Camshaft center support bearing for 9000RPM ultra short stroke

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jseng1

jseng1

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Norton cams flex in the middle causing loss of lift and unwanted valve bounce. The photo below (courtesy of Roger McHardy) shows a simple solution - an aluminum bronze partial bush held in place with two 10-32 screws. made undersize and machined in place.

The center of the cam in trued up first.

Center support is for a smooth ramp race cam in an ultra short stroke motor that has been hitting 9000RPM. BSA lifters and Beehive springs of course.

Early cases shown with the web around the cam which can be (and usually is) removed.

Camshaft center support bearing for 9000RPM ultra short stroke
 
Where are the retaining screws accessed? From the outside?

Neat concept, I'd hate to think of what would happen should it ever let loose
 
Clever. I think I have some pictures from a slightly different way of doing it from a few years back, maybe from Herb Becker. I'll post them if I can find them. Probably not quite as solid as a full circle bearing, but that's a bit more complicated to do. And it does seem like it should work pretty good in limiting the cam flex.

Ken
 
acadian said:
Where are the retaining screws accessed? From the outside?

Neat concept, I'd hate to think of what would happen should it ever let loose
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One 10-32 screw underneath the web on the inside and one underneath from the outside front of the cases. Loctite would be in order.
 
lcrken said:
Clever. I think I have some pictures from a slightly different way of doing it from a few years back, maybe from Herb Becker. I'll post them if I can find them. Probably not quite as solid as a full circle bearing, but that's a bit more complicated to do. And it does seem like it should work pretty good in limiting the cam flex.

Ken
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It was Herb Becker who did this around 15 years ago for the 500 cc Ultra Short Stroke we developed. I sent Jim Schmidt pictures and he circulated them on this forum years ago. It (middle bearing support) was done for a variety of reasons.

This 500 Herb developed went to 10,500 and made a really trackable power, and lots of it.
 
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Dances with Shrapnel said:
It was Herb Becker who did this around 15 years ago for the 500 cc Ultra Short Stroke we developed. I sent Jim Schmidt pictures and he circulated them on this forum years ago. It was done for a variety of reasons.

This 500 Herb developed went to 10,500 and made a really trackable power, and lots of it.
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That's the one I was thinking of, John. I thought I'd saved the pictures, and I probably did, but now I can't find them. Too many years of stuff on my computer. I thought his method was pretty cool at the time.

Ken
 
Didn't the Matchless twins have a central bearing similar to that in the 60's? 360 crank though!
 
That is the one Ken. Still have all the bits and it may come together again but as a 360 crank. I had a new solid billet 360 crank made for it but it all sits. A few other projects have gotten in front of this one.

I think of Herb Becker's work, creativity and mastery of machining and design and smile.
 
Dances - Is that a single screw holding in the center bearing?

Its a good idea to have a center support for the 480 cam that I think you were running. I have an asymmetrical 480 now that would have taken some strain off that valve train.
 
Alan (acotrel) suggested a thicker cam which, in theory, has some merit but in execution is difficult and a bit of a can of worms with regards to clearances and machining.

Making the camshaft diameter the same or larger than the cam base circle poses some challenges in machining and grinding in order to avoid stress risers. If the cam shaft is larger than the base circle, think about how you would transition from an acceptable filet radius on the base circle to an acceptable filet radius adjacent to the cam lobe. Think along the lines of a Möbius strip; makes my head hurt.

Our problems with the subject 500 Norton were self inflicted; the primary factors being a 180 degree crank and resultant cam lobe timing and how that loaded the cam shaft and cam drive train. For the speeds and component loads it was too much for that single cam shaft and four lobes so a middle support was indicated. That middle support only kicked the can down the road to the cam tensioner and chain failures which was resolved by implementing an all gear drive cam which promptly kicked the can down to a crank timing pinion failure. I’ll see if I can find and post a picture of the gear drive.

Ultimately the 180 degree crank was one way to resolve crankshaft failures but based on our experiences, it was a wrong choice. In addition to the above valve train issues there were crank middle main and rod bearing lubrication challenges.

The path forward in this particular case is a billet 360 crank and complement cam and valve train with proper engineering design aka Front End Loading (FEL) engineering. The trial and error approach to cam and valve train design alone is too inefficient with regards to time, money and resource for this particular application.

This bit about a middle bearing support for a Norton big twin cam may be interesting to a few but is really sooooooo far removed from most norton owners real world challenges.
 
Seems like flex and loss of lift could be eliminated better with a center cam support rather than going to heavier steel pushrods.
 
jseng1 said:
Seems like flex and loss of lift could be eliminated better with a center cam support rather than going to heavier steel pushrods.
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Gets down to problem definition. Where is the problem? What is the problem?

Who suggested heavier steel pushrods to eliminate cam flex. This is confusing! I think you just inadvertently mixed up oranges with Orangutans. I understood Alan (acotrel) suggesting that a thicker (larger diameter) cam shaft might be a better option.

I've never heard of loss of lift due to cam flex as being a problem. Three, six, ten or fifteen thousandths loss of max lift probably amounts to a fart in a wind storm. Of importance is how cam flex (really valve train dynamics) may impact the valve timing events and to a lesser extent the area under the valve time-area curve. Furthermore, my hunch is with 0.015 deflection of a cam that it would fatigue rather quickly.

The best 750 Ultra Short Stroke I had run was with a Steve Maney alloy barrel, cases, custom billet crank and steel pushrods with an N480 cam.
 
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Dances - Please don't misunderstand me.

I am not saying that steel pushrods cause cam flex - I am saying that Norton cam flex results in more loss of lift than pushrod flex.

In a long ago earlier thread you were posting the idea that steel pushrods made more horsepower than alum pushrods because steel had less flex (less length compression). Comstock said the same thing. The assumed loss of HP being due to loss of lift with alum pushrods - assuming they were flexing. But no one said anything about how much lift or HP was lost because of pushrod flex.

There is also loss of valve control because of cam flex. The spintron has proven that at high RPM the long Norton cam flexes so much that it bends in the middle at peak valve lift, then when the valve lands back on the seat, the cam rebounds and pushes back on the lifter - causing the valve to lift back off its seat - in other words "valve bounce". In the spintron vid you could actually see the rocker pushing against the tip and opening the valve.

Comstock missed this in his spintron tests so I pointed it out to him. He then looked at what the cam was doing (instead of just looking at the valve) and confirmed that yes - the cam was rebounding and pushing the intake valve open causing the valve to bounce (as much as 3 times). Causing loss of intake charge and HP as well as risking valve tangle.

Pushrod flex is probably not a cause of loss of lift anyway. It may actually create more HP. Rememeber that Nascar racers found more power with pushrods that flexed and then lofted the valve over the nose of the cam for more lift than they were getting with pushrods that didn't flex. Later they just made the cams bigger to match the loft and used non flexing pushrods.
 
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