KR-1S.co.uk Forum

I've been told KR engines can be a bit rattly sounding at low revs/tickover but sound smooth when they're riding and under load. I've fitted a new engine which seems ok but has an odd sound.

Only happens above 4k revs. On throttle it's all fine. Roll off and come off load and it's got a tinkly little noise (sounds like a small m4 nut is trapped in a port). Happens at part throttle down to closed throttle. Soon as the engine revs drop below 4 it goes away completely.

Has anyone experienced anything similar? The engine has a rebuilt crank, bearings and seals, original pistons with new rings and untouched bores. I got the engine complete so haven't been into it, just worried it might be a ring catching a port

you won't hear a ring catching a port (at least, that's what I believe, I'm ot a 2-stroke guru).

do you hear the same when revving the engine at a stand still ?
Or revving in gear with the rear wheel of the ground ?

I suspect something isn't tightened properly and starts to vibrate.

It's an odd one. In neutral at idle it's not there. Build the revs slowly and it starts at almost exactly 4k. Build the revs quickly (a good handful of throttle) and it's quiet as they rise, then soon as the throttle shuts and the load comes off it just tinkles a bit as the revs die till it gets down to 4 again, then it goes away.

At idle and up to 4 the engine sounds normal. Crossed my mind that I'm running it heavy on oil at the moment and that might be having an effect, apart from that I wondered if the kips valves might be a bit loose. If they were that's not something I'd worry about.

Might have to carry on for a while and if it doesnt go away swap my other engine back in and check it over on the bench.

Could be one of the power valves rattling, you could try holding the linkages whilst revving it or installing elastic bands to help tension any free play in the linkage rose joints or power valve shafts.

otherwise it could be any thing lose like resonating chamber, exhaust etc