Shelby-Right
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- Jan 28, 2022
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All the good steel went into those Rolls Royce merlins ! .The "fragile" crankshafts were the result of using a cheap grade of cast iron.
They don't do things by half!!
All the good steel went into those Rolls Royce merlins ! .The "fragile" crankshafts were the result of using a cheap grade of cast iron.
They don't do things by half!!
Some early motors only had two.A lot of (admittedly low power) Brit four cylinder car engines first appeared with only three main bearings, though most grew to five eventually (Rootes, BMC A and B series, Ford 'Kent')...
Cheap and cheerful???
TBH I was trying to quote some popular models that would have been contemporary to our bikes, but can't claim unlimited knowledgeSome early motors only had two.
It could be that the mass was centralised between the bearings to prevent a rocking couple which may be present with outside weights, amplified by the firing pulses.Maybe Norton would have been better off with more counter weight on the outer webs closer to the bearings and less in the middle trying to bend the crank .
I think there really is something to be said for careful assembly. This is just anecdotal from my experience working on these bikes when they were new or near new but Nortons seemed to be the bikes that came with the most careful assembly. Triumphs were a distant second and BSA wasn't even in the running. Sorry, to all you BSA guys, but these bikes, in my opinion were just lashed together and pushed out the door. To be fair, I think that a great deal of the BSA's problems stemmed from an engine design that was quite happy to be 500cc but never really took to the performance upgrades or the displacement increases. I might be wrong. These engines too might be a whole new animal if assembled with care.I don't think people today give enough credit to the fellows that designed and assembled these engines. I've owned and worked on nortons since 1965. I have had five Mk-3, one of which back in 1975 I had modified , Bored out and sleeved to a true 940cc, over size valves, heavy duty valve springs, the highest lift cam I could get for the street, 34 mm mikuni carbs ,had the push rods shortened ,had to have the front of the block case relieved to allow for the over size cylinders to fit ,had 12:1 compression ,dyno tested at 80 hp and never did anything to the crank. Put many a jap and hog on the slaughter wagon with that bike and never had any malfunctions let alone with the crank!!
I think the Britisk motorcycle industry found the shortest way to a good answer Most recent bikes which have three main bearings probably have roller bearing big ends. So oiling is not such a big problem.I think it was due to horizontally split crankcases. It’s difficult to have a middle bearing except for maybe the way AMC twins did it as mentioned above. Horizontally split cases make multi cylinder support much easier. The British motorcycle industry was not big into updating tooling as in spending money, so they stuck with the way things were done with the single cylinder machines.
Not only British 4-cyl cars, I´m a Fiat guy and they adapted the 5 main bearing strategy sometime around 1968-69, before that it was 3 main bearings. My 6-cyl Fiat (straight 6) from 1959 have only 4 main bearings, that engine was made until 1968. I´m sure lots of other car manufacturers did the same.A lot of (admittedly low power) Brit four cylinder car engines first appeared with only three main bearings, though most grew to five eventually (Rootes, BMC A and B series, Ford 'Kent')...
Cheap and cheerful???
It didn’t say that in the adverts.it is a commuter bike.
Hi Jim,I think there really is something to be said for careful assembly. This is just anecdotal from my experience working on these bikes when they were new or near new but Nortons seemed to be the bikes that came with the most careful assembly. Triumphs were a distant second and BSA wasn't even in the running. Sorry, to all you BSA guys, but these bikes, in my opinion were just lashed together and pushed out the door. To be fair, I think that a great deal of the BSA's problems stemmed from an engine design that was quite happy to be 500cc but never really took to the performance upgrades or the displacement increases. I might be wrong. These engines too might be a whole new animal if assembled with care.
Your points are well taken. My intent was not to cast dispersion on any one brand. There is plenty of that to go around. These were just my observations from a time, long ago. By carful assembly I am including issues such as careful machine work. By the time our favorite machines were being built the machine tooling was not the best. Many components were turned out with "close enough" as the final spec. Add to this the fact that these bikes were being constructed with parts that were themselves not subject to riggorious quality control standards and you have the issue that built the British bike reputation. Least you think me biased I will include all of Harley-Davidson offerings at this time plus a large part of the offerings by Ford, General Motors and Crystler. It was a mess. It took the Japanese to show us the way to zero defect manufacturing that we take for granted today.Hi Jim,
I must confess I’m a little dubious about what you say as it does sound a little biased.
I guess the true test of the bike as a package of design, material and assembly would be their reliability and service life.
I really cant answer which of the ‘big three‘ pommie bikes provided the best combination of performance and reliability although I suspect the problematic bearing design of the BSA twins might discount them.
Being a Norton forum it would be reasonable for there to be a resounding shout that Norton provided the best reliability and horsepower. I guess the factory’s warranty claim records would tell us a lot about the various bikes reliability and quality control. Even that would be biased by the average demographic of the person who bought the bikes. Is there any evidence to suggest that Triumph owners were wilder or less dedicated to maintaining their bikes than Norton owner or visa versa. again I don’t know.
But all the talk regarding care of assembly is missing one really important point. That is the fact that a really well designed and manufactured engine shouldn’t take extreme skill or care to assemble. It should fit together like a Lego set. I imagine that was companies like Honda’s great advantage. With very accurately machined components they didn’t need highly trained staff to assemble the engines, more like a production line.
just a thought
Alan