Help - CR250 82 / 83

[Digga]

Thx Brett
I have just measured mine & it is near enoguh the same at 134mm (maybe 0.5 mm less).

What about the maximum distance that the rod travels into the cylinder? I measured from the base of the case/cylinder flange to the max height that the rod can travel & got approx 99mm taken at the very top of the rod.

Unless you happen to have a motor apart, then we will have to wait until your next rebuild/service etc to check

[Digga]

I have just had a quick look & the piston comes right flush to the top of the barrel on the perimeter with it about 2 -3 mm higher than flush in the centre (height of the piston head curve/dome). With the head on, the piston at TDC is about 12 mm from the top of the head when measured through the plug hole.

Not sure is these measurments are OK or not 

[GMC]

They change the compression ratio by different size combustion chambers in the head.
Bumping up the compression may have been the inspiration to add another head bolt.

Don’t know any measurements for your model but the piston flush at the outside of the piston is normal, the higher part of the piston in the middle fits into the cavity in the head