Pistons like the one you showed will leave scoring in the cylinder walls. Even if they look minor they can really pump oil up into the combustion chamber.

The skirt has been eaten away. Go a liitle deeper and make sure the cylinder can be fitted only in one direction. The same goes for the piston, make sure it fit's the right way.
Your donor motor has been running i hope, so clearance should be o.k. on that piston/cylinder combo.

 

Yeah that's what I'm counting on. I'll be swapping over the piston, cylinder, and head. Both the cylinder and piston go on in only one direction. The other 2wd engine ran smooth and quiet before pulling it out of the ATV, so I'm hoping it'll do the same to this engine!

 

While waiting on gaskets for the top end install, I picked away at some other things on the front end.

Pulled off the calipers because the front brakes were sticking, found both calipers to be locked up... So have a new set of those on the way. Replaced a bent lower control arm with a spare I had. Had to take a 3 jaw puller to the hubs to get them off. They're SUPPOST to just pull off with minimal effort, when they're assembled correctly and the splines on the front axles that they slide onto are greased... yeah, they weren't... they were rusted pretty solid in place... Soaked for about 3 days with PB blasted, hammered on, and then the 3 jaw puller was the final trick. Replaced those hubs with some spares I had as they had some broken off wheel studs. I could have replaced just the wheel studs, but I already had the two spare hubs with all of the studs still good on them, so I just swapped them out lol. A little grease on the axle splines and they slid right on. Also changed the front diff fluid and flushed out the old rusty looking brake fluid out of the front lines. So now I'm waiting on the gasket kit so I can put the top end back together on the engine, and front calipers so I can put the front wheels back on lol.

SO glad I had so many spare parts for this stupid thing. Saving me a lot of headaches and ordering of random odds and ends.

 

Quite some progress. Nice work man.

 

So I'm still waiting on USPS to delivery the dang top end gasket kit to I can get the engine back together... In the mean time I decided to take a shot at the locked up front calipers, even though I have brand new aftermarket ones on the way :P

Compressed air would NOT get the piston to budge... So I applied the old grease gun trick. Pulled off the grease nipple adapter from my grease gun and it just barely threaded into where the banjo bolt goes for the brake hose. Maybe a thread and a half before it locked up because the threads are different. BUT, it was enough to work. Started pumping grease into the caliper, and low and behold the pistons popped right out

After way too much time cleaning them up, I actually REUSED the old original seals in the calipers. I figured they weren't leaking before, just seized up from sitting and being dirty. So after a REALLY good cleaning and reassembly, full fresh brake fluid flush and bleed, I'm happy to say that the calipers seem to work just fine, and so far don't leak at all! So yay, free fix! Assuming they hold up lol. Guess I'll just toss the new aftermarket ones on the shelf for backups when they come in.

So for now it's at least back on it's wheels.

 

Cool if for a change something can be fixed. Nice job on polishing the brake piston.

Good luck - they may hold up for a long time.

 

Little more progress made on the ATV today. Gasket kit finally arrived! So I got to stripping the head, cylinder, and piston off the parts engine, got everything cleaned up, and all bolted together. Then installed a new starter solenoid so I don't have to jump it off with a screwdriver every time... Tidied up the wiring a little bit, hooked up the battery, and got it to turn over and move some oil around. No fire just yet, no gas hooked up and the coil is unplugged, I just wanted to circulate some oil around. Also it was 12:30am at this point and I didn't want to **** off the neighbors lol.

But it WILL fire up tomorrow! And hopefully not make any unusual noises lol

 

 

Cool it's running on the first turn of the starter. Great work.

 

Yeah it runs great! Left the fuel shut off and the coil disconnected and just turned it over for about 20 seconds before hand to get some oil flowing. Hooked the coil back up and turned the gas on, turned the choke on and hit the starter button, and it roared to life! I'm super proud of myself lol mainly with the timing chain part. I've never messed with one on a small engine like this and it was the part I was the most nervous about getting right. But it wasn't that difficult at all so long as you follow proceedure.