brittle norton sprocket failiure

The sprocket that broke was slightly different to the original,the boss has smaller radii to the sprocket face,the failiure started at the woodruff key area,there is a grainy dark stain where the crack appears to have started prior to the breaking.
The alignment was checked ,as the P11 has "11" spacers in the engine gearbox plates to frame ,the clutch basket had a very slight movement,the alignment is not as critical as a commando, so should not be confused.
Oh by the way anybody working with one of these bikes,firstly make sure the oil tank does not leak and fit it first into the bare frame,ignore this at your peril.
On the subject of the P11 do not believe the doom merchants, that say they do not handle,they have never ridden one,these bikes are the best kept secret of the bike world,some of the early bikes have stiffer front fork action,that can cause it to head shake on bumpy roads but not too dangerous,just turn down the damper a turn or two,to find the limit of one of these you will not have a licence for long,I would say that the P11 handles about the same as my atlas that I had years ago,not a patch on a mates 88SS,wow!! did that go,and handled very well.on the subject of beauty of a bike try the G15,now that did handle better than an Atlas,certainly vibrated less and much more comfortable ride.
 
peter james owen said:
...the boss has smaller radii to the sprocket face,the failiure started at the woodruff key area,
Click to expand...

That is about the only spot a stress failure could start from,look closely at the broaching and the relief at the corners

Google DR650 third gear failure for a similar situation,that was solved by a billet set coming onto the market after I sent my complete transmission to Nova Racing Transmissions in the UK for the development.
The gear could split into three pieces destroying the engine in some cases,over hardness may have been a contributing factor.
 
Also have a look at the taper or remnants of the sprocket taper for metal fretting indicating looseness or high spots. I can see where a key that stands too proud of the taper is going to put abnormal stresses on the sprocket. Can the key be salvaged and assessed?

Better to have answers to these questions before going to battle.

Good luck and let us know what you find out.
 
If any body wants to see the broken sprocket,E -mail me petejowen@hotmail.co.uk.At 64 there must be a way of putting the pictures on here but it is beyond me.
As one of the HY-CAM info group [P11 and N15/ MatchlessG15/AJS M33]and any body wants any info or query just ask,I am organising a gathering of the AMC HYBRIDS at the VMCC stanford hall in july,where you can see a number of these dessert sledges all together.
As a long time customer of RGM having spent over £2,500 in the last 10yrs,with very little complaint,I do feel very disappointed to be treated like I have,looks like I will take my custom back to Les at norvill,making sure that no AMC hybrids people buy any sprockets or any parts from RGM in the future .
RGM were cheaper, but looking at the Norvill they have actually brought some prices down,[thats very unusual for these days].
Back to Rgm the parts I wanted to put my very tidy P11 back being in the state it was before the engine sprocket broke. The parts I needed, were in their stock, I wanted my helmet replacing with my nearly new jacket ,as for the shock and bruising to me, I was going to put down to being part of riding bikes . the wife thought the bang to my head had done me harm,but all I wanted was my bike back to being good again.
 
peter james owen said:
If any body wants to see the broken sprocket,E -mail me
Click to expand...

brittle norton sprocket failiure
 
certainly seems to be a bit thin at its weakest point, on top of the keyway where no doubt it cracked first, what is the diameter of the sprocket there? compared to a OEM.
 
Mmmmm, I must say I initially thought this was a gearbox sprocket too.
Tapered sprockets are a little more complicated.
The surface finish on the taper of that sprocket looks really odd, quite grey ??

Have you tried to file this sprocket - can it be filed. ?
Rockwell 58 doesn't seem overly hard when looking at a chart of Rockwells,
but then I don't know what a typical sprocket would test at either.
Or if they are hardeded right through, or are left with a soft core (anyone know ??).

Can you still apply bearing blue to the taper on a half sprocket, and see how it fits to the taper on the crank.
If the fit is not all that good, it could have applied a great deal of pressure on the key and keyway, and that would not be good.
It is getting murky to say if thats a possible manufacturing fault, or a fitting up point though....
 
madass140 said:
certainly seems to be a bit thin at its weakest point, on top of the keyway where no doubt it cracked first,
Click to expand...

Yes, its keyway goes about right up to the slight taper on the top of the flange there.
A dommie sprocket here for camparison (not P11 note) has a good 1/8" metal between the keyway and edge of the taper on the hub/flange.
 
P.S. If the key itself is too big (tall), it could have applied a lot of pressure to the sprocket too,
as the sprocket nut was tightened up and forced the sprocket tighter on the taper ?
This would have to be very carefully looked at...
 
peter james owen said:
As a long time customer of RGM having spent over £2,500 in the last 10yrs,with very little complaint,I do feel very disappointed to be treated like I have,looks like I will take my custom back to Les at norvill,making sure that no AMC hybrids people buy any sprockets or any parts from RGM in the future .
RGM were cheaper, but looking at the Norvill they have actually brought some prices down,[thats very unusual for these days].
Back to Rgm the parts I wanted to put my very tidy P11 back being in the state it was before the engine sprocket broke. The parts I needed, were in their stock, I wanted my helmet replacing with my nearly new jacket ,as for the shock and bruising to me, I was going to put down to being part of riding bikes . the wife thought the bang to my head had done me harm,but all I wanted was my bike back to being good again.
Click to expand...

An example of Les Emery customer service.

http://www.nortonownersclub.org/noc-cha ... /407567438.

Regarding hardening of the sprocket, it is typically only a surface finish a few thou' deep the core of the part remains unhardened but the material should be strong enough for the purpose it's designed for. The fracture suggests that sprocket is of the same hardness all the way through. I mentioned previously, Peter apparently had no problems with other sprockets.
 
Pictures can be deceiving but...
Note the grain structure at the fracture,also the change in direction at the initial failure which was always going to be at the base of the broaching.
You then see the jagged secondary fracture on the opposite site.
 
Thank you Les form posting the pictures for me,the mark on the bottom picture is when the sprocket with the chain attached jammed against the alternator stator,the primary drive was all locked up when I took off the primary case.
I will take a picture of the standard sprocket next to the broken one,then we can see the difference.
There is no difference in sprockets from the domminator 88,to the P11,including the Atlas,they were all the same fit, at 5/8 x 1/4 they all used single strand chain
Dunstall,Curley,lawton and wilson,all used the same sprocket,thats why you can get them in 18T to 23T,that was the quickest way to gear a racing bike,as well as changing the rear sprocket as a fine tune to the overall gearing.changing the gear box sprocket was another way but was time consuming during a race meeting.[one tooth on the gearbox was equal to three on the rear.]also the clutch would be hot for quite a while,especially after practice.
Talking of chains, some racers used a slimmer chain,as the 88 and 99, were used on the atlas and on commando racers,and even on Rob north Tridents so they could use wider tyres.
 
To my canny eye, after looking at the photo of the broken engine sprocket, I would say that the crack appears to have happened at the quenching stage of the heat treatment, you sometimes get metal components that will crack when heated to the high temperatures required to obtain hardness, it has happened to me in a tool made from 2.5 inch steel bar.
Technically, the sprocket should be hardened and tempted, or……………
Could this sprocket have gone through without being tempered :?:
The crack may not have been obvious after heat treatment, short of getting it crack tested afterwards you wouldn’t have known that the crack was there.
http://www.mee-inc.com/rockhar.html

Quench cracks
The volume changes, which occur when austenite is cooled, are: a) expansion when gamma iron transforms to ferrite; b) contraction when cementite is precipitated; c) normal thermal contraction.
When steel is quenched these volume changes occur very rapidly and unevenly throughout the specimen. The outside cools most quickly, and is mainly martensitic, in which contraction (b) has not occurred. The centre may be troostitic and contraction (b) started.
Stresses are set up which may cause the metal either to distort or to crack if the ductility is insufficient for plastic flow to occur. Such cracks may occur some time after the quenching or in the early stages of tempering.
Quench cracks are liable to occur:
a) due to presence of non-metallic inclusions, cementite masses, etc.;
b) when austenite is coarse grained due to high quenching temperature;
c) owing to uneven quenching;
d) in pieces of irregular section and when sharp re-entrant angles are present in the design
http://www.keytometals.com/Articles/Art12.htm

http://www.technologystudent.com/equip1/heat1.htm
 
Hello again
The person who analysed the broken sprocket was, Barrie ratcliffe, E-mail = ratclffebarrie@gmail.com.
If you want more info give him an E-mail,
I will be at Brooklands in june,at the Norton day,where I will have the sprocket with me,the P11 will be running by then ,I have given up on RGM,enough is enough just put it down to being ripped off again.
 
peter james owen said:
Yes I had the sprocket analysed it was done overnight The cumbrian supplier had not done this in three months,it was made in birmingham of 58 rockwell,ideally it should be EN24,but 58 rockwell is OK!!.
It had been well over hardened creating the brittleness.!! ,sombody left it in the vat too long.bought a new sprocket 22T as I wanted to gear up for normal roadwork.
Click to expand...
If this sproket was EN24 it was the WRONG material. En24 is a through hardening alloy steel. designed to be a 60/65 ton steel supplied in condition T. this gives Rockwell hardness of 31C. 31 Rockwell c is soft, not hard.therefore way to soft to be used in a sproket. however if the hardness is 60Rc, or more, then no drawing or tempering has taken place and the material is used in the fully hard condition. No wonder it shattered. when a steel is hardened, it is always in the fully hard condition. it is tempering or drawing that slightly reduces the hardness and gives some toughness.
2 approaches can be used for sprokets. The first is to use a .45% plain carbon steel. this may be through or flame hardened. The desired hardness range is 47/50 Rc. no harder than 50 as then can be weak. therefore drawing is necessary. the other is to use a low carbon alloy steel, 4320, 8620, or EN36A. this types of steel are special case hardening grades. you need at least 30 thou depth of case at 60Rc and the core at 31 Rc. there are applications for both types. If I was doing an engine sproket, I would go the case hardened way. making a rear wheel sproket the flame hardened option is the more practical.

EN 42 is a special spring steel. I would not use this. Fully hard teeth at or over 60 Rc seems an invitation to trouble.

So, dont be timid and always ask what the material is and a description of the heat treatment. you will probably get the stalling treatment but dont give up. there are NO "trade secrets "here, only advertising blurb .. sproket engineering was sorted out a long time ago. most probably dealers would not understand what you are asking anyway.
hope this helps
Corrections and contrary advice welcomed. Best wishes Bradley
 
There is no way a sprocket should fail like that, ever. As mentioned by others it is probably a combination of incorrect heat treatment, material quality and detail design, you might be able to get an analysis done at an engineering university if there is one close (I did a lot of failure analysis while I was doing postgrad). Just looking at those pictures I wouldnt necessarily conclude it is a brittle failure though.
Also the tooth profile of that sprocket doesnt look right either, does the chain sit nicely?
 
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