Overtightened Spark Plug

[knowledge boy]

Yesterday I replaced the spark plug, today I broke down, I removed the new plug and found that it had been flattened and (by the piston I assume). The bike won't start with the old plug in, it struggles to turn over with a lot of clanking noises. have I done goofed?

[Jge64]

are you saying the piston collided with the spark plug?

[knowledge boy]

I'm guessing so as the damage looked mechanical

[Jge64]

Yeah, this is either the piston being connected incorrectly or the wrong plug installed (too long)

I would say a dealer visit is next.....

[gn2]

What plug did you fit and what was the original plug?

If the replacement plug was too long and the piston has hit it, your engine could be toast.

[knowledge boy]

NGK CPR7EA-9, got it from a Honda dealer,

[knowledge boy]

Here are the plugs, new and old

[Jge64]

Wow....thx for the pics, keep the recept for the plug, you may have a case if its the wrong plug....

Do they (or did they) look to be EXACTLY the same length?

[gn2]

If the new plug is the same model as the old plug and the one you got is definitely marked on the plug as the right one, (not a wrong one in the right box) I don't see how overtightening it could have got it far enough into the cylinder for that to happen.

[knowledge boy]

Wow....thx for the pics, keep the recept for the plug, you may have a case if its the wrong plug....

Do they (or did they) look to be EXACTLY the same length?

I am 90% sure they were the same length, I have put my tools away for now, and the old plug is in the bike, I will take it out and compare what is left of them later.

[knowledge boy]

If the new plug is the same model as the old plug and the one you got is definitely marked on the plug as the right one, (not a wrong one in the right box) I don't see how overtightening it could have got it far enough into the cylinder for that to happen.

I followed the instructions in the user manual, 1/2 a turn, loosen then 1/8 of a turn.