Rieju MR300 piston end gap specs?


New member

Anyone knows what is the actual piston end gap min and max spec? Could not find the Rieju workshop manual anywhere.

Gas gas manual states 0.5mm to 0.8mm
My old original S3 piston was 0.4mm
The new S3 piston that I am about to replace is 0.25mm

Nothing matches!

What do I do??

What do I do??
Always follow the piston manufacturers specifications. See, different companies can use pistons/rings made of different alloys from one another hence leading to different specs for their particular piston and ring setups. Again, follow the instructions that are specific to the piston you're using.
Thanks, that's good to know.. But for next time!
I was in a bit of a hurry so I decided to file it down to 0.4mm same as the original piston i removed since it was the same brand (S3).

Unfortunately S3 didn't specify any specs or any range of gap clearances, which I think they should.

I assume that I am still within spec.

A good ring gap is usually 0.005"-0.007" per inch of bore.
Meaning if your bore is 72mm (2.83inches), you want to be inbetween
2.83 x 0.005: 0.014 inches: 0.35mm
2.83 x 0.007: 0.02inches: 0.51mm
You want to be inbetween 0.35mm - 0.51mm