Intrigued by your query so I had a look at my spares books and they seem to differ from your source. My TS250 book specifies C4 fit bearings for mains and gearbox for the 5 spd motor. The only C3 fit is for the clutch outrigger bearing which is mounted in a steel drum whereas the others are mounted directly in the alloy. The ETZ motors are the same which is predictable as they are very similar in construction – indeed many of the bits are interchangeable. The 4 speed TS motor is specified as C3 for the main bearings C4 for gearbox so I wonder if your reference book has got them mixed up. I suspect the slightly tighter fitting for the 4spd engine is because its mains are lubricated by gearbox oil (rather than petroil as in the 5spd motors) so probably run a bit coooler.
Let us know if you get any better answers.
- This reply was modified 8 years, 6 months ago by Peter Fielding.