'71 750 Commando Valve Guides, Cast Iron? 850 Parts Swap?

Someone suggested that I move this post over here.

I'll probably be posting quite a bit on this bike...I've already posted about rear wheel offset and "tilt." I appear to be on my way to solving that one. The question I have today:

I have 2, 750 heads. One is complete, off of a running motor. The problem with it is that it has 3 broken fins. When the restoration is finished, I want to to look as decent as possible. The other head is missing everything, no valves, springs, rocker spindles, etc. The head missing everything has no broken fins but appears to have sat in a non-optimal environment; aluminum is oxidized and will need vapor blasting. Also the valve guides appear to be cast iron and they look moderately corroded. The seats will also need to be re-cut.

I also have an 850 head from a '73. Looking at the part #s it appears that the rockers and spindles from the 850 will work in the 750 head that I want to rebuild but the valves have different part #s.

Question: Are the valves different on an 850?

Next question: I want to get new valve guides in the head I'm rebuilding, are the bronze guides as good as the cast iron guides? Is there a "hot setup" that most people wind up using? Kibblewhite ok?

If I do go with cast iron guides, are there any special procedures for extraction? Installation?

I've heard that it may be possible to bore out the guides slightly and basically re-line the valve guides. Is this viable or mythology?

A lot of questions....much thanks in advance. I'm sure I'll have even more and often stupider questions.

Removing and reinserting guides can scrap a head, K-liners are the less risky way.

kommando said:

Removing and reinserting guides can scrap a head, K-liners are the less risky way.

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Anybody know who does it in America....mid south?

Engine Dynamics is West Coast (http://www.enginedynamics.com/) but the go-to place for machine work on Brit bike heads in this vicinity. Give them a call

I'm not sure about iron guides in a Commando head but l have only dealt with 71 up engines and they all had bronze guides from the factory. Could it possibly be an Atlas head? This info might help sort out which heads you have.
If the 850 valves have different part numbers they are likely different in some aspect. If the parts number on the rockers, spindles and hardware have the same parts numbers I would assume they would work. Can anyone out there with more experience confirm this?
You can remove the old guides by heating the head and using a drift. Same to install. I have done this but you have to remove every bit of carbon around the guide or you risk scoring the guide bore. Oversize guides are available if the bore is knackered. Better is to have a machinist remove most of the guide by boring and pick the remainder out.
Kibblewhite valves and bronze guides will work a treat. After the bronze guides are installed they need to be reamed back to proper clearance as they tend to collapse a bit during installation.
One bike I installed the guides myself and had them reamed and new seats cut by a local machinist. You have to have seats recut if the guides are replaced.
Two bikes, I got lucky, I miked the valve stems and bores and the wear was within specs so just a light hand lapping and they were good to go.
The 74 850 I had Baxter Cycle completely redo. Not cheap but came back looking like new.
I've heard of knurling the guides or installing liners but have don't have any personal experience.

Give the head to a competent machine shop familiar with Nortons .

Banzaibob816 said:

Anybody know who does it in America....mid south?

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Leo Goff in Memphis (Memphis Motor Works)

Is Leo still working. Haven't heard anything about him in a long time. These two still seem to be active.
Big D Cycle in Dallas
Baxter Cycle in Iowa