Understanding "thrust bearings" and "thrust c

[mailman]

I almost hate to ask this, as it makes me seem ignorant....but I want to learn, so here goes.

I've read lots and lots of posts in this forum, and understand most of what I'm reading. I understand cam bearings and main bearings and rod bearings and what they do. I understand the way crank and cam journals and case saddles can be reground and require other-than-standard bearing sizes ..but I don't understand thrust bearings.

I've seen the terms "thrust bearings" and "thrust cut"....I just can't picture what they are. I've not yet split a VW a/c engine case, but hope to do an engine build in the future. In the meantime I'd like to learn as much as I can about how they work.

Can someone explain these things so a novice can understand them? Thanks!
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'64 Bahama Blue Beetle / steel sunroof
'64 Bahama Blue Beetle Sedan (future ragtop)

[Muffler Mike]

http://1800vw.bizhosting.com/mainbearingList.htm

here is a side view of a thrust bearing. Basically instead of just being flat, it has flanges on the side that the crank and flywheel run against to keep the crank from moving too far forward or backwards (axial)

a lot of other types of motors have a similar flanged bearing burried in the middle of the motor where the crank runs on both surfaces. with ours, we can put shims in between the flywheel and thrust bearing to adjust end play (axial movment)

edit.
If you look at the picture below, the bearing on the right side of this crank is the thrust bearing and once the flywheel is added, that makes up the second thrust surface. that thrust bearing is held in place axially by the case. the case has been cut to a certan width so the bearing will not move side to side via the flanges of the bearing.

_________________
Muffler Mike
http://MufflerMike.com

[mailman]

Muffler Mike,

Thanks, man! That's what I needed to see...

So to limit axial movement of the crank, is the only adjustment shims behind the flywheel? Or are there different thrust bearings with wider flanges available?

Also, to what are they referring when they are talking about re-machining a used case and mention a "thrust cut"? Is this in reference to the diameter of the thrust bearing saddle (that's my guess)? If so, why would it be mentioned as a separate issue from the rest of the crank bearing machining?

Thanks for the help, and the picture helped a lot!
_________________
'64 Bahama Blue Beetle / steel sunroof
'64 Bahama Blue Beetle Sedan (future ragtop)

[Muffler Mike]

I know a picture is always worth a thousand words, thats why i try to use em as much as reasonably possible because some times it is hard to get a point across when trying to write it down on paper or in this case, an internet posting.

from a thrust cut term, this is where the saddle of the bearing width is narrowed probably because things got loose and that thrust bearing beat on the side of the case saddle.
So one can take a thrust cut and clean up the side surface so a bearing will fit properly again.
then if the case bearing saddle is narrowed, you can purchase thrust bearings that have a thicker flange. Same dimension on the outer width, but one side is typically thicker going into the saddle. Then you can custom cut the flange to width to fit the case or make the case fit the bearing.

when you look at that link http 1800 bla bla bla, the "B" dimension is made thicker and makes the inside dimension narrower.

edit. picture again.
this is the back saddle, if you notice the sides of the saddle is a machined surface, one comes in with a cutter and cleans the side surface up when a thrust cut is done. (just under where the pencil is)
http://mufflermike.com/1972.jpg
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Muffler Mike
http://MufflerMike.com