1973 Commando Roadster MK V: Combat Motor?

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CommandoMKV

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S/N: 220635 - Amal 32mm carbs - Black cylinder - Manufactured 1/73
With having all the above, could this be a very late Combat motor, with the Superblend crank bearings?
I just bought the bike from a private owner down in southern Alabama, and have not had a chance to even get it running, much less do any internal engine inspection.
I was hoping that someone could tell me that my estimation is correct, that this is indeed a Combat motor and MK V model.
 
MkV? Yes.
Combat? Unlikely, as the Combat series ended during MkIV production at 211110.
Superblend? Yes, unless they've been replaced then probably the original R&M/RHP 6/MRJA30 'Superblends'.
 
On one of the parts sites (I think CBS) had a parts listing for 32mm replacement carbs for the 750 Combat motor...and that is where I made the assumption that this might be a Combat motor. Regardless, my two sons and I will have a great time bringing this one back to life. It has 21k miles and has been in an actual barn for the past year. Lot of cleaning up to do and getting it mechanically sound, before starting to invest in the new parts that may be needed.
Thanks for the quick response.
Just a little back ground, I was an 18 yr. old mechanic in 1973, working at the Super Motorcycle Center in Norfolk, Va. It was run by the Minor family (English) and where I sold my Dad a 1973 750 Commando Roadster Combat....so a long family history with the venerable Norton machines, and continuing it with my two sons.
 
CommandoMKV said:
On one of the parts sites (I think CBS) had a parts listing for 32mm replacement carbs for the 750 Combat motor...and that is where I made the assumption that this might be a Combat motor.
Click to expand...

The 32mm carbs continued but with two new '32mm' cylinder heads. The RH5 'low' (standard) compression and RH6 'high' compression (midway between standard and Combat) all models having the standard camshaft.

http://www.classicbike.biz/Norton/Parts/1970s/Commando_Parts_73-74.pdf
Group 2.

Amal also lists the 1973 specification Mk1 carbs as 'Combat' and which is often copied by vendors but it's incorrect.
http://amalcarb.co.uk/carbspec/carburettor/spares/id/5495/
 
CommandoMKV said:
How can you determine if the head is an RH5 or RH6?
Click to expand...

It would be stamped immediately above the right-hand exhaust rocker cover as in the (850 RH4) example below. A Combat head would usually have a 'C' under the head steady.

1973 Commando Roadster MK V: Combat Motor?
 
CommandoMKV said:
S/N: 220635 - Amal 32mm carbs - Black cylinder - Manufactured 1/73
With having all the above, could this be a very late Combat motor, with the Superblend crank bearings?
Click to expand...
This is a good example that serial numbers and build dates are not in sequence. I have S/N 2208XX and S/N 2212XX and both tags show mfg dates as 11/72!
 
CommandoMKV said:
Thanks for the link.
How can you determine if the head is an RH5 or RH6?
Click to expand...

I too have seen RH5 and RH6 a bit more haphazard stamped on the heads. Not neat like the 850's. Look for an R and a 5 or 6 on top of the head
RH5 squish band depth is standard .125", the RH6 will be cut 20 so .100" squish band... both "approx"...
 
CommandoMKV said:
S/N: 220635 - Amal 32mm carbs - Black cylinder - Manufactured 1/73
With having all the above, could this be a very late Combat motor, with the Superblend crank bearings?
I just bought the bike from a private owner down in southern Alabama, and have not had a chance to even get it running, much less do any internal engine inspection.
I was hoping that someone could tell me that my estimation is correct, that this is indeed a Combat motor and MK V model.
Click to expand...
I used to own and ride 220627 which was a ‘73 750 MkV with RH6 head. As Dave said these are high compression engines and the last iteration of the 750 engine. These do not have a combat camshaft. Sold this bike in ‘87.
 
CommandoMKV said:
On one of the parts sites (I think CBS) had a parts listing for 32mm replacement carbs for the 750 Combat motor...and that is where I made the assumption that this might be a Combat motor. Regardless, my two sons and I will have a great time bringing this one back to life. It has 21k miles and has been in an actual barn for the past year. Lot of cleaning up to do and getting it mechanically sound, before starting to invest in the new parts that may be needed.
Thanks for the quick response.
Just a little back ground, I was an 18 yr. old mechanic in 1973, working at the Super Motorcycle Center in Norfolk, Va. It was run by the Minor family (English) and where I sold my Dad a 1973 750 Commando Roadster Combat....so a long family history with the venerable Norton machines, and continuing it with my two sons.
Click to expand...

Tell us more please. How did you find the bike ... and how much did you pay? Sounds like you have more than a "little" back ground in Nortons. Even a Norton mechanic; back in the day? How cool is that :cool:
 
L.A.B. said:
MkV? Yes.
Combat? Unlikely, as the Combat series ended during MkIV production at 211110.
Superblend? Yes, unless they've been replaced then probably the original R&M/RHP 6/MRJA30 'Superblends'.
Click to expand...
Agreed, but I think they still made "high performance" 750s and didn't call them Combat (or sold off actual Combat bikes).

I have this on my site but am embarrassed to say I don't know where I got the info - pretty sure from a book: "In truth, the high performance engines were still sold even into 1973, but they were not called Combat. " I'll try to figure it out.
 
marshg246 said:
Agreed, but I think they still made "high performance" 750s and didn't call them Combat (or sold off actual Combat bikes).
Click to expand...

"High performance" in that those models had the 'high' compression (but not as high as Combat) 32mm carb RH6 cylinder head but without the Combat camshaft.

No specific 'Combat' parts are listed in the parts book from 212278 and the owner's handbook for that period only refers to "10:1*. (H.C.) or 8.9:1 (L.C.)" compression ratio.
http://www.classicbike.biz/Norton/OwnersManuals/70s/73Commando-OwnerMan.pdf

*Edit: The 10:1 figure seems somewhat optimistic as Norton Service Release N3/23 quotes: "9.3:1 with base gasket" and "9.6:1 without base gasket" for RH6.
 
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A few points: for the north americans
1. high performance IIRC a 750 commando (45cid/ 55hp?) is approximately similar to a 350hp/327cid corvette.
2. yes the RH6 -.020 head is only semi Hi comp but still big port (my RH5 measures only 31mm)
3. Not to put words in JimC mouth, but we spoke at the most recent Virginia rally about my RH1 28.5MM head out performing (at the 92 rally dyno session) ALL other stock commandos. My bike otherwise being a stock "combat tune" with a temporary RH1 head due to it being screwed by a "professional" machine shop. I temporarily exchanged the head to allow my redoing my own rebuild. At that time Jim seemed to agree with me about better performance with the RH1 head over the big port RH3 combat tune head. I did not originally realize how good it was until Leo Geoff, who observed the runs, told me so.
4. Any further defining 73's as "higher" performance IMO, is pale compared to the 2S camed full combat.

discussed a bit here: https://www.accessnorton.com/NortonCommando/2s-cam-hits-cam-follower-tappet-guide-in-barrels.18676/
 
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L.A.B. said:
"High performance" in that those models had the 'high' compression (but not as high as Combat) 32mm carb RH6 cylinder head but without the Combat camshaft.

No specific 'Combat' parts are listed in the parts book from 212278 and the owner's handbook for that period only refers to "10:1*. (H.C.) or 8.9:1 (L.C.)" compression ratio.
http://www.classicbike.biz/Norton/OwnersManuals/70s/73Commando-OwnerMan.pdf

*Edit: The 10:1 figure seems somewhat optimistic as Norton Service Release N3/23 quotes: "9.3:1 with base gasket" and "9.6:1 without base gasket" for RH6.
Click to expand...
Thanks, that makes more sense and I'll update my site.
 
nortriubuell said:
Tell us more please. How did you find the bike ... and how much did you pay? Sounds like you have more than a "little" back ground in Nortons. Even a Norton mechanic; back in the day? How cool is that :cool:
Click to expand...
My oldest son came across the Roadster on Facebook Market (of all things), and the owners said they had it posted for about 1.5 months, with no real interest. Bought it within two days of finding it, and paid $3k...for a Roadster with 21,121 original miles on it. Many thanks to my son for making the 12 hr. round trip, from outside if Nashville, TN to southern Alabama to retrieve this beauty.
It had been put in an actual barn because of a busted throttle cable, and there it sat for over a year. The one thing Vince Minor (owner of Super Motorcycle Center) taught me (in addition to ALL of my foundational mechanic skills) was that you bring a bike back to life whenever you can...and never let them die if you help it.
Had to hear it run at least one time before I started the tear down for the engine rebuild & overall refresh of all the existing factory parts.
Changed the oil, flushed the carbs, set the points, and with a fresh battery, oil, fuel and plugs, the MK V started on 6th kick!! (have video of that moment) It was determined to show us it that it wanted to run...and now that it is in our hands, it will keep on running for a very long time!!
Oh, BTW it has an RH6 head !! (see attached photo). Haven't inspected the camshaft, but would a Combat cam work with this head's compression ratio? I remember back in the day we would install well annealed solid copper head gaskets in the Combat motors to try to avoid their tendency to sometimes become coil-bound....and though this altered their compression ratio, at least they maintained a compression ratio by continuing to run.


1973 Commando Roadster MK V: Combat Motor?
 
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2S cam will work with any 750/850 version head but you must remove the insulation washer under the intake spring perch.
On your engine#, a 2S cam would be an after factory add on.
Yes your head ID is in the earlier (than 850) position...
At one time there were thicker than stock head gaskets. I don't know anymore.
The stack of copper gaskets I have is only .008 to .010" thicker than regular flame ring gaskets. Now I would not trust a gasket alone to fix the risk of coil bind.

Back "in the early 2S combat tune days" the defective spring perches were a source of coil bind until the factory discovered and fixed the problem.
 
Do the late 750s have stud bolts, or is the cylinder the same as the earlier 750. What about the short stroke 750s? I assume they must have studs. Is that correct?
 
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