Piston markings…

[Acaciastrain360]

Me again… does this ‘0’ marking mean that it’s a standard sized piston?

4541BF57-DE4D-4E52-8C24-D5E890D268B8.jpeg

Thank
Youuuuuu

[flybynite]

Me again… does this ‘0’ marking mean that it’s a standard sized piston?

Can't say I'm 100% sure about the "0" none of the pistons I have here have it but the 83.98 is a standard 84mm piston size

There are also markings inside that can tell you a lot like the make etc

Looks to me like a 2.5 low compression piston but can't tell further without seeing the side and underneath the skirt walls

[Acaciastrain360]

Me again… does this ‘0’ marking mean that it’s a standard sized piston?

Can't say I'm 100% sure about the "0" none of the pistons I have here have it but the 83.98 is a standard 84mm piston size

There are also markings inside that can tell you a lot like the make etc

Looks to me like a 2.5 low compression piston but can't tell further without seeing the side and underneath the skirt walls

Thanks for you reply, it is a 1989 325i SE and was automatic

Is there any relevant difference between a low compression and a standard engine?

I’m currently rebuilding the engine and needed to know for the piston ring set… but I will take more pictures for you and see if it’s low comp as I may need a different head gasket? Or not?

Anyway thank you

[flybynite]

Thanks for you reply, it is a 1989 325i SE and was automatic
Is there any relevant difference between a low compression and a standard engine?
I’m currently rebuilding the engine and needed to know for the piston ring set… but I will take more pictures for you and see if it’s low comp as I may need a different head gasket? Or not?
Anyway thank you

No real 'standard engine' aside from the Cat engines there were two : M20B25 early high comp 9.7:1 and later low (technically medium) comp 9.4:1

Have a read here
https://www.e30zone.net/e30wiki/index.php?title=M20

For a facelift SE those pistons look correct as 9.4:1 pistons. If it was a chromie 325 then it would probably be a 9.7:1.

AFAIK all the changes were in the piston crown and skirt, everything else (rings gaskets etc) should be the same. More will depend on if the head or block has been skimmed.

I'm sure if you search there are comparison photos like here
https://www.r3vlimited.com/board/forum/ ... 25-pistons
HTH

[Acaciastrain360]

Awesome thanks man! Yeah it’s fully serviced etc and neither head or block has been skimmed, nor do they need it… it’s a lovely little engine. I’m just rebuilding as it done 170k and been standing for about 11 years!

Thanks again I really appreciate the help