E30 Zone

Hey guys...quick question, is it possible to fit a B25 crankshaft into a b20?the one currently in my 320i is of no use...plze help!

Claudio27 wrote: ↑

Sun Sep 15, 2019 12:07 pm

Hey guys...quick question, is it possible to fit a B25 crankshaft into a b20?the one currently in my 320i is of no use...plze help!

The 325i crank has 4mm more stroke (75mm) than the 320i (71mm) which means your piston is 2mm higher and will probably cause valve or head clearance problems. You would need special pistons or you may be able to machine the 320 ones down as they are flat-top.

If you want to make it a 325 you need to bore it to 84mm to use the 325 pistons and need to change the cyl head.

A lot of work either way. Surely a 320 crankshaft is not hard to find? They tend to be left over when people bore out and make stroker engines. I had one I could not get rid of for ages, sent it for scrap in the end

So there's no other way to manuavre round the valve clearances with an oversized head gasket or something either?But I'm going to see what my local machine shop can DO, maybe they can still save MINE...BEFORE I go and source a new one.

2mm is more than a normal thicker head gasket would give you (it will give you extra 0.2mm or 0.33mm), unless you went with a thick MLS gasket which will be expensive and a waste of money on that engine.

The only thing that might work is if you could get M20B23 pistons, they are 80mm and flat top for the 731 head but the crank is supposed to be 76.8 so you would be 0.9mm down on your existing B20 giving it little compression but some of that could be skimmed from the head and block.

Not sure if the 323i made it to SA

Easier to find another B20 crankshaft or get yours ground and oversize bearings