Cylinder head identification help required

A couple of pictures would say lots more, Paul.

Paul.The one you have just bought is, I am quite certain, a 650SS head. Mine has the same casting number, 23166, it has 1.406" inlet valves, and top oil feed.

The one you have fitted at present, with a 1.5" inlet valve, and a side oil feed sounds like a later Atlas item. Does it have anything stamped on top of the rocker box?

There were 4 versions of the 650SS cylinder head used in the decade that it was in production. Two were for the spigotted barrels and two other version were produced for the spigotless barrel. Typical of the Norton factory was using similar castings to serve several purposes.

The 1961 cylinder heads had casting number 22707 on top next to the inlet cover. This number was also used on the earlier 99 head from 1959 on. Plus it was also used on some of the Nomad 600cc engines and the 99SS. Despite the same casting number the exhaust porting angles and carb mountings are completely different.

The next version of the 650SS came as a result of the bike building moving to Plumstead. (Woolwich)............The second head was almost identical to the first. There are a few minor changes in the casting and machining but nothing to stop the head going straight onto a set of spigotted 650 (or even 88 and 99) barrels. The only real problem here is that the casting number, 23166, which also appears on the first Atlas 750cc cylinder heads.The two heads are not easily interchangeable due to slightly different head bolt spacings. This time the number is on the underside of the casting and generally at the front.

The first 650 cylinder head for the 1965 spigotless barrel, wore casting number 25319. Just like its stablemate the 750 Atlas head. Again it was on the underside. You can not use this head on a spigotted barrel unless the spigots are ground off.

And to finish the series.......once Commando production began.... the last of the 650SS motors and the Mercury follow-on used a head with number 06-0380. Which just happens to be the same number used on the early Commando, last Atlas and Hybrid 750 engines. But with different inlet valves.

Inlet valves for the 88,99 and 650 engines were 1.406" in dia. The bigger 1.50" valves were used on the Atlas 750 and Commando cylinder heads. (plus the 750 hybrids). Adding more confusion is the valve lengths changed when spigotless barrels and heads made an appearance. They are slightly longer and the push rods for these engines slightly shorter. All by around 0.010"..........and just before this happened the rockers were changed to accomodate a pressure oil feed system.

More info on these heads can be found in Roadholder issue 302 or at -http://atlanticgreen.com/nhth.htm

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This looks like a Commando head.

The Commando head had side rocker oil feeds and I can also see letting stamped by the rocker cover. The Norton factory stamped from RH1 up to RH10 depending on the model the bike was being produced for.

What is the socket head screw doing in the front rocker cover? in picture "wp_20141228_006-jpg" of the Commando cylinder head?

Previously Alan Throssell wrote:

What is the socket head screw doing in the front rocker cover? in picture "wp_20141228_006-jpg" of the Commando cylinder head?

On my Dommie....this was the position of a breather. I had one each side. They must have worked as a pressure reliever as I never had dripping covers, leaking side plates or even head gasket problems.

Aren't the bolt spacing are different from the 650cc Dominator to the Commando?

Yes..........Measure across the spark plug position. The bolt centres will be about 52mm on a 650 head and 55mm on a Commando or Atlas.