Combat wannabe

Hey guys, just something I am curious about. My '71 matching numbers roadster has a right side disc brake and a black painted barrel. It wants to be a combat so bad!! It is definitely a 71 and has the timed breather etc.. How common was it for guys to switch out front ends for a disc setup? Seems like it was something pretty common as a retrofit. I can't find any "c" markings on the head but the black barrel has a patina that goes with the overall aged (unpolished) look of the bike leading me to believe it's been there for awhile. The last owner mounted 930's so I'm not sure what it had before he gave up trying to get it to run. Any way to check for a combat head without taking it off the motor? Just afraid I've been setting the wrong valve clearances. It has a steel tank but one steel side cover and one glass so who knows where it's been in its life! Thanks and have a great holiday season.

The RH1 cylinder head does not have any markings, but it does have the small ports to suit the stock 30mm carburetors.



Black painted cylinder (should be silver) with + 0.020" slotted pistons.

Stand out factory issued look, very cool uniquely Norton style. i've ridden and ridden with a standard '71 to know with the standard small ports and 30 mm carbs it will out pull a Combat or match it till over the ton. To get Combat to show off their advantage requires almost injurious rpm into crank and case flex. Main injury is lower gear use eats up AMC's dry run sleeve bushes that only get drain splash oiling when in constant easy cruise 4th. Clutch can wobble and that eats up other things faster. When I was into testing these difference my 2 Combat would lift front as rpm passed 6800 and would hang on into red zone or until factory valve train floated out of control to make note of tach passing semis in time.

The '72-'73 crankcase has webs inside to strengthen it. It was supposedly for the combat requirement. It was very common for Commandos with drum brakes to be converted to disc in the 70s and 80s. Also very common for non combat 750s to get cylinders painted black to look like the "famed" combat. After so many years of precious owners making changes to original machines it's very difficult to use these characteristics to identify what it was going out the factory doors. Although some seem to believe there were '71 combats produced, the literature and records indicate the combat was a 750 MkIV model with the later crankcases....etc.

As soon as I could put a disc on mine, I got the kit that upgraded the front end. Trying to stop in traffic in the summer heat with a passenger and drum brakes wasn't a lot of fun. I liked it so much, I put a disc on the rear too. Nice to be able to lock up both wheels at will. Sleeveing the M/C later sure helped my right hand.
When I did the top end, I painted the silver barrel black. I didn't care about trying to look like a Combat, black barrels just look better on a Commando. I did mill the head to raise the compression ratio to 10:1. Ported the head and added 32mm carbs also. So, it's almost a Combat, less the 2S cam. No regrets, the longer Dunstall kickstart lever eased the kicking effort of a higher compression ratio. Instead of engine bearing problems of a Combat, I put a Barnett clutch in and blew the transmission drag racing back in the day.....At least that got me to upgrade to a 5 speed.
I love my '71 after updating the center stand, side stand mount and adding an oil filter, vernier iso's and a headsteady.

These days, I wouldn't bother with the head work. Just find '74 manifolds and mount 32mm's to the 30mm head. Experience of the learned came to the conclusion that the Commando head flows best with that configuration.
Of course, there are other carb options......

The heart of a Combat is the cam.

I offed a "C" head for a very good RH1. Very little work to bring only the end of the ports to 32mm. Fresh guides and valves homed to the seats ala Comnoz, Bee hive springs to take it pass advertise redline and I was good to go.

Sure, front disc is better,particularly after market, and bigger carbs is relative to the cam on a 750 but not necessary. But, if you put in a hot cam then the entire bike should be bullt and bettered to accommidate it. I think it's a weakest link type of thing. You should cover all the bases like gearbox, primary, valve train, timing side, swing arm, wheels and bearing, and suspension to name a few that come to mind.

Really, it's the cam that makes it a combat, I feel. For me the JS stage 2 is the ticket.

Just a note, the 'web' in DS case of '72 is only a baffle to keep direct crank oil sling out of the breather hose hole and more to collect and pump out. Early references on moving oil drain to rear had web completely removed. Now we know just lower the TS case floor to expose oil passage into pump and oil with flow around the web as normal.

Comnoz showed that what ever funnel down he did on a long tube manfiold reduced flow so suggest some day try a small port head with 32 carbs and leave the step down flow tripper lip in the way and see what ya think about normal wisdom.