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Big End Bearings

Norton Models (not Commando or P11)

Re: Big End Bearings

Postby J. M. Leadbeater » Tue May 31, 2016 3:33 pm

I thought the crank haves were forged in EN16. If not I wasted a few hours learning all about how to weld them at the Welding Institute place outside Cambridge a few years ago..... Luckily as I worked for G.E.c. who had an account with them my lesson cost ME nothing.......
As one is suppossed to have a film of oil between the jounal and shell there should be very little wear. AND even less if one changes the oil on a regular basis and filters it. In the 70s I never ceased to be amazed at the number of Middle East customers coming into a friends shop for spares who only bought new std size shells for their old BSA and Triumph motorcycles and only very rarely bought other sizes..... Mind you I bet their oil cost a LOT less than ours and thinking about it I bet they used Rotella........

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Re: Big End Bearings

Postby Rohan » Tue May 31, 2016 3:55 pm

texasSlick wrote:
I repeat ... If the journals are not case hardened, then they should have been. It is disappointing to think Norton took such a cost saving measure, making the crankshaft journal a sacrificial metal in lieu of the readily changed and relatively inexpensive bearing shells. The main journals are in ball/roller bearings, and hardening is not required, and likely not desirable.

This is good information to know. If I ever open up my Atlas again, I will harden the journals, either by nitriding, or by the simple method of a dirty oxy-acetylene flame. The auto industry method is usually induction.
Slick


A lot of cars used cast iron cranks, nice soft journals.

Perfectly satisfactory, as long as the oil is changed regularly.
As JM points out.

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Re: Big End Bearings

Postby texasSlick » Tue May 31, 2016 5:45 pm

Rohan wrote:
texasSlick wrote:
I repeat ... If the journals are not case hardened, then they should have been. It is disappointing to think Norton took such a cost saving measure, making the crankshaft journal a sacrificial metal in lieu of the readily changed and relatively inexpensive bearing shells. The main journals are in ball/roller bearings, and hardening is not required, and likely not desirable.

This is good information to know. If I ever open up my Atlas again, I will harden the journals, either by nitriding, or by the simple method of a dirty oxy-acetylene flame. The auto industry method is usually induction.
Slick


A lot of cars used cast iron cranks, nice soft journals.

Perfectly satisfactory, as long as the oil is changed regularly.
As JM points out.


I was being a little facetious in saying the crank was "sacrificial" .... sort of like the electrical engineer's joke about putting a $3.50 transistor in a circuit to protect a ten cent fuse.

Nevertheless, all modern engines use hardened journals and regularly run 250K - 350K miles before overhaul. Of course, other technology is responsible in part for this longevity, but if soft journals are perfectly acceptable, no auto mfgr would go to the expense of induction hardening their cranks. This technology was available in the 60's, I am simply surprised the journals were not hardened.

Modern cranks are generally deemed scrap after 3 re-grinds because the case is gone. The Norton re-grind diagram I posted listed only three. Foolish me to think there was a common reason for a three re-grind limit.

Since journal hardening digresses from the OP's original question, I'll leave it at that. I regret advising him to forget further grinds based on the loss of the case hardening, which never existed.

Slick
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The Second Law (of thermodynamics) rules.
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Re: Big End Bearings

Postby Rohan » Tue May 31, 2016 6:30 pm

As any taxi driver or truck driver will tell you, if it doesn't cool down it will never wear out.
Its corrosion that eats out engines...

Nortons had a problem with breaking cranks as power outputs grew.
Thats why the journal size was increased, from 1.50" to 1.75".
Getting too far undersize -for strength - is why the shells don't go too far down in size.
And why metal spraying or hard chroming is quite a useful solution to worn journals.

That guy on fleabay looks to be parting out a whole 650 mercury. For shame, for shame...

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Re: Big End Bearings

Postby Bernhard » Thu Jun 02, 2016 5:08 am

kommando wrote:Note Jim Comnoz has cut a complete crank and did hardness tests.

commando-crankshaft-porn-t8365-480.html

by comnoz » Sat Dec 07, 2013 5:26 am
I have sliced up and tested a stock crank. It tested 48rc everywhere- cheeks, shafts and crankpins. I have not seen any sigh of post cast heat treatment. Jim

My own crank and the T120 and the 2 B25 cranks I have are all soft with no sign of hardening, never saw it being done when I worked at the engine factories in Austin Rover in the 80's (exception was the Triumph Stag crank, this was hardened but I never saw that line), the latest engines were then polished after grinding but still not hardened.


I worked at a Petter diesel engine factory for 2 years and can tell you it was common practice to take a couple of cranks from a batch that had been heat treated (no I admit I do not know what type) and cut them up on the Cincinnati tool and cutter grinding machine with the brown parting wheel (not the black one as it burns) the parts were then sent to the laboratory for checking. The depth of hardness of the crankpin journal was easy to see, and if this wasn’t up to spec. then the whole batch was sent back to the heat treatment works to be redone. But these engines being diesel run at 20:1 compression ratio.

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Re: Big End Bearings

Postby texasSlick » Thu Jun 02, 2016 2:21 pm

Bernhard wrote:
I worked at a Petter diesel engine factory for 2 years and can tell you it was common practice to take a couple of cranks from a batch that had been heat treated (no I admit I do not know what type) and cut them up on the Cincinnati tool and cutter grinding machine with the brown parting wheel (not the black one as it burns) the parts were then sent to the laboratory for checking. The depth of hardness of the crankpin journal was easy to see, and if this wasn’t up to spec. then the whole batch was sent back to the heat treatment works to be redone. But these engines being diesel run at 20:1 compression ratio.


And these engines no doubt run 1 million miles before overhaul.

Slick
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Re: Big End Bearings

Postby Rohan » Thu Jun 02, 2016 4:26 pm

texasSlick wrote:And these engines no doubt run 1 million miles before overhaul.


And as any taxi driver or truck driver will tell you, if it never cools down it will never wear out.
Even without mythically hardened journals.

Taxi motorcycles al;so did some fabulous mileages, before the concept of taxi motorcycles disappeared
(in the western world).

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Re: Big End Bearings

Postby Bernhard » Fri Jun 03, 2016 6:19 am

texasSlick wrote:
Bernhard wrote: I worked at a Petter diesel engine factory for 2 years and can tell you it was common practice to take a couple of cranks from a batch that had been heat treated (no I admit I do not know what type) and cut them up on the Cincinnati tool and cutter grinding machine with the brown parting wheel (not the black one as it burns) the parts were then sent to the laboratory for checking. The depth of hardness of the crankpin journal was easy to see, and if this wasn’t up to spec. then the whole batch was sent back to the heat treatment works to be redone. But these engines being diesel run at 20:1 compression ratio.


And these engines no doubt run 1 million miles before overhaul. Slick


You are quite right, it amazes me how many old ones are still out there in garden sheds etc. from the UK TV Channel 42 repeat of Henry Cole and Sam Lovegrove of Shed and Buried;

http://www.travelchannel.co.uk/shows/shed-and-buried

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Re: Big End Bearings

Postby Onder » Fri Jun 03, 2016 11:06 am

It seems to me that cranks arent wearing out as much as their surface gets ruined by material circulating
in the oil. Like pieces of the engine.
Ive never rebuilt a bike engine that didnt need a regrind. Size might be good but the surface wasnt.

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Re: Big End Bearings

Postby Rohan » Fri Jun 03, 2016 2:41 pm

Having an oil filter in the lube system helps here, considerably,
if owners won't change the oil before it gets too dirty.

The oil that came out of a (well) used Commando (850) was more like the consistency of a thin tar.
With fairly low miles, I had wondered if the oil had ever been changed.
Thank goodness for an oil filter...

GM did some published research into oil filters some years back now.
They found if the filtering was done down to 4 microns, an engine life of 300,000
to 400,000 miles should be commonly possible - about double current durability. (watercooled car engines)

Most filters, even at best, are 12 microns.
And many considerably more...

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Re: Big End Bearings

Postby J. M. Leadbeater » Tue Jul 19, 2016 3:26 pm

Rohan is possibly partly correct and Norton certainly had a problem with breaking cranks with most breaking across the drive side big ends outer 90 thou radius but this is due to the clever souls(Moderator please note I am being VERY polite in describing idiots) at Norton in Birmingham, at AMC and later at NVT not knowing anything about stress raisers ..along with having sweet nothing in the way of inspection or quality control 9like most of British industry at the time and later in my experience...
he operators, probably on piece work rates, did NOT correctly clean out to the drawing with a big drill the oil way inside the D.S. crank half. Mr Negus told me the drawing showed the outer edge of the drill to finish within the area of the crank web but the operators did not often if ever do so leaving the sharp outer edge of the drill finishing DIRECTLY beneath the big ends outer 90 thou radius. Sharp corners are stress raisers thus many Norton cranks were correctly ground with perfect 90 thou stress REDUCING radiuses in them at each end of the big ends but beneath the D.S. outer radius they left a perfect example of a crank breaking stress raiser. Or as my friendly G.E.C. Senior Metalurgist said after examining our second broken crank...' Who was the idiot who left that stress raiser inside your crank at a point of maximum stress?' Had NVT produced new crank halves decades ago the stress raiser would not of existed because Mr Negus told me that whilst the drawings were correct he had had them amended so that the problem would never occur again. NVT were having a small batch of new crank halves test machined by Laystall Engineering in Wolverhampton which I had heard about so I said to Mr Negus whilst on a spares buying trip something like ...I hope you are ensuring the stress raiser inside the DS half no longer exists. I then had to quote Mr Hopwoods comments on the subject (It leaves something to be desired in technique) and drew out a sketch. On a subsequent visit Mr Negus told ne the drawings had been amended but that the cost of machining was so great non were going to be produced for sale to the public.
When I told a friend in the trade all about the stress raiser I thought only I knew about he replied ' Oh I thought you knew all about it, I have been removing it for years from my and my customers road and race cranks...they break if you dont'.
Everyone should know about it..Yee gods I have been going on about it for years......
I understand that the privately entered Commando ownerd by Mr Negus which usually finished endurance races whilst tre official works entries rarely if ever finished a 12 hour race let alone a 24 hour race broke its crank shortly after finishing second to the Honda 4 in the Spa 24 hour race in , without looking up the press cuttings, 1973??? AND GUESS WHERE IT BROKE!! Even saw one for sale on E bay a few years ago with the D.S. crank broken rihgt across the big ends outer radius..... UK built Comet airliners fell out of the sky killing LOTS of people thanks to a stress raiser and in doing so handed over to Boeing a vast world market place for their new 707s....and later 747s etc
Stress raisers. 'Something every Engineering student spends a few hours learning about which most then forget in later life and in so doing kill and injure lots of innocent people........' John Rennick, my friendly very helpful G.E.C. Senior Metalurgist who spent hours passing on information and doing testing for me and alll at G.E.C.s expense.....which was jolly decent of them!

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Re: Big End Bearings

Postby Rohan » Tue Jul 19, 2016 4:33 pm

Long discussion...

It is rumoured that Tridents cranks were changed after every 2nd race meet.
Or they broke.
As they'd found from experience.

A lot of race teams do this, for all sorts of parts.
Nortons always changed the clutch every race, and after practice, in the IoM.
Valve springs too.

Thats just the stress of racing ...

Redesigning to have more metal where its needed would have been one solution,
but for small cash strapped firms thats probably not an option....

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Re: Big End Bearings

Postby J. M. Leadbeater » Thu Jul 21, 2016 7:59 am

If you go using cranks for racing that were designed and manufactured for road going use it should come as NO suprise that you reduce componant reliability and life. I doubt that cranks were changed after every couple of races although Chris Vincent changed his on his BSA twin sidecar race motors on a regular basis especially when they did a self destruct on the last lap at Brands Hatch just before reaching the finish line...that failure was a tad spectacular!! But Chris Vincent worked at BSA and bits became mislaid off of production lines all over the place in those days...

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Re: Big End Bearings

Postby Rohan » Thu Jul 21, 2016 4:04 pm

The cranks WERE changed, often, in the race Tridents - Slippery Sam etc.
It is noted someplace they weren't changed after their 2 races somewhere,
as they should have been, and the crank broke on its next race.

How do you redesign a road crank to be a race crank without a complete motor redesign ?
If the crank simply isn't strong enough, it needs more metal, and bigger bearings to suit, etc etc etc.

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Re: Big End Bearings

Postby acotrel » Thu Jul 28, 2016 2:54 pm

How do you case-harden the journals on a crank without adversely affecting the webs ? My answer was to hard chromium plate and regrind the journals, however many chrome baths are not up to scratch to do the job. I've tried nitriding, however in a high-revving motor with medium stroke wear is still a problem. As I understand it the Triumph Trident cranks were made planar then twisted to give the journal offsets - sounds butcherous to me.
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