Norvil Belt drive

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Just installed a Norvil belt drive and was amazed by the lack of proper instructions... Is it normal that the front pulley is "only" one mm on the first half moon (woodruff key?). Which spacer goes behind the clutch basket on the gearbox shaft (the one with an inside shoulder or?). I put everything together and it seems ok but a plan/illustration would have been better!
Yup, I too had the comprehensive instruction leaflet!
I mostly 'used the force, luke' to get mine together, and it's ok, but I found the front pully came loose after about 1K miles, reaming out the guide over the woodruff key. So I fitted a new pully and really clouted it onto the shaft, just like Les eventually told me to! and super tightened it, too.No problems since then, but, with hindsight, I removed a perfectly satisfactory OE setup and replaced it with something I ALWAYS have reservations about. Now the single Mikuni conversion, that's another story........

Ride safe

Paul -750 Combat (they really fly- usually apart!)
belt drive - single mikuni


Your comment about a perfectly satisfactory OE primary drive is the reason I haven't jumped for a belt primary. Another is if the crankshaft seal leaks, it doesn't make any difference to the chain drive.

I want to hear your story about a single mikuni. My one and only Norton is a '72 combat roadster. Remembering back to some club rides in the early 80s, I was side by side on my '73 750 Mk5 with a '74 850 that had a single mikuni. At around 90mph my 750 with dual Amals accelerated away while the 850 ran out of steam. In the real world "legal speed" I suppose the advantages of the mikuni outweigh the disadvantages. It seems a waste, though, for a combat engine that's tuned for high rpm performance to be held back by lack of carburetion.
illf8ed & eyeguy
Some quick arithmetic shows twin 30mm Amals with 1413.72 sq. mm area. To get the same area from a single carb you will need to have a 42.43 mm dia. throat. In theory though since the firing order is 180 degrees a smaller carb should work, however in real life apparently it doesn't.
I have seen Mikuni kits with 34 mm, 36 mm and 38 mm carbs but it seems everyone uses the 34 mm probably because throtle response on the larger carbs being poor. With that in mind I started looking for a large bore constant velocity carb that may be suitable. What I found was a 42 mm CV carb for Harley Sportsters sold under the Screaming Eagle brand. Now if I can just figure out how to put it on the Norton we may have something; high flow with good throtle response.

Hey guys,

It's fascinating how seamlessly we transitioned from belt drives to carburetors!

Two 30mm carburetors will generate a much higher fuel velocity than a single 42mm carburetor. And this higher velocity seems to help produce more power up to a point.

Does anyone know why Norton made 30mm 850 Commando heads for one year (1974) only??? The very next year Norton reverted back to 32mm heads, strange. Perhaps EPA?




The combat and my previous '73 750 Mk5 have 32mm Amals. The other guy had a 34mm mikuni on his '74 850 that couldn't keep up. We were twenty something at the time, so you know both of us were trying to win.


The combat and my previous '73 750 Mk5 have 32mm Amals. The other guy had a 34mm mikuni on his '74 850 that couldn't keep up. We were twenty something at the time, so you know both of us were trying to win.
what's next, seatcovers?!
I've a 34mm Mikuni with K&N filter. The bike starts first lunge, idles, and pulls very strongly at lower revs, at least as torquey as the twin setup. It does get a little asthmatic at high revs(5-5500)but mostly I use it as a street bike, and seldom get to race other commandos at 95mph these days, and, when I do race Gixers, R1's etc, they're usually too busy laughing to notice that it's a single carb! I just feel that the advantages mean a) more response at lower revs-real world speeds b) lesstime setting up-more time enjoying riding c) something to irritate trailer show- bike owners as it's not completely original!d) better petrol consumption.
Now, the Peter Williams camshaft profiles, there's a story.............!


Good ahead, let's talk about seat covers. I never really liked the replacement one made in England anyway.

What gas mileage do you get with the single mikuni? I'm getting 55-60mpg with resleeved 932 Amals.
This thread has me all confused. My Corbin gunfighter works great but I can't figure out how to mount the mikuni to my belt drive.

-Smart Ass
Get on the case Smart Ass
I've installed my Corbin Cam (gunfighter profile, fairly soft but forgiving on the transmission) wihout instructions BTW, but my Peter Williams seat is a real pain, it just looks too small and seems way too lumpy for my tastes. In an interesting diversion back to the original thread, I would state that the one real advantage of belt drive is that I managed to fit an extra steel plate in the clutch, which makes it lighter than ANYTHING else I've ever ridden, including hydraulics! Also, it occurs to me that, should you break down in the middle of nowhere, like Birmingham or Hull, you could remove the belt and improvise a rabbit snare, using the rogue sparking from under the tank to light your fire and cook your prize catch.........

In England, it's raining......................

Fifty five to sixty miles per gallon is phenomenal gas mileage there Illf8ed! Must be the seat cover???

Speaking of rabbits eyeguy, I've been told that you can tell if a wild rabbit has worms by rubbing the fur on its belly the wrong way. If by doing this you feel lumps, the rabbit has worms. No lumps means it safe to eat. (From the book: A Day No Pigs Would Die)

I have a floating speck in my eye, anyone know what this is all about???


If it moves as you stare at a plain wall, it's prob. a 'floater', a smll piece of debris in the jelly of the eye (the vitreous). If it's statice go see your Optometrist NOW it may be a detachment.
With good isolastics these tend not to shake loose, so check your clearances!

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