Can a Norton engine run without vibration?

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1. The cheap ass Norton factory determined the least cost of metal mass for effective isolation was 52% in 750's and 54% in 850's. I come to this blunt conclusion by the testimony of racers survey of heavy vs light cranks and finding that BF to everyone in the world [-1], is only modified to allow frame and pilot to tolerate it, nothing else, even if there something else about BF to tap into.

2. hobot and then Jim Schmidt have recorded the Norton engine orbitals both in isolastic and in solid mounted engines. Jim at one mid spot in solid mount, hobot at all three rubber mounts. Nortons at mid 50's BF bounce the front in an arc pivoted on the rear iso. There is also front to back motion involving both iso's from the drive tire thrust/pulses independent of engine orbitals, though both combine in use.
Can a Norton engine run without vibration?


3. I slurred the correct term by using gyroscopic smoothness instead of flywheel smoothness which is just 2nd law of motion of inertial moving mass effects alone. Gyroscopic precession is the countering force and motion a gyro gives when a slight force outside it is applied. Gyroscopes can resit motion from some level of outside force. We all feel it in the need to counter steer to help lean after a certain speed, about 10-12 mph in C'do case and wheels. It hold my baby at same angle she left the ground while pivoting a bit in flight to land as same angle thank goodness.

4. The harder the tires are aired the more the isolastics have something firm to isolate against. When air borne such as the small drop of instant blow out or longer time in ledge leaps, the harsh 360 vibes appear till landing or terra firma.

5. I know a C'do can essentially disappear to pilot sensation but do not believe that uncanny state can be attained in a pure factory set up. One of the innovators of isolastics sold the rest of the magic kit to Harley.

6. My P11 jumped 4 lane hi ways following the road crown about 4 ft up, if I blipped throtte front lifted if I tapped rear brake front dipped. This is example of flywheel transfer of moment of inertia to whole bike/rider.
 
jseng1 said:
comnoz said:
Jim C said:
Approximatley 52% will make a motor shake the same up and down as forward and rear - if the motor is hanging weightless in space.
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Where does this come from? Who determined it & how?

Jim S
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That is simple physics. [yeah simple- right] It would be 50% except that the verticle shaking forces vary between TDC and BDC because of rod agularity. IE. The upward jerk is greater than the downward jerk so it takes 54% to create the best compromise in the vertical direction and then you reduce it by 2% to compromise on the horizontal plane.

So you end up with 48% of the reciprocating weight unopposed at BDC, 56% of the reciprocating weight weight unopposed at TDC and the full weight of the counterbalance [52% of the reciprocating weight] unopposed at 90 and 270 degrees. That is as close as you can get to minimum shaking forces at the main bearing.

And by the way, those figures are approximate and depend on the actual stroke and rod lengths. It has been a long time since I actually went through the math to come up with the exact figures. Jim
 
DogT said:
comnoz said:
So the JS pistons and rods will reduce the piston/rod weight, >>>yes they do help <<<

I suppose adding a balance shaft or levers is out of the question in the existing motor? >>>it has been done, but it is not a minor modification<<<

My original question was really about the inherent vibration in the motor, not dealing with the iso mounts.

Dave
69S
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comnoz said:
>>>it has been done, but it is not a minor modification<<<
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Interesting, care to share, that was what I was getting at, not that I'm going there, just trying to understand balanced engines, if that's what they are called?

Dave
 
Here is one way to do it.
wart-tell-you-t9405.html

Using a third rod and dummy piston.
If you add enough weight to the crankshaft counterweight to completely offset the reciprocating weight of the rods and pistons [100 % balance factor] then the engine will not shake in a vertical plane. But that big old weight you had to add to the crankshaft will be unopposed at 90 and 270 degrees so it would shake fiercely forward and rear. So you add an extra heavy rod and piston at 90 degrees to oppose the crank counterweight on the horizontal plane. That will give perfect primary balance and all that will be left to shake the engine will be differences in inertia between TDC and BDC and the odd movements of the rod themselves. Secondary shaking forces.

That is why 90 degree v-twins are so smooth. Jim
 
Wondering if just incorperateing that ' third weight ' in the appropriate bit of the flywheel is feasable .So no extra parts .As in haveing counterweight 90 Deg to ordiary positioning .OR BOTH .
Meanig ' the counterweight ' masses go at 90 and 180 ish to the crankpins . Thats what im getting at with the rant . The Counterweight positioned to ballance the greatest Dynamic Load , the
' power Pulse ' so as the rotational force is made the best use of .

Getting sophisticated AND keeping it simple , as opposed to getting complicated mechanically and looseing half the power befor youve got it out of there , like a TX Yamaha . :roll:
 
Matt,
It would do no good. Any weight you put on the crank would have to be offset by a weight on the other side of the crank and you would just end up with a heavier crank and the same vibration. Jim
 
In a Word.

Definately NOT .

Like saying a twin wont work without a torsional dampner on the Crankshaft . ! They dont, but they do . :shock:
(Look at the big ' Cam / Spring ' sucker like on Dynamo Triumphs , deleteing was another ' Er Woops ' 'Developement ' .)
 
jseng1 said:
Matt Spencer said:
with a Crank Shaft balance factor of 50 % ( 50% of whats at the other end of the conrod ) presumably osscilates equally fore & aft / up & down , on the rubbers .
going for a Balance Factor of 72 % would preumably decrease the vertical & increase the longitudinal ' osscilation ' .
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Who can qualify this 50% balance factor being equal "fore & aft / up & down" ? Has anyone actually done a physical scientific test with a Norton? And does it hold true for solid mounted Norton motors?

The answer to the vibration is lightweight pistons - mine have extra lightening and are down to 170 grams each, bare. I ride an Atlas and smile.

Jim S
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You mean your teeth fillings don’t come loose any more? :roll: :D
 
No bike runs without vibration, with the possible exception of the inline 6's. Those would be the closest. Certainly no twin can run without vibration. A balance shaft only helps but does not cure primary and secondary vibes. Best thing to quell vibes is a huge old flywheel on a 90 degree twin (like ducati or guzzi). Those would be the smoothest possible twins.

Sorry. Personally, i don't find anything wrong with the norton vibes. Way better than my Triumphs or my Suzuki 2 smoke.
 
Here's one that has vibration-less cycle potential. Of course Norton had the Wankle type rotary already.

[video]http://www.youtube.com/watch?v=-bny77SEefQ&feature=related[/video]
 
http://www.dinamoto.it/dinamoto/8_on-li ... /twin.html

This is a link to a paper about engine balance. The thing I found interesting, (if I understand it correctly), is that stroke and rod length come into play just as much as reciprocating mass. For the amplitude of the primary imbalance, it's directly related to stroke (r), but rod length doesn't factor in. For secondary imbalance it's related to the square of the stoke and inversely affected by the rod length. So my daydream motor is going to have light weight rods and pistons and a de-stroked crank.

The last animation of a 360deg twin shows the primary and secondary imbalances to be vertical, can't be right is it?
 
rpatton said:
http://www.dinamoto.it/dinamoto/8_on-line_papers/twin%20motors/twin.html

This is a link to a paper about engine balance. The thing I found interesting, (if I understand it correctly), is that stroke and rod length come into play just as much as reciprocating mass. For the amplitude of the primary imbalance, it's directly related to stroke (r), but rod length doesn't factor in. For secondary imbalance it's related to the square of the stoke and inversely affected by the rod length. So my daydream motor is going to have light weight rods and pistons and a de-stroked crank.

The last animation of a 360deg twin shows the primary and secondary imbalances to be vertical, can't be right is it?
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It is correct if there is no counterweight on the crankshaft. 0% balance factor. It would shake up and down fiercly but no shake on the horizontal plane..
If you added a couterweight to the crank with 52% of the total reciprocating weight then you would see 52% of the force to the left and right and 56% of the force up and 48% of the force down after secondary forces are added.

Destroking can help vibration if you are willing to make the engine smaller. If you want bigger pistons to maintain the same displacement then the added piston weight will offset the gain of the shorter stroke. No free lunch. Jim
 
First - something interesting about lighter pistons:

If you just lighten the pistons and don't change the flywheel counter weight of a Commando crank, the balance factor goes up and the motor runs smoother even if you started with the "ideal" balance factor with the original pistons because - the higher balance factor gets closer to 100% and so reduces the up & down shaking, but the fore & aft shaking stays the same because the lighter pistons do not affect the counterweight shaking forces at 90/270 degrees. So the fore & aft shaking stays the same but the up & down shaking is reduced and this is why you don't HAVE to rebalance a Commando crank for lightweight pistons - it will still run smoother with less stress.

As for the 52% BF - I respect science but don't trust it until I see empirical evidence. I've tried it in solid frames and it was pretty bad and seemed better when rebalanced to around 70% And where were the scientists when so many were recommending 85% BF in solid framed racers (one of the reasons Kenny Cummings broke his first Maney crank)? Also note that Norton factory roadraces use a higher 62% balance factor, if they knew what they were doing - then why the 62% instead of 52%?

I don't buy the opinion that different frames need different balance factors because each frame may have different & increased vibration but I have seen that it only applies to a specific RPM range and not the overall RPM range. I saw this when I was designing & building frames - or when breaking a motor mount and feeling the "buzz" which came & went at different RPMs. And who has ever done objective & verified testing at 7000 RPM where things get really intense?

With 72% the orbital motion of the motor is a perfect circle at 4000 RPM but elongates dramatically above 6000 RPM indicating that 72% is too high and the shaking is worse fore/aft. So why is it a perfect circle at 4000? Are there unknown variables such as crank flex that come into play and screw up the nice clean world of our logical but limited math calculations?

Presently I think the BF for all Nortons should be somewhere between 54% and 68%. Note that speedway and Manx motors use 68% for vertial engines and percentages in the mid 50s for steeply inclined speedway motors. Kenny Cummings recently set up a crank for a customer with a removable plug in the counterweight (Ken Canaga also I think). If this plug/weight could be changed through the sump plug then this would be a good way to experiment altering the BF and employ the “scratch” test where you use a mounted needle point to scratch a piece of metal attached to the motor to record the orbital motion at different RPMs and view the scratch under a microscope to see actual orbital motion of the motor.

Jim S
 
The 52% balance factor only works with a motor hanging in space or using isolastics. Even then it may require small changes due to the weight of the barrel and trans and cradle assemby.

When you bolt it rigidly into a frame then everything changes and predicting how much vibration the rider feels is only determined by experiance or cut and try. Even the modern motorcycle manufactureres will use computer modeling based on prior experiance and then play with the results until the end product feels right when you ride it.

The fact that an engine is moving around in a circle in a rigid frame does not mean that is the best for rider comfort or minimun stress on the cases. There is a whole lot more to it than that.

I would agree that reducing the piston weight will reduce overall vibration levels without a rebalance but it would be better with a rebalance. Jim
 
For me this whole discussion is really about finding the best BF whatever the weight of the pistons. The pistons are getting light enough (especially with extra lightening, under dome 3D milling etc, down to 170 grams) that adjusting the BF for the comfort of your hands & butt is less of a concern than taking as much stress as possible off the crank & cases - especially for racing.
 
jseng1 said:
For me this whole discussion is really about finding the best BF whatever the weight of the pistons. The pistons are getting light enough (especially with extra lightening, under dome 3D milling etc, down to 170 grams) that adjusting the BF for the comfort of your hands & butt is less of a concern than taking as much stress as possible off the crank & cases - especially for racing.
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In my experiance I have not found a particular balance factor that seems to work universally. In a ridgid chassis I usually just start at around 60% and then start going up until it is acceptable. Around 65% seemed to work best in my N15 chassis but I have gone as high as 80% in an aftermarket featherbed looking for the sweet spot.

Acording to what I learned in school 50 to 55% is going to provide the least stress on the cases but if that excites a harmonic in the assembly then that would not apply. Jim
 
jseng1 said:
For me this whole discussion is really about finding the best BF whatever the weight of the pistons. The pistons are getting light enough (especially with extra lightening, under dome 3D milling etc, down to 170 grams) that adjusting the BF for the comfort of your hands & butt is less of a concern than taking as much stress as possible off the crank & cases - especially for racing.
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Are your pistons 170 gr bare - no rings, clips and pin? How much are they complete ready to install? How heavy are your rods? I once rebalanced my 850 Commando to 68% dry and it was worse vibrating until it went above 4500 - then it was slightly better than stock.
Look forward to your weight numbers - I want to calculate an idea and need some real numbers of lightweight stuff.

Thank you

Regards

Hartmut
 
jseng1 said:
Also note that Norton factory roadraces use a higher 62% balance factor, if they knew what they were doing - then why the 62% instead of 52%?

Jim S
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The factory specified a 62% balance factor for roadracers with isolastic mounts, but they also used a different mix of rubber bumpers in the isolastic mounts to give them a different frequency response curve than the stock Commando, which was balanced to 52%. The 52% BF and softer isolastics in stock Commandos was picked to minimize the vibration perceived by the rider in the speed range most commonly used on the street. The 62% BF and stiffer isolastics in the Production Racer were picked to minimize vibration in a race bike that lives in a higher rpm range. Maybe the factory really did know what it was doing after all.

Ken
 
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