Vintage Dirt Bike Q & A

Need quick but accurate answer. Sent cyl to shop only to find out it's been bored 3 over already. I bought a 3 over piston but have lines on a couple of std bore MR cylinders.

Tks,

Bob

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75 CR 250M1 Elsinore
83 Rokon Trailbreaker
99 BMW R1100RT

The MR250 cylinder is almost identical with a 75 or 76 CR250. Only difference I see is the exhaust port height for the MR is 1mm lower for more torque. You could modify it by having a shop raise it or just try it as is. Wiseco still should have pistons up to 2mm over for the 75 CR250.

The only other difference is the MR head came standard with only four large head studs and one (front) small stud. The other three holes for remaining studs are there, however and I believe they are tapped for the studs.

Your are correct about the head studs. I purchased three more studs for my MR250 and used a CR250 head gasket. Eight works better than five in making a good seal.