Help! What caused this scratch on the piston?

[Scruffy]

Well with the help of Bruce at gizmomotors, i think we figured out what the problem is. When using a RCMK crankcase and the cy +2 crank, you have to replace the outer bearings with oil seals. The reason is the RCMK crankshaft is straight allowing it to get a good seal in the outer bearings. The cy crankshaft is tapered and doesn't seal in the outer bearing causing a huge air leak on both sides of the case. Ordered outer seals and will hopefully have everything reinstalled by the weekend.

 

[Scruffy]

Seems Bruce at gizmomotors knows his stuff. I replaced the outer crankcase bearings with oil seals like he saidand reinstalled the 990 carb. Give the starter a couple of slow pulls to get some gas into the engine and she fired up in 6 pulls. A little adjustment to the carb and she purred like a kitten, a very loud angry kitten lol. Engine sounds great. And this thing definitely has some compression. Jerked the starter handle out of my hand twice. Cant wait to get it run in so i can open it up and see what shes got.

 

[Scruffy]

Also installed the snappy rc ultimate fuel kit with full force fittings. Turned the buggy on its side and no leaks at all.