Thrust Bearing Widths

Who is the best person to rebuild your engine? You...

Moderator: sparkmaster1

Post Reply
Ark1
Posts: 13
Joined: Wed Jul 20, 2016 11:17 pm

Thrust Bearing Widths

Post by Ark1 » Mon Jul 03, 2017 11:08 pm

Hey guys! I had an engine assembled and went to set the crankshaft thrust. FInding it was way off ( I don't remember exact measurements, months ago) I tore down the engine to figure out the reason why. Upon pulling the thrust bearing I found it was .005 wider than an old bearing I had lying around (measured front to back) Anybody ran into this? Guess I'll order another set and hopefully it's machined right!
You do not have the required permissions to view the files attached to this post.

User avatar
Marc
Moderator
Posts: 23727
Joined: Thu May 23, 2002 2:01 am
Contact:

Re: Thrust Bearing Widths

Post by Marc » Tue Jul 04, 2017 9:32 pm

Overall width can be compensated for by the thickness of the shim stack between bearing & flywheel (and can be reduced by simply applying some elbow grease using a sheet of glass with some solvent-flooded wet-or-dry sandpaper).

What's of more concern is the inner width between the flanges. Your "wider" bearing also is obviously narrower there so if this bearing was in your engine, your case has been machined there, while the other one appears to be Standard width. The bearing should fit snugly; if the case is hammered, reducing its width so the bearing is sloppy, the remedy is to machine the thrust surface of the case to accept a bearing with a narrower internal width. Standard "oversizes" are 1mm and 2mm but many builders prefer to remove no more than necessary from the case to clean up the surface, and then have a thicker-flanged bearing turned narrower on a lathe to achieve a perfect fit. If the bearing you were using fits your case properly and the only issue is the overall width, simply sand it down if you can't set the endplay properly any other way. The thrust surface on the flywheel can also be taken down on a lathe. Three of the thinnest (.24mm) shims stack up to just over .028" BTW.

https://web.archive.org/web/20130130230 ... nglist.htm
The diagrams at the top of this page are poorly drawn, the width arrows (dimension "F") for all three sizes continue at the right side all the way to where the inner side of a standard bearing would be...but with that in mind you should be able to see the point.

Ark1
Posts: 13
Joined: Wed Jul 20, 2016 11:17 pm

Re: Thrust Bearing Widths

Post by Ark1 » Tue Jul 04, 2017 10:29 pm

Yea, one's a std thrust & the other's 1mm cut. But the outside widths was the part I was thrown off by. It would've taken five shims, (or 4 excessively thick shims) to get the endplay in spec. That's why I pulled it apart. The case is a fresh align bore and thrust cut ( .020 over, and 1mm on the thrust)

User avatar
Marc
Moderator
Posts: 23727
Joined: Thu May 23, 2002 2:01 am
Contact:

Re: Thrust Bearing Widths

Post by Marc » Thu Jul 06, 2017 4:33 pm

You've lost me, if the overall width of the bearing is greater why would a thicker shim stack be needed? Seems like you'll only exacerbate the situation by going to a narrower bearing.
Perhaps the flywheel has had its thrust surface taken down a lot.

I don't subscribe to the "three and only three shims" dogma, IMO VW went that route to enable all normally-conceivable stack thicknesses with a minimum number of parts rather than for any "engineering" reason, so I'd have no qualms about using four (or even five) shims if necessary.

viewtopic.php?f=18&t=137434&p=1085816

Post Reply