Broken spark plugs


New Member
Tracking my 2017 390, about 2500 miles on it. I had a head gasket issue that showed up as a stalled engine, pulled the plug (original) and the electrode arm had broken off. The bike had been overheating a couple times and using some water.

New plug and the bike would run but there was water in the exhaust so I pulled the motor and replaced the head gasket.I did not skim the surfaces. Put it back together with the same plug and went racing. Ran great- set a PB. But it lasted a day then lost power at high revs. Pulled the plug and it’s broken again!

This time there are no signs of head gasket issues otherwise. Leakdown test seems good. (about 1-2% lower reading on the motor side.)

what would you do now? What would cause the plug to break? Its a stock engine with stock gaskets and this new plug is an NGK non-iridium.



It is not broken off but instead looks melted off as it would in a severe case of engine detonation occurring.