Crank not turning freely - any ideas?

[Jxmiddle]

Lammie running well but I couldn't help fiddling. Dropped the needle a notch and gave it a fast run (which was v good ). Stopped to check plug which looked fine but when tried to restart it appeared seized. Couldn't move kick start at all. Rocked back and for on in fourth and poured oil in plug and after a while it freed. Rode home carefully. Stripped top end, showed no evidence of seize. Odd.

Rebuilt and went for a run. Stopped to check plug and again on restart it was locked solid. Couldn't free and got a lift with some nice people selling roadside cherries (another story). Stripped down and crank was not turning freely around bdc. Seemed to be rubbing to the point that it was very difficult to turn at all. Removed crank and checked all bearings, everything looks good, no sign of anything broken. Put crank back in and it's now it appears to be turning freely.

Hate to rebuild and have it happen again. Any ideas?

[Jxmiddle]

Immediately had a thought as I finished typing. When I put crank back in I just slid mag housing on and did not put flywheel on. Logically that would would indicate flywheel is the issue?

[Adam_Winstone]

Crank twisted?

[Adam_Winstone]

What flywheel?

[coaster]

Check the pickup retaining screw is tight, also a good ideat to check that the stator securing bolts are tight and the the mag flange nuts/studs aren't fouling the flywheel.

[Jxmiddle]

Thought you might be interested in the discovery of the problem (though perhaps not the cause). On pulling everything apart found the following issues:
- the mag side main bearing had gone (though not badly), the drive side one also looked unwell
- the locking was caused by the flywheel catching on the stator plate leaving gouges in both
- there was a hairline crack on the face of the mag housing and a radial split at the back
- the crank was 'out of alignment' and on pulling apart one of the big end shims had almost been destroyed

Not quite sure what caused what but the solution is £££££

A local experienced motorcycle tuner suggested drilling a hole in the top of the carb and putting a screw in to stop the slide opening fully. When I questioned how he knew my riding style (wot) he said he'd seen the inside of my engine!