Damaged Glow Plugs
 

Hey Guys
Been running the same motor for 2 years now, same fuel and same factory plug. For some reason yesterday the coil on the plug was going every run. Thankfully I save my old plugs and was burning them up and not new ones. Don't know why this was happening, this motor has been great since day one. OS VG .21. It got up to 250 when one of the plugs went but this motor usually runs 200 to 225.
Any help would be great.
Thanks

I'd pull it apart and look for damage to anything else like pitting on the piston and button. Could be a rear bearing failing and the pieces are taking them out.

Check to see if the coil is flattened into the plug. Engines without the treated crank tend to wear the crank pin, or it may simply be time for a new connecting rod. Either way, too much play here may allow the piston to travel too far up in the cylinder, hitting the glow plug. Or, as 2fst2c pointed out, a bad rear bearing would cause the same issue.

when the bearings or bushings get too sloppy this is what happens, the piston is going too far up the sleeve, getting close to the head button, and increasing the compression which damages the coil