MyE28.com

Slowly progressing in putting the internals and cylinder head from a donor M30B35 (E32 735i Auto) on my M30B34 block. I have a few questions about reusing the pistons retrieved from the donor block:

1. Is the wear on the piston skirts acceptable? The pistons are all round and within specs according to the bentley manual.
2. Is the top of the pistons in good shape? I though that originally the surface on the top is smooth rather than rough as seen on the pictures.
3. Is it better to use the crank from the M30B35 or should I just put the one that is in better condition. (I am going to use the rods that the M30B35 pistons were mounted)
4. Any preference on piston rings (apparently the BMW dealer ones are out of the question.)

PS. I am going to replace the main and rod bearings and of course all timing components in the rebuild. Yes and the pricey oil pump.

Pictures:

Top view:


Exhaust side:


Intake side:

Mild scuffing like that on the pistons is no problem as long as they are OK on size, and even up to .1MM wear is just fine. The rough casting is the way they came too, some pistons have a nice smooth machined surface, but with the odd up and down shape of B35 pistons they don't. Use whatever crank is in better shape, they're the same, and not normally a wear item unless it's been abused as in run low on oil. I prefer Deves rings to the Goetze/Nform that are much easier to find, but they may or may not be hard to find where you are.

The scuffing isn't too bad. The pistons that went into my turbo car had almost that much and they're doing just fine.

BMW rings are the best, but Deves also seem to work.

Also had similar scuffing on the M30B35 pistons I'm putting into my E23. Everyone here also said don't worry about it.

Isn't Goetze the OEM supplier for the M30 piston rings? Haygood back in Jan sent me Schöttle Motorenteile (SM) rings instead, which I believe is also OEM for some BMW and MB engine models. Couldn't really vouch for them since I haven't installed them yet.

Thanks for your replies guys. Should I do anything on the scuffed surface (i.e. scotch brite them) or should I leave them alone?

One more question regarding exhaust manifolds from B35 and my E28 original exhaust. I know they do not fit due to the different output flange but is it only the flanges that need modification or a repositioning of the exhaust tubes in the exhaust is needed as well?

Really looking forward to see if the power difference from the conversion can be felt. Too much money and effort is going in that so I hope it does.

nikos_kalogridis wrote:Thanks for your replies guys. Should I do anything on the scuffed surface (i.e. scotch brite them) or should I leave them alone?

Leave them alone, they'll be fine.

nikos_kalogridis wrote:One more question regarding exhaust manifolds from B35 and my E28 original exhaust. I know they do not fit due to the different output flange but is it only the flanges that need modification or a repositioning of the exhaust tubes in the exhaust is needed as well?

Bump, were you able to just get the output flanges replaced, or did you have to reposition them?