CRANKSHAFT balancing Australia

comnoz said:

Dances with Shrapnel said:

You can have your cake and eat it too and I have a few Nortons that demonstrate that just fine; plenty of mid range torque/power and silly great peak power. It is all in the state of tune and design.

BUT

What we are talk about at this point in the thread is an apparent loss of peak power if going to a lighter flywheel. I still cannot get my head around that one.

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It has to do with the ability to efficiently store the energy produced during the power stroke and release it during the next three strokes. Power can be wasted when you are speeding up the crankshaft and everything connected to it and then slowing it back down over the next three strokes. Too much velocity change on a per revolution basis wastes power. Jim

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Good point for me to cogitate on over the Christmas season. If one believes classic physics, energy can neither be created nor destroyed - I think it is something like the first law of Thermodynamics and then there's that pesky little thing about entropy. Won't bore anyone here but the nickle tour of Thermodynaics is what gozintoo must equal what gozoutta (simple math).

So when you speak of efficiency, that apparent loss of power must be accounted for. Some thoughts are:

Energy going into useless additional vibration?
Heat?
Additional Noise (a form of vibration)?

I can see my way through understanding where a lighter crankshaft will result in greater load reversals (strain reversals, maybe better stated as strain cycling) on all things including drive train components. In the elastic range, all components are springs with some inefficiency where some portion of the force transfer is lost to heat. So maybe, just maybe, the load leveling effect of a heavier crank reduces the magnitude of the strain cycles on components. If this is the lions share of the loss then it will show up as heat; that is increased heat of everything seeing the load cycles.

Jim,

Any net peak power difference numbers you care to share with us; from records or recollection? How about low and mid range power differences?

It would also be neat to measure (before and after - heavyweight versus lightweight) crankshaft velocities (by crankshaft degree).

The power differences I have measured on my dyno have been so small they could have been caused by other variables so they are hardly worth mentioning. I will say that as I got ridiculously light with crank weight the measured power dropped off throughout the powerband. It still could have been caused by other things such as clutch slip or tire slip. I suspect some of the loss was from the power used to make it shake so much. Vibration increased a lot when the crank got lighter.

Note that the more cylinders feeding power to the crank the less the need for inertia.

I have done speed mapping using 60 triggers per revolution to try and figure out why I had such a tough time getting my fuel injection to predict engine speed changes. I was shocked by how much faster the crank is moving on the power stroke than it is 1/2 revolution later. Since the original injection firmware was designed for a multicylinder car engine that was not taken into consideration.

I am sure most of the power lost is given up as heat and moving things that do no good. [vibration]
There would also be lose from drivetrain slack- as the crank speeds up and slows down the drivetrain can not follow that exactly so power is lost to noise and friction.

One other thing I often wondered about. When the powerstroke is so much faster that the compression stroke how much does that affect the ability of the other cylinder to fill with charge. I am sure it would affect it just like any increase in rpm.

quote="comnoz"]

There would also be lose from drivetrain slack- as the crank speeds up and slows down the drivetrain can not follow that exactly so power is lost to noise and friction.[/quote]

Personally I like lighter cranks and I lightened mine about 3 or 4 pounds less than stock. I could adjust the RPMs quicker and that made for quicker shifting and the rear wheel didn't slide so much when downshifting & entering turns because the flywheel spun up quicker (plus the bike weighed less). For me it made for lower lap times. But I did seem to notice that the inner splines of my bronze clutch plates were beating out much quicker. I once tried fiber plates (run dry) and the centers were more than 1/2 gone after a race because of the crank speeding up & down within each revolution due to the slower compression & faster power pulses.

'made for quicker shifting and the rear wheel didn't slide so much when downshifting '

I suggest the weight of the standard commando crank is ideal for it's application, and it is not simply coincidence that filling the hole in the flywheel with steel, gives a balance factor perfect for racing with a rigidly mounted motor. I tried to race my Seeley using the standard commando gearbox - It was revolting! - It was extremely difficult to make smooth downshifts at high speeds, which are essential for safety. The 4 speed close box is beautiful, and I now have a 6 speed TTI box which I am yet to use in anger. If you have to use a heap of revs on every downshift, you cannot expect adequate response fron that heavy crankshaft. With a close box, you just blip the throttle and snick the next gear down, and the change in revs is minimal. I've had idiots tell me that ' if you've got a torquey motor, you don't need a close box' . I suggest they've never used one. My four speed CR cluster cost $700 - 'cheap at half the price' ! The only problem lies in getting the bike off the line during a clutch start with that high first gear.

I share the same opinion and experience as jseng on the matter of a lighter flywheel. It comes down to "effective mass" of the whole motorcycle system.

I suppose I have not hit any wall yet with lightening things up for performance where lighter diminishes performance. I did have severe drive belt shredding and breakage issues on my short stroke Seeley but remedied that with a special drive belt. I attirbuted it to the crankshaft accelerations during each stroke with the light weight billet crank I was using.

@acotrel Although I think you have one extra gear (six speed instead of five speed) than you really need I am sure you will be happier than a pig in excrement with how it transforms the bike.

I just wish I'd had the TTI 6 speeder when I was racing my short stroke 500cc Triumph years ago. I used a close 4 speeder, and I used to drop the gearing right down, soften the suspenson and drop the tyre pressures and really go for it. I once led a field of Z1 and H2 Kawasakis with it for the first lap. It was a top end motor, but with the low overall gearing it ran out of puff at the end of the straights. With a 6 speeder it could have reached it's max on the straights by climbing up through the gears using it's maximum torque. They would never have caught me.

I am runninng the TTI six speed on my 500 ultra short stroke Norton where it is needed.

I am also running the TTI six speed on my 750 ultra short stroke and even there I tend to regret not staying with the five speed. It gets busy on a race course and I hate it when I am bearing down on a corner and cannot remember what gear I am in or what gear I need to drop down to. How I wish for the days of 4th, 3rd and sometimes 2nd. It really is a matter of lack of track time over the last several years. The good thing on a down shift is generally if you go down one too many on a six speed it is more forgiving than on a four speed where it can be disasterous and upsetting.

I have at least one rider who likes the six speed. For me I can see it having an advantage on the 750 ultra short stroke on some high speed sections such as Daytona where a wind shift within a couple of hours can make the finer jumps in the higher gears handy.

I live in Benalla and our local circuit is Winton Motor Raceway, 11Km away. It is 3Km around, and has a tight twisty section and three decent straights. The 6 speeder should be ideal. I've used a 6 speed box in a two stroke, and both my cars are Mazda 6 with six speed manual boxes , so I am used to keeping count.

So you have not raced your Norton Seeley with the six speed yet. 3 km track is likely tight so you may be spending lot of time shifting. That's fine if you think you can get it to work to your advantage.

http://www.trackpedia.com/wiki/Image:Winton.jpg

Interesting little track.

As you said numerous times, torque is a great attribute in a race bike (or something like that). I had the opportunity to race one of Herb Becker's Commandos with a rather hot motor (std stroke) an a rather smallish but technical track called Grattan.

http://www.trackpedia.com/wiki/Image:Grattan.gif


I can almost consider this my "home track"and recall only needing 3rd and 4th gear. It was a close ratio 4-speed. I recall getting better lap times on that (getting onto it cold) than the lap times I was getting with the 750 ultra short stroke and a six speed and considerably more power :roll:

'I suspect some of the loss was from the power used to make it shake so much. Vibration increased a lot when the crank got lighter.
'

It is a definite effect and the energy has to go somewhere . Better if you use it to spin a slightly heavier crank and sent it through the back wheel ?

Mc Intosh appears to do a bit , in regard to gearboxes .

http://www.manxnorton.co.nz/catalogue/c ... =1&c_id=34

AMC catledog .



says here the schafleitner ratios are (Top ) 1 , 1.11 , 1.29 , 1.56 , 2.08 , & 3.13 ( on first . )

AMC 4 speed , stanard ( Both are road bike ratios ) 1 , 1.22 , 1.7 , & 2.55 for the 4 speed .

from JAMPOT Archives . note , a Jampot is a AMC shock absorber , not a Whiskey receptical . click on link for SCHAFLEITNER 6 speed intro .
http://archives.jampot.dk/Technical/Tra ... e_Sep_1963).pdf


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MOTOR CYCLE S SEPIEMBER 1963 - AJS and Matchless Archivesarchives.jampot.dk/.../Transmission/Six_of_the_best_-_6_speed_gear...You +1'd this publicly. Undo
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Now the Austrian Schafleitner six-speedcr is available for A.M.C. roadsters. ... this ittcreases gear-box width by only a little,. Schafleitncr six-speeders :2: ...


getting back to the FLYWHEEL line of thought ; The rotateing components are all flywheels of a type .
Most immediate after the Crank is the Clutch Assembly then the Rear Wheel assembly . :?

relative mass particularly of the clutch ( and primary ratio )/ Crank are interlinked in respect of INERTIA .
particularly if the Chain is Direct rather than being interfered with by a Slipper Tensioner . As some might
say it is on a Unit Twin or the Mk III Commando .More power down the drain , even if its on the overrun .

Nova still supplies a 6-speed based on the Shaftleitner design, with ratios at 2.25, 1.737, 1.428, 1.227, 1.108, 1.00, but they recommend using it only for up to 500 cc singles and twins, and do not recommend using it in a Commando because it is not considered strong enough.

Ken

Bruce Verdon mentioned that his TTI boxes are based on the Schafleitner . He claims they will cop 80 bhp easily. I specifically asked that question when ordering my 6 speed box. I suggest the steels are better now than when the Schafleitner boxes were made back in the early sixties. Modern alloy steels are usually made in plants with vacuum degassing techniques, so the sulphur and phosphorus inclusions are much fewer. We don't usually make them in Australia - all imported if the application is critical.