New Valve Seats

Twin Pots

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Triumph Bonneville 1967
FJR 1300 Yamaha
I think we all know the very idea of fitting new valve seats in a Triumph 650 alloy head is considered somewhere up there with Custers last stand for risk and a high chance of failure. Consequently I have been doing my usual indepth research to hopefully avoid scrapping this 68 Bonni head I picked up as a spare. It seems completely removing the old seat with its annoying reverse taper is no longer the method to use. It certainly involved a huge amount of metal removal, welding up the hole left behind and re machining. Not hard to see why this is a disaster waiting to happen, very time consuming and very expensive. Talking with Kibblewhite it seems they prefer to machine only just enough of the old valve seat that a new valve seat has steel on steel interference fit rather than with the aluminium of the head. This does seem a much better, quicker and hopefully cheaper method with far less risk of scrapping the head.
I would very much like to hear from anyone else who has had this job done. If I can fit new powder made seats for example (Kibblewhite do these as well) they are supposed to cope perfectly with unleaded petrol. I just need to investigate what valves go with what seat material. Not all are suitable with each other. The truly scary bit is finding a machine shop that can genuinely do this job. They all say they can! I would be a lot happier if I was in the UK or the USA where there are so many great machine shops that handle Triumph and have the experience.
 

CarlS

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Interesting information. Good post.
 

speedrattle

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older thread, but timely, as the ancient heads are getting well used. i have two 1973 bonneville heads with seats that are pretty badly recessed. i showed them to the machinist who does the rest of this stuff for me. he said that rather than try to get the old cast-in seats out that he also would simply bore them straight in for new pressed-in seats.

he does virtually any old engines, from antique gravely tillers to recent 800-hp mud trucks. the heads i have aren't usable without higher seats, so when i have it done i'll come back here and post the results.
 
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