Looking for new piston rings and/or new piston barrel sets 602 M4 machine (Ami 6 and AK 350) but can't find any anywhere?
Questions.
Would cylinders from M28 fit
Are the gudgeon pins the same as M28
Conrod lenght the same?
What is the piston ring groove sizes on M4

Too many questions but what to do?

Thanks in advance

Viking

Peter,

M4 pistons rings aren't readily available, however this company can make them up:

http://piecesdetachees2cv.free.fr/

M4 and M28 barells are identical. So M28 pistons will fit however, I'm led to believe that due to the shape of M4 heads, fitting M28 pistons in an M4 can lead to unusual compression ratios of up to 12:1, which sounds great, but apparantly doesn't work well in practice.

Gudgeon pin is the same.

Is a conrod the same as a push rod? If so, pre '63 M4s had push rods that were almost 2 inches shorter than post '63 ones. However, on post '63 M4s the pushrids are the same length as M28 ones - there's pictures of this under '1969 AK350' in the 'Your A-Series' section.

Two useful contacts:

Lucy Cutler, has probided various bits for the M4 in my 350 and assited with fitting the pistons/rings:
lucycutlerATtalktalk.net

Pete Abbot, 2cvGB Van Expert - he has a Belgian M4 powered van too:
pete&bevAT2cvers.4ever.org.uk

And if I hadn't chucked away a set of M4 pistons/rings that were shot last week I'd have measured them for you - sorry

AND also - I've come accross three different types of heads fitted to the M4. Late M4s had valve stem seals. early ones do not. There seem to be two types of early head, with subtle differences in the inlet and exhaust cavities. Late heads have dished exhaust valves, early ones don't, but again, they're interchangable - everything seems ok so far!

Well received informations, thanks very much

Conrod is the shaft if you like between the big end and small end (crank shaft and piston)

Spoken to Retrodesign, no M4 parts in stock and will not stock any. No sales on rare engines.

Shall make contact to these fellows

Had this shipped to me. There may be other sizes but not sure. looking forward to see the measurements from your pistons