Valve seats

Has anybody had experience replacing valve seats on Commando 850's. Found that seats have been worked on before and cut deeply and incorrectly. Also found that valves have no real margin left on them and have been sitting on the edge of the face for many years????. New valves are fairly inexpensive but cannot seem to find replacement seats in parts manuals. Can submit pictures later if you want. Still removing carbon inside exhaust and intake chamber and head sitting in tank overnight but will know more clearly how deep seats go into head tomorrow.

If I must cut more valve seat out, are there valve and piston combinations that compensate for the reduction in compression ratio?

If its just the inner edge of the seats , maybe larger valves will catch the less recessed area and sit flush or out at the face .
valve head diameter near the size of the O.D. of the seat , so ' seating ' area is about 1 mm from the edge is o.k.

Flareing the hollowed / recessed area back into the port if artfully done wont slow it down .

Problem with sunken valves is theyre masked initially so youve lost effective lift . Fitting a high lift cam isnt going to make life any better.
But with the bigger valves if they work might .

Jim Comstock

I will Prussian Blue them soon and find out exactly where the face sits in the seat.

I replace lots of them. I have them custom made to my specs. I always bore the cutout enough to insure a good fit. Jim

Years ago when I needed to replace an intake valve in a big valve Dunstall head I found a BMW automotive valve that was the same except for a slightly larger head diameter that could be turned down to fit perfectly on a lathe. I dont remember what year or model it was ~1975 or so, 4 cylinder. That might be a way to go if you re cut the seats.

Most automotive machine shops have access to many sizes of valve seats. I've had a local machine shop install many valve seats in auto and motorcycle heads.

They do a nice job and I've never had any issues.

I've used Kibblewhite valves for several of my projects.

Norvil motorcycles have them n stock, I just bought a set from them, ordered with a credit card they arrived in Hong Kong within 10 days.

motoracer8 said:

Most automotive machine shops have access to many sizes of valve seats. I've had a local machine shop install many valve seats in auto and motorcycle heads.

They do a nice job and I've never had any issues.

I've used Kibblewhite valves for several of my projects.

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Thanks guys, found a nearby machine shop who was very knowledgeable. Discussed issue with machinist and said same thing as you did regarding many valve seat options and said will do with no problem.

Good new in all of this. Measured STD. pistons and cylinder bore and everything is still within spec. There is less that 0.0002 runout in cylinders from top to bottom. Was very impressed. Valve guides are also still within spec but valves stems were on the minimum thickness size.

Things are going well over all.