125-200cc CR125 and 144 scored piston and cylinder (Pics and vid)

The first pics are the 125cc piston and cylinder before the 144 kit.







The videos are the 144 con rod, piston, and cylinder. I just installed the kit, and rode for an hour. I stopped to swap pipes and looked into the exhaust port and saw scoring. I'm wondering if the connecting rod is to blame? There's no up and down play, only side to side. The two look similar in damage. I'd like to get this sorted out before I do the 165 kit and the same thing happens. Are both the cylinders done for? Or can they be used for the 165?


View: http://www.youtube.com/watch?v=6w9OUSdXkDk



View: http://www.youtube.com/watch?v=x9v2o6z22ls

Your 125 cylinder will absolutely need to be re-nikasilled as the lining has been flaked off above the exhaust port. Side to side play is built into the crank so it can self align. The 144 cylinder might be ok once you remove the melted piston material from the walls. You will need to check for grooving.

Did you wipe your crank down before you shot the video? It is awfully dry. What oil are you using for pre-mix? At the very least you are running very hot and something is causing that. It is either gas(lean), oil, or coolant related. Neither cylinder is ruined in the long run but will need some attention.

I agree, looks more like you are burning them down. Compression leak, to small a main, forgot to put oil in the gas, that sort of thing.

Thanks for the replies. As for oil, I was running 25:1 in the first tank of gas and 32:1 was in my fuel can. I didn't wipe down the rod. Maxima Super M is the oil I used for the mix. 460 main, 35 pj. The 144 may need the same as well during further inspection. A little flaking around the center of the exhaust port.

Yes, I made sure to add coolant in the system. My first 2 stroke experience isn't going so well ha.

Check that you don't have a flow problem in the coolant system. Blockage, bad water pump gear, . Maybe an air leak. Check that you don't have a partial blockage in your main jet/crud in the float bowl.

What's the best way to check for a bad water pump gear? When draining the coolant, everything drains fine. And there was coolant dripping out of the cylinder when I removed it. I installed the jets before I even ran the bike.

pop the waterpump cover off and rotate it with your fingers when you do this the engine should turn over, some one may have left the nut loose that holds the waterpump onto the shaft.

not good and yes definetly needs relining
sorry to see an engine in that condition.

good luck with diagnosis

Any chance your air filter isn't seated properly and you're getting dirt or sand in?

The water pump seems to be working fine. Spins freely while moving the crank. I double checked and the air filter was sealed fine.

What's the numbers on the cylinder mean? "B" Size? The piston says "A". The ring around the cylinder, does that mean the base gasket is too thick? Would this be an issue?

Base gasket would not cause this problem. The ring around the top of the cylinder is just where the pistons ring(s) have not worn the cylinder. There is still part of the piston crown above the ring groove so probably fine. I would really be looking at an air leak causing a lean condition as both pistons are indicating a lot of exhaust heat. Did the bike idle normally or was it erratic? Check around the reed block. Sure looks like a lack of lubrication to me though.

Those are just casting and version numbers. The ring travel looks correct in the picture. There is only ~.010" of variation from stock base gasket dimension either way with base gasket changes. You need to first do a leak down test of your top end to make sure you have no air leaks. There is a thread on here that describes the procedure. I have seen things like a warped intake manifold cause these kinds of issues. Also even if there is coolant everywhere in your system doesn't mean you don't have a blockage. There are two ways into every area of the motor. I have seen a rag stuffed into the hoses to stop leakage during rebuild be left in and block flow, etc.

I am still a bit worried about the lack of oil film showing up in your pics. I wonder if you had the fuel separate on you and lost your lubrication. Just a thought. There should always be about 1/8" of oil in the bottom of your crankcase. Check for this and if there isn't any there you might have found an issue.

Scoring like that for the full circumference of the piston is almost always a lubrication issue.

Probably a dumb question, but are you sure that you are calculating/mixing the premix oil correctly?

Sorry to hear about your bad luck.

The first start up after installing the 144 seemed to idle perfect. Even after the piston failed it still ran. I mixed 2 gallons of fuel at 25 to 1. I poured 10.2 ounces of oil in the fuel can and shook it up. How long should I shake the can for? I used Maxima Super M. Is this a bad oil? The expansion pipe has a rubber oring, and a thin exhaust gasket between cylinder and pipe. I don't think it should have a leak there. The rubber boot for the exhaust pipe and chamber seems a bit loose. I assume I have to rebuild the top end before I can do a leak down test? What do I need to look for around the reed block? The mouning bolts are tight.