[Russ]

Hi  Russ,
In my view seat replacement should be avoided unless absolutely necessary. It is never good to bore out parent material  and press in a new bit for several reasons. First it will weaken the head, which already has two large valve holes and a plug hole across it's diameter and although Sunbeams are not prone to this as a rule, it is possible for a crack to propagate across the three holes, especially when you press in a tight fitting seat.
Second, one continuous piece of metal transfers heat far better than two pieces joined together, however closely - the  interface between the two will inevitably resist  heat transfer and that's not good considering an exhaust valve can only lose heat through the seat and the guide (which also has an interface with the casting).
Third, I believe unleaded type seats are too hard to recut without specialist equipment and you can't exactly 'pop them out and replace them'! They run a pretty serious interference fit something like 5 thou I believe - we're not talking leaving them in the freezer for this job! I'm not sure how they can be removed, possibly spark eroded and split?
Personally I'd just get the 90 valve reduced to standard size or open out the port to suit.
Cheers Rick     

okeedoke duly taken note Rick it'll be coming together as soonas the bits arrive......cheers....

[Rick Parkington]

Hi  Russ,
In my view seat replacement should be avoided unless absolutely necessary. It is never good to bore out parent material  and press in a new bit for several reasons. First it will weaken the head, which already has two large valve holes and a plug hole across it's diameter and although Sunbeams are not prone to this as a rule, it is possible for a crack to propagate across the three holes, especially when you press in a tight fitting seat.
Second, one continuous piece of metal transfers heat far better than two pieces joined together, however closely - the  interface between the two will inevitably resist  heat transfer and that's not good considering an exhaust valve can only lose heat through the seat and the guide (which also has an interface with the casting).
Third, I believe unleaded type seats are too hard to recut without specialist equipment and you can't exactly 'pop them out and replace them'! They run a pretty serious interference fit something like 5 thou I believe - we're not talking leaving them in the freezer for this job! I'm not sure how they can be removed, possibly spark eroded and split?
Personally I'd just get the 90 valve reduced to standard size or open out the port to suit.
Cheers Rick     

[Russ]

ok my learned friends....so the shop now has Valves and guides in stock....Yay....so the next part of the rebuild can commence which will be to refresh my cylinder head with said new valves and guides....I intend to buy the M90 G&S Valve of which there is only one type listed so first question is......is this Valve suitable for both inlet and Exhaust....logic is telling me it is......next question is..... this Valve has a slightly bigger head diameter of 1.75" compared to 1.687" standard M9 size listed.....Ok so slightly bigger diameter (1.6mm to be precise) so I'll need to get the seats cut to suit fair enough.....next question is.....should I instead of faffing about getting the Valve seats Re-cut direct into the cylinder head as original or should I get the head machined to take a suitable Valve seat insert instead?.....I'm not too sure as the only real benefit I can see is eventually over time it will preserve the cylinder head by only having to pop out and replace worn valve seats....if you see what I mean or are there any other benefits?....and finally my last question.....who makes and sells Valve seats for 1927 Model 9's