Billet Crankshaft

acotrel

acotrel

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Jun 30, 2012
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About 50 years ago, my friend/rival built a 650 Triumph twin racer for a wealthy car guy. In discussions prior, I mentioned Puma cases and Nourish crankshafts. BOth were purchased, and built into what was effectively a Bonneville motor. I loaned my two Triumph race kit pipes to get the bike going. The car guy rode the bike at Calder Raceway and immediately crashed it. That bike has a history of winning many Pariod 3 HIstoric championships in the hand of Noel Mercer - who is no slouch as a rider.
I was wondering who makes billet cranks for 850 Commandos. When I was building my 850, I was always too lousy or skint to make a crank. In any case, appropriate steel if bought in Australia might have a lot of sulphide inclusions, and be more likely to break.
During my life, I have learned something about money - it comes and it goes. I think a billet crank with Jim Schmidt;s long rod and light pistons might be excellent for raising the rev limit.
Who makes them ? If I get rich again, I would probably invest.
 
it may not be billet( one piece) , but the Molnar/TGA seems very good spec materials etc, at £1850.
 
jan nelder said:
it may not be billet( one piece) , but the Molnar/TGA seems very good spec materials etc, at £1850.
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It seems to be the only easily available crank at the moment after the demise of Nourish (Billet) and Maney (3 piece) as suppliers.

When they were both available, you could choose lightweight Maney or heavyweight Nourish to suit your preference. I prefer lightweight for a race bike, but the heavyweight might be a better choice for road use.

When last available both of those were lower priced than TGA, the Maney one I bought was around £1500, including special stroke and balancing, but that was over 10 years ago. Nourish would have been cheaper.

I don't think the 3 piece construction has limited potential rpm as much as the valve gear.

Something I am learning about getting older.....the likelyhood of getting rich (again!) reduces.....but the time wasted dreaming about how you might spend it doesn't! :p
 
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Here's what I have seen in the states Al. They are halfway down the page and if you aren't familar with American vintage flattrack its a good page of ads to read. Made in Michigan, the heart of the US steel industry by guys who know what they're doing. Yeah i'm trying get rich again, relatively speaking, so I can do the same motor build. Good luck with it, i'm headed to the shop.

 
edgefinder said:
Here's what I have seen in the states Al. They are halfway down the page and if you aren't familar with American vintage flattrack its a good page of ads to read. Made in Michigan, the heart of the US steel industry by guys who know what they're doing. Yeah i'm trying get rich again, relatively speaking, so I can do the same motor build. Good luck with it, i'm headed to the shop.

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Great link and thank you for posting it.
Dangerous though, way too easy to start buying those upgrades I keep telling myself are so badly needed.
 
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I am really kicking myself. Unti 1983 I worked in an ordnance factory making better gun barrels. I was so busy that I did not ask whether a billet crank could be made there and at what cost. It was only wnen I was moving up to my next job, that I discovered our factory would have been happy to make it, and the guys in the Planning Section would have made sure it was cheap. THe next job I had was Head Of Laboratories in an explosives factory.
I have never been money-motivated - only ever applied myself out of interest. My Seeley 850 is just something I developed out of interest. It amaazess me how much potential it has. A billet crank would be another step forward.
The three piece crank is held together with bolts. I think if it could be watched with a strobe light when it is spinning at 7000 RPM, it would be seen to grow bigger in the middle.
I do not know if I will ever race again, but I do not want to leave the project while it is still not finished.
I now actually believe the heavy crank is the right way to go. But the Norton crank might have been better if it was one-piece. Another 1000 RPM would be good. My motor will go there easily with a bit of valve work..
Whenever I rode my Seeley 850, I felt as though I was sitting on a bomb.
That crash Doug McRae had at Daytona was a really big one. We should not have to ride with much restraint.
Triumph did not seem to have much trouble making the Bonnelille twin crank one piece.
 
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I have never raced to win races. For me, it was always about developing the bike. Technically road racing is extremely interesting and doing it well is difficult. So it is worth doing.
A lot of thought has gone into my Seeley 850. When I built it, I had a head start. I had raced my Triton 500 for a long time and I had a fair idea about what actually works. I built the Seeley 850 because something like it had previously existed and had been raced successfully.

 
You guys probably think I am a bit strange. What I look for in life is mental exercise. My ego counts for nothing. When I raced, it was only ever about doing it better. If you are mid-field in a road race, somebody will always have a go at you. If you can out-ride them, you have achieved. In my life, I think I have only ever won two races. It does not matter because I was never about becoming the best road racer in the world.
In a minute my Seeley 850 will probably end up in the hands of somebody who will not know how to use it to best advantage.
 
edgefinder said:
Here's what I have seen in the states Al. They are halfway down the page and if you aren't familar with American vintage flattrack its a good page of ads to read. Made in Michigan, the heart of the US steel industry by guys who know what they're doing. Yeah i'm trying get rich again, relatively speaking, so I can do the same motor build. Good luck with it, i'm headed to the shop.

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That is one vey cool website..
Thanks....👌
 
When I was a kid, I had several 650 Triumphs and have broken one of the three piece cranks. It happened when I rode the bike over a rise at high speed. A journal broke, but the motor did not explode and I was able to ride the bike very slowly home. I had heard the rattle.
The only reason I raced and persevered with my 500cc short stoked Triton was it was almost impossible to blow up. So it was cheaper, and almost fast enough to compete with bigger capacity bikes.
The first time I raced the Seeley 850, I had not raced during the previous 20 years. You would not want to know it, an 1100cc CB750 Honda spread its motor in front of me during the start. I just jumped sideways and went around it. Luckily there was no-one coming from behind me.
The 63mm stroke billet crank in my 500cc was made the right way, the flywheel was held on the same way as in the 60s 650 motors - with the radially located bolts and a dob of weld on each head.
The one-piece Triumph 650 cranks are good, but the one with the light flywkeel is worthless. I don't think the heavy flywheel can be bought as a spare.
With my Norton 850 crank, I have corrected the balance factor by screwing and gluing a steel plug into the hole in the counterweight of the flywheel.
The last time I raced. out of three starts, I only got one good one. - because I was using a 4 speed close ratio box with a very high first gear. In that start, I revved the motor to about 5,500 RPM and dropped the clutch. With the heavy crank, it does not matter which gear you use, if you rev the motor high and drop the clutch, the bike will jump fast emough.
After that race I bought the TTI 6 speed close box which should make things easier. But that steel plug in the crank is still a worry - it should not be there.
My old mate also rode my Seeley 850 a few times, but he also knew how to survive a crash.
The next guy who gets my Seeley 850 needs to know about the crank. A motor exploding at high speed is very dangerous - on the start line is bad enough. When you are racing, you need to know what is likely to happen. A crank letting go, might come from nowhere.
 
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Plenty of people develop their bikes way beyond the specification and time of life they can ride it. Pursuit of improvement is a natural desire.

Admitting to yourself that it's time to put someone else's arse on it is more difficult.
 
Al, All the old racing talk aside, I doubt you could break a 3-piece Molnar crank today unless you tried intentionally to do it.

I know how well JSM parts work for spin up and high revs. Very well is my take. My next build coming up soon will have a Molnar crank in it as well as a lighter clutch. Goal is a 360lbs Norton 750 based twin hot rod sleeper with a license plate. Not in a Commando frame though. A lighter slightly shorter P11 frame.

Point is yeah a different crank from what you have and the JS rods, pistons, and valve train would do what you are imagining.
 
Schwany said:
Al, All the old racing talk aside, I doubt you could break a 3-piece Molnar crank today unless you tried intentionally to do it.

I know how well JSM parts work for spin up and high revs. Very well is my take. My next build coming up soon will have a Molnar crank in it as well as a lighter clutch. Goal is a 360lbs Norton 750 based twin hot rod sleeper with a license plate. Not in a Commando frame though. A lighter slightly shorter P11 frame.

Point is yeah a different crank from what you have and the JS rods, pistons, and valve train would do what you are imagining.
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Agreed. Although a billet crank certainly seems intuitively better, bolt up Maney cranks don’t break, at least not via the bolts. Then again, AFAIK stock cranks don’t even break there either.

So, there’s no need to let unavailability of a billet crank stop you Al.

Molnar’s crank is also heavier than Maney’s, so would appear well suited to your needs.

And conveniently… Molnar’s cranks are available… just a phone call and credit card away…
 
edgefinder said:
Here's what I have seen in the states Al. They are halfway down the page and if you aren't familar with American vintage flattrack its a good page of ads to read. Made in Michigan, the heart of the US steel industry by guys who know what they're doing. Yeah i'm trying get rich again, relatively speaking, so I can do the same motor build. Good luck with it, i'm headed to the shop.

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Hi edgefinder,
Do you have any info on Ro-Dy crankshaft quality via reviews etc? Also, do you know if they are still in business?
Thanks,
Ed
 
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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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Billet Crankshaft

Billet Crankshaft

Billet Crankshaft

Billet Crankshaft


Ro-DY Billet Process
 
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