Bowraboy's GRiSO

Made horrible farting noises. Compression test showed 170 psi on the right. Is good! Unfortunately LHS shows only 120 .

So off it comes.

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Exhaust valves are all pitted and Manky and there are weird marks in the exhaust port but no signs of piston damage . That's where the issue lies, the rings are still perfect at 90,000km!

Anyway given its age and distance travelled we're going to service both heads and it should be good for another 100,000. Don't think we'll bother pulling the other barrel, just the head.

What caused the pitting? Corrosion? Water intrusion?
Please post pics of the valves if possible?

Found the same thing on my Sport last year - had done 140,000 km. Pitted valve seats all round. Put in new rings and found the old ones were exactly the same size - so still in spec. Put the new rings in anyway, so still have a good set as spares (for Ron). Replaced guide seals and every other gasket in the top end.

Why? who knows...

If the worst thing that happens is the valves and seats need resealing after 100 odd thousand km, it's not too bad.