Commando Shortstroke tuning experience

Re: Norton Seeley shortstroke Racer rebuild

Dances with Shrapnel said:

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.

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There might be some oil on the cirkumference of the hole. Dont think it will stuck but the oil is changed very frequently so there might not be a buildup. I will of course report what i notice after liftkng the barrel at some time ahead.

Re: Norton Seeley shortstroke Racer rebuild

Dances with Shrapnel said:

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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On the face of it I agree with you because it seems that more weight would absorb vibration.

BUT

Lighter cranks creating more stress is not proven (as far as I know) and Steve Maney for one says otherwise - that lighter cranks actually reduce stress on the cases etc.

Testing in the aircraft industry seems to support Steve. Removing weight from a propeller allows the designer to significantly reduce the weight of the motor mounts because stress is reduced. The prop acts as a flywheel. The props can be precisely balanced but the lighter props win out.

This debate could be endless. A reasonable compromise is best but no one wants to be dragging any more weight around the track than necessary. See my comments about lightened flywheels (only down to about 20 lbs) in the "80HP at 8700RPM by Herb Becker" thread.

Re: Norton Seeley shortstroke Racer rebuild

Dances with Shrapnel said:

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.

Click to expand...

jseng1 said:

On the face of it I agree with you because it seems that more weight would absorb vibration.

BUT

Lighter cranks creating more stress is not proven (as far as I know) and Steve Maney for one says otherwise - that lighter cranks actually reduce stress on the cases etc.

Click to expand...

Sorry Jim, unless you (or anyone else) can demonstrate some solid argument against some very fundamental laws of physics, I am going to disagree here. Keep in mind that Steve is using very heavy (durable) crankcases and not the crankcases that Swetune is using which are stock (or near stock) so further lightening of the crankshaft for Swetune will have its price in stress on the cases. Furthermore, Steve tends to lighten the reciprocating mass. If you want to reduce stress, lighten the reciprocating mass and get the BF near 50% (that BF not recommended for Seeley Mk2 frames and other solid mounted arrangements). And finally, I never heard or read Steve Maney making that sort of assertion; could it have been confused with lighter reciprocating mass which I would agree with.

jseng1 said:

Testing in the aircraft industry seems to support Steve. Removing weight from a propeller allows the designer to significantly reduce the weight of the motor mounts because stress is reduced. The prop acts as a flywheel. The props can be precisely balanced but the lighter props win out.

Click to expand...

Has everything to do with the gyroscopic effect of a large diameter rotating mass which would be enormous for larger diameter propellers. A quick roll, yaw or pitch of an airplane would place enormous stress on engine motor mounts if running a very heavy propeller. Really a different problem from that to which we are discussing here.

jseng1 said:

This debate could be endless. A reasonable compromise is best but no one wants to be dragging any more weight around the track than necessary. See my comments about lightened flywheels (only down to about 20 lbs) in the "80HP at 8700RPM by Herb Becker" thread.

Click to expand...

I was running 16 lb crankshaft on my 75 mm stroke Norton engine AND Steve Maney cases and it was just fine with plenty of drive out of the turns and good stability settling into the turns and good engine durability. The advantages of a lighter crankshaft include less torque required to spin up the rotational mass upon acceleration and simply less mass to accelerate translate down the track..........the gift that keeps on giving. Recommending an ideal (arbitrary) weight reduction is pointless as there are so many factors to consider including engine stroke, where the weight is removed (rotational versus translational mass) and other factors.

Re: Norton Seeley shortstroke Racer rebuild

Dances with Shrapnel said:

Steve tends to lighten the reciprocating mass. ... I never heard or read Steve Maney making that sort of assertion; could it have been confused with lighter reciprocating mass which I would agree with.

jseng1 said:

Removing weight from a propeller allows the designer to significantly reduce the weight of the motor mounts because stress is reduced.

Click to expand...

Has everything to do with the gyroscopic effect of a large diameter rotating mass which would be enormous for larger diameter propellers. A quick roll, yaw or pitch of an airplane would place enormous stress on engine motor mounts if running a very heavy propeller. Really a different problem from that to which we are discussing here.

Click to expand...

Dances

Here's a quote off Steve Maneys website at his cranks:
"This incredible weight reduction dramatically improves acceleration, and reduces stress on the crankcases"

Yes airplane propellers do create a lot of stress to the gyroscopic forces you mention (precession) but I thought I'd throw in my example anyway (light cranks need a little help in this heavy weighted discussion group). I like the lighter weight cranks on the track, heavy smoother cranks on the street. And like I said - on the face of it I agree that heavy cranks would absorb more vibration. But still - gyroscopic forces in Norton cranks will increase with flywheel weight and contribute to the stress - no where near as much as a prop - but something. I remember the statement more like - a few pounds off the prop can save hundreds of pounds in the airframe. Bikes lean and turn similar to planes. Maybe I'm stretching it but its interesting.

As far as Steve's reciprocating weight goes. His 750 pistons weigh nearly the same as stock hepolite at high 240s to low 250s or so grams depending on overbore. And there isn't much room for lightening as Steve's 750 crowns are about .150" thick. Hepolites have thicker crowns but thinner skirts. Numbers are for Bare pistons per each.

Steves 850 pistons are also about the same weight of Hepolites in the 315grams and up range depending on overbore. I don't know the crown thickness of his 850 pistons. How much they can be machined to lighten them is an unknown for me as I don't have one on hand.

By comparison to the above - JSM 750 pistons are appox 65 grams lighter each.
JSM 850 pistons approx 100 grams lighter each.

Re: Norton Seeley shortstroke Racer rebuild

[quote="jseng1
Steves 850 pistons are also about the same weight of Hepolites in the 315grams and up range depending on overbore. I don't know the crown thickness of his 850 pistons. How much they can be machined to lighten them is an unknown for me as I don't have one on hand.[/quote]

The 850 pistons have a crown thickness of .350", leaving a lot of material for machining domes, dishes, or just lightening. The 77 mm pistons weigh 317 grams, with the weight going up some for the larger bores (78 mm and 81 mm).

Ken

Re: Norton Seeley shortstroke Racer rebuild

Ken
I figured Steve's 850 pistons had thicker domes but didn't know how much.

Getting back to flywheel weight. If you associate it with reciprocating weight and take it to extremes to make things obvious - for example cut both the reciprocating weight and flywheel weight in 1/2 - this should work because there is less reciprocating weight for the flywheel to stop and start. A much heavier flywheel with corresponding heavy reciprocating weight is going to exert higher stresses and vice versa.

Re: Norton Seeley shortstroke Racer rebuild

lcrken said:

[quote="jseng1
Steves 850 pistons are also about the same weight of Hepolites in the 315grams and up range depending on overbore. I don't know the crown thickness of his 850 pistons. How much they can be machined to lighten them is an unknown for me as I don't have one on hand.

Click to expand...

The 850 pistons have a crown thickness of .350", leaving a lot of material for machining domes, dishes, or just lightening. The 77 mm pistons weigh 317 grams, with the weight going up some for the larger bores (78 mm and 81 mm).

Ken[/quote]

We´ve had a couple of them since we´ve had left hand piston failure 3 times. There´s a lot of material to get rid of on the crown. We did a flat bathtub squish and had a 5 mm flat dome up in the chamber. Still lot of material, BUT still very heavy pistons and I think every one agrees to that lighter pistons being better.
The weight of the piston can´t get much lighter machining of crown material. You got to move the piston pin closer to the oil ring gap just as Jims pistons.
I fancy Jims pistons better but would like to have a flat dome upwards instead of a hemi. In that way you may do angle squish as well as we did on my Triumph.

Re: Norton Seeley shortstroke Racer rebuild

lcrken said:

[quote="jseng1]
Steves 850 pistons are also about the same weight of Hepolites in the 315grams and up range depending on overbore. I don't know the crown thickness of his 850 pistons. How much they can be machined to lighten them is an unknown for me as I don't have one on hand.

Click to expand...

The 850 pistons have a crown thickness of .350", leaving a lot of material for machining domes, dishes, or just lightening. The 77 mm pistons weigh 317 grams, with the weight going up some for the larger bores (78 mm and 81 mm).

Ken[/quote][/quote]

Herb Becker did some pretty creative additional weight reduction on an old pair of Steve Maney race pistons. Along with the typical thinning out beneath the crown of the piston, Herb used a ball end mill to carefully remove metal above the wrist pin (below the crown yet in the wrist pin boss) while maintaining wrist pin to crown support. I was amazed at how much material he was able to remove from the two bosses. This is a way to accommodate deep large valve pockets by lowering the wrist pin and subsequently the rings pack.

Re: Norton Seeley shortstroke Racer rebuild

jseng1 said:

Dances with Shrapnel said:

Steve tends to lighten the reciprocating mass. ... I never heard or read Steve Maney making that sort of assertion; could it have been confused with lighter reciprocating mass which I would agree with.

jseng1 said:

Removing weight from a propeller allows the designer to significantly reduce the weight of the motor mounts because stress is reduced.

Click to expand...

Has everything to do with the gyroscopic effect of a large diameter rotating mass which would be enormous for larger diameter propellers. A quick roll, yaw or pitch of an airplane would place enormous stress on engine motor mounts if running a very heavy propeller. Really a different problem from that to which we are discussing here.

Click to expand...

Dances

Here's a quote off Steve Maneys website at his cranks:
"This incredible weight reduction dramatically improves acceleration, and reduces stress on the crankcases"

Yes airplane propellers do create a lot of stress to the gyroscopic forces you mention (precession) but I thought I'd throw in my example anyway (light cranks need a little help in this heavy weighted discussion group). I like the lighter weight cranks on the track, heavy smoother cranks on the street. And like I said - on the face of it I agree that heavy cranks would absorb more vibration. But still - gyroscopic forces in Norton cranks will increase with flywheel weight and contribute to the stress - no where near as much as a prop - but something. I remember the statement more like - a few pounds off the prop can save hundreds of pounds in the airframe. Bikes lean and turn similar to planes. Maybe I'm stretching it but its interesting.

As far as Steve's reciprocating weight goes. His 750 pistons weigh nearly the same as stock hepolite at high 240s to low 250s or so grams depending on overbore. And there isn't much room for lightening as Steve's 750 crowns are about .150" thick. Hepolites have thicker crowns but thinner skirts. Numbers are for Bare pistons per each.

Steves 850 pistons are also about the same weight of Hepolites in the 315grams and up range depending on overbore. I don't know the crown thickness of his 850 pistons. How much they can be machined to lighten them is an unknown for me as I don't have one on hand.

By comparison to the above - JSM 750 pistons are appox 65 grams lighter each.
JSM 850 pistons approx 100 grams lighter each.

Click to expand...

I have searched and now see Steve made the statement on his web site regarding his light weight racing crankshafts; I must have dismissed that years ago. He has the first part correct where "This incredible weight reduction dramatically improves acceleration" ; this from reason and my first hand experience. As for the "reduces stress on the crankcases", well that is incorrect.

So, unless someone can demonstrate some solid argument against some very fundamental laws of physics, I am going to disagree with the assertion that a lighter crankshaft will reduce stresses on the crankcases, it is just the opposite. I do agree that reducing reciprocating mass will reduce stresses on the crankcase.

As for gyroscopic forces of a crankshaft on a crankcase (your propeller analogy), it is a fart in a wind storm. I have yet to hear of a premature crankcase failure due to someone flicking their Norton repeatedly into and out of turns. Having said that, I could see some improvement on 'flickability" with a lighter rotating mass but that would be along the lines of a handling enhancement and not one of durability.

From my experiences with light and extremely light weight 750 crankshafts, I am not sure if I can say one way or the other whether I felt a difference in flickability or lightness of handling due to lighter crankshafts. I can say that the 500 cc Ultra Short Stroke that Herb prepared in a Seeley Mk2 frame was scary in terms of how it would so readily drop in and jump out of turns; it had a teeny 59.6 mm stroke 180 degree configuration with a center bearing and virtually no flywheel mass. Herb also achieved this phenomenal flickability with one of his race Commandos; both the Seeley and Commando had serious front end geometry changes so it is difficult to say but on his Commando my hunch is it was mostly front end geometry and not lightened crankshaft.

Re: Norton Seeley shortstroke Racer rebuild

Dances with Shrapnel said:

lcrken said:

[quote="jseng1]
Steves 850 pistons are also about the same weight of Hepolites in the 315grams and up range depending on overbore. I don't know the crown thickness of his 850 pistons. How much they can be machined to lighten them is an unknown for me as I don't have one on hand.

Click to expand...

The 850 pistons have a crown thickness of .350", leaving a lot of material for machining domes, dishes, or just lightening. The 77 mm pistons weigh 317 grams, with the weight going up some for the larger bores (78 mm and 81 mm).

Ken

Click to expand...

[/quote]

Herb Becker did some pretty creative additional weight reduction on an old pair of Steve Maney race pistons. Along with the typical thinning out beneath the crown of the piston, Herb used a ball end mill to carefully remove metal above the wrist pin (below the crown yet in the wrist pin boss) while maintaining wrist pin to crown support. I was amazed at how much material he was able to remove from the two bosses. This is a way to accommodate deep large valve pockets by lowering the wrist pin and subsequently the rings pack.[/quote][/quote][/quote][/quote][/quote]

It is possible to remove a lot of weight from the Maney pistons by contouring the bottom of the crown and removing some weight from the pin boss, but, as you pointed out, it is really time consuming. When we designed the Maney pistons 16 years ago, we lowered the ring pack to provide room for the large valve pockets, but didn't move the wrist pin because we wanted to be compatible with stock con rod length. We left the extra material in the crown so the pistons could be tailored to individual race engines. These pistons were originally designed for race engine builders, not drop-ins for street bikes. There is enough material in the crown that the pistons can be easily turned down in a lathe or mill to the stock 850 deck height, or machined to a dish contour to lower the CR but keep the stock squish area, so they have been used successfully in a number of street bikes. For race bikes the crown can be tapered or stepped to get a much higher CR, or even radiused on edge to get a squish effect in the full hemi short stroke heads. It's a very versatile piston, but at the cost of requiring further machine work for anything except a drop-in 10:1+ CR engine. I've thought of doing a run of 850 pistons with minimal crown thickness (and weight) and lower CR for street bikes or racers who don't mind skimming the heads or cylinders for higher CR, but didn't think there would be enough market. For most street bikes, a cast piston is probably a better choice than a forged one like ours, and significantly cheaper.

Ken

Re: Norton Seeley shortstroke Racer rebuild

Crank weight.

My main concern about too light of a crank is not about stress on the crank cheeks and cases. Both heavy and lightweight bottom ends seem to blow up or wear out just fine. My concern is if a light flywheel allows the crank to speed up and slow down too much each revolution. When I went to a light crank I noticed that the inner teeth of my clutch plates were wearing out faster - but this could have been due to gained HP from other improvements.

Modern Ducs have practically no flywheel - but their 90 deg layout helps smooth things out.

Some people feel strongly one way or the other about crank weight - I do not. When racing I was more concerned about the overall weight of the bike and so I reduced weight everywhere I could including the crank. I pushed hard and did a lot sliding. Downshifting into turns would break the R tire loose and the lighter crank helped. And as I've already covered - shifting was quicker because the RPMS responded instantaneously to the twist grip flicks.

After all the talk - the one thing I like the best is a quote from I don't know who - "Heavier cranks won't give you more HP, and neither will lighter cranks."

Re: Norton Seeley shortstroke Racer rebuild

lcrken said:

Dances with Shrapnel said:

lcrken said:

[quote="jseng1]
Steves 850 pistons are also about the same weight of Hepolites in the 315grams and up range depending on overbore. I don't know the crown thickness of his 850 pistons. How much they can be machined to lighten them is an unknown for me as I don't have one on hand.

Click to expand...

The 850 pistons have a crown thickness of .350", leaving a lot of material for machining domes, dishes, or just lightening. The 77 mm pistons weigh 317 grams, with the weight going up some for the larger bores (78 mm and 81 mm).

Ken

Click to expand...

Click to expand...

Herb Becker did some pretty creative additional weight reduction on an old pair of Steve Maney race pistons. Along with the typical thinning out beneath the crown of the piston, Herb used a ball end mill to carefully remove metal above the wrist pin (below the crown yet in the wrist pin boss) while maintaining wrist pin to crown support. I was amazed at how much material he was able to remove from the two bosses. This is a way to accommodate deep large valve pockets by lowering the wrist pin and subsequently the rings pack.[/quote][/quote][/quote][/quote][/quote]

It is possible to remove a lot of weight from the Maney pistons by contouring the bottom of the crown and removing some weight from the pin boss, but, as you pointed out, it is really time consuming. When we designed the Maney pistons 16 years ago, we lowered the ring pack to provide room for the large valve pockets, but didn't move the wrist pin because we wanted to be compatible with stock con rod length. We left the extra material in the crown so the pistons could be tailored to individual race engines. These pistons were originally designed for race engine builders, not drop-ins for street bikes. There is enough material in the crown that the pistons can be easily turned down in a lathe or mill to the stock 850 deck height, or machined to a dish contour to lower the CR but keep the stock squish area, so they have been used successfully in a number of street bikes. For race bikes the crown can be tapered or stepped to get a much higher CR, or even radiused on edge to get a squish effect in the full hemi short stroke heads. It's a very versatile piston, but at the cost of requiring further machine work for anything except a drop-in 10:1+ CR engine. I've thought of doing a run of 850 pistons with minimal crown thickness (and weight) and lower CR for street bikes or racers who don't mind skimming the heads or cylinders for higher CR, but didn't think there would be enough market. For most street bikes, a cast piston is probably a better choice than a forged one like ours, and significantly cheaper.

Ken[/quote][/quote][/quote][/quote]

I see your point when you designed them for use with stock rods as this was then what most people used. At that time they were the best to use and you could lighten them some and people could do what they wanted. It´s still a good piston when use with stock rods or in original short stroke rod length that we used. Then we could use angles or domes as we wanted and deeper valve pockets if needed. The same thing wash´t obtainable for the T140 were istead I used cast alloy pistons did squish areas at the periphery angle squsih milled down head and deepened the valve pockets. We needed to do this with the deep Tri hemi to get up compression. Still just got it up to 9.5:1 which though worked good with those pistons. The problem was the rings which needed to stand that compression. When we had piston failure it was because of faulty ignition. Still got 68 Hp rear wheel. The cast material was also lighter but as you know weaker the forged.

Re: Norton Seeley shortstroke Racer rebuild

Agree Jim though a properly configured lighter crankshaft will yield greater acceleration and that is a fact.


Jimmy Comstock is a firm proponent of heavier crankshafts yielding better track lap times for him. I have always tried to reconcile the utility of crankshaft rotational mass with the apparent need to smooth out and reduce the acceleration and deceleration of a crankshaft and drive train throughout its four stroke cycle. As you bring up the Ducatis apparently having virtually little rotational mass and they are very fast I have a hunch that the need for heavy rotational mass to "smooth out" goes away as the rpm increases (ie modern Ducatis). From my experience and preferences for racing I have not found the "too light" condition yet and my experiences are all over the road (pun intended) with respect to bore, stoke, displacement and firing order. I am pretty sure one of the heaviest configurations is the 750 Nourish I am currently running with a 180 crank; it has no problem with power though I think (seat of the pants assessment) my 750 Norton USS had significantly better drive out of the corners and overall acceleration.

Re: Norton Seeley shortstroke Racer rebuild

lcrken said:

we lowered the ring pack to provide room for the large valve pockets, but didn't move the wrist pin because we wanted to be compatible with stock con rod length.

Click to expand...

Ken,

I obviously stand to be corrected on the wrist pin. In my mind I was contrasting the Steve Maney pistons to the Jim Schmidt pistons which use a longer rod and probably eliminate any opportunity (or need) for lightening in the wrist pin boss area since the wrist pin is already stuffed closer to the piston crown, but I would like to take a look at it. Both the Maney and JS Motorsport packages are good and both have their place and utility. I have used both.

Re: Norton Seeley shortstroke Racer rebuild

Update:
Got the cam from Jim. Upwelded from a donor core. Looks good.
Breather mounted.

A little report on the progress for the short stroke racer.

Because of using Jims falt pistons and long rods I had to add on the welding in the head for not loosing to much compression. Valves and seats got an overhaul and mounted some new comp cam seals on valve stems. Then some beehive springs and got some titanium top collars made for a correct mounting height and to avoid valve bounce.
Used JS pushrods shortened for the correct valve geometry.
My old titanium were though lighter and are a lot stiffer
Aprox measured and calculated CR 10,5:1
Strenghtened the drive side with a bolted alloy plate and into the frame it went.
The frame repaired and new paint.
All engine plates polished.

Swetune said:

A little report on the progress for the short stroke racer.

Because of using Jims flat pistons and long rods I had to add on the welding in the head for not loosing to much compression. Valves and seats got an overhaul and mounted some new comp cam seals on valve stems. Then some beehive springs and got some titanium top collars made for a correct mounting height and to avoid valve bounce.
Used JS pushrods shortened for the correct valve geometry.
My old titanium were though lighter and are a lot stiffer
Aprox measured and calculated CR 10,5:1
Strenghtened the drive side with a bolted alloy plate and into the frame it went.
The frame repaired and new paint.
All engine plates polished.

Click to expand...

I'm looking forward to your results when you get it running. I wish you had posted a photo of the head combustion chamber before you bolted it on.

How did you fit your PTO reinforcement plate? Did you heat it and shrink it on?

Hi Jim,
I was to post a picture on the head but I noticed that i forgot to take any. However my friend took some and I will try to get them to post em.
The combustionchamber needed to get smaller in order to get a decent compression ration so first it had been welded only on the side opposite the sparkplug so we welded the sparkplug side as well. That way we got a combustionchamber at 48cc taking care not to disturb plug area.
The piston protrudes some up above the coppergasket so effectively we got about 10.5:1 with the flat piston

As for the plate I did it to exact same (not shrink ) and it was chamfered on the inside. Then carefully pressed on and bolted.

Talked to Steve M and Comstock to and that made me not weld it. However it can be removed and later glued with What you suggested. Simply wasnt time to get the glue.

The machine was started 4 weeks ago and raced the week after. I'll post more soon

Engine mounted. Time to check gearbox lining up. Changed the gearbox to a 5 speed Quaife and that didn't line up with the front. Besides changing bearings i had to get a new plate done for the mainshaft support. That took some time but now the chain is free from supportbearing and at an ok position not to far out on mainshaft.
Time to get front pulley, belt and clutch basket on and of to the new crank located ignition from maney

So the Quaife 5 speed was a different story. Bought used 5 years ago for a Seeley project I thought it would be great instead of the 4 speed. Used of course by some Gary twaites in the Uk for a 1000 cc Norton.
Dismanteled it and called Hemmings to get bearings. Now this is interesting Mick and Rod Q were totally confident that the layshaft should be the bakelit ballbearing from Portugal TB special. Even though i,ve used rollerbearings with no failure before I took Mr Hemmings and RQ advice and used that. You can't say that they're not experienced.
Now the mai bearing is special as well. Ground down to get a clip securing it. Can't understand were it should go to in a fixed gearbox. But...
To be assembled in 3 rd he said. Ok no problem.
BUT why was it possible to gear it through and feeling there were false neutrals and a feeling that it could go past 5 on the camplate. Asked M but answere though must say some helpful: Old used box, no one knows what had been done before.
5 times had it a part to check. Nothings wrong there. Must be the mechanism in some way. Well got it to gether and on the test it seemed to perform well. But in a race at full speed in 4 to 5?

Turned out to be a problem in the first race....
Will get back to that later.

Now the Maney crank ignition.
Ready for mounting... no
Made for his crank not for Nourish that is shorter.
Had to remake the special nut I have with an outside thread and then make a new alloy mounting piece for the pickup magneto



Nut with outside thread shown