generator mounting bolt missing

[aviationfred]

I got an email last night from the guy with the two XJR1300's in SoCal. He pulled the #4 plug and the threads galled at the very top.

So, since all of the threads did not gall, how does one explain the galling of the upper threads?

Randy - RPM

My initial thoughts from looking at the photo is.... Possibly at some time in the past. The #4 spark plug was cross threaded and damaged the upper threads in the head. The offending plug was removed and the threads cleaned up. I new plug was installed and threaded in ok and gripped well enough on the lower threads. Just a WAG actually.


Fred

[racerrad8]

My initial thoughts from looking at the photo is.... Possibly at some time in the past. The #4 spark plug was cross threaded and damaged the upper threads in the head. The offending plug was removed and the threads cleaned up. I new plug was installed and threaded in ok and gripped well enough on the lower threads. Just a WAG actually.


Fred

I deleted the photo somehow from my phone last night. It was kind of fuzzy, but there were indications the aluminum galled into the end of threads as he removed it. He said it took a bunch of effort to remove and the new plug will not start into the head.

The other three plugs came in & out just fine.

Randy - RPM

[Flynt]

how does one explain the galling of the upper threads?

If they galled evenly, you'd have perfect mating of the lands and grooves for the entire time with even pressure everywhere...  I've never seen this happen and the galling is a bit random depending on where the load is or where it is hottest.  The upper threads make it sound like a bit of an off-spec (too wide spacing?) hole loaded up the upper end and caused the galling.

Then again, wtf do I know...

Frank

[Flynt]

I got an email last night from the guy with the two XJR1300's in SoCal. He pulled the #4 plug and the threads galled at the very top.

So, since all of the threads did not gall, how does one explain the galling of the upper threads?

Randy - RPM

My initial thoughts from looking at the photo is.... Possibly at some time in the past. The #4 spark plug was cross threaded and damaged the upper threads in the head. The offending plug was removed and the threads cleaned up. I new plug was installed and threaded in ok and gripped well enough on the lower threads. Just a WAG actually.


Fred

Occam's Razor...  we have a winner.

Frank

[Dads_FJ]

I got an email last night from the guy with the two XJR1300's in SoCal. He pulled the #4 plug and the threads galled at the very top.

So, since all of the threads did not gall, how does one explain the galling of the upper threads?

Randy - RPM

He installed his spark plug upside down?