Manx Norton’s have more in common with Moto GP bikes than we might think…

Just stumbled across this, I thought it an interesting read:

Whilst on the Manx theme, can anyone tell me the peak power output, and at what rpm. And the peak torque output, and at what rpm, for the different current Manx motors of 86mm, 90, and 95 bore?

No Manx Norton knowledge… on this Norton forum ?!?!

You don’t need me to tell you that not many of the forum members ride around on Manx racing bikes.

According to Motor Cycling April 11, 1957 article.
Long stroke (pre -56) on Shell A fuel 30M (499 c.c) 40.5 B.H.P at 6000rpm. 40M (348 c.c) 33 B.H.P. at 7000 rpm On methanol 44.5 and 34.
Short stroke (-56 onwards) 30M 47 @ 7200, 40M 35 @ 7300.
According to Roy Bacon book Norton singles.
Short stroke 1954-1963
30M 47 @ 6500. 40M 35 @ 7200.
Though the factory max safe revs are set for 6 laps on the TT. Factory said you could rev 500 more on short circuits.
Have not noticed any valve float on the 40M at 8200 rpm. About torque don't know. as I usually keeps it over 6000 rpm. Empty under 5000.
No idea about the big bore ones now for sale.

Triton Thrasher said:

You don’t need me to tell you that not many of the forum members ride around on Manx racing bikes.

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Well there are plenty out there! I hoped that one or two might lurk around on this forum …

Good question Fast Eddie, it would be interesting to know what they are getting out of the new shorter stroke engines, Norton tried a few different bore and stroke combinations but stuck with the basically square design at the end, although no money to play with.

My thoughts are the newer aftermarket engines have gained a bit from the extra revs they can safely rev to, that gives you a bit more to play with, extra gears help a lot, when they brought in the clutch starts I was still slipping the clutch when the front runners, using 5 speed boxes were nearly out of sight at the starts.

Spent a day with with Jack Carruthers (Kels Dad) checking over my Manx engine, and he said that if Kel was going for the money he used to over rev the Norton, but they would have to check and replace the valve springs after the meet, in a normal GP meeting he would hold the revs to 7250.

I don't think there would be a great HP gain but maybe more flexibility due to wider torque range which results in an easier ride but quicker.

I would like to know what torque they are getting out of the latest speedway 500cc engines as they certainly hoot along.

Burgs

Burgs,

I intend to talk to Andy Molnar sometime soon so hope to glean a bit more info then.

From what I can gather, the 95mm bore short strokes are north of 60rwhp and weigh 118kg. To put that into perspective, a MK111 Commando would need around 110rwbhp to match the power to weight ratio (whereas they‘re low 40s in reality, good ones at least).

I think increased revs is the only route to more power, the BMEP is about as good as it can get now, so more bangs per second is the only route to increased propulsion, until we find a different understanding of physics at least !

Of course, a narrower power band is fine with a modern 5, or even 6 speed box. To a degree…

But what I don’t know is, does that extra BHP come at a (to me at least) unacceptable loss of lower end torque. I’ve spoken in depth to a couple of guys running modern 86mm x 86 (one Summerfield and one Molnar) and they rave about the broad spread of power and torquey engine. I don’t need Harley style torque… but I don’t want a 4 stroke 2 stroke either !

can now get CNC machined inlet tracts, which helps with repeatability of critical dimensions, and running on thin modern oils may help slightly?

jan nelder said:

can now get CNC machined inlet tracts, which helps with repeatability of critical dimensions, and running on thin modern oils may help slightly?

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Yup all of that, plus reduced valve angles allowing repositioned valves and a redesigned combustion chamber.

This also allows compression ratios that were previously not possible (due to having valve to piston clash risks) and which can be run on good super unleaded petrol.

90 years of continual development pays dividends !

You still have the modern noise limitations, silencers steals horsepower.
Mine has 11:1 CR at .030" squish, needs double spark plug gaskets to keep plug gap.
Intend to run a dyno test this winter if time allows.

Mike40M said:

You still have the modern noise limitations, silencers steals horsepower.
Mine has 11:1 CR at .030" squish, needs double spark plug gaskets to keep plug gap.
Intend to run a dyno test this winter if time allows.

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Yes, modern silencer requirements definitely steal power. I’m also not sure that side of things has been fully developed yet personally.

Fast Eddie said:

Burgs,

I intend to talk to Andy Molnar sometime soon so hope to glean a bit more info then.

From what I can gather, the 95mm bore short strokes are north of 60rwhp and weigh 118kg. To put that into perspective, a MK111 Commando would need around 110rwbhp to match the power to weight ratio (whereas they‘re low 40s in reality, good ones at least).


When F750 racing,or whatever it was called,kicked off in the UK , there was I thinkan overbored Petty Norton among the hopefulls ... It gotnowhere and one wonders why. It presumably would have been around 60bhp.. I think if memory serves me Hailwoods gave around 50...

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Interesting subject.. the Manx was builtfrom reynolds 531...there may be ighter and stronger tubing available for those not interested in period correctness

oldmikew said:

Interesting subject.. the Manx was builtfrom reynolds 531...there may be ighter and stronger tubing available for those not interested in period correctness

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Not if you're bending the tubes, hot or cold. There are incredible steel micro alloys available, but they generally get their strength from hardness, which doesn't lend itself to forming, even with a high dollar (6-figure) CNC mandrel bender.

Reynolds' (for instance) most up-to-date (non-Austentic stainless) alloy is 853, which is heat treated and would not respond well to forming, and you'd not be able to find it in walls and lengths to build a moto frame to begin with. Reynolds does offer a 631 alloy, which is a bit stronger than 531, so can be drawn thinner, resulting in a lighter frame, but not by much. Mmmaybe a pound. 631 is a cold formed, (non-heat treated - so good for forming) air-hardening alloy, meaning it gets to it's final ultimate strength within the HAZ after a fusion weld or bronze braze. It is offered in diameters, walls and lengths appropriate for moto main frames, but you'd be back to 4130 for the subframe, gussets, and fittings.

...But really not worth the huge extra expense for the absolute marginal weight saving over an off-the-shelf 4130 frame.

There's titanium, but Lordy, that would be expensive, and you'd have to reasonably increase all the diameters if you don't intend to wiggle down the track and guess where you'll be exiting all the corners. Would be an exciting ride though!

Interesting stuff there. How does T45 stack up in your comparison above? It’s a popular with several builders I believe.

I read years ago that the original 531 frames were supposed to be re annealed every couple of seasons and replaced after a certain time. Anyone know if that’s true or just folklore ?

So far my -59 frame has no problems. But Ken Sprayton ( The frame man ) had a lot to do during the TT. Though I don't push my bike as hard as they did back then.
More concerned with the 60+ old magnesium alloy parts.

Fast Eddie said:

Interesting stuff there. How does T45 stack up in your comparison above? It’s a popular with several builders I believe.

I read years ago that the original 531 frames were supposed to be re annealed every couple of seasons and replaced after a certain time. Anyone know if that’s true or just folklore ?

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You know, I'm not very familiar with T45. It's not common in the States. Most, if not all, 4130 and T45 tubes will be seamless drawn, and have similar alloying elements, but the devil is in the details. For instance, 4130 is easier to weld compared to 4140, which is easier to machine, but the differences in the alloying elements are minute. Tiny changes of molybdenum, chromium, manganese, etc, create vastly different working properties.

My "expertise" in metallurgy is only based on my career in steel fabrication, so I only really spend time on things that are directly pertinent to the job at hand, rather than a lifetime of research on alloying theory. How T45 stacks up is not something I've ever spent energy on, but I believe it's not quite as hard and tough as 4130, which would make it easier to form. Don't know how it fusion welds, but I'd guess by the European popularity, it welds well. I'd be happy to learn if anyone has first-hand experience.

I'd guess if one were to re-anneal a complete bike frame, you'd be looking to reintroduce some ductility to the work hardened areas of the frame, making the entirety a bit softer. I would expect better results from heat treating a frame to make it harder/tougher and just retiring the frame after a number of years of hard racing. Then again, if the bike has one of those turnbuckle head steadies, maybe a bit of softness would be better? In either case, the desired end result would be a more homogeneous structure that would disperse more force throughout, rather than having failure prone heat affected zones (HAZ) at the joints.

Considering Francis Beart used to change all bearings between every meet, maybe it's all just superstitious mental hocus pocus, and it doesn't really matter.

I have no first hand experience. But I can tell you that Andy Molnar says this about his frames: “Featherbed frame and swing arm, made to original drawing but using lighter gauge T45 tube” and that he welds them.
Whereas I know of at least three other featherbed frame makers who also use T45 and the braze them together.
I‘ve had several T45 frames, inc a Manx rep, and can confirm they felt light, especially next to a ‘steam pipe’ road bike featherbed frame! But I’ve never compared to a genuine Manx. I can also confirm that they held up well in use. The only frame I’ve ever broken in race use was a ‘steam pipe’ original slimline frame.

Fast Eddie said:

Burgs,

I intend to talk to Andy Molnar sometime soon so hope to glean a bit more info then.

From what I can gather, the 95mm bore short strokes are north of 60rwhp and weigh 118kg. To put that into perspective, a MK111 Commando would need around 110rwbhp to match the power to weight ratio (whereas they‘re low 40s in reality, good ones at least).

I think increased revs is the only route to more power, the BMEP is about as good as it can get now, so more bangs per second is the only route to increased propulsion, until we find a different understanding of physics at least !

Of course, a narrower power band is fine with a modern 5, or even 6 speed box. To a degree…

But what I don’t know is, does that extra BHP come at a (to me at least) unacceptable loss of lower end torque. I’ve spoken in depth to a couple of guys running modern 86mm x 86 (one Summerfield and one Molnar) and they rave about the broad spread of power and torquey engine. I don’t need Harley style torque… but I don’t want a 4 stroke 2 stroke either !

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I don't think it's quite that bad for the poor old Commando.

If the dry weight of the aftermarket Manx is truly 118 kg ( the Norton Manx was much heavier, about 140kg dry) then we need to add oil and fuel
So 118 kg is 265 lbs.
With 30 lbs of fuel and oil the weight is now 295.
Let's put me on it, as I would love to ride one someday!
295+ 240 ( inc gear) = 535
535÷ 60 rwhp= 8.92 lb per horsepower.
Thats a racing bike, no lights or charging system etc.
We could put a Commando in that condition and easily get the dry weight down around 380lbs.
Add the same 30 lbs fuel and oil and it sits at 410.
Add me or a similar sized rider and we have a total riding weight of 650 lbs.
650÷ 8.92= 73 horsepower

That's a lot for a Commando, but it is possible, as you know! To be straight, it does require replacing the entire engine and gearbox with Commando look alike performance items.


It is also possible to build the Commando at 300 lbs including road equipment.
I won't bore you with those numbers, but the do get quite good vs the Manx.

Glen

I’m not entirely sure what you’re getting at? Of course, if you reduce the weight and increase the power (of anything) you’ll increase the power to weight ratio!

Although I didn’t call it out specifically, I was referring to a standard weight, standard power mk111.

But even with your figures, you’d still need 73 REAR WHEEL hp to keep up with the Manx…

And I think we both know that although that’s possible, there ain’t many of them in real life !

My point was simply by way of comparison, for anyone who enjoys their stock MK111… imagine what it would accelerate like with a little over double the horse power. Cos that’s what a modern Manx must be like!