Combat or not?

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dragonfly

dragonfly

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Greetings from a newb. I'm thrilled I've found this website and overwhelmed at the knowledge you guys possess. Forgive me for this inquiry cause I'm sure this has been disscussed before. I suspect I have a Combat engine, but not quite sure. My Roadster is titled as a 73 but has 72 on the frame badge. Serial #221426 with 932 Amals and a silver barrel not black. I cannot find a "C" stamped on the head. Maybe hidden under the head steady. The cooling fins are closer together where the head meets the barrel. I'd like to know definitativly so as to address issues associated with the Combat.

Any thoughts are graetly appreciated.
Jerry
 
Regardless of whether its a combat or not if its a 72 then the crankcase issue needs to be sorted as the large sump plug was dropped from all 72,s , the breather was mounted on the back on the crankcases, and the oil return pick up was in the wrong place for high revs. Sort the oil pick up point and replace the breather with a reed valve breather, fit superblend main bearings and you are all set. The specific Combat issues are pushrods being too long and other possible issues like valve spring coil bind (Norton's fix was to removed the insulated washers under the lower spring keeper).

A number in the 220000 range will not be a 72 or a Combat but a 73 MkV
 
very doubtful you have a Combat motor, which had the little higher compression and cam

the Combat was just a little quicker in a quarter mile some 40 years ago, really about the same as your standard just depending on two riders of different weights, rear tire conditions, etc etc

Combats had the barrels painted black, your's are silver, and also you say no C stamped on head

I think you have a "standard" 750, either 72 or 73 doesn't really matter that much

any other questions let us know
 
Thanks for the replys. I'm actually relieved that I don't have the Combat engine. So...if it's a 750 MkV do I still need to address issues like wet sumping, layshaft bearing, breather?
 
Combat left such a bad taste of financial disaster they stopped issuing them soon as model year ended. Anyone could of shaved the head and put in 2S cam by this time, which to me is a good thing. Only two ways to know if built to basic Combat specs, hold WOT in lower gears past 6800 when seeming 3rd piston kicks in on mine and begins to G pull wrists for low leaping wheelie before shift or mic - degree the rocker/valve lift to see if about matches 2S graph/charting. All Commando are about the same till mid 6000's near 90 mph then the 19-20T sprocket Combat has distinct advantage to me. If you get knock - ping on low octane then someone raised compression with standard cam so may destroy itself w/o enough octane. Sorting the simple engine ain't even half of what a Commando may need going though. May have poor push rod length if shave head w/o diddling the push rods too. But they still run dang good, just louder head ringing and more wear on valve stems-guides.
 
Another clue as to the combat head is the inlet port should be 32mm and 932 carbs should be fitted as opposed to 930 carbs fitted on standard engines.
 
RennieK said:
Another clue as to the combat head is the inlet port should be 32mm and 932 carbs should be fitted as opposed to 930 carbs fitted on standard engines.
Click to expand...

Post-Combat, "standard" model RH5 and RH6 750 heads also had 32mm inlets with 32mm 932 carbs, so that wouldn't necessarily identify a model as being a Combat, and 221426 should make it a '73 model (750 MkV).

http://atlanticgreen.com/nhth.htm
 
Ok....that's the clincher. The carbs are 932 32mm and the head is stamped RH6. So it's a standard 750. Gotta look for a layshaft bearing.
 
I have 221382, and it has black barrells. Lots of talk about that layshaft bearing lately. I never even heard of the problem before, but now it's on my list.
 
If its done over 10,000 miles the the laysharft bearing should be OK as the ones that blew up didn't make it that far and it was mostly the 850s that had the problems.

Ashley
 
dragonfly said:
Ok....that's the clincher. The carbs are 932 32mm and the head is stamped RH6. So it's a standard 750. Gotta look for a layshaft bearing.
Click to expand...

Not quite. The RH6 head has 0.020" milled off for a compression ratio of about 9.5:1 and 32 mm ports. The "standard" 750 has 8:1 compression with 28.5 mm ports. The Combat head had 0.043" milled for a 10:1 compression ratio and a 32 mm port job. This puts the RH6 more or less halfway between "standard" and Combat spec.

The MkV 750 used the standard cam where the Combat got the 2S grind.
 
and it was mostly the 850s that had the problems.
Click to expand...

what?

the 850s were the last three years of the Commando production, Norton had from 68-73 to figure out
the layshaft bearing situation and decided to build the 850s with "inferior" bearings?

say this is not true...

why or why?
 
It's true. Just to save a few cents per bearing and keep themselves in business for 45 or more years supplying more gearboxes and shafts and gaskets. Smart hunh ? :wink:
 
Those in the know told me Norton could of sold everything it could make in the 70's but was sucked down by BSA-Triumph absorption, so as supplers dried up d/t no payment, down the ladder of next lowest bidder. When ya read the several histories of what when wrong with Combats and the dealerships claims and customer and magazine news, Combats deserve the nick name The Combat Bomb. Boy howdy though with the Norton management out the way and and a knowing wrencher I am hooked on Combat Cream of the Crop pretty much like they were issued, eventually then supply shut off. Main issues I get with mine is tires go away under 4000 miles and no way does a police need no stinking radar to detect you double the limit and way to eager to power too fast into some turns for me. Chains suffer more too on a used Combat, ya get used to rear slightly spining out leaving places or tippy sharp turns. Out here the most dangerous asspect is I only think it sane to go 90 in opens but that when the pull suddenly gets better, so feels like please, oh please please please let me go and can another 25 mph easy. Hopped up is even better.
 
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