Combat motor identification (2013)

Hi,

I'm new to this forum having just joined as I am now the proud owner of a 72 Commando. OK, it is in about 5 boxes and some bigger chunks.... but is pretty much all there.

I have a couple of initial questions that hopefully someone can help me with:

1) Does this bike have the Combat motor? Can this be figured out from the serial no - 201598. It is a '72 bike with disc front end.
2) I also have an 850 motor that came with it (apparantly in good shape) - so as the 750 motor definitely needs a complete rebuild, apart from any cost savings, would it be an idea to fit the 850 - is the 850 motor 'better''?

I'm sure there will be a ton more questions once I rip into it when it finally arrives in the UK from the US.

Forum looks great, a real mine of info

Thanks

Jim

Hey Jim
If the 750 engine is in pieces, check the top of the head for the "C" stamp. It will be located just under where the head steady bolts to the head.
Second check the cam for the 750 for the 2S or SS marking. If you have both of these then you have a combat.

If the suspected combat engine is apart, or even more so if it is not a combat, if you are thinking of reusing the pistons check to make sure that the pistons are "combat" pistons, as the early 750 pistons had a tendency to break if pushed, due to a poor design in the skirt with the oil slit. ( you can search the piston differences on this site)

Cheers... I hope this helps, and if I am off on any of my info or left some gaps, the other members will chime in shortly.

P.S. if the combat motor is in good shape and if it is a combat then once rebuilt proper it would be the motor of choice.
My 2 cents
Oh, and don't forget to address the lay shaft bearing issue if your gearbox has not yet been rebuilt at some point. Over looking this could be hazardous to your health.

STOLEN from HOBOT .





COMBATS 32 m.m. ( 1 1/4 in. ) Dia. intake ports , and manifold bore . Has ' C ' stamped on top of head . ( probly under the headsteady , being english . )
" S S " stamped on the Camshaft ( Nothing to do with the unpleasantness involveing Mrs Hitler boy , Adolf ) .
A closer gap betwixt Head & Barrel , as the 10 : 1 Compression Ratio is induced by PLANEING the Head Face .
The Pushrods are also shorter . Silver Barrels NOT , Generally , Black Barrels are Combat . :?

Combat specs are a good base for starting a Go Faster Norton . Being Basically 1970 Production Racer ( P.R. ) Engine Specs .

So the best bet is a 10:1 Comp. S S cam 850 with 34 or 36 carbs . and a gearbox mainshaft outrigger bearing .
put together with infinite care patiance and cleanliness with exacting tolerances & better valve springs collets & keepers
& a BSA A65 advance unit . And a larger rear tyre . And one of those revolveing numberplates like James Bond has , if possible .

tridentperu said:

1) Does this bike have the Combat motor?

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Yes, roughly 12 out of 10 Commandos produces in 72 have a Combat engine. :mrgreen:

Honestly, if the engine is in need of a rebuild build it to the spec you want. There is tons of info around an cams, ports etc. so take your time. Probably the best read here is Jim Comstock head flow testing thread. There are some comments on the Combat head in this thread - e.g. this one - and from Jim's comments I'd be tempted to say that a Combat head is not the preferred version. If you don't see the C and find 30mm ports count yourself lucky and hand the head over to somebody who knows how to port a Norton head.


Tim

Welcome to the forum Jim, nice to have another contributor that owns a "real bike" :wink:
Good luck with the Commando
sam

Thanks for all the replies - from what I remember there is no C stamped into the head, but i'll have to have a good look when I eventually get the pile of parts back home.

Cheers

J

You can measure the valve lift and compare it to the specs in the workshop manual. The inlet valve has a huge lift on the Combat motor, .441 as compared to .375. Enough that even a worn cam should show up a difference. After 40 years you won't really know what you have unless you tear it down and have a good look at it. If you want a Combat motor, of course you can always make your own. You can get high compression pistons without shaving the head and there are lots of cams to choose from.

Russ

Where exactly would one find the C on the head?
Picture would be great
C

https://www.britcycle.com.au/product/norton-commando-750cc-cylinder-head-4/

Thanx!

Nice big fat “C”

To surgeon said:

Nice big fat “C”

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Probably wasn't a Hi-Rider originally then. More likely a Roadster as it has a Roadster tank, disc front brake, and 7" headlamp.

Another telltale for factory made combats... original carbs would have been Amal 932/19 and 932/20. My combat 201881 is not that far from your serial number. The “C” if present is in the center on top the head usually covered by the head steady.

L.A.B. said:

Probably wasn't a Hi-Rider originally then. More likely a Roadster as it has a Roadster tank, disc front brake, and 7" headlamp.

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Correct, I converted it to a hi rider,(I had one in 1978)