Fortunately, I only needed to replace the plug on the vertical cylinder, which was the only one showing impact damage. What internal issues would cause contact with the spark plug?

Quote from: ungeheuer on March 25, 2026, 12:39:51 PMSmashed my left thumb with a big fat hammer today 

it usually hurts when you do that.

Smashed my left thumb with a big fat hammer today 

Quote from: stopintime on April 10, 2024, 12:17:08 AMDon't know. Probably won't know. These are labelled "796 big bore 90mm". Their dome is lower and might give a softer combustion (so they say). Have been 11:1 so maybe the same...

Were the pistons a direct drop-in or did you have to use a thicker base gasket (or machine the piston) to achieve the optimal compression ratio?

Those are the correct plugs. If they were too long, both plugs would have been damaged by contact with the piston...No?

Both plugs should be ok and the two sites I checked for "reach" (thread length it seems) list 19mm on both. So, probably correct plugs (even if that doesn't helpp you much...)

New update: The timing belt is intact and appears to be in good condition. Here is the video:

https://youtube.com/shorts/bVtvMjHaBsM?feature=share

The next step is to pull the cylinder head to see what's happening inside.

Regarding the spark plugs: I went to AutoZone, and they recommended the NGK DCPR8E based on my bike's year, make, and model. Previously, I was running Champion RA6HC. Do you think the cross-reference could be the issue? I suspect a piece of the broken plug may have dropped into the cylinder and caused the obstruction/damage.

 

Good morning

What plugs are they (looks too long)?