commando crankshafts

hi all
does anyone here no if the dowel hole on the crankshaft flywheel off norton commando 850 is the same diameter between mk2 and mk 3
because i am looking at getting molnar flywheel which is made for early crankshafts mine is a mk3 crank i allready no that i have to drill the bolt holes out to 3/8 but what about the dowel hole

The 850 Mk3 crank has a dowel stud...

...earlier cranks had a dowel.

L.A.B. said:

The 850 Mk3 crank has a dowel stud...

Andover Norton Parts Drawings - Andover Norton Factory Parts - Commando Parts

Andover Norton Parts are the only Norton spare parts in the market manufactured to original drawings, within the factory-approved tolerances, from the correct materials, and with the correct finish.

andover-norton.co.uk

Andover Norton - CRANKSHAFT DOWEL STUD - 06.5671

CRANKSHAFT DOWEL STUD

andover-norton.co.uk

...earlier cranks had a dowel.

Andover Norton Parts Drawings - Andover Norton Factory Parts - Commando Parts

Andover Norton Parts are the only Norton spare parts in the market manufactured to original drawings, within the factory-approved tolerances, from the correct materials, and with the correct finish.

andover-norton.co.uk

Andover Norton - DOWEL (NMT 2105) - 06.7558

DOWEL (NMT 2105)

andover-norton.co.uk

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But, in answer to the question - if the dowel & dowel stud are the same diameter then the earlier dowel with fixing plates would work well, no?
...and knowing Norton, they would not change tooling unless absolutely necessary!

robs ss said:

But, in answer to the question - if the dowel & dowel stud are the same diameter then the earlier dowel with fixing plates would work well, no?

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I don't believe they are the same.

why not ask Mr Molnar himself - if its made to order perhaps he'd make it for the MK3?

Molnar should speak for himself, but the answer when I made an enquiry for a variant of his billet crankshaft was, he needed to make a minimum of 10 pieces, and I had to provide the engineering drawings.
Fair enough, the man needs to get his merchandise sold. Count me in for a couple of samples, if you are able to place a bulk order.

What wonders me is, why doesn't AN produce a Mk3 billet crankshaft? Yes, several dimensions are different to the existing version, but the basic layout is identical. and the manufacturing sequence should be identical. Few preparations would be necessary, so paying for development costs should require only few samples sold.

- Knut

Exciting news!
Molnar will start making Mk3 crankshafts, but he needs a minimum order of 3 pcs. to get into action.
They can be either short-stroke or long-stroke. As I am prepared to order two samples, who will join me?

-Knut

mdt-son said:

Molnar should speak for himself, but the answer when I made an enquiry for a variant of his billet crankshaft was, he needed to make a minimum of 10 pieces, and I had to provide the engineering drawings.
Fair enough, the man needs to get his merchandise sold. Count me in for a couple of samples, if you are able to place a bulk order.

What wonders me is, why doesn't AN produce a Mk3 billet crankshaft? Yes, several dimensions are different to the existing version, but the basic layout is identical. and the manufacturing sequence should be identical. Few preparations would be necessary, so paying for development costs should require only few samples sold.

- Knut

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Yes, it's an easy engineering task to make MK3 crankshaft's, but there needs to be the volume to make it viable. Andy is being very generous in doing three as a MOQ. In the past 4 years I have only been asked for one MK3 crank. Trying to guess demand is hard, I wish I made more unbalanced crankshafts these have now sold and the customers are well happy with them.

When talking to Molnar ask about the studs that go thru cheek pieces and center section. The AN replacements are not the interference fit that I would like to see. I called ARP and they were not interested in making them. Another thing to ck when drilling 3/8 holes and assembling.

mdt-son said:

Exciting news!
Molnar will start making Mk3 crankshafts, but he needs a minimum order of 3 pcs. to get into action.
They can be either short-stroke or long-stroke. As I am prepared to order two samples, who will join me?

-Knut

Click to expand...

If there are 3 pieces which make billet crank production viable, what is the price per piece when it is a viable activity ?

acotrel said:

If there are 3 pieces which make billet crank production viable, what is the price per piece when it is a viable activity ?

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You can assess it yourself by visiting MPL/TGA:

- Knut

mdt-son said:

You can assess it yourself by visiting MPL/TGA:

Norton Twin Engine

Engine Parts Norton Twins Dominator Commando Tritons Cafe Racers

www.tga.co.uk

- Knut

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If you mean this - it is not a billet crank, it is 3-piece.
The crank in my short-stroke 500cc Triumph engine was billet - forged one-piece.
When you rev a 3 piece crank, you rely on the bolts to hold it together as it changes shape. If it is balanced for high revs it is probably better. I limit my standard crank to 7,300 RPM - sensibly it could go to 8000 RPM. But I am chicken.

acotrel said:

If you mean this - it is not a billet crank, it is 3-piece.
The crank in my short-stroke 500cc Triumph engine was billet - forged one-piece.

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I would have preferred a one-pice crankshaft, but if no one is available at the counter, you have to use what's there. "billet crank" is not a design feature term, it just means the crankshaft (bits) are made of steel billets, i.e, a rolled or forged lump of steel. So. a 3-piece crankshaft can still be a billet crankshaft, it depends on the manufacturer's choice of material supply and manufacturing. The alternative to using billet material is the use of a cast material (an ingot).

To be more precise, if a non-bolted billet crankshaft is important to you, you will have to ask for a "billet one-piece crankshaft".

Have you ever heard of a standard 3-piece Norton crankshaft exploding due to ruptured bolts? I haven't. Those 6 high-tensile bolts form a stiff joint with the 2 outer bolts resisting the cyclic tensile load due to bending. A one-piece crankshaft offers more bending stiffness at the center section, but for a road bike running at medium revs and occasional high revs, the bolted crankshaft is good enough. For a high-reving race engine, the 3-piece crankshaft works too, provided you replace the crankshaft bolts regularly.

The bolted joint of a 3-piece creankshaft will have to be manufactured to close tolerances of course. If done rigfht, the crankshaft is balanced and behaves exactly as a one-piece crankshaft. The balance factor is determined based on the rev band mostly used, so a race engine will usualle be balanced differently to a road engine. Balancing is not an issue when discussing these crankshaft designs.

- Knut

I suggest that if you can shine a strobe light on a normal Commando crank spinning at 7000 RPM, you could watch the centre grow bigger, as the bolts stretch. My balance factor is 72%, and at 7000 RPM, when I change up, I usually see about 7300 RPM. It feels as though it wants to go to 8000 RPM.
I have had Triumph 650 motors and revved every one of them regularly to 8000 RPM. However I am not prepared to do it with the Norton 850 motor, and the way I use that motor - I do not really need to.
The Commando 850 motor is a piece of shit, however It really works. I am surprised it is so good with so little modification. When I raced it, I beat 4 cylinder 1970s superbikes which were also using methanol.
To my mind, it should not be able to do that. The first time I looked inside it, I shuddered. The only reason I bought it, was it was similar to what Gus Kuhn used in the same MK3 Seeley frame.

It might be interesting to get one of the new 961 motors and race it in a Seeley frame. With some things speculation is no substitute for experience. Speculation is what many university professors do. They often get two points then extrapolate, without recognising the pattern. The Norton Commando motor does not make sense when you rationalise it normally. I really like it.
I did not know how to use my Seeley 850, until the last time I raced it, and I might never get back there again. But it amazed me that it can be so effective, and easy to ride, when you know how to use it. You just flick it into a corner while braking behind the guys in front of you and almost immediately blast under and past them. It does not take brains.
I learned to race by crashing.

How is balancing not an issue when looking at crankshaft design, surely the rotating mass and the weight of the pistons etc need to be considered along with the working envelope the crank will to fit and rotate in.

Madnorton said:

How is balancing not an issue when looking at crankshaft design, surely the rotating mass and the weight of the pistons etc need to be considered along with the working envelope the crank will to fit and rotate in.

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It's an issue if you consider design out of context, but in this case (Molnar's crank design vs. AN's one piece crankshaft, for instance) balancing is not an issue, meaning balancing is straightforward and can be dealth with in the same manner as a standard Norton crankshaft, except in case of Molnar's crankshaft, the bolt-on counterweights can be manipulated rather than the flywheel itself.
Do you see a principal difference?

- Knut

PS. For clarity, I added "these crankshaft designs". We are not discussing general crankshaft design here.

acotrel said:

I suggest that if you can shine a strobe light on a normal Commando crank spinning at 7000 RPM, you could watch the centre grow bigger, as the bolts stretch. My balance factor is 72%, and at 7000 RPM, when I change up, I usually see about 7300 RPM. It feels as though it wants to go to 8000 RPM.

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Al, you are probably right, and so what? It just means the counterweights need to be of slightly different size (and probably larger) for a race engine operating in this rev band. BTW, do you think your one-piece crankshaft is completely straight at 7500 rpm? Think again.

Crankshaft deflection will be accounted for when spinning the crankshaft at the balancing machine. Outer bearings are also affected by crankshaft design (in this context) but that's another discussion and NV already adressed it.

- Knut

Gents,
latest news from Andy is that no one has stepped forward to order a new Mk3 crankshaft. That's sad.

He also conveyed to me that if he is going to make them, the bolt pattern and size will be to 750/850 spec, as the deviating Mk3 pattern requires new tooling which isn't commercially viable.

- Knut

I don't think Andy will be holding his breath on anyone contacting him, there is just not the demand for MK3 cranks or pieces.
Surely it would be cheaper to pick up a basket needing restoration and break it for the spares you need, or search globally for the piece you need.