I originally posted this at the end of another thread, but it occurred to me that I would get more answers if I started a new topic. Here is my original post:
Regarding a three-angle valve job: In my limited experience, it seems impossible to *really* do this for the simple reason that on a Triumph, the valve seat and the valve guide bore are nowhere near Concentric. You can cut a 45* angle, but any 60* angle you try to cut will go maybe half way around the seat before you start cutting into your contact area. And if you tried to cut a 30* angle, you would cut into the aluminum because of the way the factory cut the seats to begin with. Unless you consider the angle between the seat and the chamber as the third angle, of course.
Anyway, I've long been confused as to what people mean by a three-angle valve job on a Triumph, and if there's anyone who knows, it would be you! Please enlighten.
A three angle (30-45-60) valve grind works if you put the guides in right - with a puller that sits in the seat. If you just pound them in they will likely be off and you will have problems cutting the seat. Since the seats were cast into the head they are likely to be off a bit, some worse than others. You can always cut the head for a new seat that is Concentric with the guide bore.
Using the puller is in fact the best way. I've done many three angle jobs and yes, you do cut the aluminum sometimes. The fifteen deg. cutter helps with this. If you use a Neway cut the 45 first and then lap the valves, even though they say you don't have to, to see where the valve is seating. The you can determine how far you want it from the valves edge (30 deg.) and how much you can open her up (60 deg.)
On the heads that I have done, I have used a puller with a device that sits in the seat. The problem is that it puts the new guide in exactly the same position as the old guide. I only have to remove a few thousandths to recut the seat, but it's way off center just like the old cut.
I have seen some seats that were 3/16" thick on one side and 1/16" thick on the other, by the way. You couldn't possibly cut a 60* cut without obliterating the seat on the narrow side, unless you want to angle the guide so the valve sits on aluminum. And although most seats aren't that bad, they are all somewhat off. I love my Triumph, but it's easy for me to see how the Japanese came in and ate Britain's lunch.
When you buy your lathe, make a plug with a 45 degree champher that sits in the vavle seat, thread a 1/4-20 rod in, long enough to go through the guide and another 1-1/2 times the guide length. Get a coupling nut (~1" long) and a washer to push the new guide into the head.