Vintage Dirt Bike Q & A

Started rebuilding a Cr250m 1976 model engine, The piston that was thought to be stock 70.0m had a 50 stamped onto it, the bore is measuring around 70.5m, my problem is the bore is scratched. How much can this cylinder be bored out again since it is already .50m over, please respond need to know my options, don't think resleeve is a option

Wiseco makes 70mm to 72mm pistons in .5mm increments (338M07000, etc.).

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

I wanted to keep original bore of 70.0m but hard to find the jug, so I will take mine from 70.5m up to 71.m just to clean and true it up a bit.
Somewhere I read of drilling to small holes 3m down from the bottom ring on the intake port will help the piston oiling, has anyone heard of this, if so please share some thought, I will be going Wiesco

only if the exhaustport is bridged.

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80 CR250Ra
80 CR250Ra
78 CR250R
80 CR80
82 Bultaco Sherpa 340
78 Bultaco Pursang 250 MK12
76 Bultaco Frontera 370 MK10
76 Bultaco Alpina 250
73 Bultaco Lobito 125 MK6
76 Suzuki RM125A
90 Kawasaki KX250