Billet Crankshaft

Al, when is that last time you started your Seeley 850 and rode it?

I started and test rode my Norton a few miles yesterday. It is a nice 750 rider with a lightened stock crank and a good selection of JSM parts in it. Makes me happy anyway.

I'm too much of a simpleton to worry about all that 3-piece crank flexing science, and I don't race, so I don't stay at high revs that long. I just happen to like a motor that spins up quick, and I do not short shift. All the lighter weight parts make sense to me for my style of riding.

Mr Molnar uses a balance factor of 75% for solid mounted Norton twin engines, and 52% for ISO mounted engines. My current crank is 62% and smoothest at lower RPMs, or when close to 7000 RPM when the entire package wakes up. Mr Molnar says I'll like my ride a lot more with his crank. Of course one would expect him to say that, but I actually believe on top of making a sale he knows what he is taking about. I also choose TGA because TGA balances the cranks to the customers rod and piston specifications before shipping the cranks out. I'm not sure if the nice billet crank manufacturers do that. I don't think Ro-Dy does, which means somebody else has to get involved. I have too many cooks trust issues. :)
 
acotrel said:
I think that when a 3 piece crank spins high, the bolts that hold it together must stretch and allow the crank a certain amount of bend, depending in the balance factor. If the balance factor is low, there is a lifferent radial load on the centre due to centrifugal force, than if the balance factor is high. It has always been my opininion that Japanese motorcycle engines get their power from revving high with lighter internals. So material properties are probably not so important. Comparing British bikes to Japanese might be like comparing a Bentley to a Bugatti. The concept is different.
I don't like Japanese carburettors, because I think the zinc content of the aluminium is too high. Most fuels these days contain ethanol. The steel which is used in Japanese motors is probably made in mini-mills and might not have so much in the way of alloying elements. In their motors, it might not matter so much, because their motors usually do not slog. Even in the old days Manx Nortons would sometimes crack a flywheel.
But I have always believed British bikes are made of better stuff than Japanese. What happens with a Commando crank is probably a lot different from what happens in a Japanese motor. We should be able to rev a Commando motor to 8000 RPM easily, without failure. I do not think stronger crankcases are the answer. I think the Atlas motors used to cop 8000 RPM. That extra 1000 RPM in the rev limit,, might make a big difference My 850 motor often sees 7300 RPM on upchanges, and it feels as though it can spin higher very easily. Just not wise to do it with a 3 piece crank ? Why do the good main bearings in Norton motors have barrel-shaped rollers - to accommodate the bend in the crank at high revs ?
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I think you're wrong with logic on bolt-up cranks.
The middle inch(ish) of a "billet" crank does very little to resist bending.
The ring of bolts/studs in a "bolt-up" crank are far less in area than the outer metal in a "billet" crank but make up for that in 2 ways in that they:
1. Are usually a much higher grade than the parent steel of the crank.
2, Are stressed to "proof" - i.e. just past the limit of elastic elongation, so have an extremely high clamping force holding the whole thing together.

Something that would definitely be superior to a machined "billet" crank would be one that was upset forged from something very high strength (EN26 maybe) and "finish" machined afterward.
The upset forging process creates granular flow lines near corners and also locks helpful stresses into the crank.
Haven't heard of it being done for a Norton - maybe someone else has.
 
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The Nourish Triumph cranks appear to be made out of a piece of bar stock without forging. Then two flats are machined to create the weight bias. The shaft ends up almost trianguler when looked at end on. I was a bit surprised when I first saw it, but I cannot think of any reason the flywheel needs to be round. The trouble with making a crank that way is, if there are going to be sulphide inclusions, the would probably be in the centre where the main bearings and drive take-off are. In big barstock, there is sometimes a pipe up the middle
My friend who built that Triumph motor had also built a Triumph motor using a Norton crank. So It might be possible to fit a crank from a 1960s Triumph 650 into a Commando motor, using an adapter for the oil pressure at the drive end.
 
acotrel said:
The Nourish Triumph cranks appear to be made out of a piece of bar stock without forging. Then two flats are machined to create the weight bias. The shaft ends up almost trianguler when looked at end on. I was a bit surprised when I first saw it, but I cannot think of any reason the flywheel needs to be round. The trouble with making a crank that way is, if there are going to be sulphide inclusions, the would probably be in the centre where the main bearings and drive take-off are. In big barstock, there is sometimes a pipe up the middle
My friend who built that Triumph motor had also built a Triumph motor using a Norton crank. So It might be possible to fit a crank from a 1960s Triumph 650 into a Commando motor, using an adapter for the oil pressure at the drive end.
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As long as you're prepared to accomodate the performance compromises that come with Triumph parts;)
 
Schwany said:
Al, when is that last time you started your Seeley 850 and rode it?

I started and test rode my Norton a few miles yesterday. It is a nice 750 rider with a lightened stock crank and a good selection of JSM parts in it. Makes me happy anyway.

I'm too much of a simpleton to worry about all that 3-piece crank flexing science, and I don't race, so I don't stay at high revs that long. I just happen to like a motor that spins up quick, and I do not short shift. All the lighter weight parts make sense to me for my style of riding.

Mr Molnar uses a balance factor of 75% for solid mounted Norton twin engines, and 52% for ISO mounted engines. My current crank is 62% and smoothest at lower RPMs, or when close to 7000 RPM when the entire package wakes up. Mr Molnar says I'll like my ride a lot more with his crank. Of course one would expect him to say that, but I actually believe on top of making a sale he knows what he is taking about. I also choose TGA because TGA balances the cranks to the customers rod and piston specifications before shipping the cranks out. I'm not sure if the nice billet crank manufacturers do that. I don't think Ro-Dy does, which means somebody else has to get involved. I have too many cooks trust issues. :)
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Schwany, the last time I started my Norton was before two of my friends died a few years ago. Since then I have been battling a grief problem and the raceway has gone stupid. When I rode it, I had just fitted the 5 speed box, and everything which could go wrong, did go wrong.
I have since pulled the whole transmission apart and now only have a few bits to re-assemble. But I lose enthusiasm too easily. For me, my Seeley 850 has just been another interesting development project. But when the weather cools off, I intend to ride it again to make an on-board video. I have always tried to make the bike as good as it can be, and the last time I raced I probably achieved enough to satisfy most people. I just have this weird mindset which makes me feel my efforts are incomplete.
I would like to see how the bike would perform, if it's motor could be revved reliably to 8000 RPM. Even when it is revved to 7000 RPM, it is fast enough to win. And that really surprises me.
I am not bragging when I say that I ride a bit better than most other guys. I shudder when I think about the way i learned to do that. - IDIOCY ! But I am still competent.
I never believed my Seeley 850 could be so ugly inside and still do anything. It sat unraced for 20 years. I built it in 1978 and first raced it in 2001. I think I have only raced it 4 times. But for me, it is the best ever and I have ridden a few.
Something so bad should not be so good. There is nothing really trick about it. I just built it and it worked.
 
robs ss said:
As long as you're prepared to accomodate the performance compromises that come with Triumph parts;)
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I don't think anybody has broken a one-piece Triumph 650 crank. The usual failure is pulling the back out of the crankcases. However the light one-piece Triumph crank is not worth having , unless the fly wheel is replaced. I don't think a flywheel can be bought as a spare part.
 
You are quite wrong about Triumph cranks Al. The weak spot is the sludge trap drilling. Even a 650 can break a crank through that big hole if revved high enough frequently enough.

A Norton crank is stronger than a Triumph crank for sure. The main weakness being the flywheel.

A Molnar crank will almost certainly be indestructible, Andy knows his stuff.

But even with an indestructible crank, you’ll not get any benefits from trying to rev to 8k without serious work to cams and ports etc.

This has been well documented by Comnoz and others. But I’m really not sure why you want to increase the revs so much in search of power given the amount of writing you have dedicated to teaching us all that increasing power has no benefit in racing …?!

But seriously, if all you want to do is have one last ride to document it on video, then why not just prepare it and ride it? You don’t need a new crank etc to do that mate.

As the old saying goes: “Life is what happens to us whilst we’re busy making other plans…”

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acotrel said:
Schwany, the last time I started my Norton was before two of my friends died a few years ago. Since then I have been battling a grief problem and the raceway has gone stupid. When I rode it, I had just fitted the 5 speed box, and everything which could go wrong, did go wrong.
I have since pulled the whole transmission apart and now only have a few bits to re-assemble. But I lose enthusiasm too easily. For me, my Seeley 850 has just been another interesting development project. But when the weather cools off, I intend to ride it again to make an on-board video. I have always tried to make the bike as good as it can be, and the last time I raced I probably achieved enough to satisfy most people. I just have this weird mindset which makes me feel my efforts are incomplete.
I would like to see how the bike would perform, if it's motor could be revved reliably to 8000 RPM. Even when it is revved to 7000 RPM, it is fast enough to win. And that really surprises me.
I am not bragging when I say that I ride a bit better than most other guys. I shudder when I think about the way i learned to do that. - IDIOCY ! But I am still competent.
I never believed my Seeley 850 could be so ugly inside and still do anything. It sat unraced for 20 years. I built it in 1978 and first raced it in 2001. I think I have only raced it 4 times. But for me, it is the best ever and I have ridden a few.
Something so bad should not be so good. There is nothing really trick about it. I just built it and it worked.
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Basically, I wanted to know if you would be riding enough to get much out of making the changes.

Are you really going to race again after putting it back together? You gots some serious nads if that is still your end goal.

What I am doing with my Norton is purely hobby stuff just to see if I can make it a little quicker. You have 8 years on me. In 8 years, I hope I still know where my driveway is.

Ugly stock parts work, and realistically would be enough for my use, but what would I do with my spare time? lol
 
My wife does not want me to race again, but my interest in my bike is probably what is keeping me alive. I definitely want to do the onboard video, and will probably do it when the weather cools down around April. There are a few logistics to be dealt with- such as actually getting access to the track, now that the car club who own it has gone stupid.
The other day, my wife took the young grand-daughter to our local pool. Just before she was about to leave, she stood in a step and her feet went from under her. She is now in a wheel-chair with a broken ankle and a very sore bum. I now see why she was worried about me racing. For me racing at Winton Raceway is not a problem - I could do it wearing a blindfold. But for her, me racing might be a big problem.
As far as the billet crank is concerned - if you were painting a picture, would you not want to complete it ?
When I ride my motorcycle, I always know what it is doing. If it does things better, I usually know it. If I race, I always change up at 7000 RPM, and down at 5,500 RPM, and I am conscious of whether the bike understeers or oversteers. With me, it is just a habit.
When I built the Seeley 850, it was only because it was a good thing to build. It now interests me to find out just how good it could actually be. The last time I raced it, it really surprised me. I did not ever think I could do something like that with it, when I rode under the three superbike leaders at turn two. I had them cold - they were never going to catch me. The clip for the fuel line is right up under the tank, and tightening it needs a very long screw driver. So it got missed.
 
I suggest the Commando is a very under-rated motorcycle. It has obviously been modified to become a moderately docile commuter when it could have been a sports' bike. It does not take much to make one really get up and go. - I never would have thought that.
In the 1970s, one of my mates told me Commandos were good, but he also told me I did not need a close ratio gear box, when he had never used one.
 
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Coula, Woulda, Shoulda! The Commando was already touted as "The First Production Superbike". Strange since Triumphs kept beating them at the Production 750 TT.

IMHO, since Norton actually designed and assembled motorcycles rather that built them, they were hamstrung. There's always extra cost when you sub things out.

Norton's actual problem was marketing and sales, not so much the product. Still today, if you design and want to sell a product, if you don't get the marketing and sales right you'll either fail due to buying too much product and not selling or buying enough but at such a high cost that the product costs too much to sell.

Norton, the bad/good: Cost more than others/Somewhat eliminated vibration.

Of course, this tread is not really talking about Norton Commandos - just some parts taken from Norton Commandos or possible aftermarket parts for Norton Commando engines.
 
In large population areas, most people probably do not need or want a high performance bike which vibrates when it is revving low. And runs smooth when it is going fast.
If the crank in a Commando is not rebalanced for high revs and you rev it high - seems to be the cause of cracked cases. But there is another thing, super-blend bearings fix a bearing failure problem - they probably self-align better. If the crank flexes when it is revved high, it might be due to a balance factor which is too low. The low balance factor might also slow the throttle response.
There is almost nothing which has been done to my 850 motor - when I try to change up at 7000 RPM, it is very difficult to avoid over-revving. I nearly always see 7,500 RPM. So I don't think much else might be stopping a normal 850 from revving high. - Certainly not cams or comp. ratio. A restrictive exhaust would. It is easy to lose 1000 RPM off the top that way.
 
acotrel said:
In large population areas, most people probably do not need or want a high performance bike which vibrates when it is revving low. And runs smooth when it is going fast.
If the crank in a Commando is not rebalanced for high revs and you rev it high - seems to be the cause of cracked cases. But there is another thing, super-blend bearings fix a bearing failure problem - they probably self-align better. If the crank flexes when it is revved high, it might be due to a balance factor which is too low. The low balance factor might also slow the throttle response.
There is almost nothing which has been done to my 850 motor - when I try to change up at 7000 RPM, it is very difficult to avoid over-revving. I nearly always see 7,500 RPM. So I don't think much else might be stopping a normal 850 from revving high. - Certainly not cams or comp. ratio. A restrictive exhaust would. It is easy to lose 1000 RPM off the top that way.
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I didn’t say an 850 can’t rev Al. I said that without port and cam work you’ll get NO BENEFIT in revving to something like 8k. But you do get to enjoy all the downside of increased wear and risk of blow up.

If you have regularly been revving a stock crank in stock cases to 8k you are incredibly lucky to have not grenaded the engine.

Unless you’ve changed the way the engine works significantly, it’s gonna produce peak power a little over 6k. Period.
 
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marshg246 said:
Coula, Woulda, Shoulda! The Commando was already touted as "The First Production Superbike". Strange since Triumphs kept beating them at the Production 750 TT.

IMHO, since Norton actually designed and assembled motorcycles rather that built them, they were hamstrung. There's always extra cost when you sub things out.

Norton's actual problem was marketing and sales, not so much the product. Still today, if you design and want to sell a product, if you don't get the marketing and sales right you'll either fail due to buying too much product and not selling or buying enough but at such a high cost that the product costs too much to sell.

Norton, the bad/good: Cost more than others/Somewhat eliminated vibration.

Of course, this tread is not really talking about Norton Commandos - just some parts taken from Norton Commandos or possible aftermarket parts for Norton Commando engines.
Click to expand...
They rarely won due to regular failures of the gearbox which did great service in the Matchless G3L...
I recently saw a photo of a late factory racer that actually had a Triumph gearbox fitted.
Returning to the subject at hand, British bikes in general have always had huge flywheels, possibly a function of the fuel they were designed around in the 1930s?
I seem to recall Nourish were big in sidecar racing, where the additional inertia of a heavy crank is possibly a good thing.
Bevel Ducatis redline at 7500 rpm. Didn't do Mike Hailwood any harm.
 
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I don't know if I am reading things right AL but you talk so much about how good your Seerly is then you come out and say you have only raced it 4 times, building it in 78 but racing it in 2001, that's a long time and by your own words really that's not much time at all, and for a stock motor to rev to 8000 RPMs now that's a big ask, I don't know reading all your post about racing your Seely am I missing something as you say one thing then now you are saying something different, I an confused,my 850 is balanced, has a hot cam and major port work running it up to 8000 RPMs for long periods of time would be pushing it, but you racing a stock motor at thoughs revs, something is not right, you be better to put a stock Norton GB in your Seely and ride it on the road instead of the track,as what you tell us and amount of time you have really spent on your Seely just don't make sense to me, I live to ride, your time on your Norton just don't add up but you keep telling us how good it is for such little time you have been on it.
Sorry if I am a bit spectical about what you say as you been drumming it into us for so long and really you haven't really ridden it that much by your own words, or am I missing something.

Ashley
 
acotrel said:
I think that when a 3 piece crank spins high, the bolts that hold it together must stretch and allow the crank a certain amount of bend, depending in the balance factor. If the balance factor is low, there is a lifferent radial load on the centre due to centrifugal force, than if the balance factor is high. It has always been my opininion that Japanese motorcycle engines get their power from revving high with lighter internals. So material properties are probably not so important. Comparing British bikes to Japanese might be like comparing a Bentley to a Bugatti. The concept is different.
I don't like Japanese carburettors, because I think the zinc content of the aluminium is too high. Most fuels these days contain ethanol. The steel which is used in Japanese motors is probably made in mini-mills and might not have so much in the way of alloying elements. In their motors, it might not matter so much, because their motors usually do not slog. Even in the old days Manx Nortons would sometimes crack a flywheel.
But I have always believed British bikes are made of better stuff than Japanese. What happens with a Commando crank is probably a lot different from what happens in a Japanese motor. We should be able to rev a Commando motor to 8000 RPM easily, without failure. I do not think stronger crankcases are the answer. I think the Atlas motors used to cop 8000 RPM. That extra 1000 RPM in the rev limit,, might make a big difference My 850 motor often sees 7300 RPM on upchanges, and it feels as though it can spin higher very easily. Just not wise to do it with a 3 piece crank ? Why do the good main bearings in Norton motors have barrel-shaped rollers - to accommodate the bend in the crank at high revs ?
Click to expand...
But......what bearings are you going to use with a billet crank? Same ones I reckon!
 
Bruno Perlinski builds some of the most competitive 750 long stroke Nortons in France, probably Europe.

We were talking about revving my short stroke to 8000, which I have done on occasion, but don't do regularly.

He told me he NEVER revs his motors above 7000rpm.

Wrong goal for an 850 for sure. Do remember that Maney built 1007 motors with 3 piece cranks.

I am with FE, a Molnar crank would not let you down....and if you have faith in the other parts....you talk about exploding flywheels......he can supply a flywheel only!
 
acotrel said:
Why do the good main bearings in Norton motors have barrel-shaped rollers - to accommodate the bend in the crank at high revs ?
Click to expand...
They are not barrel shaped, they have a bigger crown on the edges so as the crank starts to bend like a skipping rope the roller edges do not dig into the roller track. The 'Barrel shaped' explanation was marketing speak to make out the solution was a new feature when the bearing manufacturers had known about adding extra crown to the edges of roller bearings for heavily loaded applications. The whippy crank gave the same edge loading as a heavily loaded bearing so they applied the larger crown.

What is crowning in bearing?

In this bearing the radius of rollers are increased in the order of micrometers to avoid edge loading. This modified geometry is called crowning.
 
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