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 Piston Ring Sizes 
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Joined: January 15th, 2013, 12:54 pm
Posts: 12
Post Piston Ring Sizes
G'Day from Australia chaps (and chappettes, let's not assume!). It's a while since I posted in this forum but I've been a bit busy.

Recently I've been going through my stock of bits and pieces preparatory to doing some engine reconditioning and have a bit of a puzzler.

I have an apparently brand new pair of barrels with pistons and gudgeons. No worries, thinks I to meself, I'll just order a set of rings for these pistons and all will be both Hunky and Dory to use them.

Careful measurement reveals that the ring grooves are 2mm, 2mm and 3,5mm. The only set of rings close to this seems to be 1.75, 2, 3.5 (Der Franzose P/N 10148). I can't help feeling that a ring with 0.25mm vertical clearance will very quickly destroy what is otherwise a brand new piston.

The pistons are a high domed variety, stamped, along with the usual arrow and AV, with 8.5 and an E underneath the 8.5. I'm assuming these are therefore 8.5:1 compression jobbies. Oh, and they're 74mm diameter.

The only identifying marks seem to be a casting number inside which appears to be FM with 55048 under it and an E under that. Gudgeons appear to be 20mm floating type but the circlips are also missing. (Piston has circlip grooves)

Short of buying two sets of rings (not a financially preferred option) so I can get 4x2mm compression rings, I'm wondering whether I can actually use these, and certainly what manufacturer they may be from.

Any information and/or guidance you blokes can provide will be greatly appreciated.

Cheers, Pottsy.

Coming to you from Beautiful Down Under Melbourne, Victoria, Australia

September 3rd, 2018, 3:36 am
Firing on two.
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Joined: October 22nd, 2014, 10:59 pm
Posts: 970
Location: South-Limburg
Post Re: Piston Ring Sizes
Here a firm that has lots of spings in all sizes.

September 4th, 2018, 8:23 am
Firing on two.

Joined: November 2nd, 2011, 12:35 pm
Posts: 521
Location: Charente-Maritime
Post Re: Piston Ring Sizes
Burton do the same set of rings, it appears: ... _8024_8025

Might be worth an email to them just to check but I agree about the large clearance, it does seem rather a lot.

September 4th, 2018, 12:14 pm
Agony Aunt - You have a car problem? Speak to Ken

Joined: March 6th, 2009, 1:40 am
Posts: 3597
Post Re: Piston Ring Sizes
have you tried paging the oracle, aka Roy Eastwood at ECAS 2CV Parts?
If anyone knows which make of pistons you've got, he will.
The nearest I know of were sets used on M4 602cc engines, which had 2mm compression rings, 2mm scraper rings, but either 4.5mm or 5mm oil control rings...


September 4th, 2018, 10:40 pm

Joined: January 15th, 2013, 12:54 pm
Posts: 12
Post Re: Piston Ring Sizes
Hi Ken.

Roy has identified them as Floquet Monopole brand, which explains the FM cast under the crown.

Maybe if I buy a set of the M4 rings as well as a standard set of post 1976 rings I can use the M4 top ring and the other two from the other set. A slightly more expensive way to go, though.

I 'll see if I can source spacers over here in Australia first perhaps.

Of course, I could always whip over to Morocco to the factory and maybe have them make up a set for me. Possibly a bit more expensive again! :)

Thanks for your help, Pottsy.

Coming to you from Beautiful Down Under Melbourne, Victoria, Australia

September 7th, 2018, 12:05 am
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