Commando Shortstroke tuning experience
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lcrken
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Re: Norton Seeley shortstroke Racer rebuild
I'm curious if there was a reason you decided to bore the lightening holes from the bottom, instead of from the top as Nourish did. I posted a picture in this thread of the way Dave did it on the first short stroke 750 crank he made.
short-stroke-750-build-t5490.html?hilit=750 short stroke
It always looked do me like it would have been better to bore the holes from the bottom as you did, or even just all the way through, but I never thought to ask Dave why he did it that way.
Ken
I'm curious if there was a reason you decided to bore the lightening holes from the bottom, instead of from the top as Nourish did. I posted a picture in this thread of the way Dave did it on the first short stroke 750 crank he made.
short-stroke-750-build-t5490.html?hilit=750 short stroke
It always looked do me like it would have been better to bore the holes from the bottom as you did, or even just all the way through, but I never thought to ask Dave why he did it that way.
Ken
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Re: Norton Seeley shortstroke Racer rebuild
When I worked at a Brit bike shop as a teenager they told me that the right side ran cooler because of the extra oil blowing to and from the timing chest. The left cylinder was usually given another .0005" clearance.
Something weird happened with that piston. Maybe it was worn in the middle of the skirt and later it overheated and nearly seized - as shown by the scuffing on the side of the skirt.
When I worked at a Brit bike shop as a teenager they told me that the right side ran cooler because of the extra oil blowing to and from the timing chest. The left cylinder was usually given another .0005" clearance.
Something weird happened with that piston. Maybe it was worn in the middle of the skirt and later it overheated and nearly seized - as shown by the scuffing on the side of the skirt.
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Re: Norton Seeley shortstroke Racer rebuild
Does lightening the crank help much if you've got a close ratio box ? I can see value in it if you are using a standard box where inertia makes down-changes a bit more difficult. I tend to keep the revs between 5,500 and 7,000 RPM or even a smaller range when racing. Keeping the heavy crank spinning while doing race changes seems to give the quickest acceleration. If you are relying on throttle response, the commando is slow. The motor seems to almost spin up at the same rate regardless of the gearing. There is a difference between torque and horsepower.
Does lightening the crank help much if you've got a close ratio box ? I can see value in it if you are using a standard box where inertia makes down-changes a bit more difficult. I tend to keep the revs between 5,500 and 7,000 RPM or even a smaller range when racing. Keeping the heavy crank spinning while doing race changes seems to give the quickest acceleration. If you are relying on throttle response, the commando is slow. The motor seems to almost spin up at the same rate regardless of the gearing. There is a difference between torque and horsepower.
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Re: Norton Seeley shortstroke Racer rebuild
One thing which terrifies me with the heavy crank is getting off the start line with a high first gear during a clutch start. I use a heap of revs and ride the clutch out very quickly, keeping the motor wound up high. Then I start race-changing. I hate think what that is doing to the main-shaft. Once that crank is spinning, there is no stopping it.
One thing which terrifies me with the heavy crank is getting off the start line with a high first gear during a clutch start. I use a heap of revs and ride the clutch out very quickly, keeping the motor wound up high. Then I start race-changing. I hate think what that is doing to the main-shaft. Once that crank is spinning, there is no stopping it.
Re: Norton Seeley shortstroke Racer rebuild
Thanx Mike,
I´m not sure I have the space for mounting a steering damper there. When I brake it might touch the fender. I will check with the fairing on. My own is not in the way and it´s not heavy as well.
Is the scott unit light?
Cheers
/M
Brooking 850 said:Swetune, here is a pic of an alternative way to mount a steering damper. Scott unit fully adjustable
Upside down on the the bottom yoke
Regards Mike
Thanx Mike,
I´m not sure I have the space for mounting a steering damper there. When I brake it might touch the fender. I will check with the fairing on. My own is not in the way and it´s not heavy as well.
Is the scott unit light?
Cheers
/M
Re: Norton Seeley shortstroke Racer rebuild
Hi Ken,
Thanx for your interest,
I started tuning a T140 and had an idea of lightening that big flywheel so I milled it thin at the top and checking with balance bob weights as to how much I had to to on the balance weight side. However it´s cast iron and it can´t take pressure and making it to thin so it cracked. Then I started making a balance weight in a tensile steel (I can´t recall the name) and noted that if I lightened the outer circle and very much in the center the dynamic balancing was easier. And it made sense to me as lightening the farthest distance from the center go crank will effect the momentum the most.
Then it´s easier for me to mount the crank to do the holes as well. It helps doing this symmetrically when you go on balancing.
I can just say that when I dynamically balanced the lightened Triumph crank (1.5 kg) it took me two days to get it right. This crank took about two hours of dynamically balancing.
It´s easier to balance a heavy than a lighter parallell twin crank as the heavier builds up a momentum that compensates the side movements better,
However my idea has always been to reduce stress by lightening but it´s harder the lighter then crank gets.
The machine can´t really see whats happening if the led hand or the right hand of the crank twists. Then you don´t know where to work on the balance: left o right hand.
My Triumph is though a real fast revving machine and little vibration compared to before when it was more grunt power.
lcrken said:
Hi Ken,
Thanx for your interest,
I started tuning a T140 and had an idea of lightening that big flywheel so I milled it thin at the top and checking with balance bob weights as to how much I had to to on the balance weight side. However it´s cast iron and it can´t take pressure and making it to thin so it cracked. Then I started making a balance weight in a tensile steel (I can´t recall the name) and noted that if I lightened the outer circle and very much in the center the dynamic balancing was easier. And it made sense to me as lightening the farthest distance from the center go crank will effect the momentum the most.
Then it´s easier for me to mount the crank to do the holes as well. It helps doing this symmetrically when you go on balancing.
I can just say that when I dynamically balanced the lightened Triumph crank (1.5 kg) it took me two days to get it right. This crank took about two hours of dynamically balancing.
It´s easier to balance a heavy than a lighter parallell twin crank as the heavier builds up a momentum that compensates the side movements better,
However my idea has always been to reduce stress by lightening but it´s harder the lighter then crank gets.
The machine can´t really see whats happening if the led hand or the right hand of the crank twists. Then you don´t know where to work on the balance: left o right hand.
My Triumph is though a real fast revving machine and little vibration compared to before when it was more grunt power.
Re: Norton Seeley shortstroke Racer rebuild
Hi,
To my experience parallel twins have such high a momentum because of the twin goes up with both rods and pistons which have to be in someway compensated by a balancing that can´t be perfect without counterbalancing shafts and so on. This means that the pull on the downstroke is really high and the force thus is not uniformly even all 360 degrees of the drive. You can see that on the front belt wheel where on a tuned twin theres is marks only on one side of the belt wheel. This is transformed via the clutch to the mains haft which if you don't have a cush unit gets a lot of momentum. My Triumph twisted the mainshaft really bad. I made a outrigger bearing sto help the mains haft to cope with the forces but you really need a cush unit. Either in on the crank, the cloth or rear wheel. It´s helps as well to get a smoother power curve when twisting the grip. I´m not very fond of highsiders which may happen more easily.
The twin Tri Nort or BSA out accelerates because if the built up momentum in the heavy crank which as well stresses all components in the engine as well as the engine block. Look what happens to the chain how it works on a twin compared to another engine set up. It´s like a skipping rope. The same happens inside the engine like a skipping rope the heavier the crank is.
So in my opinion I still want the momentum but I want it faster revving and I also need the hp which is useful battling triples and fours on the straight.
You are all correct in that you want to keep the revs up to keep the momentum because the crank is a slow heavy piece to get into motion
We tested the engine in 2002 and it was producing 90 Nm on the rear wheel and 72 Hp at 7500 RPM at a smooth power curve.
The momentum was comparable to Carl Fogartys SB Ducati 998 procucing about 95 Nm: No need to work on the momentum. Get the engine parts smoother lighter faster revving
/M
acotrel said:
Hi,
To my experience parallel twins have such high a momentum because of the twin goes up with both rods and pistons which have to be in someway compensated by a balancing that can´t be perfect without counterbalancing shafts and so on. This means that the pull on the downstroke is really high and the force thus is not uniformly even all 360 degrees of the drive. You can see that on the front belt wheel where on a tuned twin theres is marks only on one side of the belt wheel. This is transformed via the clutch to the mains haft which if you don't have a cush unit gets a lot of momentum. My Triumph twisted the mainshaft really bad. I made a outrigger bearing sto help the mains haft to cope with the forces but you really need a cush unit. Either in on the crank, the cloth or rear wheel. It´s helps as well to get a smoother power curve when twisting the grip. I´m not very fond of highsiders which may happen more easily.
The twin Tri Nort or BSA out accelerates because if the built up momentum in the heavy crank which as well stresses all components in the engine as well as the engine block. Look what happens to the chain how it works on a twin compared to another engine set up. It´s like a skipping rope. The same happens inside the engine like a skipping rope the heavier the crank is.
So in my opinion I still want the momentum but I want it faster revving and I also need the hp which is useful battling triples and fours on the straight.
You are all correct in that you want to keep the revs up to keep the momentum because the crank is a slow heavy piece to get into motion
We tested the engine in 2002 and it was producing 90 Nm on the rear wheel and 72 Hp at 7500 RPM at a smooth power curve.
The momentum was comparable to Carl Fogartys SB Ducati 998 procucing about 95 Nm: No need to work on the momentum. Get the engine parts smoother lighter faster revving
/M
Re: Norton Seeley shortstroke Racer rebuild
Jim,
That sound more as reasonable explanation to it. The timing case is also where this engine breathes and the 750 cc ventilates cool air mor on the right hand side.
Then what happens if you block that breathing and use the reed valves in the block?
I think it would be a good idea to get more coolant air around the cylinders and a very efficient oil cooler to get temperature down.
/M
jseng1 said:
Jim,
That sound more as reasonable explanation to it. The timing case is also where this engine breathes and the 750 cc ventilates cool air mor on the right hand side.
Then what happens if you block that breathing and use the reed valves in the block?
I think it would be a good idea to get more coolant air around the cylinders and a very efficient oil cooler to get temperature down.
/M
Fast Eddie
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Re: Norton Seeley shortstroke Racer rebuild
First thing I'd say is that Dave Nourish is not a fan of light flywheels. Second thing to say is that he definitely knew what he was doing, so there must have been a reason...
Now, I'm not sure if I'm looking at this right or not, but by drilling the crank as Dave does it seems he'd be able to remove relatively more metal whilst maintaining a relatively high flywheel weight, thereby achieving a lighter crank and keeping a heavy flywheel (relative to boring from the bottom).
If that makes sense...?!
lcrken said:
First thing I'd say is that Dave Nourish is not a fan of light flywheels. Second thing to say is that he definitely knew what he was doing, so there must have been a reason...
Now, I'm not sure if I'm looking at this right or not, but by drilling the crank as Dave does it seems he'd be able to remove relatively more metal whilst maintaining a relatively high flywheel weight, thereby achieving a lighter crank and keeping a heavy flywheel (relative to boring from the bottom).
If that makes sense...?!
lcrken
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Re: Norton Seeley shortstroke Racer rebuild
Yeah, Dave wasn't much on light crankshafts. After he made the short stroke crank for me, I had him make another one in standard 89 mm stroke, and he refused to do the same large lightening holes in it.
I've always preferred a heavier crankshaft in the Norton, but it's really the rotational moment of inertia that counts, not the weight. It's just that the large moment of inertia is normally achieved by more weight.
The new owner's of Dave's business seem to be perfectly willing to do more crank lightening with the same style of large holes Dave used.
I had a titanium design engineer once try to convince me that a titanium crank, with the weight added where needed with heavy metal (Mallory metal, tungsten, depleted uranium, or whatever), would be perfect for a Norton twin. That one was too crazy for even me.
Ken
Yeah, Dave wasn't much on light crankshafts. After he made the short stroke crank for me, I had him make another one in standard 89 mm stroke, and he refused to do the same large lightening holes in it.
I've always preferred a heavier crankshaft in the Norton, but it's really the rotational moment of inertia that counts, not the weight. It's just that the large moment of inertia is normally achieved by more weight.
The new owner's of Dave's business seem to be perfectly willing to do more crank lightening with the same style of large holes Dave used.
I had a titanium design engineer once try to convince me that a titanium crank, with the weight added where needed with heavy metal (Mallory metal, tungsten, depleted uranium, or whatever), would be perfect for a Norton twin. That one was too crazy for even me.
Ken
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Re: Norton Seeley shortstroke Racer rebuild
Even if you block the timing side case vents and use a one way reed valve - oil fills up the timing chest and levels out by draining back through the right side main bearing. There is also a little oil blowing back and forth through the intermediate timing gear shaft. All of this is happening on the right side. So the right piston is experiencing more oil splash and is getting a bit more cooling. Good reason for giving the left piston .0005" more clearance - especially since you've had overheating on the left side.
Swetune said:
Even if you block the timing side case vents and use a one way reed valve - oil fills up the timing chest and levels out by draining back through the right side main bearing. There is also a little oil blowing back and forth through the intermediate timing gear shaft. All of this is happening on the right side. So the right piston is experiencing more oil splash and is getting a bit more cooling. Good reason for giving the left piston .0005" more clearance - especially since you've had overheating on the left side.
Re: Norton Seeley shortstroke Racer rebuild
That makes sense to me and if I really wanted to lighten the crank as much as possible I should probably have done that method. I agree on that drilling from the top first would probably get the crank lighter than drilling from the bottom for achieving the same balance goal.
My holes are both on the bottom and from both sides. I don´t think my method differs a lot from Daves achieving the same goal.
It was just much easier for me to drill at vertical surfaces than angled.
The center of the crank with the main bearings is the line that separates the both sides and if you want to lightening a crank without changing balance factor you need to reduce the sides accordingly and keep in mind to reduce the the weight more than the small and big ends because of the balance factor as I see it.
Fast Eddie said:
That makes sense to me and if I really wanted to lighten the crank as much as possible I should probably have done that method. I agree on that drilling from the top first would probably get the crank lighter than drilling from the bottom for achieving the same balance goal.
My holes are both on the bottom and from both sides. I don´t think my method differs a lot from Daves achieving the same goal.
It was just much easier for me to drill at vertical surfaces than angled.
The center of the crank with the main bearings is the line that separates the both sides and if you want to lightening a crank without changing balance factor you need to reduce the sides accordingly and keep in mind to reduce the the weight more than the small and big ends because of the balance factor as I see it.
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Re: Norton Seeley shortstroke Racer rebuild
If you remember your old 650 Triumphs, the Saint had the light one-piece crankshaft and the Tiger had the heavy crank. I don't think anybody wants the light crank, the motor is never as good with that in it. And the balance factor is important, it affects the way the power is delivered. When the motor is spinning around 7,000 RPM on a sweeping bend at high speed, you need SMOOTH.
If you remember your old 650 Triumphs, the Saint had the light one-piece crankshaft and the Tiger had the heavy crank. I don't think anybody wants the light crank, the motor is never as good with that in it. And the balance factor is important, it affects the way the power is delivered. When the motor is spinning around 7,000 RPM on a sweeping bend at high speed, you need SMOOTH.
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