M21 piston rings

[maddogmargetts@yahoo.co.u]

Just about to put back my M21 barrel after having hardened valve seats put in and one of the piston rings "came apart in my hands". I don't think it was me as I did not try taking it off but at any rate I need a new set or at least a new top one. Scouting around and reading about them it seems that getting +060 rings is not so easy as I expected. Do people usually have these made when in this situation? I wonder if rings are more or less generic in that provided they are the correct size and type it doesn't matter what is used. I was also bewildered just how many different metals are used for different types. I wonder also if I could fit +040 or even +020 if I made sure the gap in the ring is big enough?

[AdrianS]

If you fit +20 or +40 rings they will have a much bigger gap than  the +60 rings.
Go for the correct size. I think most manufacturers rings will fit your piston unless it it is a special which may require dedicated rings.

[Pete Gill]

Hi John
Is there a noticeable ridge in the barrel at the top ?  I have had the experience of a top ring hitting a worn ridge at the top of the barrel and breaking into two.

Pete

[Stubaker58]

I've just changed the rings on a Bantam piston anD the instructions with the (Hepolite) rings spoke about a stepped ring for the top groove designed to clear any ridge at the top of the barrel.

Are such things still available?

[leon bee]

I just saw them in some ancient literature somewhere: ridge dodger rings, they called them. Never seen one in real life.

[Mike Farmer]

 

I've seen em available for Old Paraffin tractors but not seen one since Kitchener built sink units. In truth I suppose if you have difficulty in getting normal ones you aint very likely to get dodgers.

Mike

[idie]

The last ones I bought for my Velocette had a step dodger top ring.