Headwork Needed When?

Its been about 12,000 miles since any valve, guides, etc work done.
How long typically, very easily ridden, do the springs, valves, guides and all "last"?
Colorado Norton Works is showing a very complete head rebuild for $1000 on their website, this seem reasonable?
Thanks for any comments

When it has a smoky exhaust :lol:

You can't really give a mileage, you go by how the bike performs but at 20K you could take a look inside and assess the internals, it should be needing new rings but not a rebore by then anyway.

As Kommando says, if there are no problems or odd signs then leave well alone. skimming faces and replacing guides will all remove metal. I wouldn't pull a good engine apart at less than 40000 miles if it has had regular oil changes.

When a Commando engine is sweet, it can put quite high mileages on. I don't consider there to be any precautionary mileage related parts replacements in a Commando engine except perhaps rings and big-end shells if it's feeling a bit tired.

If you have to remove the head, e.g. for an exhaust port repair then it is well worth dismantling it and checking valve and guide wear but dependent on your annual mileage, don't be too paranoid.

Smokey exhaust can be as much a symptom of valve / guide wear as piston/ring/cylinder wear.

Then again, a simple bit of "wet sumping" can cause a significantly smokey exhaust, and requires nothing more than draining the crankcase to remove excess oil bypassing the oil pump when the bike is left sitting!

I agree that "when it starts smoking" will be your first key to something being worn. Classic Commando symptoms of worn guides is smoking at idle or when blipping the throttle. Backfiring that doesn't go away with conventional remedies can indicate a valve not seating (leakdown test to be sure). The stock cast iron intake guides on my 850 needed replacing at 8500 miles but the bronze replacements lasted 30000 with no problems. I've heard of people putting well over 100,000 miles on a Norton without engine work, so the proverbial YMMV applies.

I had a smoky exhaust and was using significant amounts of oil at 10K miles and the only problem I could find was that an intake valve seal had come off and I was leaking oil out of the head gasket around the pushrod tunnels. Valve stem clearances, ring gaps and bores were all in spec. So I think you need to be careful in assuming some specific amount of wear just because you are burning oil in a Commando.