erosion on head

[Michael S]

Hi everyone.
While I am dealing with the front cylinder woes, hopefully successful, I thought that I had better just look at the rear cylinder even though it seemed to be in fine fettle.
What I found was an eroded hole next to the spark plug hole about 10mm long 4mm wide and a anotherone just touching the exhaust valve seat about 5mm and a couple of mm deep, they were carbonised as the rest of the head
The compression was good and the gasket has no untoward marking
Question is do I do anything about the holes.
Looks as if it has been like that for the eight or so years I have had and used the bike.
Any ideas how it happened
Picture available if I knew how to add it this message

Michael

20240613_155929 (1).jpg (364.62 KiB) Viewed 2824 times

[George 350]

That has the look of something going through the engine, either a plug had failed badly or something has been injested at some time, judging by the other marks there.
If it was running well before, then it will probably be OK afterwards as well. What is the piston like? Any corresponding marks there?
Of course in an ideal world it would be 'new' head, but if all your threads are good, valve seats look good, then it is probably better to stay with it. Perhaps round off any sharp bits near the plug to be on the safe side.
Only other way out is welding, recut plug thread and skim it, but a lot of work and cost for how much gain? (Pains me to say that though).
Good luck,
George

[norbert]

I agree with George.
Obviously these are the scars of an older accident. If not, the piston and barrel should have the same look and the motor wouldn´t work. If it worked with this head before, keep on running and save the money for other things to come o for something completely different

[Michael S]

Thanks for the replies
I have now cleaned and inspected the piston and bore.
Clear damage in two places on the piston head but not enough to cause ongoing issues
A fine vertical line on the exhaust side of the bore otherwise a very nice clean bore with no lip at all at the top.
The probability is that I will go with the comments of George and Norbet.
Thanks
Michael

[Steve Brown]

Thanks for the replies
I have now cleaned and inspected the piston and bore.
Clear damage in two places on the piston head but not enough to cause ongoing issues
A fine vertical line on the exhaust side of the bore otherwise a very nice clean bore with no lip at all at the top.
The probability is that I will go with the comments of George and Norbet.
Thanks
Michael

Yes, go with the advice above. That definitely look like FOD to me. (foreign object damage) Ancient too, I would look very closely at similar marks on the piston though-that will have more stress on it.