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Big End Bearings

Norton Models (not Commando or P11)

Big End Bearings

Postby Possum » Sun May 29, 2016 8:43 pm

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

Is it possible to get new slippers at 1.690" diameter? (0.060" oversize)

If so, where?

Cheers, Possum

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Re: Big End Bearings

Postby Rohan » Sun May 29, 2016 9:43 pm

It may be easier to find them in undersize.
(it had to be said !).

Don't know where though, that sounds like a lot.
Tried your trusty local Norton dealer ?

It is possible to get big end bearing surfaces built up by metal spraying, or by electroplating (hard chrome).
Someone proficient in these could probably advise.
I've seen craftsmen doing this with a huge oxy flame on the footpath in India (!).
The journals are steel, so this isn't as diabolical as it sounds...

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Re: Big End Bearings

Postby Triton Thrasher » Mon May 30, 2016 1:18 am

They're usually called bearing shells, rather than "slippers."
Last edited by Triton Thrasher on Mon May 30, 2016 4:27 am, edited 1 time in total.
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Re: Big End Bearings

Postby Rohan » Mon May 30, 2016 2:51 am

Triton Thrasher wrote:Going from 1.700" to 1.690" looks like 10 thou (0.010") undersized to me.


They started life at 1.750"
so they'd already be 50 thou undersize we'd imagine.

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Re: Big End Bearings

Postby texasSlick » Mon May 30, 2016 6:29 am

Sometimes a picture helps

Image

I would say the journals have been ground down past the case hardening. If 060 undersized shells could be found, the crank journals are likely to wear very fast.

Chrome electroplating followed by re-grinding to original specs is the preferred method to re-vitalize this crank. However, if you can find the plater, then precision grinder to do the work, the cost is likely to exceed a new crank.

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Re: Big End Bearings

Postby Rohan » Mon May 30, 2016 3:21 pm

That diagram only shows the journals down to 30 thou undersize...

How much is a new crank ??!!

I recently saw an old 4 cylinder crank that had been hard chromed and ground on all the mains and big ends,
cost was very reasonable. So for just 2 journals should be economical....

Case hardening of the journals - hmmm ?
Be interesting to know the specs on that.

Flame metal spraying with hard facing powder would automatically provide new hardened journals,
and add strength back to thin journals. Nothing to lose... ?

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Re: Big End Bearings

Postby triumph2 » Mon May 30, 2016 9:02 pm

Saw this on Ebay today.
http://www.ebay.com/itm/1968-1969-1970- ... 28188e3a5c
Make an offer?
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'69 Norton Mercury 650
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'05 Triumph Rocket III
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Re: Big End Bearings

Postby kommando » Tue May 31, 2016 1:28 am

The crank was not hardened but left soft for shell bearings, a useful way to extend big end life is ammonia nitriding.

Doubt you will find a 60 thou oversize bearing unless some other application in another engine was to fit, there was a guy who ordered non std under sizes up to 80 thou undersize bearings for the Triumph Dolomite Sprint engine back in the 80's but all trace of him has disappeared.
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Re: Big End Bearings

Postby Bernhard » Tue May 31, 2016 3:04 am

kommando wrote:The crank was not hardened but left soft for shell bearings, a useful way to extend big end life is ammonia nitriding.

Doubt you will find a 60 thou oversize bearing unless some other application in another engine was to fit, there was a guy who ordered non std under sizes up to 80 thou undersize bearings for the Triumph Dolomite Sprint engine back in the 80's but all trace of him has disappeared.


mmmmm…..what :?: :shock: ..... news to me that the big ends are not hardened and temped :?:

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Re: Big End Bearings

Postby J. M. Leadbeater » Tue May 31, 2016 4:17 am

Norton employed Vandervell big end shells and they made them std along with 10,20 30 and 40 thou undersize. Decades ago I was told no more were to be produced as the cost of setting up the production line to make them wouyld be FAR more expensive than they would of made flogging these shells for the next zillion years. A P. only listed 10, 20 and 30 undersize shells.
Decades ago there was I believe a 1275cc British Layland car (1275 Mini??) big end shell that went down to 0.060 and possibly 0.080 undersize which was only 0.001 or so bigger in fitted shell diameter but I doubt they are still avaliable. I have just spoken to my friendly Norton expert (a real one rather than the more normal / common Norton exspurts) and he used these shells in Norton engines decades ago. Norton cranks were also often employed to give larger capacity BSA and Triumph twins because of the longer stroke of the Norton crank and the big ends were reduced down to 1 5/8 to take the BSA and Triumph rods.....
Get you crank welded and ground back to standard BUT get that drive side half examined FIRST to ensure it is not cracked in the area of the D.S. big ends outer 90 thou radius. Unforrtunately at AMC and later NVT they knew sweet nothing about stress raisers and on many cranks successfully managed to introduce a stress raiser into the inside of the D.S. crank half leaving it directly beneath that 90 thou radius which is put in to REDUCE the stresses at this point of MAX stress in the crank. Of course the crank drawings showed the machining correctly with the drilling operation taken well into the web thus positioning the stress raiser where it would NOT cause a problem but it was quicker and easier NOT to follow the drawings especially if on piece work rates of pay and there is no inspection ............ I suspect mismanagement knew there was a crank problem but hoped that failures would occur long after the warrety period was up and that people would blame the guy who reground the crank!! After talking to Mr Negus he checked the crank drawings and found them correcrt but told me he had another instruction added to hopefully ensure any future cranks would be correctly machined but test machining at the time by Laystall Engineering of Wolverhampton showed it far toooo expensive and non, apart from the test pieces were produced and I assume the BIG pole of crank forgings they had were dumped into the scrap bins..... The cranks machined by Laystall Eng were correctly machined and Mr Negus later told me they balanced out without a preoblem.
A friend has customers cranks built back to standard but the Company doing it has rejected a couple of cranks because they examined them and found them cracked and thus scrap. Tis better to scrap the crank than have the crank break when it is rotating at high revs.........it is also a LOT cheaper!!
Its lall very well buying cranks off of E Bay or at auto jumbles but what makes you think that the person flogging it is not doing so because they know the crank is cracked well on its way to failure and as a 4 piece crank it is worthless......... Years ago I binned two D.S. halves after a friend and I had all our spare cranks checked by a certain aircraft Company... you could not visually see the cracks but as sure as God made little apples the cranks were on their way to failure.....I could of shoved the crankis back togerther and sold them and the buyer would of been non the wiser. .....till bits of crank and crank case etc flew about...... Funny thing is I know a few people who would of sold them........

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Re: Big End Bearings

Postby kommando » Tue May 31, 2016 7:58 am

mmmmm…..what :?: :shock: ..... news to me that the big ends are not hardened and temped :?:


Just take a file and draw it over a non critical surface, it will mark easily like mild steel does, just confirmed it on my 750 crank, took no effort to make a scribe line using the edge of a file.
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Re: Big End Bearings

Postby texasSlick » Tue May 31, 2016 9:11 am

kommando wrote:
mmmmm…..what :?: :shock: ..... news to me that the big ends are not hardened and temped :?:


Just take a file and draw it over a non critical surface, it will mark easily like mild steel does, just confirmed it on my 750 crank, took no effort to make a scribe line using the edge of a file.


Did you draw the file across the journal? The journal can be case hardened (case means only a limited depth of the surface) while the remainder of the crank (and the deep interior of the journal) is not hardened.

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.

How many miles are on this crank? It has had 5 (assuming ten thou per cut) and is in need of a sixth. I put 1/2 million miles on my pickup's engine before a ten thou cut on the crank was necessary (it was rebuilt at 254K miles without a crank grind). Given that our 2 cylinder engines cruise at twice the rpm of an 8 cyl, that still equates to 250K miles that we should expect.

Slick

BTW, I would NOT draw a file across my journals.
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Re: Big End Bearings

Postby kommando » Tue May 31, 2016 10:11 am

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.
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Re: Big End Bearings

Postby texasSlick » Tue May 31, 2016 1:31 pm

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.


Well that settles it!

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.

http://www.gh-ia.com/processes/hardenin ... hafts.html

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Re: Big End Bearings

Postby Triton Thrasher » Tue May 31, 2016 3:19 pm

making the crankshaft journal a sacrificial metal in lieu of the readily changed and relatively inexpensive bearing shell


Iron without hardening is a lot harder than shell material.
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