Why ball bearing mains?

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From all I've read and experienced so far, that is there is no way to stop the crank jump rope shape at hi rpm, so decision on TS bearing seems to pivot on do ya want most the binding loads transferred and shared by cases more via balls or more on the bearing edges with a barrel shaped roller no matter its marketing name. There was a prior comment that Norton had special bearings made up, so only stupid people would not buy that kind - yet there is absolutely no evidence of any manufacturer ever making a non barrel shaped roller for crank use in the era Noton came up with a cute name. If I ever attempt to run Peel 920 to 9000 I'm going with HD 11 ball bearing again, like that old school dragster builder did.

Why ball bearing mains?
 
JRD said:
On 750 SF Laverda you had 4 ball bearings AND roller cages in the outer primary cover on both crankshaft and gearbox shaft acting as outriggers . quite clever
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Roller cages on the outer primary cover - nice touch.

Would be interesting to see a picture of that crankshaft/bearing configuration if someone would oblige.

Did the 750 Laverda have a middle main bearing?
 
hobot said:
If I ever attempt to run Peel 920 to 9000 I'm going with HD 11 ball bearing again, like that old school dragster builder did.
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only 9K ???????
I would have thought that the great Ms. Peel would do those RPM's at idle.
 
Dance's ,Two centre bearings! I will attempt to scan a picture from the very poor manual.

Dances with Shrapnel said:
JRD said:
On 750 SF Laverda you had 4 ball bearings AND roller cages in the outer primary cover on both crankshaft and gearbox shaft acting as outriggers . quite clever
Click to expand...

Roller cages on the outer primary cover - nice touch.

Would be interesting to see a picture of that crankshaft/bearing configuration if someone would oblige.

Did the 750 Laverda have a middle main bearing?
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Thanks john robert bould.

Middle bearings say a lot.

Ball bearings would not need to deal with much out of alignment due to deflection since that type of configuration is a stiff set up.
 
Ball bearings would also not need to deal with impossibly heavy loads once you have so many bearings to share the load.

So no need for a pair of super heavy duty roller bearings = aka superblends...

BTW, a lot of the old brit single cylinders had a pair of ball bearings on the drive side.
Makes the engine wider though, so the twins didn't get it.
 
But Look at that Italian Craftsmanship . :)

THE TRIUMPH STORY . Dave Minton .

One other oddity arose from the unit construction T120 . :shock:
Any innocent who dismantles a Triumph 650 twinwill find himself faced by the paradox of a ball race main bearing on the highly stressed drive side
of the crankshaft and a roller bearing , with its 2.5 times greater load bearing qualities , on the timing side .
While not ideal it was a satisfactory compromise that allowed for heat expansion on the timing side crankshaft end thanks to lateral bearing tolerance ,
impossible on the drive side because of the vital need for unfailing chain alignment .
When , with the introduction of the unit-construction T120s, drive side main bearings began failing the natural assumption was that the ball races were finally overstressed .

In reality, the problem lay in the much stronger crankcases of the one piece engines.
They no longer flexed and through their strength allowed the crankshaft no flexure , so the bearing broke up . :shock:
Quietly Triumph adopted a ball race with greater inbuilt tolerances and by so doing simply resolved the problem .
 
Matt Spencer said:
Quietly Triumph adopted a ball race with greater inbuilt tolerances and by so doing simply resolved the problem .
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What does that "greater inbuilt tolerances" mean ??

Is that a Matticism = sloppy old loose fit.
Or something more precise, like a C3 class bearing....
 
In reality, the problem lay in the much stronger crankcases of the one piece engines. They no longer flexed and through their strength allowed the crankshaft no flexure , so the bearing broke up . :shock:
Quietly Triumph adopted a ball race with greater inbuilt tolerances and by so doing simply resolved the problem .
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Dear Dances we've two good references now that agree with hobot statement that balls allow more shaft flexure than even barrel shaped rollers, so cancel your sharp remark that I was misleading anyone. Mark G, internet has permanent memory so we shall see if I'm misleading anyone on Peel's rpm potential to tolerate.

Btw does a bigger or smaller OD crank shaft have much effect on how hi it can spin rods and not turn into too much of a jump rope?

Why ball bearing mains?



Interesting molecular level animation of small bearing and shaft
[video]http://www.youtube.com/watch?v=RosHyQUw5jI[/video]

Turbine jet boat main center thrust bearing ain't a roller
http://www.youtube.com/watch?v=pj_wwCxp7J0

This is how I'd remove crank shaft flex issues if I had unlimited funds.
[video]http://www.youtube.com/watch?v=0H0stoFw3DY[/video]
 
Follow your dreams hobot.

Matt Spencer knows stuff yet he is quoting someone who said something presumably some time ago. I don't necessarily agree with what Matt is presenting on the matter but that is ok and we are still waiting to find out what "greater inbuilt tolerances" means ?? As for the other reference, I don't see any other credible reference.

It has already been stated by myself and others that you really cannot constrain the crankshaft whip much at all with bearings and/or cases (in the context of a Norton twin bottom end) but I am repeating myself here...again.

You see an excellent application of ball bearings where they can survive (Laverda crankshaft). Not so for a Norton twin. Comstock does not use ball bearings. Colorado Norton Works no longer uses ball bearings, Herb Becker does not use ball bearings, even the Norton factory stopped using ball bearings. So you have a point which is????

If you really want to run a ball bearing then go ahead as what will happen is a main bearing failure will occur sooner rather than later. Somewhat benign if that is your necessary mode of learning.

So follow your dreams man.
 
It has already been stated by myself and others that you really cannot constrain the crankshaft whip much at all with bearings and/or cases (in the context of a Norton twin bottom end) but I am repeating myself here...again.
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Well there ya go Dances, our common camp ground is, at some point our cranks flex no matter what. Do we want to try to restrain crank or try to let it whip?
I don't see how you don't see that balls have more tolerance for shaft flexing inside them before binding than barrel rollers,: therefor balls don't transmit as much leverage on their case bores as rollers do or can. There can't be much advantage one way or the other as we got examples of racers surviving with either type. I've got one foot in your camp by using 2 superdupers in heavy Maney cases in Peel, but I will limit her to a few extreme test events to 8000 but if I wanted to exceed that I'd go with a ball on the TS. I'm activity hunting online for bearing info to back up your or my views but so far not successful. I'll ping a bearing maker and see if they can set us straighter.

My only experience is a Combat with a ball and a roller held unloaded @ WOT for about 4 seconds and rode away 2000 miles w/o cracked cases or bearing failure but crank cheeks did bend some. The ball and roller live on in Wes's '71 over 4 yr now but not being over rev'd. Good enough for my dream machines.
 
hobot said:
Btw does a bigger or smaller OD crank shaft have much effect on how hi it can spin rods and not turn into too much of a jump rope?
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Larger diameter mainshafts and/or rod journals mean more overlap/less separation between centers. That means the crank cheek will flex less. The larger shaft and journal diameters mean they will bend less. Overall, larger diameter shafts and/or journals make for a stiffer crankshaft. That's why people like Kenny Dreer (and some others) experimented with larger diameter mainshafts and bearings. The difficulty with larger bearings is that they use up more horsepower in friction, particularly the larger rod journals. And it only gets worse if you're doing the ultra short stroke, high rpm thing like some folks on the list. :D That's why modern bikes try to use the smallest possible diameter shafts and journals. Additonally, in the Norton, it's difficult to go with much larger rod journals because of clearance between big end and cases, unless you are going with a shorter stroke. The standard main bearings in Commandos seem to stand up well enough to 100+ HP at the crankshaft in some of the large displacement race engines used today, so this might be another one of those solutions looking for a problem.

Ken
 
Sometimes a flexible crank is bad, sometimes its good

I remember reading about Bill Elliot racing his Fords in NASCAR back in the '80s. His brother Ernie mixed parts from the two Ford V8s, the Windsor and Cleveland. He ended up turning a ridiculous amount of metal off the Cleveland crank the fit the smaller Windsor journals. The crank shaft, which had a breakage problem, flexed rather broke. It seems the crank had been too stiff, and the turning down had restored some flexibility. Elliot's success on the track got a lot of attention - and money. Ford got involved and shared this knowledge with other teams.
 
I went with the 35mm main journals on my 75mm short stroke for just the reasons Ken mentioned above (increasing journal overlap). This is nicely outlined by Charles Fayette Taylor in Volume II of "The Internal Combustion Engine in Theory and Practice", a must read for serious engine builders who want to know.
Below is a picture of the subject crankshaft:
Why ball bearing mains?

It has been through several abusive race seasons (is there any other type?) and I continue to have the piece of mind that it will not break.....which allowed me to move on and focus on other component failures. :lol:

In hind sight I probably could have secured adequate race duty durability with 30mm main journals due to 1.) superior metal quality and 2.) overlap of rod journal to main journal as mentioned by Ken above. We run roller bearings exclusively (as ball bearings are not up to the task). We never had a bearing failure.
 
lcrken said:
The standard main bearings in Commandos seem to stand up well enough to 100+ HP at the crankshaft in some of the large displacement race engines used today, so this might be another one of those solutions looking for a problem.
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It really depends upon how you go about getting the power. On the 1,007cc you really do not need to rev it too high to get the power. With a 750 ultra short stroke you need to rev the hell out of it to achieve peak power (although it still maintains a very nice trackable power and torque curve).

I agree with you that if you get the metallurgy right and a few design elements right (ex. adequate filet radius) and the heat treatment and surface treatment you can achieve a high degree of high performance durability with the 30mm main journals.

On the 500 Ultra short stroke we went with significantly smaller rod journals to reduce friction losses and even for the 750 ultra short stroke, smaller rod journals may have some merit but greater (safer) gains can be had elsewhere in the design and tuning.
 
Rohan said:
Crank weight ?
Upper rpm limit ??
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I recall the crank weighed in at 17 lbs.

At 8,350 rpm the mean piston speed is around 4,000 fpm (comparable to 7,000 rpm on an 89 mm stroke at 7,000 rpm)

I have taken it to 9,500 rpm on occasion but no real need to go there as you are well beyond the useful torque curve and funny things start to happen with the valves. On launch and in lower gears I'll take it to 8,700 to 9,000 rpm semi regularly but really no need to go past 8,500 rpm. The bike has a TTIndustry six speed (could have easily stayed with a five speed) and things happen real quick when under way. Rods are custom aluminum billet by Herb Becker. Cam is a Megacycle N480 and compression ratio is 12.6:1.

The bike is smooth with plenty of trackable power. When I first got on this bike the power delivery reminded me of a DC electric motor.
 
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