Commando Shortstroke tuning experience

Re: Norton Seeley shortstroke Racer rebuild

In general, I am also a heavy crank fan these days.

It is a 'horses for courses' discussion I think though.

I road one of Dave Degens 650 Triumph racers that had had a LOT of effort put into lightening the crank assembly and valve train to obsessive levels. There is something really sweet about a super crisp and free revving 360 degree 4 stroke twin IMHO, and that thing felt like it was some serious factory exotica and not 'only' a re worked road bike motor. With Dave on board it was staggeringly fast as it clearly matched his very aggressive riding style.

I would certainly consider trying a Maney light crank in my Cdo on the next rebuild, I think it would compliment the JS internals I have. It may not make it much faster on the road, but it would be fun!

Re: Norton Seeley shortstroke Racer rebuild

Now I´ve been doing most of my racing with a Triumph T140 with a stock crank which is heavy and balance to 77-78% std factory. I would say I agree on that it´s nice to have that momentum going out of the bends. However it´s not very helpful getting a top speed or there fast if you let the revs go down to low.
I lightened it rebalanced it to 74% and as some say it was crisp but still have the momentum. I know this as we use to race together my dad and I. Me on the Triumph af he on the short stroke Norton. We did very similar on the track and on the bench they were very similar except for the Nm were I had 82 and he had 90.
I would guess this was not just in the weight of the crank but rather that the head of the Norton had a better combustion chamber as to effectiveness in squish and angles of the valves. The hemi Tri is very hard to get a high compression ratio as because of the deep chamber. He had 11:1 in compression. I had 9.8:1.
And this was because I welded the chamber and did both flat and angle squish. The Nortons momentum may very well been the result from heavy crank and compression squish or a combination.

Maybe we are talking about incomparable things here. The Triumph T140 crank is heavy and I lightened it about 800 grams and still there´s momentum.
Now a Std Norton crank is also heavy maybe I would guess a little heavier than the Triumph crank. Still people lighten it. Maney does which I guess he has a reputation for doing nice Norton pieces. At first he started with std cheeks and a steel balance and lightened them. Then the upcoming cranks are now all high tensile steel and lighter than std.
I would think these new cranks in most opinions are a nice piece of working very well.

Now to the nourish crank. This is in perfect material and one pice. If you compare it to all of the other cranks I mentioned It´s so much heavier that even the lightening work I did can't compare it in weight to the T140 and all Norton cranks.

This really heavy weight is moving putting a mass strain on the material and to my opinion is way to heavy were cases break and so forth. Even though I lightened it a lot it is still comparably heavy.

My dad change the balance from Daves 85% to about 77% which as he told me today leave him with his balls less vibrating intact on the straight. It was awful to ride. I tried it this summer after his rebalancing and it was smooth but revving a little to slow.

Now as if you put in lighter parts and above all moving parts you need to lighten accordingly or the balance will change dramatically upwards.
I changed the balance to 66 or 67 dynamically in the process as well lightening it.

So I will tell you what I think when I test it but I respect everyones opinion in how they like their enginecaracteristics

Cheers

Re: Norton Seeley shortstroke Racer rebuild

Swetune said:

This really heavy weight is moving putting a mass strain on the material and to my opinion is way to heavy were cases break and so forth. Even though I lightened it a lot it is still comparably heavy.

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A heavier crankshaft provides inertial mass (momentum) which reduces the reactive forces (impulse) on the main bearing supports. The momentum I refer to is the larger the mass of the crankshaft, the more force one needs to apply to get it to move radially. The impulses are the forces due to acceleration of the necessary mass out of balance (bob weights and rod piston accelerations) and the resultant forces necessary to constrain the crankshaft at the main bearing journals. A heavier crank will be kinder to your cases and frame.

Swetune said:

My dad change the balance from Daves 85% to about 77% which as he told me today leave him with his balls less vibrating intact on the straight. It was awful to ride. I tried it this summer after his rebalancing and it was smooth but revving a little to slow.

Now as if you put in lighter parts and above all moving parts you need to lighten accordingly or the balance will change dramatically upwards.
I changed the balance to 66 or 67 dynamically in the process as well lightening it.

So I will tell you what I think when I test it but I respect everyones opinion in how they like their enginecaracteristics

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Years back Steve Maney recommended a 75% balance factor (BF) for the Norton Commando with a Seeley Mk2 frame and he has since moved that recommendation up to 78% (BF). This is the BF used by the majority of the race Norton Commando Seeleys (Mk2) currently active here in the States. I have been happy with it on an Ultra Short Stroke (75mm) as have others with 89mm stroke and I would be reluctant to deviate from it.

Re: Norton Seeley shortstroke Racer rebuild

The bike I raced for 12 years as a kid in the 60s and 70s was a 500cc 63mm (stroked 650) Triumph Triton. You had to be 110% on top of it everywhere, however it gave a magnificent adrenalin rush particularly on a very big circuit. The Seeley Commando is a world apart - I don't need the sort of anxiety I used to have before riding the short stroke Triton. Even when I think about it these days, I still get nervous. I will say one thing about that bike - these days I'm never going to crash. Everything which can happen to me, HAS happened. There is no way the Seeley can grab me by the throat.
I like to see guys trying to go short stroke and light crank, it is probably the way to get the max. But who needs the sort of self-discipline required to ride it ?

Re: Norton Seeley shortstroke Racer rebuild

This could be made to go fast :

http://www.motorcyclespecs.co.za/model/ ... 5%2083.htm

Re: Norton Seeley shortstroke Racer rebuild

To find the ideal balance factor you really need to actually measure the vibration in a scientific way. I had to make some crude tools to measure the vibration and find which way the motor is moving at various RPMS. The balance factors that are passed down and recommended are repeated by word of mouth. Usually they are not even specified as being wet or dry balance factors.

For solid frames - Your higher balance factors work by shaking the bike forward and backward more than up and down. This is necessary for heavy pistons to keep the rider from bouncing off the bike - the bike slides under your butt and so you get the impression that its smoother. But it puts stress on the crank and still works your wrists and can crack up everything. Only when you bring down the reciprocating weight can you reduce the balance factor closer to a number that shakes up and down about the same as forward and backward. That way everything is smoother and the stress is spread around.

I just got off the phone with Herb Becker. He's built a couple motors with my lightweight pistons and longer rods. He told me that after some recent tuning he's getting 8700RPM on the dyno. Thats news to me. Now I'm waiting for photos of the parts when he gets around to tearing it down.

Re: Norton Seeley shortstroke Racer rebuild

'But it puts stress on the crank and still works your wrists and can crack up everything. Only when you bring down the reciprocating weight can you reduce the balance factor closer to a number that shakes up and down about the same as forward and backward.'

How many bikes have you raced where the motor has been rigidly mounted ? What do you do when the handlebars grow bigger in your hands ? When you talk about 'ideal balance factors', perhaps sometimes you need to go there and work backwards . I use 72% dry on the Seeley, because that is as much as I could get by filling the hole in the flywheel and not drilling the other side much. With that balance factor, not so much shakes loose and falls off. When the motor is idling the bike moves forwards and back wars, at 7000RPM it feels almost vibrationless. If it was vibrating forwards and backwards under my butt, I'd feel it through the handle bars.

Re: Norton Seeley shortstroke Racer rebuild

Swetune said:

Now a Std Norton crank is also heavy maybe I would guess a little heavier than the Triumph crank. Still people lighten it. Maney does which I guess he has a reputation for doing nice Norton pieces. At first he started with std cheeks and a steel balance and lightened them. Then the upcoming cranks are now all high tensile steel and lighter than std.
I would think these new cranks in most opinions are a nice piece of working very well.
Cheers

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I replaced the std flywheel on my T140 for the early TR6P type - I was told it was called the 'Thruxton' flywheel, and balanced it to the factory spec. Even running low comp pistons the difference was very noticeable - far snappier, better acceleration and reduced vibes across the board. I was able to bin the standard rubber mounts for the handlebars in favour of solid mounts without any detriment to comfort.
I won't be reverting back to the standard flywheel anytime soon.





I spoke to Steve Maney and he was very strongly of the opinion that less weight in the crank has to be a benefit, especially when decelerating, for reducing the stresses on the drive side of the crank and cases.

I can understand a heavy flywheel being an advantage for dirt racing where breaking traction is a regular occurrence, and the increased inertia would help prevent over-revving. Perhaps this is why Weslake & Nourish engines were designed this way?
For road and track use the increased inertia would only serve to resist acceleration and increase stresses under deceleration.

My Ducatis have virtually no flywheel, and seem to do OK.

Steve Maney appears to have removed as much mass as possible from the flywheel; this one is now in my 750 motor:

Re: Norton Seeley shortstroke Racer rebuild

B+Bogus said:

...I spoke to Steve Maney and he was very strongly of the opinion that less weight in the crank has to be a benefit, especially when decelerating...

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For me, that is what it's all about - braking hard into a hairpin (which we have a lot of on sprint-hillclimb tracks) can be a nightmare if you have a heavy crank.

Re: Norton Seeley shortstroke Racer rebuild

I have ridden three types of Triumph 650 as well as the Seeley 850 with both standard and close ratio 4 speed gearboxes. The 650 Triumph (Saint 650) with the light crank, never performs as well as the one with the heavy crank. With the Commando engined bike, the first thing I noticed was that using the standard box, every down-change needed a heap of revs and the bike was difficult to ride smoothly. With the 4 speed close box and the crank rebalanced to 72%, the bike is spot-on everywhere except during a clutch start. I still have not been able to afford a practice day to try the Seeley 850 with the 6 speed close box. In theory, it should be unbeatable.

Jim, if the motor in a nornal commando only vibrates in the vertical direction, doesn't that mean we only need vibration damping in that direction ? So in theory, it might be a good idea to fix the ends of the swing arm pivot to the Z-plates, so that there is positive connection between the rear wheel contact patch and the handlebars ?
I suggest that when you are balancing the crank, it is not only the mass of the components which you are balancing. The energy from the combustion process acts against the counterweight. Changing the balance factor and the crank mass probably affects the torque characteristics of the motor ?

Re: Norton Seeley shortstroke Racer rebuild

With a close ratio gearbox, the heavy crank is not a problem when braking into a tight corner unless you are a lazy rider and don't play the right tune with the gearbox. I never have a problem with that, my steering is so quick that in corners you don't even have to think about it, - where you put your mind, that is where it will be. On a hairpin bend, I brake right down into the corner while changing down and almost immediately get straight back onto the gas without rolling in the middle of the bend. The only thing which is dangerous about my bike is that you need to know approximately how much the bike will tighten it's line under power coming through corners, if you relax when racing. So when practising, there is always the tightest corner where I take note of how it is behaving - the rest are then easy.
You have an option, if you bike handles like mine you don't want a vicious top end motor - mine is built to pull like a train.

Re: Norton Seeley shortstroke Racer rebuild

B+Bogus said:

Swetune said:

Now a Std Norton crank is also heavy maybe I would guess a little heavier than the Triumph crank. Still people lighten it. Maney does which I guess he has a reputation for doing nice Norton pieces. At first he started with std cheeks and a steel balance and lightened them. Then the upcoming cranks are now all high tensile steel and lighter than std.
I would think these new cranks in most opinions are a nice piece of working very well.
Cheers

Click to expand...

I replaced the std flywheel on my T140 for the early TR6P type - I was told it was called the 'Thruxton' flywheel, and balanced it to the factory spec. Even running low comp pistons the difference was very noticeable - far snappier, better acceleration and reduced vibes across the board. I was able to bin the standard rubber mounts for the handlebars in favour of solid mounts without any detriment to comfort.
I won't be reverting back to the standard flywheel anytime soon.

I spoke to Steve Maney and he was very strongly of the opinion that less weight in the crank has to be a benefit, especially when decelerating, for reducing the stresses on the drive side of the crank and cases.

I can understand a heavy flywheel being an advantage for dirt racing where breaking traction is a regular occurrence, and the increased inertia would help prevent over-revving. Perhaps this is why Weslake & Nourish engines were designed this way?
For road and track use the increased inertia would only serve to resist acceleration and increase stresses under deceleration.

My Ducatis have virtually no flywheel, and seem to do OK.

Steve Maney appears to have removed as much mass as possible from the flywheel; this one is now in my 750 motor:

Click to expand...

Hi there,
My first race bike was a T140 mounted in an oil in frame and I raced with the stock T140 flywheel. The advantage to the heavier flywheel is obviously the momentum in the forces that are created and I thought that was smooth but I wanted some faster response to the throttle as I had to have it high in revs most of the time to create speed.
First I lightened it by milling it down about equally byt the cast iron was so brittle that it cracked when I mounted it. So I had to think about something else. This was back in 2002. So I made one in tensile iron reducing the weight about 1,9 kg I think it was. Rebalanced it to 74% dynamically which is a big difference to ordinary static. When I dynamically checked the balance on a stock T140 the balance factor was 78 %. The result to lightening the crank was a quicker engine and I think the vibration was a little less but not much. I think the reason to this is that the heavier crank is much more forgiving and doesn't move that much as to a lighter crank. This is a fact I have experience as the t120 67 had a lighter crank balance to 85 and that vibrated more than the heavier T140 and the even heavier 1969, which however I felt had the least vibration.
Now I don't want that heavy crank in an race engine. I want I lighter because of less stress, presumably more effect. But to do that I need to lessen the balance factor and it is more difficult to balance dynamically as it moves more easily compared to the heavier crank.
My dad used the norton with Dave N 85% balance and it vibrated as hell and cracked the cases. Even though he got about 85 Nm on the rear wheel. Me on the other side had a quick revving faster responsive engine lightened 1.8 kg at least. And what was my momentum on the bench? 82 Nm!!. I can live with that. Now I ported and tuned the head and this engine myself and dad is a Maney stage II. And you know what that costs I guess.
/Mats

Re: Norton Seeley shortstroke Racer rebuild

acotrel said:

With a close ratio gearbox, the heavy crank is not a problem when braking into a tight corner unless you are a lazy rider and don't play the right tune with the gearbox. I never have a problem with that, my steering is so quick that in corners you don't even have to think about it, - where you put your mind, that is where it will be. On a hairpin bend, I brake right down into the corner while changing down and almost immediately get straight back onto the gas without rolling in the middle of the bend. The only thing which is dangerous about my bike is that you need to know approximately how much the bike will tighten it's line under power coming through corners, if you relax when racing. So when practising, there is always the tightest corner where I take note of how it is behaving - the rest are then easy.
You have an option, if you bike handles like mine you don't want a vicious top end motor - mine is built to pull like a train.

Click to expand...

I can absolutely see your point and we may race differently. As you say having a heavy crank gives you a high momentum if you can keep the revs up. We have a rider here being fast keeping revs up using the gearbox as well but even he reduced the total weight of the crank similarly as to Maney. It would be good to have both momentum and responsiveness as I think I have on the T140 racer as the momentum was similar with the much heavier short stroke Norton crank engine.
Then you have the freight train and the fast revving responsive engine when you need it.
I would say you can't compare the Nourish crank to a standard or Maney crank. Our Nourish was so heavy that it was hard lifting. I guess I have lightened it to a weight that it even though is heavier that the Maney Crank.
I have one and I will weigh it to compare and get back on this. Now the balance factor is a different story. As single is balanced to 50% and a parallell twin is two singles bolted together and theoretically as the 50% is best for the single that would make sense balancing the twin to 50% which we know does´t work. However as 50% is best for effect it makes sense to close up to 50% which Commando tried with tyne isolastic. My spare T140 race engine is balanced to 62% and lightened and there is really not much more vibration than the T140 on 74%. I haven't tested the rear wheel effect on this engine and that is hard to compare as well as the 74% engine has nikasil lined alloy barrel with a little different porting. However I wash´t disappointed in the 62% engin´s handling and it feels like it has more power compared to 74% that is probably mor radically tuned.
Just my thoughts on it.

Re: Norton Seeley shortstroke Racer rebuild

So 2 weeks ago I checked the crank in the case and noticed the endplay being 7/10 mm which was way to big. I´m not sure if the former guy that had the engine made this mistake or if dad forgot to check it while changing bearings.
However shimmed it to 2/10. Crank cleaned and together. Jims longer rods are mounted.
Went over to the USA with the family and at the same time getting some parts to the rebuild.

By the way I weighed and compared one standard norton crank with that of Maney and our Nourish lightened crank. Will get back to you on the weights little later.
However I can say that Maney was the lights weighing about 8 kg and std Norton around 10 very similar to the lightened Nourish. So we´re not talking ultralight cranks.

Got Jims radiused cam which should be about the same profile as the 7S. Sent him a core and the cam looks very nice welded and hardened.
So Now it´s time to mount the crank case venting after having milled the cases and plugged all holes to the timing side.

Re: Norton Seeley shortstroke Racer rebuild

I don't think many single cylinder cranks are balanced to 50%. A motor with a short stroke, light crank might make more horsepower and be more responsive, however they are usually more difficult to ride well. Also the acceleration you get from the heavy crank if you do race changes using a close ratio box is very hard to beat. I don't know how anyone ever raced a commando with the heavy crank and the standard ratio gear box. I tried it and it was hopeless. I couldn't do anything smoothly - it was always a heap of revs on the down-change and coming up through the box the bike was sluggish. What I find is that if you don't rely on throttle response to get acceleration, however keep the revs right up near the limit and race change, the bike is excellent It is almost impossible to bog down the heavy crank once it is spinning.
I raced with a short stroked Triumph engine for many years. With the Triumph I always had severe anxiety - none of that with the Norton. Of course, the Norton is much bigger capacity, however I am amazed at how good the near-standard motor really is.

Re: Norton Seeley shortstroke Racer rebuild

acotrel said:

I don't think many single cylinder cranks are balanced to 50%. A motor with a short stroke, light crank might make more horsepower and be more responsive, however they are usually more difficult to ride well. Also the acceleration you get from the heavy crank if you do race changes using a close ratio box is very hard to beat. I don't know how anyone ever raced a commando with the heavy crank and the standard ratio gear box. I tried it and it was hopeless. I couldn't do anything smoothly - it was always a heap of revs on the down-change and coming up through the box the bike was sluggish. What I find is that if you don't rely on throttle response to get acceleration, however keep the revs right up near the limit and race change, the bike is excellent It is almost impossible to bog down the heavy crank once it is spinning.
I raced with a short stroked Triumph engine for many years. With the Triumph I always had severe anxiety - none of that with the Norton. Of course, the Norton is much bigger capacity, however I am amazed at how good the near-standard motor really is.

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I think also it´s a riding style thing. Me and my dad used to race together. Me with the T140 rickman and he with the Norton short stroke with the by then really heavy nourish crank. I would agree that he always was trying keeping the revs up as he would loose to much in going to low in revs. He used a 4 geared quaife and really almost always use 3rd and 4th. In the chicanes he used 2 but using that gear somewhere else on the track would leave him behind. I also tried to keep the revs up and as high gear as I could as this would promote speed around the circuit. However this lighter crank was more forgiving if going down in revs and it was as fast and even faster in acceleration. This is what I´m trying to achieve. I´m not into doing an ultralight crank. Because of the discussion I weighed a std norton crank at 10 kg a Maney at 8 and I think the now lightened Nourish was 10 with rods. So this crank is somewhere in between. Before it weighed around 10-11 kg.
I forgot the note what I wrote down but will get back to you on the exact weight difference.

Re: Norton Seeley shortstroke Racer rebuild

Swetune said:

So 2 weeks ago I checked the crank in the case and noticed the endplay being 7/10 mm which was way to big. I´m not sure if the former guy that had the engine made this mistake or if dad forgot to check it while changing bearings.
However shimmed it to 2/10. Crank cleaned and together. Jims longer rods are mounted.
Went over to the USA with the family and at the same time getting some parts to the rebuild.

By the way I weighed and compared one standard norton crank with that of Maney and our Nourish lightened crank. Will get back to you on the weights little later.
However I can say that Maney was the lights weighing about 8 kg and std Norton around 10 very similar to the lightened Nourish. So we´re not talking ultralight cranks.

Got Jims radiused cam which should be about the same profile as the 7S. Sent him a core and the cam looks very nice welded and hardened.
So Now it´s time to mount the crank case venting after having milled the cases and plugged all holes to the timing side.

Click to expand...

I enjoy following your progress here and you are working with a great platform - short stroke Norton in a Seeley Mk2. It does not get any sweeter than that.

You have drilled your Nourish crank bob weights from the top and if you have not day-lighted out at the bottom of the holes they will trap oil and filter dirt (through centripetal forces) in a similar fashion to that of the crank sludge trap. The perched oil in your balance holes will throw your balance factor off a bit. I remember a discussion earlier in this thread about how Dave Nourish drilled from the other side and maybe this is why.

I suggest drilling a drain hole through each drill hole pocket so that all the oil will drain once spinning. Make it big enough drain hole so that it will not get plugged by minor debris.

As for a much lighter crank, as I mentioned earlier in this thread, I would steer away from it as it will be more stressful on the factor crank cases you are running.

Re: Norton Seeley shortstroke Racer rebuild

Dances with Shrapnel said:

Swetune said:

So 2 weeks ago I checked the crank in the case and noticed the endplay being 7/10 mm which was way to big. I´m not sure if the former guy that had the engine made this mistake or if dad forgot to check it while changing bearings.
However shimmed it to 2/10. Crank cleaned and together. Jims longer rods are mounted.
Went over to the USA with the family and at the same time getting some parts to the rebuild.

By the way I weighed and compared one standard norton crank with that of Maney and our Nourish lightened crank. Will get back to you on the weights little later.
However I can say that Maney was the lights weighing about 8 kg and std Norton around 10 very similar to the lightened Nourish. So we´re not talking ultralight cranks.

Got Jims radiused cam which should be about the same profile as the 7S. Sent him a core and the cam looks very nice welded and hardened.
So Now it´s time to mount the crank case venting after having milled the cases and plugged all holes to the timing side.

Click to expand...

I enjoy following your progress here and you are working with a great platform - short stroke Norton in a Seeley Mk2. It does not get any sweeter than that.

You have drilled your Nourish crank bob weights from the top and if you have not day-lighted out at the bottom of the holes they will trap oil and filter dirt (through centripetal forces) in a similar fashion to that of the crank sludge trap. The perched oil in your balance holes will throw your balance factor off a bit. I remember a discussion earlier in this thread about how Dave Nourish drilled from the other side and maybe this is why.

I suggest drilling a drain hole through each drill hole pocket so that all the oil will drain once spinning. Make it big enough drain hole so that it will not get plugged by minor debris.

As for a much lighter crank, as I mentioned earlier in this thread, I would steer away from it as it will be more stressful on the factor crank cases you are running.

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Thanx for your encouragement
The crank is not lighter than Stev Maneys now. And it´s actually little less than std. I have to think about that you wrote. as I see it the centrifugal force works from the centre and outward which means that when starting the engine and there is oil at the bottom they might dig it up at first but I think the centrifugal force will force it outward from the holes. This might actually be good, splashing the underside of the pistons and the cylinder liner that has proven getting so hot.
Inside the channel of a crank the centrifugal force also works outward against the inside wall which is actually were you find the sludge when you typically clean the sludge trap. There is almost always in a very dirty crank a small center hole and the oil clay at the periphery

Re: Norton Seeley shortstroke Racer rebuild

As far as riding style is concerned, I suggest we all adapt to the bike to get around as best we can. The quickest way round is when bikes handling complements the motor and gearbox. These days there seems to be two ways to go - either 'point and squirt' on a bike that tends to run wide in corners or get on the gas extremely early in corners on a bike that tends to tighten it's line. I suggest the light crank suits the former and the heavy crank suits the latter. I think trying to make a commando based bike into a 'point and squirt' bike is a futile and expensive exercise. However that is not to say it won't be successful on certain circuits.

Re: Norton Seeley shortstroke Racer rebuild

From looking at the photograph of the crankshaft and balance hole, no doubt the whole hole will not be filled but it certainly looks like it can trap some oil. This is why I brought it up.

I do not see an easy way of testing this but use some judgement through inspection. How much, if any, oil is retained may be inconsequential or it may be significant.