Combat engine C Stamp location?

Hi Richard,

It's stamped on top of the head near the front but is very helpfully covered up by the head steady making it almost impossible to photograph!!!!! It should have 32mm concentric carbs (when new).

The engine breather exits the rear of the crankcases (when new)

Apart from the barrels being painted black (when new) I can't think of any other means to identify a combat engine just by looking but I expect the experts on here may know more, i would be interested to learn of any other means.

All the above items can and probably have been changed over the years except the "C" stamp ,(which you can't see) welcome to planet Norton.

The combat engine had the head planed to increase the compression. Although it is not possible to say if it was done by the factory, it's quite clear when viewed from the side if this has been done.

If it's a wombat, there will be very little gap between the top fin on the cylinder and the lower on the head.

Do you have a side on view of the top end ?

A combat from within the range would have also had a disc brake, all non combats were drum during the combat period. If you wanted a disc brake then you got the brake and the combat engine. For some reason most (if not all ?) of the Interstates from the period were combats. As all the changes could be added later then you really need to see all the clues.

1. In the right serial number range

2. C stamped on head

3. Planed and ported head

4. 32mm Concentric carbs

5. 32mm to 32mm manifolds

6. Disc brake

7 Black barrels

8 The high lift cam

Once you have the mains sorted and the oil return pick up relocated from the front to the rear its a reliable engine.

Combats and non combats in 72 all had the breather at the back, no sump filter and the oil return pick up from the front.

To me it looks like the head has been skimmed like the Combats were. The C on top is very easy to falsify. There is no easy way of deciding much else from those pictures re' camshaft etc.

The fuel tank is wrong. There should only be one stripe on a 750 tank and looking at the picture it looks like one of the narrower Interstate tanks fitted to later bikes. There were a few different shapes over the years, and then the Indian tanks.

The exhaust rings are wrong for a 750 too.

These things probably won't effect it's rideability but if you want it to be as original it's worth knowing what you're getting.

An Interstate tank from 72 would have been Fibreglass and useless with E5 petrol so a later steel replacement is good, can't tell a lot else from the pics to add to Ians other than the rear tail light is off a later bike and the front mudguard stays should be silver not black. Where is the engine breather off the back of the crankcase and then going vertical, it looks to be missing ?

The pistons shown in the rebuild photo are the early slotted type. these can crack if thrashed hard, saying that i have had a pair of these pistons in my Commando for 35 years and they lasted well. I think if you are going to explore the 6-7000 rpm range on a regular basis you might want to fit later pistons, normal cruising at 70mph is about 4200rpm

There are 2 versions of the slotted pistons, 1 is ok, the other is not. The bad version has a full slot, the good has partial slots but the pics are not good enough to see which version is fitted.

I'll stick my neck out and say that it doesn't look to me as if that is a 'planed' Combat head - The gap between cylinder and head fins looks too large.

Re: breather, is it as attached photo?

That pic is of the correct breather for a 72, but its missing from all the other pics, maybe the pipe is currently disconnected, if it is disconnected it cannot run until it is reconnected as the breather will just deposit oil over the rear tyre.

Hi Richard, I hope you get the Commando, it looks a nice bike.

For information here are photos of my Combat engine No. 206--- It is presently out of the bike. You can see the faint C stamp on top which is normally covered by the head steady. The Combat head has 0.040" skimmed off to give a higher compression ratio, this only makes the head to barrel fin gap 1mm closer than a standard engine (not much different to look at).

Regards, Alan