If going from stock crank to billet one...

The stock oil pump should be more than adequate for any normal Commando. If you've made mods that require more volume, then you might have problems. As I recall, comnoz had to add oil pump capacity when he was experimenting with oil jets pointed at the underside of the pistons for added cooling. If you were doing something else that needed a lot of oil, like maybe feeding oil to a turbo, you would probably have to add capacity.

I've always wondered what the story was behind the large oil pump that Norton added to the space frame JPN race bike. Does anyone here have any more info on it?





Ken

I read somewhere, they went to a trochoid pump because they went to an underslung oil tank and the gear pump needed a positive head whereas the trochoid didn’t. It doesn’t seem to have any extra external pipes for oil squirters but who knows what they were doing inside?

SeeleyWeslake said:

I read somewhere, they went to a trochoid pump because they went to an underslung oil tank and the gear pump needed a positive head whereas the trochoid didn’t. It doesn’t seem to have any extra external pipes for oil squirters but who knows what they were doing inside?

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That would go with my experience. My old Norton racebike had an oil tank under the motor. I had to use a trochoid oil pump for supply as the original oil pump would not pull enough depression to dependably pick up the oil from the tank. Jim

Does anyone know this company's reputation?

http://farndon.com/index.html

Oddly stroke and bore are in metric size (why that?) Are crank journals also in mm? How much should they be? With which tolerance?

Nitrited yes, but at which depth for a 850?

Nitriding is only a surface effect. If you are talking about it's depth, perhaps you are thinking of case-hardening. If you have excessive wear, you might need to hard chrome the journals. I've only ever needed to do that in a short-stroke motor which revved to 10,000 RPM regularly during racing.
I suggest the oil system on the space frame racer might have a lot to do with oil temperatures while racing on the IOM. Jim Comstock uses oil radiators on his road bike and has a modified oil system. It might be necessary when you use petrol as a fuel - one of the joys of using methanol - you don't cook your motor, that is why I always race using it.

acotrel said:

Nitriding is only a surface effect. If you are talking about it's depth, perhaps you are thinking of case-hardening. If you have excessive wear, you might need to hard chrome the journals. I've only ever needed to do that in a short-stroke motor which revved to 10,000 RPM regularly during racing.

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A friend of mine did it for his BMW crank.

acotrel said:

... that is why I always race using it.

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I'm not going to race it ;-)

acotrel said:

Nitriding is only a surface effect. If you are talking about it's depth, perhaps you are thinking of case-hardening.

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Not true. Nitiriding is a case-hardening process, and the depth depends on how long you leave it in the gas or salt bath, as well as some other parameters. Typical case depth on 4130 steel is .008" to .024". There are other metods besides the gas and salt bath, but they are not usually used for things like crankshafts.

Ken

I had the 63mm crank in my Triton gas nitrided. It still seemed to wear quickly. I had a discussion about the problem with my boss who was a metallurgical engineer. He made the statement about gas nitriding only being a surface effect. That is when I hard chromed the journals in the bath we used for plating the bores of 5 inch gun-barrels. When I had the crank re-ground, the guys at the machine shop said it was the best hard chrome they'd ever seen. The bath was regularly adjusted, cleaned and refrigerated. Even if you are not racing, crank wear can still be a problem, especially in short stroke motors if you regularly rev the tits off them.
What interests me is the material used for making billet cranks in the US and UK. Where I worked we used to make gun barrels using 3% nickel 1% chromium steel. It was made using an electric arc furnace with selected scrap. There was always a problem getting the sulphur and phosphorus contents low enough to avoid failures during mechanical testing. If you do a sulphur print on the end of any piece of barstock there is almost invariably an inclusion (pipe) right up the middle - right where the mainshafts would be in a billet crank. Very late in the piece, a smart young engineer decided we didn't need to do the hard yards, and bought an Australian made commercial product with certificate, to make barrels - the exercise was hopeless.
Decent material has sulphur and phosphorus levels down around 0.005 %. Perhaps the material you guys are using to make your billet cranks is made in vacuum degassed furnaces ?

acotrel said:

Perhaps the material you guys are using to make your billet cranks is made in vacuum degassed furnaces ?

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Yes. Typically 4340 VAR (vacuum arc remelt), or equivalent. Usually VIM/VAR, vacuum induction melt first, and vacuum arc remelt afterwards.

Ken

We don't have an aircraft industry in Australia. So decent material must be imported. I've never figured out how to control what I'm being sold by our commercial suppliers. I had the opportunity many years ago, to have a billet crank made in the factory where I worked. The problem was that to get a decent job done, it had to be a foreigner and smuggled out past the security on the gate. If it went through the purchasing system, I could not look over the trades-peoples' shoulders. The billet crank in my short stroke Triton was made long before I ever owned it and had a machining error which had to be accommodated by altering a con-rod.