Norton engine balance factor

The alleged rigidity would therefore affect them all. If the quoted racing man fits a heavy-duty ball bearing in the timing side it will have to take a lot of pain and the outer race will most likely twist in its boss. There is also danger of damaging the crankcase. Ball bearings do take up some axial loads though which roller bearings can't take up and will make end float adjustments redundant.

However, I don't think that's the point here. In a recent mail Frank Holden claims that stiffness of the cases goes into the equation. In my opinion, this is wrong - as far as I know, stiffening of the shells was made to prevent cracks, especially in the drive side boss area, and should be assessed independently of the crankshaft bearing theme.

The stiffening seems to work fine, especially when the improved Mk crankshaft and Superblends are used. As a side note, serious road racers run the Atlas with a solid one-piece crankshaft and the bearing problem seems to disappear. However, the next weak spot soon shows up - cracks around the separation flange of the crankcase. The remedy is to weld in stiffening plates along the flange. I have to agree with Knut. The whole idea of a Superblend is to allow for a bit of misalignment or flex, whereas a heavy duty ball bearing will not accommodate much misalignment of any degree.

It escapes me how combining them to support opposite ends of a flexible crank can possibly do any good at all.

Greg Kricorissian grkricor ccs. Apr I find it pretty hard to believe that the " comparatively small " alignment tolerance of a ball bearing is not sufficient for a Commando timing side. The question it seems to me is whether eliminating the problem of shimming for end float is worth the lesser capacity of the ball bearing.

The undiscussed question is - do Norton crankshafts really flex more than BSA and Triumph twin cranks, and if so why? Is it just that Nortons get to rev higher because of the Isolastics? Ben English ben.

Some comments on the Superblend discussion. Knut Soensteby appears to argue that the high compression of the Commando in comparison to the SS and cc Atlas motors is a primary cause of main bearing failure and thus the reason for the fitment of Superblends. I find this hard to accept. Remember, the SS uses a far higher compression ratio than a non-Combat Commando.

Also, it is suggested that high revs lead to stress on the crank: again, I disagree. Superblends are fitted to accommodate the kind of low-rev chugging around, which the torquey Commando motor tends to tempt from its riders.

The whole problem is that the cause of crank flex appears to be being missed. Damaging flex of the crank does not occur through the engine revved hard on the spot. If you rev a Commando motor to r. The problem of crank flex is a problem endemic to all primitive designs like the Commando and other old British motorcycles. The placement of the primary drive sprocket at one end of the crankshaft causes a massive leverage effect on the shaft whenever it is asked to move the motorcycle forwards.

The lower the revs, the greater the shock experienced by the crank. Take a look at those big AMC twins. On these, the fitment of a plain centre-support bearing on the crankshaft led to huge vibration problems and crank failures.

By allowing the crank to flex, rather than remaining rigid, the problem is somewhat alleviated. The only proper cure is to run the primary drive from somewhere along the centre of the crank's length, like modern Japanese multis do.

A Superblend is basically a roller bearing, but actually, its a barrel-race bearing. The 'rollers' are beer-barrel shaped and thus provide a broader surface of support than a simple ball bearing, whilst allowing for flex in the shaft they are supporting, a thing a plain roller can never do until it fails. They each offer far greater support than a ball bearing can, but not as much as a plain roller bearing. Generally, they are a Good Thing. As a side note, serious road racers run the Atlas with a one-piece crankshaft, the Nourish crank, yes.

This is also common on the racing Triumphs, where Carrillo rods and Nourish pistons combined with the one-piece crank give about 50cc extra swept volume to the engine. Since the Commando has plain big end bearings, there's absolutely no excuse for having a built-up crank, anyway. NVT should have switched to a one-piece, like on their Triumph engines but on the other hand, a built-up crank could allow for the use of ball bearing big ends. Does anyone know if this has ever been done?

Perhaps the key here isn't the bearings and we're all missing the real point. It could be crankshaft and crankcase rigidity that's the real key.

Yet the elimination of the crankshaft end-float issues seems to be an integral part of what's required to build a successful racing engine and I am disposed to believe that what is good for race engine reliability is exponentially better for street use. I saw this for myself when I was an engineer at Suzuki. Adding an additional main to the big bore racing fours which used one-piece cranks enabled them to finish and they subsequently dominated endurance races in the late Seventies and early Eighties.

We made the same modification to the production bikes which used built-up cranks and exhibited one of the most gorgeous classic sine-wave form crank whips at high engine speed that I have ever seen. The Knut vs. Farrell argument seems to me to be a debate between the issue of what you do to get your bike on the road and running reliably now, vs. They're both making correct arguments. I've opted for the latter on my street Commando. The barrel shape of a Superblend means that each roller supports less of the crankshaft at rest than a standard roller bearing does, but more than a ball bearing which is closer to a point support.

The advantage of the barrel-shaped roller is that the area of support on each roller can shift and possibly increase along the axis of the bearing when the crankshaft starts to whip. A plain roller can't do this under these non-ideal conditions and the edges of the roller dig into the shaft; a ball bearing will also try to dig in.

Over the years many bearing combinations have been used on British motorcycles. The ball on the timing side and roller on the drive side has a lot going for it.

The ball positively locates the crank while the roller gives a larger contact area to support the crank as it tries to move back under load. Furthermore, as the alloy cases expand, they grow much more and faster than the steel crank.

With roller bearing s the cases can move sideways without binding on the crank as they would with two balls as used on some year's Triumphs. I have no experience using two Superblends, but how is the end play controlled? I read they have to be shimmed but what actually stops the movement? It is hard to believe that anything is better suited to position a crank than a ball bearing. During the mid s there was a fad to use two roller bearings in Triumphs; everyone I knew who tried it went back to a ball on the timing side.

What works in a racer is not always good for the street. Racers are apart after every race, while street bikes are expected to run thousands of miles without major repair. The two Superblends do seem to work on the street for whatever reason, as testified to by many. The cc Norton engine produces a maximum of 54 ft. The out-of-balance force exerted on the crank by the pistons at t. It seems to me that the out-of-balance forces at high revs are a much greater source of crank flex than the effect Dan describes.

Also, as the out-of-balance forces are proportional to the square of the r. Also, Superblend rollers are not strictly beer-barrel shaped. They have a parallel centre section, about the same width as the rollers in the pre-Superblend bearings, and only taper at the ends. I have seen it suggested that the reason for the increased life of the Superblend bearings has more to do with their increased load capacity than their ability to allow crank flex. SKF has a very nice electronic notebook on bearing design and application.

It may be downloaded at www. It includes an animation showing a spherical roller bearing with a misaligned shaft and is about a 5Mb file size. It seems to me that the more out of balance crank and reciprocating assembly will flex more at high revs than one that is perfectly balanced.

Also, as someone else pointed out, the ratio of the primary will have an effect on crank flex in a different way. Perhaps these considerations may explain why there were problems with Combat engines using the roller and ball combination.

I don't have any books in front of me at the moment so I can't compare primary drive ratios. Perhaps someone with some engineering knowledge will be able to share their thoughts with me on this. There were no Combats with the ball and roller main bearing combination - the Combat introduced the roller left and roller right combination. Timing side ball and drive side roller was standard practice on all Norton twins from some point in the dark ages, until the Combat.

Fill C 1 exactly to the top with clean water. Suspend the rod from the pin eye so that the beam is exactly vertical. Very slowly submerge the rod in C 1 up to the marked centerline. If Archimedes was right, the water overflow volume is exactly equal to the volume of the submerged rod mass.

Weigh C 2, and subtract the empty weight. Multiply by the specific gravity of steel approximately 7. If curious, do the other end the same way. If not curious, just subtract your result from the total weight.

These results will be very different from the weights produced by the suspension method. Factors Affecting Balance Motors run at high speeds frequently have extra weight added, raising the factor. There have been many formulae published to calculate the exact amount of adjustment to make to the crankshaft to compensate for these factors. The adjustment is usually made by removing metal from the counterweight or cheek directly opposite the center of an imbalance caused by excess weight.

If a known and trusted factor is used, the level of component reliability and comfort is improved. The calculation must be made for the entire range, not just the power curve except for racing.

By whom? Dynamic Factors; Pressure Acting as Weight The behavior of the gas in the combustion chamber alters the effective apparent weight of the piston. The following text briefly discusses some of these factors, and the changes they cause in apparent piston weight. Pull can be positive simulating adding physical weight to the reciprocating components or negative subtracting weight , and can act in either direction up or down.

Pull acts on the rod and crankshaft assembly in the same way as the actual weight of the reciprocating components themselves, but not at the same time, not continuously, and varying in degree based on the construction and size of the motor and its operating conditions. Even at the same speed, the degree of successful compensation for out-of-balance forces will vary dramatically with throttle opening.

The motor will strangely vibrate as the throttle is opened, causing the driver to fear broken mounts, bent driveshaft, etc. Example 1 A motor with static compression ratio cruising, partially open throttle, RPM. Pull is low , as the low VE means only a small volume of mixture is present to be compressed. However, cylinder pressure is still higher than would be the case in a motor with lower CR. Pull is low due to only a small volume of mixture being ignited, but at a high ratio due to static CR.

Pull is probably very low , due to the low volume of gas to expel. Example 2 The same motor, same speed, but wide-open throttle. Pull is highest here, as the cylinder is nearly full, but resistance on the compression stroke is very high.

If the piston diameter is 4. Nearly VE open throttle, demand almost completely satisfied means that cylinder pressure will be much higher than in Example 1 above. Pull is much less high negative number. Moving on to and dusting off our copy of Irving's Motor Cycle Engineering of that year, we find him conceding that the Triumph type twin has been successful up to a point. We also find him, at this point, going into fairly great depth on the piston acceleration theme.

Assume a rod to crank ratio; he said it will be found that maximum piston speed is achieved at 76 o before and after t. For the first 10 o of rotation after t. The next 10 o produces more movement, the next 10 o degrees even more and so on until the crank and rod are at right angles to each other at which point the piston is going at maximum speed.

At this position the engine has achieved 76 o degrees of rotation after t. Thereafter as the rod and crank turn, the piston slows down until it reaches b.

Irving was very quick to point out that this fact greatly assisted the V-twin in that with both rods operating from the same crank pin when one piston was at t. Irving takes the opportunity at this point to point demonstrate that the 76 o factor also accounts for the concentration of forces into the upper arc of rotation. There was, he said, no hope of balancing out these secondary forces in a single or o twin, even partially.

Any balance weight added to counter the affect at t. In fact the only twin in current use where the secondaries of one cylinder would be balanced by secondaries in the other was a flat twin, which for fairly obvious reasons has one cylinder balancing out completely all the out of balance forces in the other.

The o parallel twin whilst balancing completely the primaries, left the secondaries completely unbalanced. Not only that, but the o twin had a severe rocking couple whereby as the crankpins alternate positions at t. The severity of this resulted from the unavoidable wide spacing of the crankpins. Irving was keen to point out that V-twins were relatively free from rocking couples owing to the pistons not reaching ends of the stroke at the same time and by not having widely spaced crankpins.

Secondary forces were a problem in V-twins, however a compromise was necessary between secondary and primary forces. He favoured a 50 o arrangement as on the Vincent twin whereas Ducati for example selected 90 o. By Honda had successfully introduced their o parallel twins, breaking the 25 year old fetish of o and even firing.

Irving felt that here was a golden opportunity to go for it. If parallel twins were still the order of the day, why not combine as many positive features as possible into one design? This was easy for him as he had been thinking about for years. Fix the crank at 76 o , he said, and you immediately have the V-twin flywheel effect, and at the maximum value.

Not far behind, you would have the near perfect arrangement for cancelling out the secondary forces 90 o would be best. The rocking couple would be slight as compared with the o vertical twin.

Primary balance, whilst not as good as the o twin, would be considerably better than the o twin and firing would be more even than with the o twin.

All in all he felt that the 76 o crank would obtain the optimum result and supplied the relevant figures to support his views. He felt that the benefits would become more apparent on a larger engine but made no mention of crankshaft flex, surprisingly so in view of his earlier bangings on about the o twin. This aspect might be difficult to qualify but it seems fairly safe to assume that with a long Triumph type crankshaft, once the pistons do not hit t. Also, if a lighter flywheel is used, any remaining flex will not be amplified to the same extent.

Irving felt that the 76 o parallel twin was in urgent need of a test. In fact he approached major factories but no one, apparently, was interested.

This is astonishing, especially since it only involved repositioning existing components - easy for a factory. If Triumph had been approached it is possible that Edward Turner, who was still very much alive and kicking at this point, would have felt needled that an erstwhile competitor and critic on the British motor cycle scene was tinkering with his work.

He was also resentful of academics as referred to in Steve Wilson's marvellous series of books British Motor Cycles Since In , do not forget that the cc Bonneville was selling like hot cakes, the Honda four was 6 years in the future and the Ducati V-twin 8 years.

It is also puzzling why Irving himself didn't do it or persuade an Aussie friend to have a go; Irving had returned to Australia in the mid fifties. Perhaps he was just too busy. He was at that time taking a deep interest in tuning the Aussie Holden car engine,a version of which, as the Repco Brabham, powered Jack Brabham then Dennie Hulme to Formula 1 World Championships in and Irving had been the designer.

These thoughts obviously struck Lee Kernich, an Aussie classic bike racer, having read Irving's article in He corresponded with Irving and eventually found time himself to do the 76 o crank conversion to his cc Triumph engined special, leading to the February article in Classic Motor Cycle.

Onwards to late when flush with the proceeds of the sale of a bevel drive Ducati twin, I purchased a Metisse Mk. Exchanging the for a tuned I had a very handy motor bike on my hands. To quote Steve Wilson again- a bike weighing no more than a but with grunt, only it vibrated. Boy how it vibrated! The inherent o shakes were amplified by the lightweight frame, making the bike virtually unrideable except for short runs.

Could Irving's 76 o crank help?. Having a stock of second hand unit spares I contrived a 76 o crank after sawing in half a standard Triumph crank in such a way that after machining, each half would be a shrink fit in a new central flywheel. Bolts were added for security and balancing was achieved by removing metal from the area between the crankpins. Overall the flywheel weight was reduced to one third of the original Triumph unit, an important point being all the balance being held in each outer web, i.

New camshafts were made by cutting standard Triumph cams in two and sleeving together each camshaft half at the appropriate positions. Twin contact breaker ignition enabled the sparks to be reset. The engine modifications took some ten months of careful planing ,machining and development.

All this theory is OK as a an academic exercise but did it work? Road testers of the picky types found that the following changes had been obtained by the 76 o crank conversion. The bike was more responsive, more so than a standard Triumph; the bike would just stomp away, with no heavy flywheel to get going. Overall gearing was much higher than standard but this was no problem, the bike just pulled away without the need for a lot of revs, even uphill.