Need new top end which way do I go??

Well guys I popped my top end on Sunday I hope to just get away with a piston and ring set. If I have to replace my entire top end I was thinking I may as well upgrade.

I have a GPracing Midi with a 5 port 50cc Polini. 17.5pbhn carb What would be the best top end to put on this engine?

same top end as before

I order a stock set up from midsouthmini

does anyone bore these motor who can give me an idea what it would cost my jug might be worth saveing for a spare.

Depending on how severe the damage is, sometimes, I say again, sometimes you can salvage it by starting with some 300 cloth backed sandpaper and sanding out the larger of the scratches and scores and them go to 800 and then 1000 to finish it off, I have saved a few cylinders this way, and used them as spares.

If the damage is really bad, with really deep scores, the cylinder would need to be sent out to be repaired, there are very few places that do this, since the cylinder needs to be re-nikasiled after the repairs. The places I have tracked down range anywhere from $125-$250 to repair and replate.

thanks for the info looks like it is cheaper to replace it if the damage is too much.

parts will be here tomorrow anyone have any assembly tips? It's been a long time since I rebuilt an engine.

Thanks, JL

dont bother trying to fix your old cylinder... did you get the gasket kit w/ your new one?... when I take out my engine(RR) I take off the faring and tank/seat pannels.. loosten the water ports on the jug w/ a pan underneath, take out the lower radiator bolts and push forward, loosten the pipe mounting bolt up top, take the air filter off and carb off but just zip tie to the side, take off the coil wire, unbolt the engine mounts, move engine back and to the side to get the chain off, grab the engine w/ right hand and lift the front of the bike w/ left hand and gently remove out the bottom, this takes about 15-20min. if your not rushing, I havent had to remove the engine in the GP "knocking on wood" yet so I'm not sure if its the same.... should be something similar...

Just make sure it's all clean and assemble it with plenty of your run-in oil, it will smoke for a bit but hey, so what.

what type of oil do you recomend?

I'm sorry, this is one of those questions that usually starts a b|tch fight, i'd rather just say use a good one and remember your brass ones arn't measured by your fuel/oil ratio so don't get carried away.

there will be more when I put the bike back together

here are a few more tear down pics

Clean the bottom half of the motor before you put it together again...Doug......

All is well in GRC land the rebuild was a success. The bike ran strong yesterday. (thanks to MidSouthminmoto for stocking the parts I needed for the 50cc Polini)