cylinder base o-rings needed?

[exdirtbiker]

I popped one of the "cylinder base o-rings" while cleaning the jugs.
Seems like they don't do anything, as the top of the block is not round, so they don't even touch all the way around.
I think I read 1 post somewhere that said "leave them off" but "search" has let me down.

I'm cheap... but not that cheap... they're $3 each. But ... why are they there ?

[tkent02]

I'm leaving them off on the advice of an engine guy on here. Says he's been doing it forever.

[rapidray]

I have NEVER put them back in!
Ray.

[exdirtbiker]

Thank you !

[chuck hahn]

To answer your actual question of why they are there..................The basic intention for them is that the jugs will expand away from the cylinders a thousandth or so when the engine is hot. The head being bolted on keeps the cylinders still, but oil ( in their theory ) will seep up between sleeves and then jug casting itself..thus the sealing by use of the orings.

[tkent02]

Seems like the O rings would need to be pushed against something to seal at all, but it only contacts the base gasket with nothing under it at least in part of the circle... makes no sense to me. Not sure what a bit of oil seeping up behind the sleeve would hurt anyway.... Oh well I'm doing without them.

[chuck hahn]

Me neither ..but thats what they are supposedly there for. Least thats what was explained to me way back when i had the same questioning.

[Brendan W]

I had to tap them in and was wondering why and came to pretty much the same idea about the block getting away from the sleeves. Maybe oil could burn up or something and stop the block coming back fully, in theory ?