KR-1S.co.uk Forum

Hi there,
First time on this (or any, for that matter) Forum and was looking for some information.

I've just bought a 1989 KR1 with a bottom end failure. I don't know what the exact problem is, as I haven't opened it up yet, but I've got the engine sitting on the bench ready for action. I also have a spare with a knackered top end, but good bottom end. However, if the crank in the good bottom end is fine, can I simply remove it and put it in place of the potentially knackered crank in the other engine? Or will this cause other problems?

Any advice would be appreciated.

BPS

Welcome to the forums.

It would probably be easier to do it the other way around in my opinion, but essentially either way you do it, should be fine.

You won't fully know until you get them stripped though.

Thanks for the response.

I'd thought about doing it the other way round, but I was concerned about the possibility of differing wear patterns on the bores and piston heads... It usually isn't a big deal but it can have an effect I believe.

What's wrong with the top end on the engine?

pistons/barrels from the good bottom end should be fine if there in good nick. budget for genuine head gasket and base gaskets though. definitly dont scrimp on little ends/clips or gudgeon pins. may aswell sling some new rings in while yer at it.

the engine with the duff top end (good bottom?) would sound like the basis for your new motor - transfer the good barrels and head from other motor to this one...

... does slightly depend on how bad that top end failed though - if there is potentially too much shrapnel gone down inside or the engine has been opened and exposed to the outside elements you might have to disassemble both motors completely to start with.

... with a minor top failure (such as ring snag/exhuast port) advice I have (been given and) used previously... you can flush the crank and bottom end in place on the motor with some methylated spirits to swill out any debris. if alot (more than one or two minor pieces) came out or there is much unaccounted for missing chips or is meths pours out too dirty then take it all apart. With the pistons off and some meths in the crank activate the rods by hand to spin the motor for any signs or rumble or grinding

IF its ok to reuse bottom end complete, then relubricate conrod big ends with 2 stroke oil. Thoroughly/spotlessly clean everything. Replace small end pins and bearings, clips, pistons and rings with new items. (Download) consult service manual for other checks on rod play and cylinder measurements.