750 heads

rvich said:

If you were going to put Amal carbs on a 750 Fullauto head, what do you need for manifolds? For that matter what do you use on the 850 heads? Are they 30mm?

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The fullauto heads all have the same ports. They are 32mm at the flange and standard manifolds will fit. Jim

Curiosity got me finally and I got an old Combat head off the shelf to check:
Using some ID telescoping gauges and a caliper as measuring tools:

The left intake measured 28.65mm from floor to ceiling in front of the valve guide & 28.27mm cross wise.
31.80mm from top to bottom at the entry & 31.86mm cross wise at the entry; Manifold opening.

The right intake: 28.49mm floor to ceiling & 28.76mm cross wise in front of the guide.
31.78mm top to bottom & 31.84mm cross wise at the manifold opening.

This is not to be taken as a controled scientific exact measurement procedure---but just a quick check to see what this particular Combat head may disclose.

Looks like it is tapered not 32mm all the way to the valve

Would be usefull to know which era of Combat heads the above measures are from, the early crude hand hogged out Wolverhampton issue or the later more refined down narrow version. My Woverhapton head was cast once and mention made to me that grind seen that opened ports up beyond wise reasonable effective.

How would one judge the big size ports CHO on a 10.5 CR 920?
Will just have to try it and see.

Would be usefull to know which era of Combat heads the above measures are from, the early crude hand hogged out Wolverhampton issue or the later more refined down narrow version. My Woverhapton head was cast once and mention made to me that grind seen that opened ports up beyond wise reasonable effective.

How would one judge the big size ports CHO on a 10.5 CR 920?
Will just have to try it and see.

hobot said:

Would be usefull to know which era of Combat heads the above measures are from, the early crude hand hogged out Wolverhampton issue or the later more refined down narrow version. My Woverhapton head was cast once and mention made to me that grind seen that opened ports up beyond wise reasonable effective.

How would one judge the big size ports CHO on a 10.5 CR 920?
Will just have to try it and see.

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Sorry---unknown what bike is was on originally. Picked it up long ago at a swap meet at Los Angeles Fair Grounds Corvette Swap Meet event.
On the bottom is a " P " stamp Two " A " stamps and what is left after milling is BIRCO casting ID.
If this helps ID it--let me know---I'll add that to my inventory parts notes for future reference if required.

Nope don't help yet till we get other CHO measures for a sense of their scope. I ping my head man and see if he still has the measures or casts. I feel my CHO+2S cam don't really come on until 6800 rpm and beyond.

303 fmj said:

hobot said:

Would be usefull to know which era of Combat heads the above measures are from, the early crude hand hogged out Wolverhampton issue or the later more refined down narrow version. My Woverhapton head was cast once and mention made to me that grind seen that opened ports up beyond wise reasonable effective.

How would one judge the big size ports CHO on a 10.5 CR 920?
Will just have to try it and see.

Click to expand...

Sorry---unknown what bike is was on originally. Picked it up long ago at a swap meet at Los Angeles Fair Grounds Corvette Swap Meet event.
On the bottom is a " P " stamp Two " A " stamps and what is left after milling is BIRCO casting ID.
If this helps ID it--let me know---I'll add that to my inventory parts notes for future reference if required.

Click to expand...

I don't know of any identification marks on the head except the RH# which may or may not be on the early heads plus the C stamp on the Combat head.

All Norton ports are finished by hand. Supposedly the early Combat heads were modified from the small port head and the later heads were cast as large port heads. There is a lot of variation in the porting in the heads. Some can look downright crude. I suspect there was more than one person with a die grinder doing the work. I know the later ports were larger all the way to the bowl than the earlier heads. Jim

OK luck of the draw then. I know history of Peels "March/'72" CHO so Ken is sending it to take comparative measures and rate flow. Would also like to talk ya into a D shaped exhaust exit.

Check out the squid bands

dynodave said:

I doubt any one has measured their head....I have never seen a stock 30mm 750 head. They all seem to measure 28-28.5mm ports or combat @32. I'm not 100% positive about the quite rare special 73 750 heads and it has been quite a while since I've had my hands on them. I own about 25-30 heads but only one 73.
The 74 850 head is 30mm designated as RH10. As far as I know it is the only 30mm.

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Hi, about those 1973 750 RH5 /6 heads , as you said they are less common, that's why I am looking for some info, cause I have one on my Seeley project , alongside a spare Combat, and of course wish to know .....

For those of us who are not likely to see hundreds of Commando heads during our lifetimes, how about some help developing a critical eye? Or will it be obvious when I look as to whether or not it is an inferior porting job?

Russ

Trained eye head workers use casting and flow benches and dyno to tell, so best wishes just eyeballing em.

rvich said:

For those of us who are not likely to see hundreds of Commando heads during our lifetimes, how about some help developing a critical eye? Or will it be obvious when I look as to whether or not it is an inferior porting job?

Russ

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As a rule of thumb, the worst performing ports have a sharp angle between the floor of the port and the valve seat. It is a result of removing too much material from the floor of the port. The better port has a large smooth radius there. The earlier small port heads had a fair radius there. [650] As the ports got larger that radius went away. It had to if they were going to make a large round port. They couldn't go up because the valve spring was there so the only place to go was down.