Return of the Anorak

I have just forked out a big wodge of hard-earned for 4 Yamaha valves. I had received some pattern ones, but I thought them a little suspect- heavier than standard, tighter radii, and rather prominent “corners” where its been machined.

So I got my precious treasure home. And compared it to the standard valves. I have it on hearsay that this head was built for the Singles TT, and is a little bit special (or was at one point).
Anyway, that was many moons ago, the exhaust valves had been replaced quite recently, and the inlets much longer ago. The (recently replaced) exhaust valves were standard. However, I noticed that the inlets (possibly quite old) had had all of the edges close to the seat machined off…

You can see the difference between the new Yamaha valve on the right, and the valve which came out on the left.

Edges have been removed (arrowed) and I also think the seat is a little thinner. I haven’t weighed them, but I am certain that the old valve will not only allow better flow; it will also be lighter.

The photo on the right attempts to show the thinner seat of the modified inlet valve which was in the engine. So I have decided to grind in the new valves, (so we know where it actually seats) then take them for some light "recontouring"- both on the inlets and the exhaust. If a job’s worth doing….

Valve grinding- a Great, British, Sunday pass-time. When you missus is away… The "Chemico" paste looks like its come right out the 1950's, and would be more use lapping in valves on a Manx! Ahhh, to dream!

andy