Combat or not

olympus · Aug 16, 2017

Clarification please

With an engine number of 200918 its below the start number I was advised of 200976
I have no "C" stamped on the rocker cover
The inlet tracts are finned & 30mm
But the spacing between lower head fin And to block fin is reduced... appreciate the photo doesn't show it that good..
It may be that over the 40 odd years that the head has been skimmed
Is what im seeing normal for a none Combat motor??

Malc

batrider · Aug 16, 2017

The Combat "C" is usually stamped on the cylinder head on top near the notch between the exhaust rocker covers . Sometimes you have to remove the head steady plate to see it. What size are the carbs, 930 or 932? Combat used 932.

L.A.B. · Aug 16, 2017

olympus said:
I have no "C" stamped on the rocker cover
The inlet tracts are finned & 30mm
But the spacing between lower head fin And to block fin is reduced... appreciate the photo doesn't show it that good..
It may be that over the 40 odd years that the head has been skimmed
Is what im seeing normal for a none Combat motor??

Commandos generally had/have a smaller gap between the fins at the barrel to head joint, even the 850s. Combats just had approximately 0.040" less.
Going by the photo I'd say it's probably a standard head, if, as you say, there's no 'C' usually stamped in the centre of the head under the head steady (although not all Combat heads had the 'C' mark) the inlet manifolds are the 30mm type (30 -28.5mm as the standard head inlet ports are 28.5mm).
Standard carbs would also be 30mm (930)

Assuming it's there, what's the date on the frame plate?

olympus · Aug 16, 2017

OK definitely have 930 carbs
Head steady off no "C" stamped on rocker cover
When you say "Assuming it's there, what's the date on the frame plate" ignorance is bliss.... what plate? and where should this have been??

Malc

L.A.B. · Aug 16, 2017

olympus said:
When you say "Assuming it's there, what's the date on the frame plate" ignorance is bliss.... what plate? and where should this have been??

https://andover-norton.co.uk/en/shop-dr ... sion-units

Originally, there would have been a red certification plate [2] attached to the headstock (by four hammer drive screws/rivets[3]) which had the frame number and (usually) the month/year date of manufacture stamped on it.

https://andover-norton.co.uk/en/shop-de ... tion-label
Or perhaps this one;
https://andover-norton.co.uk/en/shop-de ... tion-label

If it's not there, what/where is the frame number (assuming the frame has a number) which would normally match the 6-digit engine and gearbox number?

olympus · Aug 16, 2017

I'll do some digging and refer....literally. there is so much paint & snot around the headstock it could be covering a multitude of sins

Malc

L.A.B. · Aug 16, 2017

If you don't find the plate then you should find the four rivet holes, but without the plate, a '72 frame (if that's what it is) basically has no identity unless someone has stamped a number on it. Is the frame number on the V5C (assuming you have the V5C) the same as the engine (and gearbox) number?

olympus · Aug 17, 2017

You are correct L.A.B four rivet holes & no plate
V5 states the actual engine number as chassis number, and under engine number its blank
When I start the re-build in the Autumn this will be added to the every increasing "to do" list

Thanks again

Malc

gripper · Aug 17, 2017

Presuming that this is an early 750 with 30mm carbs, try and avoid the temptation to open up the ports to 32mm and fit larger carbs. The original 30mm setup is very good and performs well. In my youth I chased the power improvements by opening up the ports and fitting 32mm carbs. I wish I had left it alone.

olympus · Aug 17, 2017

Thanks for that Gripper, it was going to be one of the jobs I'd planned to do.. but wont bother now
Can I ask how it changed the engine/power characteristics??

MichaelB · Aug 17, 2017

Is it a Cam breather or a rear breather?

dynodave · Aug 17, 2017

MichaelB said:
Is it a Cam breather or a rear breather?

200918 should be obvious...

You can/should always check for combat tune: ~~200205~~* that I worked on, was a full combat tune! Head, cam and carbs/manifold and of course combat breather cases.

Factory record keeping may not have been always that good?

*Edited by the moderator as dynodave later discovered the number to be 202005.

olympus · Aug 17, 2017

Rear breather..

kommando · Aug 17, 2017

So 72 breather which is not restricted to combat engines but fitted to all 72's.

L.A.B. · Aug 17, 2017

olympus said:
Rear breather..

Yes, you sometimes hear the (200000-on) 'rear' breather referred to as a 'Combat' breather :roll: , however, neither the presence of the low rear breather (or that particular type of crankcase) is proof an engine was a Combat, as the same breather and cases were used for the '2'x series and later 750 Commandos produced in both standard and Combat tune, so before, during, and after, Combat production.

L.A.B. · Aug 17, 2017

dynodave said:
You can/should always check for combat tune: 200205 that I worked on, was a full combat tune! Head, cam and carbs/manifold and of course combat breather cases.

Factory record keeping may not have been always that good?

The Combat specification engine was supposed to have been available before someone at the factory decided it was what (nearly) every Commando owner needed.

ILLF8ED · Aug 17, 2017

Original combat from the factory or modified to combat over the many years is hard to confirm unless you are the original owner. A lot of the machines out there are a mix of parts. If you have a non combat head and standard camshaft, I recommend to re-build it to that spec. After all these years it really does not matter how it left the factory unless you're going for concourse in which case you will need factory documentation as to it's origin.

pete.v · Aug 17, 2017

Kinda makes ya wonder how many were bitza's right out of the factory.

gripper · Aug 18, 2017

With 30 mm carbs and a19 tooth sprocket it would lift the front wheel easily. opening up the ports and fitting 32mm carbs was quite underwhelming though I did not increase the CR or change the cam, as at the time these were expensive options for me. I suppose you could say I only did half the job. I would definatly stick with the 30mm carbs IF the ports are still 30mm. (They might actually be 28mm as some early manifolds are)

olympus · Aug 18, 2017

Many thanks to all

Malc

Combat or not

olympus

batrider

L.A.B.

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olympus

L.A.B.

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olympus

L.A.B.

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olympus

gripper

olympus

MichaelB

"Sons of Arthritus"

dynodave

olympus

kommando

L.A.B.

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L.A.B.

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ILLF8ED

pete.v

gripper

olympus

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