Yamaha TRX850 Enthusiasts Forum

Has anyone got experience of running in (almost any) bike motor when rebuilt with new main/big end shells?

Everything else (pistons, head etc) is as it was before the build but not sure how long I need to treat the motor with care before I can safely cane it?

It's not helped by being a trackday only bike so road miles are not an option. Would be frustrating to dawdle round any circuit getting in everyones way for 500 miles plus it would cost me a small fortune at £100 a day..

Advice so far is run it up to temperature then let it cool; repeat three times and from that point don't worry.

Small clearances and soft shells makes me feel that some running in is a good idea. There again, if clearances are good and oil pressure OK, why would anything pickup?

Probably a week or two before the motors back in but I'm forward planning and eager to hear the FCR induction noise at full throttle again.

All comment gratefully received unless it's all contradictory and leaves me none the wiser.

If you`re sure clearances are right, oil pressure good etc, cane it from the off, it`s what most race motor rebuilds get after running up to temperature a couple of times.

I'd run it gently for around 10 laps, cane it a few laps then change the oil and filter before giving it some stick.

After starting and running/cooling a couple of times I'd be riding harder and harder as the first session was under way then as suggested dump the oil and from the second session onwards for the rest of the day I'd be full guns blazing. Early 80's I ran my off the showroom floor z750 by riding home. Then up to Lakeside raceway the following day and just went hard all day. Never had an issue with that old dog..

Thanks lads.

That has reassured me that a gentle first session having run the motor to temperature a few times should be all I need.

Even at tick over it is doing 16 revs per second so a short run time should quickly take any surface irregularities off the new bearings.

Better look for a May date to get back out again.