Hitchcocks Forum

Do you guys really run these with the service manual spec of 0 clearance cold? I just had to get the valves and seats ground after only a few hundred miles since both valves were leaking badly even after the rockers were removed. I suspect the valves weren't closing completely. This is the upgraded head with Kibblewhite valves. Don't have hydraulic lifters in this one.

Never had any bother whatsoever with factory settings, and my bike did get thrashed. I always did a compression check every oil change (1500 miles) and the occasional leak back check as well, so any issues would have shown up early.

Zero clearance cold on the 350.

One ballhair on the exhaust and half a ballhair on the inlet cold on the 612.

That said, my 350 ran perfectly acceptably for about 6 months with the exhaust valve seat rattling loose in the head.

I use the recommended technique on my 350 Bullet, but I do make sure the pushrods spin quite freely. The engine is quiet and the tappets don’t seem to need adjusting at all. They certainly don’t close up, at least not since I had a new, hardened exhaust valve seat fitted. Before that the exhaust used to close right up and the bike lost compression completely after only 50-100 miles.

"Close up" meaning the clearance would decrease?

Yes! The valve moves upwards into the cylinder head. In my case enough to keep the valve from seating properly causing loss of compression.

I got very good at resetting the clearances at the road side. Thankfully a new seat insert and Hitchcock’s stainless valve cured it completely and 10,000 miles later the clearance never varies.

That may be what we're experiencing also. The seat and valve surfaces were a uniform dark brown on the contact surfaces.