Hi Guys,

I have an '01 SY250 (my first trials bike & first 2 stroke). It's had the barrel replated also piston & main bearings renewed a couple of years ago. I run it on shell alphamax & mobul 510 synthetic 2-stroke oil @ 50/1 mix. It generally runs like a sweetie. The carb mixture is set as per the manual with coolant present & correct. Today I noticed a significant knocking from the engine at tickover. The knock cannot be heard above tickover & I rode it home ok. With no previous experience of 2-strokes I'm looking for advice for my next course of action please.

Thanks, wuzzy

Hi,

You will need to figure out if the knock is coming from the top (head) or bottom end of the engine ... have a close listen and you should be able to determine the source in terms of top / bottom end knock. This will lead to your next action (top end is better).

P.S. dump the optimax in a bike of that age, it will be doing more harm than good..

Hi there,

thanks for your reply. First things first - 'mobul 510' was meant to be 'motul 510' & even better, 'alphamax' should have been 'optimax' (which you clearly sussed out). It's not just about answering the question, you've got to de-code the bugger first! P.S. Alphamax is a heavy load 12 bore cartridge which I do have, but hopefully wont need to use on the bike.

Anyway, I've had another listen & the knock is from the bottom end & I only get it when I tilt the bike to the right. It is much more from the generator (left) side so I'm hoping it may be a coil or something loose behind the rotor rather than the big end bearing. I've given the bike a wash down & taken the generator cover & centre nut off but I'll need to borrow a puller or get one made up to get the flywheel off.

Do these symptoms sound familiar to anyone maybe?

Thanks again,

wuzzy

This might sound a bit daft but have you tried pulling the clutch lever in and listening for the sound the Scorpa clutch plates can rattle sometimes - usually fixed by an oil change

Paul Mac

Thanks for that Paul, a totally logical thing to do, but I never thought of it. I've already drained the oil as I assumed the side plate I was removing was wet too (Doh!). I've ordered a small puller so I'm going to check out the generator side first but I'll try that if problem not found.

Cheers, wuzzy

All OK in generator side. Refilled with oil & checked knock with clutch in / out - no difference. Removed clutch cover & found external circlip at bottom of housing. This has come adrift from the kick idle gear which is allowing it to move when the bike is tilted to the right. No sign of damage on the gear itself so not sure yet if this is the full story. Hopefully main bearings are actually OK.

Thanks for your replies, It's great to know there's help at hand when it all goes pear shaped!

regards, wuzzy

Edited April 22, 200818 yr by wuzzy

Full story as follows;-

Circlip & washer adrift from kick idle gear.

Excessive wear on kick idle gear bushing allowing it to float on the shaft.

When bike leant to the right, kick idle gear moved on shaft and fouled on rivets which hold primary gear onto clutch basket causing the metal to metal knock at engine speed.

Thanks for your help folks, wuzzy.