I have two queries:-
1.Can 51/2 pistons be used in a pre war engine without spacers being installed ?
2. Does anyone still supply pre war R51 pistons ?
Cheers
Pete
1939 R51 pistons
-
Brock Downey
Re: 1939 R51 pistons
Hi Peter,
You and I are in the same boat. I am looking for pistons for an R5. I have not found any yet, however there is a demand for them and I expect someone will have a batch made up very soon. A friend of mine used R51/3 pistons and machined a 122" spacer for the base of the cylinder. Otherwise, the top ring comes out of the bore. I rode his R51 and it seemed fine. The other choice is to upgrade your R51 crank to R60/2 rods and R50/2 pistons. This is a recommendation I received in writing from BMW Mobile Traditions. I hate to take apart a perfectly good pre-war crank to do this. I am at a crossroads now, as I want the bike on the road in the next year. I would like to find a pre-war crank that needs rebuilding and use the later parts, possibly R50S pistons. I hope this helps calm some of your frustration concerning this mutually shared issue. Hang in there! If you have any updates, please advise. Thank you.
Brock Downey
Canada
You and I are in the same boat. I am looking for pistons for an R5. I have not found any yet, however there is a demand for them and I expect someone will have a batch made up very soon. A friend of mine used R51/3 pistons and machined a 122" spacer for the base of the cylinder. Otherwise, the top ring comes out of the bore. I rode his R51 and it seemed fine. The other choice is to upgrade your R51 crank to R60/2 rods and R50/2 pistons. This is a recommendation I received in writing from BMW Mobile Traditions. I hate to take apart a perfectly good pre-war crank to do this. I am at a crossroads now, as I want the bike on the road in the next year. I would like to find a pre-war crank that needs rebuilding and use the later parts, possibly R50S pistons. I hope this helps calm some of your frustration concerning this mutually shared issue. Hang in there! If you have any updates, please advise. Thank you.
Brock Downey
Canada