Valve seatings in heads.

[Flash]

Hi all. I am in need of either a new /recon near side head (left hand side for the yanks) for my G9 or get my old one repaired, problem with it is that the valve seat has turned in the casting causing lack of compression. Is it possible to get these repaired? if so where can I get it done and what is the cost roughly?
Has anyone had any experiance with this problem.

Regards John.

[Duncan]

John, had a similar problem on my G12, I just brought some second hand heads and used those.
Yes, they can be replaced but I am unsure of the current costs, ask any company who do lead free seats, you may need to replace the guides and valves in the process to enable them to cut the seats.

[Eric]

The replacement head is probably the easiest but if you are concerned with originality that may not be acceptable. There are usually dozens of them at most auto jumbles because its one part that almost never needs replacement unless you are very unlucky. You don't say what year your G9 is there were variations the one I know about was for 1960 those heads are very different to earlier ones.

[arkwright]

The twin heads were made at J Stones (Charlton)Ltd, they are waisted in the middle to stop them moving up or down but there is nothing to stop them revolving. On being placed in the die the alloy was cast around the seat inserts. It was the same technique used in the full width hub for the brake lining surface but they do not take the hammering that the valve seat inserts do.

[Flash]

Eric. Its a 1957 G9, I think maybe I'll have to get in contact with Kettering to see if they have a second hand one going cheap, I have been using the bike with a G11 head one side but I'm not happy with it as the exhaust pipe outlet size is different & I have had to shim it.

[deshollier]

If JSL hasn't got one you will almost certainly get one from AMC Classic Spares - www.amcclassicspares.com

[alanjennings]

If you get the seat replaced be careful who does it! I know 3 Vincent owners who changed to lead free seats and they promptly fell out! makes a nasty mess!

[deshollier]

Cheaper to get a second hand replacement head, providing it does not need much doing to it, of course. There is absolutely no need to change to lead free seats, from all I have read and from my own experience on my G9. I do use Castrol Octane Booster and have frequently been told that it is unnecessary - but it makes me feel better!

[GOLDSTAR]

Hi Guys, a question from an ill informed, why, if the valve seats are cast iron? cast into an alloy head do we need to change them to another steel/iron seat to use unleaded petrol? I have run my '61 bonnie, R90S velocette G80Cs without changing the seats or using any octane booster etc for some time now none of them seem to be any the worse for it, I say tongue in cheek!,

[GOLDSTAR]

Oh by the way I forgot, most kind regards