Undersized Bearings

[220bhp]

Hi Can Anyone Tell Me Where I Can Obtain A Set Of First Undrsize Bigend And Mainbearings For S2 Mb The Engine Shop Said They Are Not Listed.main Dealer Say Standard Only

[inc13]

Over or Undersize bearings for 20v= not exist
you can use 2,5 tdi bearings ,,,but they dont last long/over original boost pressure

been there ,done that

[hiltoa]

Pardon my ignorance, but to what advantage would undersized bearings be?

[ThatGUY]

Pardon my ignorance, but to what advantage would undersized bearings be?

I'm right there with you?

[BRY]

Take up the space where the original metal was on the crank after you have it re-ground.

[ThatGUY]

but wouldn't that be oversized?

[BRY]

Not if you measure the diameter of the journals on the crank after you grind it. The outer dimension is fixed as this locates in the block / conrods. The inner surface is the one that moves over the crank, hence this is the one which gets damage if the bearing "picks up" re-grinding the crank to remove the scrathes etc. reduces these diameters = undersize

[hiltoa]

Slowly the fog clears...

Cheers Bry - makes sense now

Sounds like a new crank then?

[ThatGUY]

I was under the impression that when you grind material off the journals an oversized bearing would be bigger and take up the extra space.

Andrew

[BRY]

You buy the bearing to fit the size that you have ground the crank to. The bearing is bigger / thicker but the size you quote is the one you can measure easily with a micrometer - it would be a PITA having to work out the thickness of the bearing required every time you ground a crank. Workshops tend to do loads of different cranks and if they can just measure the size that they have taken the crank to in order to clean it up then they just quote that size when ordering bearings.
Unless its an Audi 20v 5 pot and nobody makes them.

[hiltoa]

So I guess the dimensions aren't in any way similar to a VAG 4 pot then?

[Fat Audi 80]

@ Hiltoa, your avatar has just really freaked me out! I thought I was seeing things!

Edited to add - And I just got my 1000 post count!!!

[Mark Halligan]

Have a look here

http://www.elcome.ltd.uk/fm/index.asp?lang=11

I am at work at the moment so haven't got time to have a good look myself, but you 'might' find what you want.

Mark.

[hiltoa]

@ Hiltoa, your avatar has just really freaked me out! I thought I was seeing things!

Edited to add - And I just got my 1000 post count!!!

:mischeif: Glad to see it has been noticed - I wish it was as easy to change my 2.0E into an RS2 in real life...

And congrats on your posting milestone!

[Keeper of The Kitten]

I'll tell you one advantage of undersize bearings - reduced frictional area. Less friction = more power (did this in F3 racing to unleash the meagre output of a normally aspirated 2.0 engine, breathing through a 26mm restrictor).

Oh, but then there is a major disadvantage - reduced life...

Mind you, we were going very undersize!!

__MDC__