Loose Spark Plug

[maxstu]

I'd be concerned about the ali welded into the end of the plug thread taking out the threads in the head on the way out. Hopefully you've got away with it.

What brand/spec of plug was it. The last time I recall seeing a plug like that was out of a 2 stroke motorcycle 40 odd years ago

A good and proper German made Bosch.
It will all be exposed when l pull engine later this year. We are not camping again until next year.
Typically l sold a set of spare heads last year to Mick at NWVW.

[Stesaw]

Well lets hope the head and everything is OK, If not I guess you got bits to swap over with it need be.

[maxstu]

Well lets hope the head and everything is OK, If not I guess you got bits to swap over with it need be.

Not now... Sold a spare set of heads last July.
You really should fix that JX and shelve the 2.1...or least sell it for parts

[Stesaw]

Well lets hope the head and everything is OK, If not I guess you got bits to swap over with it need be.

Not now... Sold a spare set of heads last July.
You really should fix that JX and shelve the 2.1...or least sell it for parts

I've yet to check the heads on the 2.1, Gonna cobble a compressor together to check the seats and for any looseness. 

 
 

[scotttie]

Its lost the tip and thread is damaged and melted.

Didn't know spark plug threads could melt like this from a loose plug. I guess it was loose as in you could turn it out with your fingers?
Glad to hear you still had some useable thread to replace the plug.

[Oldiebut goodie]

It hasn't melted, it is the thread in the head that has melted - see photos.

[scotttie]

It hasn't melted, it is the thread in the head that has melted - see photos.

Sorry, I wasn't clear. I meant the spark plug thread in the heads. I understand the threads on the spark plug itself will have a higher melting point being made from steel.
 

[maxstu]

Cleaned it up a bit and took another photo.
There is some (spark?) erosion on the last four rings of thread. Easier to see by eye than photo. Plus alloy deposits. Not looking healthy.
Will check new plug later today.

[maxstu]

Went another step further and photographed plug hole thread. Looks a bit manky but okay. And new plug tightened to torque spec. So may be lucky.
Im driving back (65miles) to stableyard to arrange for a digger to sort a water pipe trench. So 130 miles return journey should test it fully.

[Oldiebut goodie]

That is even more worrying - there is no sign of melting ( unless it is hiding in the unseen portion ) of the threads so where has the aluminium come from? Endoscope needed still.

[maxstu]

Okay you win Will investigate further, and thanks for taking an interest.
Head thread damage may be on hidden side of hole. I couldnt photo that side.
Looking two photos back, the spark plug thread damage is only apparent around 1/6 of total circumference.
Could it be spark plug came loose and substantial sparking/arcing between head and spark plug wall caused the damage?

Regards
Stuart

[tobydog]

Could the plug have overheated due to lack of contact with the head plus hot exhaust gases escaping past it? That could explain the missing cenre electrode and melted ali....

How far out of it's seat was it?

[Stesaw]

One way to adjust your spark gap I guess! 

[maxstu]

About two 360 revolutions from properly seated.
It was covered with black carbon deposits too

[maxstu]

One way to adjust your spark gap I guess! 

Bugger off!