How Many Miles before Top End Job?

I have a 1972 Commando, Combat engine with an R6 head. When I bought it years ago the engine had been totally redone by a shop with a very good reputation, and it had no miles on it. Since then I have probably put about 8,000 to 10,000 miles on it.

Here is the question: how many miles can you put on a Commando before you need to do the valves, guides, seats, and seals? This assumes you are not thrashing it, storing it in a rainforest, etc. And also assumes normal maintenance is done.

I know I can take the head off and find out what my bike needs. And I will do that soon. But I am curious about what you can expect in terms of top end lifespan.

Stephen Hill

A friend of mine has just done his at 30,000 miles.

Its a mk3, the engine has never been stripped, and the cam looks so good he’s leaving the bottom end alone.

First one was at about 7000 miles, to replace factory valve guides with brass ones. Next one was at about 30K.

My 850 head has only been done 3 times in 44 years the first time in 1980 with about 24k miles on it when building it into the Featherbed frame where everything was done new guides, port job and shaved head for the hot cam but used the original valves, then about 15 years later new guides again and valves relapped and just a clean up, my head only comes off if the head gasket blows or if its leaks, so the head has only been off for servicing 3 times in 44 years last time I replaced the guides and added new valve springs, I am still running my original valves, my Norton was a everyday rider till 6 years ago, is ridden hard always and has over 160k miles on it.
So it all depends if the bike is running good, not blowing any smoke or losing or burning oil I would leave it alone, if you keep up the maintenance and change the oil regularly and if things are running good then no need to pull the head, check your valve adjustments when doing your maintenance and retorque the head every so often, these motors are very reliable if you look after them and do regular maintenance.

Ashley

Did one at 50,000, only because exhaust threads on head needed renewed. No smoke ran well. Rings very worn but standard bore , honed it put in new Emgo pistons Lapped valves in original guides. Runs great

I have well over 40.000 miles and have not touched it yet

A friend is just now doing bottom and top rebuild on an 850 he purchased new in 1973. He used it as sole transport for many years.
He retired it at 128,000 miles a few years ago. It was down in power and smoking.
It had received new pistons and rings, plus a rebore and a valve job at around 50,000 miles. He said it didn't really need it but he wanted to keep it crisp. The next run of 78,000 miles left it less than crisp
So it sounds like you are OK to about 50k miles with a top end.
He is quite easy on a bike, gets down the road but not too many 7k rpm shifts.

Glen

How far will they run? I have seen one smokey example that was at 100,000 miles and still ran.

With original iron guides they will be loose and noisy by 10 or 12,000 miles but they will continue to run a lot further.

My untouched MK3 is at 30,000 miles and still runs fine but I suspect in another 10,000 it will be getting sick.

When they are run with loose guides the seats will wear off to one side and when it gets a valve job it usually requires new seats.

With good bronze guides and Black Diamond valves the guides stay nice for 30,000+.

Of course if your looking for best performance the seats should be re-cut about every 10 or 12,000 street miles. Over that the seat gets wide enough they loose a lot of flow potential.

If you are running a stiff cam then cut the valve seat life in half.

850 heads have softer seats than earlier heads and the exhaust seats erode faster.