Hey Guys, pretty new here but so far reading through the forms, downloading service Manuals has taken my "Free Bike" which came in the infamous rubbermaid container from a friend of a friend of a friend to being able to get it completely back together with new cables, and tires and getting it out racing in the ice!my newest problem is i wiped out.. bike was completely fine, as able to start it up and get going again but after a few laps i lost compression.. got it back to the shop and found i had cooked the piston pretty good. What i noticed as well is my fuel filter had some small rocks in it, big enough to barely fit through so im guessing it was either the 50year old engine decided to quit.. or it went lean.anyways, i did the measurements and i have the 4th over sized piston already in there. I was hoping someone out there might know of a replacement sleeve, a newer cylinder, and have a lead on a new piston/Ring set?​​​​​​​Thanks for all your help guys     

Welcome & bummer about the meltdown. Just guessing but does sound like it was too lean unless the piston was already compromised with stuck rings or something & creating a lot of heat untill meltdown. Plug needs to be at the cold end of the scale for safety. Run plenty of oil in the mix if not using the pump, or crank the pump up past normal for racing & be sure its delivering. Run carburation plenty rich. You need another 4th over-81mm-piston kit if the cylinder is usable. But if you need to bore it then i used a 2X5 82mm kit in two of mine & shortened the skirt 5mm or so to match the original. Is from a "one year only" 1979 YZ400F as are longer stroked & with a reduced bore from usual 85mm in all other 400's except for "1979. You'd be lucky to find a 2X5 kit now. Plus the 81mm 360 kits are invisible but might be limited with how much i can search for [i'm in NZ], someone said that once about searching down here but i dunno, doesn't sound right. Free bikes are great--until they cost a lot of money. So hope for a good outcome.

Good info RT325 on the alternative to the 360A piston dilemma. KKromick is not alone, plenty of others have been where you are. I was fortunate to need to go just to 2nd O/S and Enduronut was able to help me out.

Might try Los Angeles sleeve WRT re-sleeving.

Wiseco 639m piston works with a spacer under the cylinder. 2.5mm thick aluminum and another gasket sets it right up. These are available in .5mm increments from 80 to 82mm. I'm running an 81.5mm in a 74 360 cylinder right now and it's been working great.

The dome height is a little lower on the 639m but it can be made to work. The stock squish clearance is a mess anyway, which is part of the reason why these bikes like to ping themselves to death.

Sounds like good info there Turbo, thanks! 

welcome and sorry for your meltdown
I went through same two years ago and rebuilt with help of the smart guys on this site.
Be sure to replace your crank seals, reseal intake reed thing, and make sure jets are at least as rich as stock and that plug is a "9" heat range and timing is set correctly to avoid my mistakes

Man this post is full of great info for us DT360A owners!