Piston hitting spark plug?

[Joeguy]

So i bought a chinese carb and in messing around still trying to get it to run right i figured id pull the spark plug to see if it was running rich, well it was definitely but also i have a nasty mark on the strap (i think thats what its called) that looks like the piston has been smacking it. I never actually pulled the plug because i had it running for a second on starter fluid when i first bought it and was just stupid and figured whatever was in there was good. The part number on it is DPR7EA, which is similar to what is called out for in the manual but i assume the little bit off that the code is means it must be a bit longer or something. Unless the plugs are made like this, but i can pretty easily see that metal has been pushed away from the area of impact. What are the odds that my piston is trashed now you think? It does still run just not well due to carb issues but thats a whole other problem.

Actually i just took a second to google both plugs and it says the reach is the same its just different resistor values and gap size, so maybe the bigger gap is why its hitting. Either way the actual one for it is on the way and i hope it just didnt do to much damage. Wish i woulda just went over the whole thing like i normally do with this stuff.

[Mech]

I don't know what this bike is but I'd doubt that nick in the side of the plug was caused by the piston. If a piston hits a plug it's nearly always right on the end of the plug, and it closes up the plug gap. That might have been hit by a valve at some time, and it might have been like that for years or since new. I wouldn't worry about that, but the blackness of that plug looks like burnt oil to me.

It would pay to check the compression.

[Joeguy]

Well compression isnt great, my super cheap gauge says 125psi, but idk how long it has been sitting so maybe itll gain some after it runs a bit. The oil level is at the top line on the sight glass so maybe i over filled a bit. Also it is a 1991 quadrunner 250 lt4wd.

[Mech]

!25 is a bit low, but it should start. That rough looking buildup could be burnt oil or be because the compression's too low. As you say, if it warms up and has a nice ride with a bit of load on the engine it might come better.

 

[Gwbarm]

Have you had it running since you got it. It doesnt look like the piston hit the plug but something did and it hasnt run since or the scarred area would be black like the rest of the plug. Maybe it snapped a ring that would account for low compression, but i would think if that happened compression would be even lower. 

[Joeguy]

It has ran for like a minute or 2, i moved it a bit just to check if it would go into gear, but its not really ride able at the moment. I showed another guy and he agreed it looks like it was hit a while ago because there is buildup on that mark too its not fresh metal. Im reading though the manual i downloaded and re jetting the carb and stuff to get it to run good hopefully, i jsut got really worried when i saw that mark.

[Mech]

The piston's aluminium, and it would get chewed up before the plug. Put it at the T mark on the crank and use a torch down the plug hole..

I don't think a piston could chew metal away like that. They bend the electrode, seen plenty of that,  but I don't recall ever seeing bits of metal worn off like that.