KX112 Detonation and Cylinder Damage

i dont think that looks too bad actually, ive had worse. In saying that maybe need to run race gas, or blend?

Leaky head gasket. Very common on the 112. Get that fixed and buy a VHM head for it.

agree, use leaded 98-105 fuel

Is that a crack in the head?

112s are ticking time bombs. So are many of the 109s. These motors are highly stressed and push the original designs to the max. T2 is a must, especially if you are milling heads and bumping the compression. Changing pistons at 5 hours not uncommon, especially if you have a rider that's hard on the gas.

I went with a Max Power Engines 105 build to avoid the 107/109/112 issues I've read about. So far it's been great. 16 hours on the 1st piston with compression still high (will change at 20), runs fantastic, plugs are good, no detonation on a T2 blend. My boy has pulled plenty of top 5 starts, even in Open Beginner against 250s and 450s! Power to weight ratio rules.

Send those photos and talk to Josh at Max Power. https://www.facebook.com/maxpowerengines He can give you very solid advice on what to do.

Hammer 663s

Yep that’s detonation damage on both the cylinder and head, however there doesn’t appear to be the same on the current piston, so maybe it’s old?
May have been caused by poor quality fuel or a number of other factors. In modified engines with high compression and a tight squish, most don’t realise the importance of centring the head on the bore. Particularly on engines without locating dowels. Even with a single dowel, the head can move side to side, and if you’re not careful, you end up with a small part of the gasket surface protruding into the bore on one side and a cavity on the other. This can amplify detonation issues.