Who makes crankcases for commandos ?

This might be good, and if well done, might not be noticed by scrutineers at historic races.

Yamaha always cutting edge, and they worked with Toyota frequently since the early Celica Supra 5MGE and other legendary engines. So it sounds like auto makers are already on to it.

Andover Norton and Molnar both sell crankcases

I thought all Norton twin engines 650 cc and above were desaxe. As the motor grew in bore they had to move the centreline backward.

Way back in NZ Castrol Six hour days some teams were trying this. Mostly to try and change valve timing??? Anyway they got caught.

If you look at Wikipedia Ford were doing it in the 1930s.

Honda has been making their CRF 450 motocross engines with offset cylinder for 20+ years. I believe the majority of the liquid 450 motocross engines are all offset cylinders these days.

I believe the speedway motors are heavily into it as well.

" Castrol Six hour "
Parrently , kwickersaki 900's the planed the head angled , to steepen the intake - enhance intake efficency . While they could get awaywithit .

Norton , its to keep the rods out of the camshaft . ike a Kent , it limmits the strokeability . Tho the reduced bore side load reduces the bore side load . And desymetricalises two stroke timing ,
as the crank at 180 or 360 isnt where it wouldbe , if it were ' on center ' . The Big End, too .

The idea is ancient, predating the IC auto engine back into steam engines. By ca. 1905-06 it was a common feature on American automobiles -- one thing it does is make hand cranking easier. I recall reading in a 1906 issue of The Horseless Age (but not at the time) in which it was proposed that ideal offset should be 1/6 the stroke, though it didn't say how they arrived there. https://forums.autosport.com/topic/126663-cylindercrankshaft-offset/

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THAT's the problem , with cars , these days . Theres NOWHERE to put the crank handle ! .
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Air cushion​

[edit]
In the conventional double-acting engine, residual steam was trapped in the exhausting cylinder after the valve closed and compressed. This compressed steam has a cushioning effect and acts to brake the piston at the end of stroke.<a href="https://en.wikipedia.org/wiki/Willans_engine#cite_note-15">[ii]</a> In the single-acting engine there is no similar effect at the end of the power stroke. This had previously been a limitation on the operating speed of single-acting engines.

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This is why all the klever dicks , who try to keep al the oil in , go slower .

Vell Knowen in two strokes , And by some , on Pre Unit Triumphs - The CLOSED C'Case ( Timed Breather - Small bore one , At That . ) The softer action across B. D. C. enhances High R. P. M. performance .
As turkys were unable to keep oil in't primary , the late units gott three holes drilled at chaincase oil level , to let the leaks back in.

Is it common practice when tuning on a dyno, to get the mixture right by using the oxygen sensor, then advance the ignition timing to get max torque? If you know the timing at which max torque occurs, the best cylinder offset might able to be calculated. But it might be a chicken and egg situation.

"Is it common practice when tuning on a dyno, to get the mixture right by using the oxygen sensor, then advance the ignition timing to get max torque? "

I recently spent a few days on a Dynojet inertia drum type dyno helping friends preparing two home-made DOHC twin plugged single engines for the Manx Classic races. Basically using the equipment and instrumentation available to typical engineering shops this process is iterative.

Since these motors have no history to fall back on you set up carbs (Gardener flat slides in this case) using your previous experience with other machines. Same with ignition timing. Then whilst ensuring the mixture stays at least close to optimal you run a sweep of runs across an ignition advance range. Range determined by experience and analysis of literature.

The process is iterative.

Remember mixture and timing is only part of the story. You will also be experimenting with exhausts, inlet tuning , valve timing. Around and around.

Even with a 6 speed box a broad ridable power band will almost always be desirable over a narrow " peak torque "

In short - the process is iterative and systematic data collection is required.

I’m not sure what all this talk of offset cylinders has to do with who makes Commando crankcases but I’ll join in anyway.
Can anyone actually prove that the offsetting of cylinders in a 4 stroke engine gives any meaningful benefit in real life?

johnm said:

Andover Norton and Molnar both sell crankcases

I thought all Norton twin engines 650 cc and above were desaxe. As the motor grew in bore they had to move the centreline backward.

Way back in NZ Castrol Six hour days some teams were trying this. Mostly to try and change valve timing??? Anyway they got caught.

If you look at Wikipedia Ford were doing it in the 1930s.

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I think Norton's desaxe was out of need.
If the bore was to be made bigger than 650 on their Dominator, in order for the piston/bore not to foul the front cam, they needed to move the axis of the crank rearward.
This happened first on the Atlas and then onto the Commandos.
Not a bad thing but not done in the pursuit of excellence.
The larger bore also meant the internally plumbed cam-timed crank-case venting could no longer work - hence the hose from the end of the Atlas' cam.
Cheers

Matt Spencer said:

on Pre Unit Triumphs - The CLOSED C'Case ( Timed Breather - Small bore one , At That . ) The softer action across B. D. C. enhances High R. P. M. performance .

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I’d take a bit more convincing on that.

johnm said:

I thought all Norton twin engines 650 cc and above were desaxe. As the motor grew in bore they had to move the centreline backward.

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There are a few threads on this site discussing the offset cylinder axis. Fact is, the Norton 750/850 were designed (or rather, modified) such that a negative offset appeared.
It has been claimed that having a negative offset benenfits piston slap. In my opinion, it increases piston slap.

robs ss said:

If the bore was to be made bigger than 650 on their Dominator, in order for the piston/bore not to foul the front cam, they needed to move the axis of the crank rearward.

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Rob, I think you got it wrong. It wasn't the axis if the crank which moved rearward, it was the cylinder bore axis, which means NV ended up with a negative offset, giving away some of the positive effects of a desaxe design. All done to save money and development time. There is no praise to Bert Hopwood for this!

hybridracer said:

Can anyone actually prove that the offsetting of cylinders in a 4 stroke engine gives any meaningful benefit in real life?

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"Désaxé" (French), means "unbalanced". It is not the crankshaft that is unbalanced, it's the valve timing. An engine designed for positive desaxe will typically provide longer durations for the downward stroke (intake and combustion), while the upward stroke (compression and exhaust) will be shorter. Sum of durations for a 4-stroke engine remains at 720 degrees of course.
Because of this effect, a desaxe (positive offset) engine needs a taylored camshaft.
The meaningful benefit in real life are
* more torque due to increased rod leverage
* more torque due to better cylinder filling (a 4V head may be required to achieve this)
* less engine clatter and less piston and bore wear.

Using an engine performance calculation program, I am confident the power/torque benefit can be demonstrated.
Less piston clatter is always welcome, isn't it?

- Knut

robs ss said:

I think Norton's desaxe was out of need.
If the bore was to be made bigger than 650 on their Dominator, in order for the piston/bore not to foul the front cam, they needed to move the axis of the crank rearward.
This happened first on the Atlas and then onto the Commandos.
Not a bad thing but not done in the pursuit of excellence.
The larger bore also meant the internally plumbed cam-timed crank-case venting could no longer work - hence the hose from the end of the Atlas' cam.
Cheers

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Exactly.

The cam pushrod tunnels stayed in the same place and they pushed the increased bore back. Centre of the bore not crank - as pointed out by mdt

Easy to see if you try to sit a set of Commando barrels on 500 crankcases.

But I don't think Al realised that Commando engines are already desaxe. His suggestion already happened from need. Around 1962.

This is very interesting theory that will, of course, be under careful study and research by all OEMs.

However, it is clearly completely beyond reality to consider it as some kind of retro fit mod to antique engines via modified crankcases.

As such it is just not relevant here at all.

mdt-son said:

There are a few threads on this site discussing the offset cylinder axis. Fact is, the Norton 750/850 were designed (or rather, modified) such that a negative offset appeared.
It has been claimed that having a negative offset benenfits piston slap. In my opinion, it increases piston slap.


Rob, I think you got it wrong. It wasn't the axis if the crank which moved rearward, it was the cylinder bore axis, which means NV ended up with a negative offset, giving away some of the positive effects of a desaxe design. All done to save money and development time. There is no praise to Bert Hopwood for this!


"Désaxé" (French), means "unbalanced". It is not the crankshaft that is unbalanced, it's the valve timing. An engine designed for positive desaxe will typically provide longer durations for the downward stroke (intake and combustion), while the upward stroke (compression and exhaust) will be shorter. Sum of durations for a 4-stroke engine remains at 720 degrees of course.
Because of this effect, a desaxe (positive offset) engine needs a taylored camshaft.
The meaningful benefit in real life are
* more torque due to increased rod leverage
* more torque due to better cylinder filling (a 4V head may be required to achieve this)
* less engine clatter and less piston and bore wear.

Using an engine performance calculation program, I am confident the power/torque benefit can be demonstrated.
Less piston clatter is always welcome, isn't it?

- Knut

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The amount of energy available for doing work is unaffected by offsetting the cylinders, regardless of the amount of change in duration of the power stroke.
Total torque remains the same, it is just distributed differently over the cycle.
Better cylinder filling? Where is the evidence? Prove it please and I will change my mind.
Less clatter and wear/friction? Maybe for half the cycle but doesn’t it increase over the other half? I can’t recall noticing any “clattering “ from any of my engines (discounting a clapped out diesel stationery engine).

Doesn't offsetting the bore to crank centre line have the same effect as offset gudgeon pins in a piston? Honda used that in the 750 SOHC engines to reduce noise & bore wear.

hybridracer said:

The amount of energy available for doing work is unaffected by offsetting the cylinders, regardless of the amount of change in duration of the power stroke.
Total torque remains the same, it is just distributed differently over the cycle.
Better cylinder filling? Where is the evidence? Prove it please and I will change my mind.
Less clatter and wear/friction? Maybe for half the cycle but doesn’t it increase over the other half? I can’t recall noticing any “clattering “ from any of my engines (discounting a clapped out diesel stationery engine).

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You are wrong on accounts one and two, at least. Empirical observations of tested engines suggests my statement on clatter i valid as well.

Here is the conclusion from a research paper on examination of a laboratory engine with offset, compared to a similar engine with zero offset. I have replaced a few words for clarity, the conclusions are unaffected.

From the present analysis we can conclude that offset design used in the I C engines are used to increase the mechanical efficiency by reducing the lining contact between piston and cylinder wall during the power stroke, thus reducing the power loss due to friction, to produce smoother internal acceleration; the offset design also reduces the return stroke angle which lowers friction between the piston and cylinder. Because of this, exhaust gas flow is promoted by shortening the time for the return stroke. A result of improved gas filling, we observe an increase in combustion chamber pressure at TDC, and the combined effect of these improvements is an increase of net torque output.

(There are graphs to back this up.)

- Knut

mdt-son said:

You are wrong on accounts one and two, at least. Empirical observations of tested engines suggests my statement on clatter i valid as well.

Here is the conclusion from a research paper on examination of a laboratory engine with offset, compared to a similar engine with zero offset. I have replaced a few words for clarity, the conclusions are unaffected.

From the present analysis we can conclude that offset design used in the I C engines are used to increase the mechanical efficiency by reducing the lining contact between piston and cylinder wall during the power stroke, thus reducing the power loss due to friction, to produce smoother internal acceleration; the offset design also reduces the return stroke angle which lowers friction between the piston and cylinder. Because of this, exhaust gas flow is promoted by shortening the time for the return stroke. A result of improved gas filling, we observe an increase in combustion chamber pressure at TDC, and the combined effect of these improvements is an increase of net torque output.

(There are graphs to back this up.)

- Knut

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Thanks, sounds promising. I need to review the paper for myself, assuming it’s in English.

mdt-son said:

Rob, I think you got it wrong. It wasn't the axis if the crank which moved rearward, it was the cylinder bore axis, which means NV ended up with a negative offset, giving away some of the positive effects of a desaxe design. All done to save money and development time. There is no praise to Bert Hopwood for this!

- Knut

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Yes- you're right - I do understand that, it was just my knuckle headed way of explaining it

hybridracer said:

I’m not sure what all this talk of offset cylinders has to do with who makes Commando crankcases but I’ll join in anyway.
Can anyone actually prove that the offsetting of cylinders in a 4 stroke engine gives any meaningful benefit in real life?

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Do you base everything you do on what has happened in the past ? - I suggest that is conservative thinking. When I first looked inside my 850 engine, I thought it could never be competitive in road racing. - I learned one thing during my life -'the system runs on bullshit and if you have a victim's mindset, you will be a victim'. My mate lined up on the grid with my first race bike - he looked around at all the other bearded idiots and thought he could do alright. He immediately found out he did not know how to ride a motorcycle. When you are lined up for a race, what should your mindset be ? There are NO geniuses, everything is a development. You cannot move forward by only looking backwards.
With my 850 engine, most things depend on the way it is used. Because it's power delivery is based upon massive torque, when it is used with low gearing, it spins up without really exerting itself. It gives the appearance that it is doing it's best. When you gear it up and use close gears, you make it pull. So you use it's torque. The other thing which helps my bike, is it's steering geometry. You will never win a drag race with a Commando. The crank always tends to spin-up at the same rate.
I always seek more torque, not more power by revving higher.
When you are on a bike, if you change up too early and the bike is still fast, that is a sign there is unused torque. With some bikes when you change up too early, the revs really drop. If you get on a normal commando , put it in third gear and rev it to 5000 RPM and drop the clutch, it would probably accelerate like a jet. I did it once by mistake, I got a real shock.