Big End Bearings

Bernhard said:

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

Slick

texasSlick said:

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

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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).

texasSlick said:

Bernhard said:

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

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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

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.

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...

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!

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....

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...

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.

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.

acotrel said:

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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Thats what forging stuff is all about - keeps the grain of the metal structure to advantage.

Possum said:

I have a 650cc crank with big-ends at 1.700" diameter and a bit ordinary looking, so it needs a regrind and new large journal end shells

Is it possible to get new journal end shells at 1.690" diameter? (0.060" oversize)

If so, where?

Cheers, Possum

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Journal end shells do not go to this size so its a large end journal end rebuild with hot metal spraying a specialist job or find a standard crankshaft

Possum said:

I have a 650cc crank with big-ends at 1.700" diameter and a bit ordinary looking, so it needs a regrind and new large end shells

Is it possible to get new large end shells at 1.690" diameter? (0.060" oversize)

If so, where?

Cheers, Possum

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Warning make sure you know what oil pump you have on the bike has there are two types the early type the 3 start pump and the later 6 start pump both you have to use different large end shells early 650 and early atlas used end shells with No oil Holes in the shells the later type did have oil holes so do not fit early bike with later large end shells unless you use the 6 start oil pump has you have oiling problems and quickly worn large journals so now you know the 6 start oil pump came out after 1964 a Plumstead up rated the old oil pump to run a double the speed by the gearing IE the Six Start oil pump

The V12 Jaguar cranks were made by forging and twisting. The process is done hot, and usually followed by further heat treatment, so there isn't a problem with residual stresses. It allows a complex crank to be made in relatively(!) simple forging dies.