Yes Piet, I hadn't taken into account the necessary work on the seats and valve gear. Thanks for the reminder.Paul,
As with all 500 heads, and Laverda heads in general for that matter, the problem compounds itself from recessed valve seats and wear on the valves themselves. Especially the 500s are fickle in regard to well-sealing valves, one crappy seat and you'll be hard put to achieve any kind of steady idle due to the extreme lack of flywheel effect. To achieve a good seal, the old valves will need to be ground and the seat inserts re-cut, with the valves being lapped-in afterwards. When you're through with that, the necessary shim will have shrunk from 2.10mm to around 1.80mm, with luck. If the guides require replacing, even more metal will need to be removed from the seat inserts. Apart from the thin shims, which aren't really a concern regarding reliability or spring pressure, the whole valve seat geometry is out the window. The 500s aren't blessed with extreme torque and power to begin with, recessed valves will further limit power output and driveability.
Miguels head will require new seats and perhaps new valves and guides. Repairing the cam bearings will close up clearances even further, possibly the "correct" shims will end up even thinner! With new seats protruding slightly into the combustion chamber, shim size can be restored and flow is greatly enhanced (see modern car 4-valve combustion chambers), releasing quite a bit of additional power to boot, making the riding experience all the more pleasurable. The needle race can be reclaimed by laser welding and regrinding, the bushes are a simple alloy or bronze item that any machine shop can knock up after the cam journals have been tidied up. All in all, a quite straightforward but lengthy repair that won't be cheap.
Motorcycle maintenance is (should be) something normally measured in hours, not weeks and months searching for indescript shims or even resorting to having to make new ones. Keeping an old dog running by the skin of its teeth isn't my idea of fun motorcycling. Do it once, do it right.
piet
The protruding valve seats reminds me of work I had done on the head of a triple I was rebuilding for somebody during the big lead free scare. I had "lead free" seats put in by a well known firm in the UK advertising the world over. A right mess they made of that.
I rebuilt that triple on an exchange basis; You do my triple, I'll do your bathroom. The triple was a mess as in rebored with new pistons but a crank with blown centre mains and thumb size bits of piston in the crankcase. It had been rebuilt by a professional. A few interesting bits came with that bike, an ex Bol d'Or fairing and a works big bore 3/1.
The bathroom was well done.
Paul