Originally Posted by uniquexme
my frenz has this BRB, fitting into Nova RB crankcase, use nova LL5 crankshaft, OS P6 turbo, with RB carb. ok, recently, he got his needle mixture mixed up, so our frenz help him to retune, we found that his LSN is only 1/2 turn, then he changed a new glow plug, ran for 1 round, and the plug blew off. so may i ask wats the problem here. previously it was ok for him, powerful engine, but now, i help him open up his engine, there is these vertical scratches on the piston. and turbo head is very slightly rough (meaning overheat i assume). so how can we help him out? thanks.
It sounds to me like the engine was detonating which caused the plug to blow and the pitting in the head button. I suggest adding .2mm head shims, see how it runs, then remove a .1mm head shim if it runs ok.
Depending on the size of the scratch, you probably won't have to worry about it. If you still have compression (different than pinch) then run it. I've run Palmaris piston/sleeves with huge scratches and they are still fast.
I would suggest also that 1/2 turn out on the bottom end is a little too low. Try turning out at least 1 turn then retune top end after you add the shims.