Cr 125r With Problems

[DIRT286]

OK my buddy has a 03 CR 125 with a fresh top end. Today we went riding but he was a lil short on 2-cycle oil so his mixture was a lil lean. after an hour or so the bike started acting funny. It was stalling very easily with the clutch pulled in and also while in neutral. It is VERY hard to start and after 7-8 kicks a loud pop comes out the exhaust. When it is running and riding around it runs perfect but once you let the revs get down it stalls and like I said very hard to start again. I took the top end off it when we got home and the top of his piston has about 10-15 small dimples near the exhaust side and it has a very tiny chip off the side of the piston also next to the exhaust side. The cylinder wall looks fine but towards the top there is some tiny marks that look consistent with the damage on the piston. Now could this have happened from just today due to the lean mix because it only has about 10 hrs on the new top end. Also the last piston that was replaced had a big chunk missing from the exhaust side as well. I am wondering if something else is causing the probelms. And just one more question, does the coolant in a 2 stroke run into the bottom end.....if not is it a big problem if coolant got down there some how
Thanks in advance
chris

[toofast4uu]

sounds like too aggressive porting, plus running too lean..next time, if in doubt, don't run it lean, ever....It only takes about 2 minutes to destroy that motor...If antifreeze is in the bottom end, then he'll need to tear the bottom end apart now, and replace the crank....once water gets in the lower end, the bearings are shot...

Sory for the bad news...

I was down in Ocean county today...where were you guys rippin it up?

[DIRT286]

the motor has no headwork done its all stock. we were at claytons. coolant got in the bottom end just from taking off the top so its not much, do you think it will be alright?

[superchicken]

sounds to me two things are wrong.Number one NEVER run the gas mix lean as cristian had said...Well if you like to do top end jobs and the occasional crank....they teach that in two-stroke 101

Number two,sounds to me the cylinders bore is out of round.Who ever is boring it there bar is creating alot of chatter witch causes the the cylinder to be out of round.and also make sure all the port openings are champhered or you will snag a ring and break it and the crown of the piston.Not to many shops will do this unless you ask.And most of the time when you do they try to charge you for it.I have had no luck with shops boring jugs so I send them out west to a top notch race shop and save 90$ with shipping.

[rpyfz450]

He's what I'm thinking...

When the exhaust edge of the piston crown has visable damage, it's usually because of excessively high combustion temperatures. This is probabaly from being too lean on the carburetor's main jet.

If you're too lean on oil, the cylinder bore would have dryed up a bit and suffered immediately. Coolant can also wash the oil away if it gets inside the engine. Do you still see the cross hatch marks on the bore?

The coolant you found may have just been from diassembling the top end, but it's important to do some foresics on the gaskets. Since this bike has done this twice now, someone should do a leak down test of the head/cyl/crankcase and also another one of the cooling passages. If coolant is getting inside the engine, it would most likely be from the base gasket. Also etheylene glycol burns bright white. Was this bike showing lots of white smoke even after it was warmed up?

How long has your buddy owned this bike, and does he know the full history behind it? Is it possible it has the wrong spark plug heat range installed? Is it possible ignition timing or compression has been altered?

Did this motor have a problem idling too high when in neutral (or clutch pulled in)?

What color is the piston crown?

[DIRT286]

<div class='quotetop'>QUOTE (rpyfz450 @ Mar 27 2006, 11:19 AM) <{POST_SNAPBACK}></div>

He's what I'm thinking...

When the exhaust edge of the piston crown has visable damage, it's usually because of excessively high combustion temperatures. This is probabaly from being too lean on the carburetor's main jet.

If you're too lean on oil, the cylinder bore would have dryed up a bit and suffered immediately. Coolant can also wash the oil away if it gets inside the engine. Do you still see the cross hatch marks on the bore?

The coolant you found may have just been from diassembling the top end, but it's important to do some foresics on the gaskets. Since this bike has done this twice now, someone should do a leak down test of the head/cyl/crankcase and also another one of the cooling passages. If coolant is getting inside the engine, it would most likely be from the base gasket. Also etheylene glycol burns bright white. Was this bike showing lots of white smoke even after it was warmed up?

How long has your buddy owned this bike, and does he know the full history behind it? Is it possible it has the wrong spark plug heat range installed? Is it possible ignition timing or compression has been altered?

Did this motor have a problem idling too high when in neutral (or clutch pulled in)?

What color is the piston crown?[/b]

I can see some cross hatch marks toward the top but not much. I know the coolant spilled into the bottom end when I disassembled it. the bike does not show much white smoke after being warm if any. He has owned the bike since brand new. no problems idling too high ever. If piston crown is top of piston then it is black. so we are gonna put in a new top end and do you suggest putting a larger jet in.
thanks

[grove]

you might want to check your power valves. A.K.A exhaust valves. over time they will get a lil loose and eventually will smack the piston. thus tacking a small chunk outof the piston and sometimes shrapnel. what you explain in your post sounds exactly like a bad power valve. check your compression and when you pull the cylinder. check the play in your power valves. have had a bike that ate a power valve and my buddies did the same thing. but those were suzuki's. your jetting is prolly fine. it wont hurt your bike to much to run a lil leaner than normal or a lil richer. you will either foul a plug or sieze the piston. if you sieze the piston a good trick is take some marvel mystery oil and put some down the cylinder through the spark plug hole. dont pour a whole lot. let it sit for day or 2. pour a lil each day. and then go out and just try to kick it slowly. also maybe tap on the kicker or cylinder lightly! i stress lightly because the cylinder is aluminum! well i hope this helps ya. take care. well i just noticed that this was posted a long time ago. well hopefully this info is still useful to someone then. just tryin to help a fellow dirtrider out.

[jeep98]