Here is a defunct head off of a 750, late style as there was an
exhaust rebreather stub broken off in it. These heads are plentiful
enough that I consider this unit surplus. It will be subject to
experimentation and act as a fin donor for big bore kits -- clean cylinders
having become almost non-existent.
A quick glance: broken off fins, a torn off rocker cover and scarred window
surface, and a bent exhaust stud port. This bike was either hit from the front HARD,
or tumbled end-over-end for a time. I almost never know why I get the parts and engines
that I do.
Note that port-work is usually done with the guides in place, but I just got a driver
and wanted to see how hard it was to remove them (dead easy). I should have included some "before" shots --
I'll have some for the exhaust. One can see that very little material was removed: a millimeter
all the way around, and you can see how far in. That's enough there. Near the seat see where
I've removed a ridge and ground a minor trench. This is to change the incident angle of
the mixture flow. Originally, it is quite oblique. Now it will tumble down to the back of
the valve and be pulled in around it. Later stages will address the full periphery of the valve.
As the ports are now, I would be tempted to address the cuts with a finer stone.
However, it doesn't actually matter. They currently have about a "160 grit" finish.
Cleaning them up to a "300" would have next to no change, and polishing finer would be
counter-productive -- see the section on laminar flow.
