1972 cr125 rebuild cylinder sizes

Hi All,

I am putting back together a CR125 from 1972, an early bike with alloy mudguards. It's all there and I have had the bike for about 15 years and rode it when I first got it, although it did have a few problems with carburation. Over the years I picked up many parts that I thought might come in useful. Now it's time to rebuild it.

I picked up a barrel on first over in good condition, as I had a new piston for this bore I decided to use it. However when I slipped the barrel on, the piston stuck out of the top a bit! The barrel is shorter (6 fins), than the one that was fitted ( 7 fins). I'm going to put the original barrel back on. Anyone know the changes to barrel/bore over the years 1972 - 1974 ?

Is the picture your old cylinder? 125 had two length rods and pistons.Post a picture of the other cylinder.

I was wrong about the barrels, they are the same, 6 fins on one side, 7 on the other. The difference is the piston, I was trying to fit a piston that was for a 74 CR125, where as mine is a 72, and they have a the pin hole at different heights! Shame to not have a fresh piston in place, I have reverted to the 2nd over jug with the existing piston, which is OK.

Top piston is for the short rod motor.Does the other cylinder have fin webs? That would be a 74 Cylinder

cylinders are not webbed as far as I can see, both are the same. As you say, it is the long rod motor, both barrels are the same. Its a pretty early 1972 bike, not seen many with alloy mudguards

The 72 125's had HVA silver forks not the Betor shown in your picture.. the frame gusset / bracket at the swingarm pivot says the frame is 73/74 also..

Thanks for the info, engine # begins 2022, so could be 1972 or 1973, cant see a visible frame number (paint). I had assumed it was a 72 due to the alloy guards. I'll try and get it going this weekend