CM200 Engine problems, Update-Piston rings fragged. oopsies

von1papen · Spanner Monkey Joined: 12 Jan 2011 Karma :

Basically on the journey up to uni yesterday I noticed a bad lack of power, a crap load of fumes being pumped out of the crank breather and I could swear I smell burnt oil.

Also there has been a oil leak between the barrel and big end plus the head n barrel. (Just had to top up oil regularly, didn't affect performance)

Is this the rings? Problem being I need the bike to get too and from uni for the exams, nevermind it being NW200 Race week here so I'll be out about about most days.

Is this just them leaking, or have they disintegrated? Don't want to destroy the barrel but I imagine if they've disintegrated inside the barrel then thats probably the case already. Bollox and bugger...

My back up bike, the cg125 is also having an engine rebuild at the moment so I totally rely on the CM (thankfully I bought a full gasket set, though it seems I have to buy £20 piston sets rather than just new rings)

nightshaddow · Nearly there... Joined: 18 Feb 2008 Karma :

if you have a compresion tester that would give you the right answer, from what you are saying it could be 1 or 2 different things,

best whip the plugs out this can be the first indication if something is wrong, also check your valve clearances,

i suspect piston rings as you said but it could also be valves/ valve stem seals
____________________
"WHAT DO YOU MEAN 100 MPH THATS IMPOSSIBLE Its chinese OFFICER."
Current rides CB 125 TDE(the next project) NS125RK ( now on the road ) CB125TDC (soon to be project 17) melody ( the nephews )

Compo · Nova Slayer Joined: 02 Jan 2006 Karma :

Another supect for fumes out of the breather pipe could be the head gasket blown.

von1papen · Spanner Monkey Joined: 12 Jan 2011 Karma :

I'm thinking its the head gasket simply because it was already shagged, and explains why it feels like its sucking in far too much air when she runs! Will know when I get her brought home, compression tested and the head removed!

Thanks!

von1papen · Spanner Monkey Joined: 12 Jan 2011 Karma :

Turns out it was the rings, one of the pistons had fully chewed itself to bits and welded to the top of the barrel at some stage, the other piston had just shattered its top compression ring!

A 0.5mm rebore, new oversize piston kits on the way from wee-moto and we're back on track Very Happy

Lapped the valves last night though I've yet to stick the springs back in and test them for leaks.

Head was full of carbon and mashed aluminum from the piston, had to scrape it off, thankfully the valves seemed to be fine.

Yes I thrashed the wee engine at the top end on the motorway but I didn't expect it to blow within 3 months! (Kept her topped up with oil) Still with all this work done she'll be like brand new, £110 for the boring, honing and piston kits which IMO isn't bad for an essentially new top end to be run in Smile