Camshaft center support bearing for 9000RPM ultra short stroke

lcrken said:

Found it. Note also the center main bearing on the (180 degree?) crankshaft.

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Ken

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I had thought about that, but don't you end up with a different barrel separation - what do you do with the cylinder head ? The other thing is about getting lubricant to both sides of the crank. It might be possible to support the centre bearing on a thin chrome-moly plate between the crankcase halves. A Yamaha 650 crank with full circle flywheels could be used.

acotrel said:

I had thought about that, but don't you end up with a different barrel separation - what do you do with the cylinder head ? The other thing is about getting lubricant to both sides of the crank. It might be possible to support the centre bearing on a thin chrome-moly plate between the crankcase halves. A Yamaha 650 crank with full circle flywheels could be used.

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No need for a different barrel separation thus the center lines of the barrel bores and combustion chambers remain unchanged. No need for a thin chromoly plate bearing support between the crank halves as the set up works as is.

The initial 180 crank was fed from the timing side only as is done with Commando 360 and Nourish 180 crank. We suffered some apparent LH rod journal oil starvation which Herb tried to resolve with an increased capacity oil pump but was ultimately resolved with a middle main bearing feed.

Cam flex is one of the most significant and most overlooked factors in high RPM Norton racers with aggressive cams. The cam can flex approx .030" at around 7500RPM and approx .040" at RPMs higher than that. Thats enough to reduce HP from loss of lift and duration. More important - the rebounding cam causes valve bounce to occur on the compression stroke which means more loss of compression and HP. Worse than that - if severe enough the valve bounce will cause catastrophic valve tangling and destruction.

The problem of cam flex is not addressed with some of the available cam/valve train analysis software. Heavier springs and heavy steel pushrods will only make it worse.

We know about this problem now thanks to spintron tests. My own spintron has taught me a few things I never would have learned without it. For increased valve stability, higher RPM and reduced valve bounce - all builders of extreme Norton engines should consider the center bearing support improvement.

JS
the Norton Commando camshaft is not ideal because the right cylinder cams are much more subject to flex than the left cylinder pair. This lack of rigidity was well understood by people like Tom Sifton and Tim Witham, Tom in particular produced camshafts with a considerable increase in the shaft outer diameter between the two pairs of cams, which markedly improved the overall shaft stiffness.

On the other hand, through drilling of the shaft, whether in an attempt to lighten it, or possibly to provide a means of feeding oil to the cam lobes, has a serious weakening effect.

Prof. Blair's 4StHead software fully accomodates camshaft flex - and a host of other things also which a spintron cannot reveal.

I'm curious to know how you measured the .030" and .040" thou flex you speak of, and the camshaft in use at the time.

I bet he's seen marks on the case that far from the cam

Snotzo said:

JS
the Norton Commando camshaft is not ideal because the right cylinder cams are much more subject to flex than the left cylinder pair. This lack of rigidity was well understood by people like Tom Sifton and Tim Witham, Tom in particular produced camshafts with a considerable increase in the shaft outer diameter between the two pairs of cams, which markedly improved the overall shaft stiffness.

On the other hand, through drilling of the shaft, whether in an attempt to lighten it, or possibly to provide a means of feeding oil to the cam lobes, has a serious weakening effect.

Prof. Blair's 4StHead software fully accomodates camshaft flex - and a host of other things also which a spintron cannot reveal.

I'm curious to know how you measured the .030" and .040" thou flex you speak of, and the camshaft in use at the time.

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The worst flexing cam is the popular cast iron PW3 cam. Can the Blair software determine the amount of flex in a Norton cam? If so then what amount of flex does it show? The software I use doesn't measure cam flex. Comstock took some measurements with a laser and I saw cam lobe interference from inadequate clearance.

JS, exactly where are you getting your camshaft deflection numbers from? Have you personally measured the deflection of the cast iron PW3 cam and other cams to support your statement that the PW3 cam is the “worst flexing”

What did Comstock measure with a laser. Last I read on Comstock’s excellent spintron work was question on what his laser telemetry could actually pick up and at what resolution. Not saying he did not do the laser measure but a reference link would go a long way as I may have missed it.

We ran steel pushrods and heavier valve spring rates with a 750 ultra short (75 mm stroke) Norton with an aggressive cam for several seasons without cam, follower or valve train problems or unusual wear. This motor would regularly see excursions to 9,000 rpm. Your results may vary.

One of the things I really like about my Seeley 850, is you can relax while riding it, instead of being 100% on top of it. It makes going fast much easier. A commando motor revving to 9000 would really keep you on your toes, especially if the crank was much lighter. I really liked that 500cc short stroke Triumph motor that I had back then, but it was extremely exacting. If you got it the slightest bit wrong, it would bite you. The two bikes are worlds apart in comparison. I still suffer from the memory - I know what can happen if you get the set-up wrong and it haunts me. I don't like featherbed frames with peaky motors. I don't know about Commando frames with isolastics - I think you could tie one into a knot.

I had a problem with the cam lobes rubbing the cam tunnel (not enough clearance). I can't tell you exactly how much cam deflection there was but I'm estimating .030" to .040" ("approx") on over revv.

I raced without a tac. I revved the motor as high as it would possibly go. I wanted to win and I didn't care. I had all the recommended clearances with lightened valve train, lightweight retainers and R&D springs shimmed to within .050" or less from coil bind. But my valves were rubbing against each other and creating flat spots on the outside diameters. At the time I thought this valve rubbing was the fault of the valve springs but later on the spintron vids showed that the problem was cam flex or "whip" pushing back on the lifters and lifting the valves when they were supposed to be on their seats.

At the RPM limits (and missed gears etc) the motor would miss, crackle and sound "fuzzy" which I thought was caused by combustion leaking past the bouncing valves.

Dances & Snotzo - you will have to go through the spintron threads and vids to reference the laser measuring and the amount of cam defletion. A good place to start is:
https://www.accessnorton.com/NortonCommando/about-time-for-the-spintron.18787/page-8

See thread #159 where it mentions .030" valve bounce.

Valve bounce is mentioned somewhere in the vids and you can also see the rocker pushing back on the valve tip - this was the 1st clue that the bounce was caused by the cam flex. There are too many vids for me to go through again.

See thread #133 "The cast iron cam deflects more and is somewhat brittle."

The PW3 has the most abrupt closing ramps I know of and causes the most bounce. Some rare Harmon Collins cams may be even worse.

BTW I also had plenty of clearance between the valves and the piston pockets and the valves were still bouncing off the pistons. The crank was flexing. I lightened the pistons, pins and even the rods but the pistons still hit the head with .050" squish clearance.

Miraculously - the motor never blew. But it developed lots of cracks, wore out ring lands and broke rings from exceeding piston speed limits.

The over stressed 750 from the 1980s when I was on a shoestring budget.

JS
The Blair software was not in existence in the '80s, so you were doing what everyone else was doing, developing mainly by trial and error. Some who have told me about your on track efforts say you were a sight to see, I wish I'd been there to enjoy the spectacle.

Prof. Blair's 4StHead software comprehensively computes the flex that occurs when a force is applied to a camshaft, but the result is fed into further computations, and is not displayed as an output.

Details of the necessary inputs include the camshaft material, distance between the bearings, diameter and width of the bearings, and diameter of the middle portion of the camshaft. The diameter of any thru hole is also required.
For the Commando camshaft, it is necessary to detail the distance of each lobe from the nearest bearing, and the intake cam of the right hand cylinder will be revealed to be in a position that is the least stiff of all the other lobes, in fact more than 50% weaker than the exhaust lobe of the left hand cylinder, which is in the best possible position right next to a bearing.

Comparing identical camshafts, one in steel, the other cast iron, the steel item is some 25% stiffer than the cast iron.

Snotzo said:

JS
The Blair software was not in existence in the '80s, so you were doing what everyone else was doing, developing mainly by trial and error. Some who have told me about your on track efforts say you were a sight to see, I wish I'd been there to enjoy the spectacle.

Prof. Blair's 4StHead software comprehensively computes the flex that occurs when a force is applied to a camshaft, but the result is fed into further computations, and is not displayed as an output.

Details of the necessary inputs include the camshaft material, distance between the bearings, diameter and width of the bearings, and diameter of the middle portion of the camshaft. The diameter of any thru hole is also required.
For the Commando camshaft, it is necessary to detail the distance of each lobe from the nearest bearing, and the intake cam of the right hand cylinder will be revealed to be in a position that is the least stiff of all the other lobes, in fact more than 50% weaker than the exhaust lobe of the left hand cylinder, which is in the best possible position right next to a bearing.

Comparing identical camshafts, one in steel, the other cast iron, the steel item is some 25% stiffer than the cast iron.

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And you are probably talking about ANY piece of steel. Steel which contains 3% nickel and !% chrome usually has a tensile strength of at least 80 TSI un-heat treated. The amount of spring is minimal.

JS, thanks for the references. I read Jim C's work and viewed his two videos on post #159. In one of the videos of note #159 Jim C. states "Hard to say if the rocker is contributing to the bounce". There is no reference in note #159 of a ".030 inch valve bounce". I think Jim C's comparative assessment of the PW cam stiffness and apparent cam deflection is captured in note #133. It looks like Jim C used a Variable Reluctance (VR) sensor in conjunction with laser telemetry on the cam as stated in note #154 but not sure how far he took it other than to see correlation of valve bounce and cam deflection activities. This brings up the question of whether the cam caused the bounce or the valve bounce caused the cam deflection. In Note #133 Jim C does mention using the laser telemetry but I am pretty sure he is attempting to measure valve bounce and not cam flexure. I think you may have mixed the two.

Not denying cam flexure exists but from what I have read of Jim C's work, and from first hand experience, it is still at best, open for debate as to significance when considering the whole of the valve train; even at extreme high speeds. yet Prof. Gordon Blair's 4StHead modeling software does account for cam flexure. This brings up another thought (hypothesis on my part) and that is maybe this is why Megacycle recommended a cold lash clearance of 0.015" for the +D Grind cam; maybe to ameliorate cam rebound. On the other hand, we ran a +D and an N480 with zero cold lash, alloy barrels and steel pushrods with no hint of trouble in the 750 USS referenced in post # 27 above.

As per Snotzo's note above, I went through this measuring of components when Prof. Gordon Blair was helping us on the 500. Not only did the camshaft receive this attention to measurement detail but so did every component from the cam shaft through to the valves (mass, material of construction, dimensions, angular mass (moment of inertia) of rockers). In my opinion, the analysis and modeling is rigorous. At one point Herb designed and implemented alloy rocker arms with roller tips and needle roller bearing for the spindle. As part of the Prof. Blair's 4StHead analysis we needed to determine the stiffness of the rocker arms. As you would guess, the steel were very stiff whereas the alloy rockers were like diving boards. Very trick stuff but we reverted back to the lightened steel rockers for durability; not to say we couldn't have made the alloy rockers work but again, the alloy rockers would have other challenges besides durability.

Something to think about when contemplating valve bounce and that is the valve head diameter and shape/profile both above (e.g. flat or dished) and below (e.g. tulip or nail) is a significant factor in valve bounce as is materials of construction and probably valve seat material properties. A steel valve has three or more times the stiffness of Titanium at room temperature. The list goes on and once you think you have "fixed" one thing you only learn you kicked the can down to another new problem that was not there before.

lcrken said:

Found it. Note also the center main bearing on the (180 degree?) crankshaft.

View attachment 14628

Ken

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Norton Porn...

Dances & Snotzo

See this vid

Notice the "severe" valve bounce at 6:20
Then expand to full screen view and study the rocker arm tip at 6:40 - notice that the rocker arm is definitely pushing down on the valve tip and forcing the valve to bounce open - JUST AFTER THE CLOSING RAMP EVENT. You can barely see the rocker arm tip but if you look closely you can see what its doing.

Notice that the exhaust valve bounce at 6:20 is not so bad as to threaten interference with the intake valve whereas the valves in my race bike were rubbing from even more severe valve bounce. I can't explain this.

(Dances - I got my thread numbers mixed up earlier when making references.)

Below are some of Comstocks quotes and thread #s (he is refering to a different/later video than the one I refer to above).

See this page and the page before it:

https://www.accessnorton.com/NortonCommando/about-time-for-the-spintron.18787/page-8


thread #123
“It doesn't look to me like the spring oscillations go along with the valve bounce. “

thread #133
“where I had observed what looked like .030 bounce around 7500 rpm the laser is saying between .020 and .030. “

thread #159
“Now I know why using a center support on the cam in my racebike made an improvement in power"….."You can see, the rocker does push the valve back open after closing. You can see the loop of the spring under the rocker. You can also see the continued flexing of the cam after the bounce. I could also see that with the sensor I have in the center of the cam.”



We can only go so far with this and with what we've seen. You may not agree but I think the long unsupported Norton cam is the major contributor to valve bounce and tangled dropped valves. Only extreme race motors really need the center cam support but I think its worth the trouble for anyone pushing the limits and I think its an absolute necessity for anyone running over 8500 RPM. Long strokes can exceed 8000 (it happens even if it shouldn't) and it wouldn't hurt to have the center bearing support in either case - and should make more HP anyway by preventing valve bounce exhaust gasses from re-entering the combustion chamber and polluting/displacing the intake charge.

JS and JC
Am I correct in assuming that the movies were taken of the valve movement for the right hand cylinder ?
If this is the case, it would be interesting by comparison to see the same movies from the left hand cylinder, because with the cams next to the end bearing, little or no cam flex will/should occur, and any valve bounce that is seen will not have been provoked by camshaft flex.

Acotrel, you should know that all metals can be deformed if subjected to sufficient force !

'ANY' steel is the steel commonly used for the manufacture of motorcycle camshafts in general, and for the Commando engine in particular.
In England the steel used is usually either EN36 or EN40, but it matters little, whatever the steel, if enough force is applied it will bend, and like any spring, once the force is reduced it will revert to it's original form unless it has been deformed beyond it's elastic limit.
It is the reversal and it's effect that is the concern of this thread

Isn't it normal practice when converting to short stroke and higher revs to get more power, to use a slower lift rate cam with less lift, but with more radical timings ? - Top end power was never a problem with large four cylinder Japanese motorcycle engines. Yoshimura cams were relatively mild as race cams go. I was involved in fitting a race cam into a Z1R Kawasaki in about 1979. It was the fastest superbike at Bathurst that year. The cam was Italian - a proper race cam. Most guys used Yoshimura cams.

Snotzo

One thing that helps reduce valve bounce for sure is more gradual closing ramps and I've already done that with the asymmetrical cams.

I've seen the pushrods at high RPM and there's no visual indication of them flexing. But something is pushing back on the rocker arm tip.

If the vids are of the left side then its time to start all over. I would have to run the spintron again and make my own cam flex measurements. But how many people would be interested in installing a center support if you showed them it was beneficial?

From memory, late Gold Star BSA cams had a more gentle closing ramp to stop dropping the valve into the cylinder. Apparently the valve becomes air-borne as the follower goes over the nose of the cam and the closing ramp catches it as it descends. If the valve closes too quickly, it is more likely to break. GP Triumph cams were valve-droppers, but race kit E3134 were not. The best 350cc British single was the 1958 7R AJS.

JS
you ask a question, how many would be interested in another support bearing for the camshaft ?
I think maybe very few would be prepared to undertake this modification, most would want to understand exactly what it would be worth in terms off enhanced performane and reliability before they committed themselves to start.

One could also ask, at what engine speed would the flex become sufficiently significant to warrant this modification ?
From your own telling of your modus operandi on a race track, no rev counter and rev it until it goes no further then change gear.
Despite this abuse, you apparently suffered no camshaft failures, and the performance was sufficient for you to win races ?

I'd still like an answer re which cylinder was being monitored by the spintron, but would add that were I in a position to build a high revving, high performance Commando engine, I would include another support bearing for the camshaft, but I would retain the original Commando type cam followers, and very unusual pushrods.

Snotzo said:

On the other hand, through drilling of the shaft, whether in an attempt to lighten it, or possibly to provide a means of feeding oil to the cam lobes, has a serious weakening effect.

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Wrong. A normal size oilway drilling (approx. 6 mm or .25") has hardly any effect on the shaft stiffness. Lateral drillings need to be smaller (approx. 1.5mm or 1/16"). Moment of inertia will hardly be affected (a change of Jy, Jz well below 5%) because the lateral drilling will be at 45-90 degrees to the cam nose.

-Knut