Hi All

I am currently blowing plugs on a motor that has been rebuilt with new P/L/S and crank, bearings are good.

Tried O'donnell 97T but the coil is collapsing and then plug blows, should I go to 99T or should I add a 0.1 brass head shim.

I believe that if you add a headshim you loose some HP???? is this correct.

Motor is an 0.12 RB T10.

As I have said this is a rebuilt motor after s napping a conrod, so if the crankcase has been dented on the inside would that be enough to increase the compression. I've had a good look, flushed the motor out, inspected the bearings etc... and connot see any real damage.

Any suggestions, thanks!

When the rod snaps usually the snapped rod hurts the crank pin,as a result a new rod will have a bit play on the crank pin.The solution is to add a shim if this is what happened..

A snapped rod does give a lot of dirt inside. You have to take out the brarings and then clean them out as also the crankcase to be sure all dirt is out. If you have not done that the yes, some left over dirt will damage the plug.

And after changing the P/S/R set you always have to check the head clearance, maybe it is to low.