shims I'm using currently measure 0.014 to 0.0145. Man, I could shoot that guy

Tom in Pa

[doc]

Others have suggested that a 4th shim could be used to take up space without impacting performance. Although I can't confirm this, I don't see why you couldn't add a shim.

Anyone know differently?

doc

[Marc]

I disagree with a couple of the "answers" provided so far, but I'm not going to rebut them here since I see no point in starting another thread on the subject when all of these issues have been debated at some length already in the thread I mentioned above....IMO any further discussion should take place there.

with the 3 largest shims...I still have 0.0055...

Use four shims and don't worry about it. I promise, it'll be fine.

[Bugfuel]

Four is fine.

Jan