Not good,
I think most on here would ask the following;
What is your jetting?
Air box lid on or off?
Type of air filter?
What exhaust are you running?
The hour is was running, what kind of running did it endure?
Oil injected or premix 32:1?
Temperature elevation?
Slightly bored?
I may have missed something but I think this should be a good start.
Using a PWK 28MM, I forget where I ended up on the jets, but from a plug chop I made sure that I was a bit rich for break in.
No Airbox, this engine is being used in a go-kart. I just have a Uni off the carb.
FMF Fatty and FMF silencer
I did 3 warm up cycles just lowly blipping the throttle. Re-torqued all the head/cylinder bolts. Then I drove it around less than half throttle for about 15 min, checked everything again, then let her rip.
Premix 32:1 with Lucas and 93 octane
80deg and sea level here.
OEM cylinder and sleve, just had it over-bored to clean up minor scoring. Forget what spec the builder ended up at, but he ordered the piston himself. It was a Pro-X cast piston with cosmetic gasket kit.
slightly bored ?
new piston ?
cast or forged ?
was it bored/honed for the exact new piston and clearances recommended for that piston ?
what was that piston to cylinder clearance ?
were the ports chamfered after the bore and porting ?
leakdown test ...check
3-5 heat cycles and retorque of head/base nuts ?
leakdown test again ?
as mentioned above...what kind of running for an hour ?
heat cycles ?
or start it and rip ?
I didn't measure the piston to cylinder clearance, I was told the machine shop made the measurements and all was in spec since they ordered the piston themselves. I could see that the ports were chamfered when I got the cylinder back. I didn't do a leakdown test a second time after break in, but did check the main with a plug chop and it was overly rich, which I wanted. I think the rest of your questions are answered above.
it got crazy hot/or improper piston to cylinder clearance
also that must have made some crazy noise lol
That's the surprising part...No strange noises, and it ran when I put it away! Tried to kick it over today and had no compression.
I'll take some pics tomorrow for you. No strange heat marks or anything on top though. Looks new.
Doesn't look like proper chamfering, but hard to tell. Did the guy have the new piston to check clearance?
I'll take better pics of the cylinder ports tomorrow. He bought the piston himself for my build, so yes, he had it on hand.
I sure hope you did not add more oil to the mix, if you did you may have leaned out the AFR just enough to cook the piston!
Did you make sure that the header pipe was free of debris before you put it on?
If there was any crap in there it may have been forced back into the cylinder by the back pressure!
32:1. Just richened up the main for break-in. Yes the header pipe was free of debris when I put it on, as far as I know atleast. I even blew it out with air before the install.
Thank you guys for the help so far!