Topic: first time 2 stroke top end rebuild

[westondc]

Ive got a 2 cycle engine that needs repair and i'm taking on the project myself. I have no experience with 2 stroke motors. The oem piston lost a small chunk but the cylinder walls look good. The bike has an auto oiler and the piston is 72mm stock. So, im planning on buying a weisco piston kit but not sure if i need to bore it .5mm over or just have it honed and keep the stock 72mm. Do i wait to buy the piston kit and have a shop check to see if it needs to be bored? Also to i trust the auto oiler or premix? This should be an interesting firt time project.

[75cb550 (kyle)]

what are you working on? most dirt bike cylinders have a nikasil coating that cannot be honed or punched out. you have to send them out to the factory so they can recoat. if you sleeve it, you can get 3-4 top ends out of a sleeve. otherwise, leave it and as is if the cylinder looks good

i say premix, just in case. that's probably just preference. better safe than sorry, though.

[westondc]

well i might be getting a bit head of myself here. well its out of a 250cc polaris atv, not really a "bike" but an engine all the same. i pulled the engine out and got the head off to inspect the piston. the cylender is good, no scoring, but the bottom of the piston is shattered. the bottom half of the engine is full of the broken piston parts  so it looks like i will need to split the cases and do a full rebuild.... not what i had expected to do. so i'm wondering how to split the cases now. the shop manual says to heat them up and use a crankcase puller. i need some pointers here. should i use this http://cgi.ebay.com/ebaymotors/Crankcase-Splitter-Separator-Tool-Motorcycle-ATV-Crank-/300392246412?cmd=ViewItem&pt=Motors_Automotive_Tools&hash=item45f0c5ec8c

[westondc]

here's a pic of my poor little engine