Norton Desaxe cylinder offset

speirmoor said:

What’s the formula for optimum results ?

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I don't think there is a formula behind this due to the large number of variables. To keep development costs low, most large manufacturers build one-cylinder test engines for trying out various configurations. Once a maximum gain is found, the design parameter is frozen.

In the world of cars, we can find desaxe values up to 14 mm (Honda K and R series engines).

- Knut

Jim
Have to tested to ensure the thick end of the gasket does not overly compress, negating the effect you're looking for?
What "effective desaxe" value are you chasing? Zero or further?
Cheers

robs ss said:

Jim
Have to tested to ensure the thick end of the gasket does not overly compress, negating the effect you're looking for?
What "effective desaxe" value are you chasing? Zero or further?
Cheers

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It will be made of steel and will not compress. You'll want to use Yamabond sealer. I'm going for .097" offset towards the front from the stock location. That should give it a millimeter or so Desaxe in the right direction. Ideally I would want about 2mm but I'm not ready to push it that far yet. They should be ready in about a month. It will raise the head about 1/32" but I have a .003" headgasket ring that will restore compression with .005" copper wire and plyobond around the pushrod tunnels and oil return (I've been using one 10 years without leaks).

If Norton designed their engines with considerations of desaxe, there are probably relevant research papers. There is a matter of angularity and the timing at which maximum thrust occurs, which must affect the torque characteristics of the motor. In that area, the Commando motor is very different from many others. It can give the impression that it is pulling as strongly as it can - when it actually is not. If you lose revs on an up-change, the acceleration rate is much slower due to the heavy crank. It affects throttle position, and means richer mixture. Everything affects everything else. Close ratio gears have a big effect on performance. In the end, whatever we end up with, we need to work with by changing gearing timings, exhausts and jetting etc.

When I want a motorcycle to accelerate faster, I usually lower the gearing. I also used to believe that bigger inlet ports give more power - so better acceleration. It takes practice to know when you are faster or slower. When the gearing is lowered behind a Commando motor, the motor does not usually spin-up much quicker. I prefer it to a light crank motor, but it must be kept spinning high.

jseng1 said:

It will be made of steel and will not compress. You'll want to use Yamabond sealer. I'm going for .097" offset towards the front from the stock location. That should give it a millimeter or so Desaxe in the right direction. Ideally I would want about 2mm but I'm not ready to push it that far yet. They should be ready in about a month. It will raise the head about 1/32" but I have a .003" headgasket ring that will restore compression with .005" copper wire and plyobond around the pushrod tunnels and oil return (I've been using one 10 years without leaks).

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You have mentioned moving the desaxe 'in the right direction', however I suggest that what is 'correct' depends on what is achieved when all the variables are adjusted to suit the change. The Commando 850 engine has surprised me - what is right seems so wrong - my Seeley 850 is beautiful in a race - that is strange. When I first began racing it, it was really weird - it took a bit to become used to the crank inertia. But it actually works very well.

acotrel said:

You have mentioned moving the desaxe 'in the right direction', however I suggest that what is 'correct' depends on what is achieved when all the variables are adjusted to suit the change. The Commando 850 engine has surprised me - what is right seems so wrong - my Seeley 850 is beautiful in a race - that is strange. When I first began racing it, it was really weird - it took a bit to become used to the crank inertia. But it actually works very well.

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If you ignore your racing irrelevance - to minimise the force on the heaviest thrust side of the piston the desaxe movement should be towards the front.
For bean counting reasons, Norton moved it to the rear.
Jim's innovation is to not treat "horizontal" as sacrosanct, instead, creating a new "horizontal", thus eliminating Norton's wrong desaxe ( and going a bit further - post #83)

'For bean counting reasons, Norton moved it to the rear.' Is that a statement of fact, or supposition ? Is there documentation of Joe Craig's and Bert Hopwood's work on engine development ? Regardless of whether the bike is for road or race use - a good engine setup is important.

I would not presume that the desaxe in the Norton motor is either right or wrong. It probably depends on a lot of other things as to what is the most suitable desaxe. I am surprised that the Commando 850 motor responds so well to tuning. It is very different.

acotrel said:

I would not presume that the desaxe in the Norton motor is either right or wrong. It probably depends on a lot of other things as to what is the most suitable desaxe. I am surprised that the Commando 850 motor responds so well to tuning. It is very different.

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I would presume. There is not a single modern engine with a "negative" desaxe.

Maybe I should convert my very fast methanol burning race engine to negative desaxe. P.S. I can't find a "tongue in cheek" smiley

hhh said:

I would presume. There is not a single modern engine with a "negative" desaxe.

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Of course not. If Jim's experiment bears out, we must all consider making new properly engineered crankcases!

It is not possible to predict what changing desaxe might do without evidence. It is almost certain that somebody has tried variations of it. Institutes of Automotive Engineers used to keep research papers.

acotrel said:

It is not possible to predict what changing desaxe might do without evidence. It is almost certain that somebody has tried variations of it. Institutes of Automotive Engineers used to keep research papers.

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There's plenty of evidence and it makes sense in theory and it works in practice. Nobody questions it.

hhh said:

There's plenty of evidence and it makes sense in theory and it works in practice. Nobody questions it.

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I am not questioning it. If somebody was going to remanufacture crankcases, they would need more than anecdotal evidence about the effects of changing desaxe. What Jim is doing with the base gasket, is a good thing. In reality, there is probably documented in formation on the effects. However with any motor, we never know the effects of a change until we work with it. The motorcycle is changed to suit its purpose, and the rider adapts to the bike. A rider who has ridden an excellent motorcycle, is often capable of improving a less perfect one. However Mike Hailwood began racing on a world championship winning Mondial 250, and was not good at conveying what needed changing to improve performance. Marc Marquez improves by crashing. Japanese motorcycles are good because the Japanese do their research. I suggest Joe Craig probably never told anybody anything. Norton were always about racing.

acotrel said:

I am not questioning it. If somebody was going to remanufacture crankcases, they would need more than anecdotal evidence about the effects of changing desaxe. What Jim is doing with the base gasket, is a good thing. In reality, there is probably documented in formation on the effects. However with any motor, we never know the effects of a change until we work with it. The motorcycle is changed to suit its purpose, and the rider adapts to the bike. A rider who has ridden an excellent motorcycle, is often capable of improving a less perfect one. However Mike Hailwood began racing on a world championship winning Mondial 250, and was not good at conveying what needed changing to improve performance. Marc Marquez improves by crashing. Japanese motorcycles are good because the Japanese do their research. I suggest Joe Craig probably never told anybody anything. Norton were always about racing.

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In this video, there is a photo of John Surtees working in the Norton factory in the 1960s -

jseng1 said:

Here's a drawing with the Desaxe layout I'm wanting to test.

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Hi Jim,
I saw your finished wedged steel plate (can't call it gasket, can we?) and was impressed. Looking forward to reading about the testing results!

Please allow me one remark: The calculated desaxe of 0.97mm at c/shaft centerline was calculated referring to the cylinder. However, the cylinder is not the essential part here, the piston's wrist pin is. In your sketch you have inferred the wrist pin is at top of the cylinder, which it isn't,
so your sketch isn't correct, is it? Also, the calculated desaxe is much less at 50% of the stroke AND accounting for the wrist pin location - I believe you will end up with a zero figure or dip into the negative domain.

Please correct me if I am wrong.

In your recent tread you claim that cylinders should be in front of the crankshaft centerline – ideally 1 or 2mm in front. I have to assume you relate this assertion to the Norton twin "as built", because the "ideal" figure very much depends on which parameter you look at.
You should mention which parameter reaches an optimum at a desaxe of 1.5mm .
Friction work is hard to calculate without making liberal assumptions, but we have to start somewhere. I think minimum friction work throughout a 720 degree crankshaft cycle should be the governing parameter as to which offset figure can be considered "optimum".

Providing a true (linear) cylinder offset of any figure requires drastic measures, a new set of crankcases likely. At this point, the "Unified Twin" offers a better starting point than the Dominator-derived Atlas engine, I believe.

- Knut