Case Reed Induction 250

balance holes filled with plugs

another term would be STUFFED crank.

stuffed? full circle ? IDK

with all the vibration this thing makes, the crank on this and my last 380 don't seem to be well balanced

I mean the balance to counteract/divide up the forces of the piston moving is done in such a way that the crankshaft volume is close to the crank cavity volume. Or even more broadly is done without voids unevenly distributed. This could be plugs in holes, Magnesium inserts which I believe is how the last of the Italian Huskies did it, Plates capping the crank. It looks like the Yamaha 250 uses a cap on the inside which is probably all that is needed as the outside of a balance hole should be pretty close to the wall.

There are threads over on ktm talk I read doing this for the 380.

ive seen cork on old snowmobile cranks..

I used cork on an old ts 125 years ago. araldited them in. gave it a descent lift

What You mention is pretty interesting to Me, as I have a 250 Maico ( 1983) and I also have a KTM 380 (2001) so I am familiar with both of there Power bands. So when the late 250 Husqvarna's changed there Bore and Stroke, what did they end up with ?

Ok, so it looks like I found the Bore and Stroke else ware on this sight. 66.5 X 70.8. It looks as though the Crank is a bit larger Diameter, and to be fitted into the early cases a little machining needs to be done.

having had both the early and late, the crank to case difference was never an issue
did not measure them but they could be swapped as the 250 cases were the same

pretty sure the only difference is where the pin is located on the crank cheek..same rod as earlier 250 and 400/430. cheek should be same outer diameter as 2premo says.

My 1970 Yamaha had the crank full circled by epoxying formed corks and sealing both ends with the epoxy. This was done in 1971 when my father purchased it. I got it in 1973 and had to replace 2nd gear in 1974 so I had to tear it down as my first engine job. The epoxy held up very well at that point and also in 1977 after a lot more hours had been put on it.

Full circling increases the bottom end compression by reducing lower end volume.