Commando stainless steel wheel spindles

I note on E Bay such things are available.
When decades ago I had a couple of sets made in a certain tool room using a grade of stainless giving the highest tensile and shear strengths shown in the British Standards book before using them I thought to myself ' I wonder if the tensile and shear strengths match those of the original materials employed by Norton???'. I wrote to Mr Hopwood asking what values I should be looking for and the stainless ones were lower especially the shear strength. I then phoned a Gentleman (the metalurgist) at Triumph at Meriden and he gave me values very similar to those given by Mr Hopwood ...
Some time later I was talking to a Gentleman employed specifically to advise on stainless steels and whilst picking his brain on the CORRECT grade to empoloy for through bolts with alloy barrels, bolts which expand at the same rate as aluminium alloys so they would not stretch the threads in the crank cases as the barrels expanded reducing the torque values when the motor was cold which was causing crank case to barrel gasket failures to occur I asked if there was a stainless that gave the tensile and shear strengths I required for wheel spindles and he told me of a very old grade that did giving me its identity and heat treatment values to use when ordering it. He even suggested a few stock holders I should try. NON had any of a suitable size in stock but could have some IF I ordered a mills worth of production!!
A friend a few years ago was half way across the USA doing a coast to coast ride on his Commando when a staionless rear wheel spindle failed...He survived the experience....I wonder what grade of stainless it was and what grade people use for the spindles available on E Bay these days?? Perhaps one of those people flogging them or producing them could inform us as to the material specification they employ......... my money is on no answer being forthcoming.
Just a thought few I suspect will think ofas they consider buying new wheel spindles......

I suppose one could add the question of was it a two piece or a one piece axle that broke. The stock steel two piece
axle will break.

Its not so much the grade of stainless but the design of the axle as to its strength, look at a Norton front axle 17mm in diameter, its never going to shear. The rear will break whether its original or stainless, many here know the original ones break because its a very poor design.
Not plugging my own products but pictured is the best design for simplicity and ease of fitment, One piece axle (stainless) there is no threaded part of the axle residing between the 2 swingarm plates therefore there is no vulnerable point on the axle, I cant imagine what abuse a Norton would take for it to shear a solid piece of 9/16" round bar, regardless of what grade of stainless it is.

Aluminum and stainless have significantly different expansion rates. Trying to find a stainless that will expand at the same rate as aluminum for head/barrel bolts is a folly and makes no sense at all.

Lots of words in this post without any substance. No actual material specifications after talking to several (name dropping) experts.

No link to what product is suspect on Ebay.

Is this of any value to anyone other than to suggest there are inferior products out there?

The grade of stainless you need to look for is 431 otherwise known as EN57. This is a high tensile Martensitic grade & has good shear strength. Most after market wheel spindles are made from 303 which is in my opinion not suitable. The original parts would probably have been made from EN16 or similar. Not sure why you would want a stainless wheel spindle anyway, as it's all hidden away and covered in grease.

I have had one break on the rear of my MK3. If you want any more evidence as to the crap that is out there just scroll down the page on the AN facebook page and see a customers experience with some bolts. Despite him working in one of the UK's top engineering companies he still got caught out, thankfully with no damage other than the cost of replacement bolts.

I'm wondering how many Commandos were made and how many broken axles have occurred? If it's very rare, I'll play the odds.
Jaydee

Years ago, racing a Commando in WERA C Superbike (before they had vintage) I broke two rear wheel axles or spindles as you are calling them - in one weekend, both at high speed at the end of the straightaway at Grattan Raceway in Michigan. Exciting, but survived both events. They were original Norton parts, old and used. No trophy that weekend. These were the only ones that I had ever had break. A few years later I made a couple of thru-bolt one-piece axles using drill rod. Never had a problem with those.

If you ride your Norton, on the public roads, with the respect that an antique deserves you will not experience any issues with stainless axles. I like Madasses approach, simplicity is a good thing.

In 34 years of selling stainless parts and fasteners RPC has never been asked to warrantee/replace a broken or miss-sized stainless part; in my old age I sometimes miss-count the number of pieces in a given kit and need to send off the supplemental piece(s) separately. There may be applications on a Norton where non-stainless parts may be more desirable, but for the vast majority of Norton owners/riders the only difference that will become apparent is that your motorcycle will not be showing rust growing from your fasteners; stainless parts can be polished (or not polished) to any degree you like without losing their inherent ability to resist corrosion. Stainless fasteners, up to 1/2", in my experience, for Norton motorcycles will gain and hold all the required torque settings established by factory and noted experts. Generally speaking my "rule-of-thumb" is simply: If you can see it (when the motorcycle is mission ready) make it stainless. What's not to like?

Matchless said:

The grade of stainless you need to look for is 431 otherwise known as EN57. This is a high tensile Martensitic grade & has good shear strength. Most after market wheel spindles are made from 303 which is in my opinion not suitable. The original parts would probably have been made from EN16 or similar. Not sure why you would want a stainless wheel spindle anyway, as it's all hidden away and covered in grease.

Click to expand...

300 Series is dead soft and hard to machine...can't be hardened. 400 series is still somewhat hard to machine compared to most steels, but can be hardened. Not sure that stainless of any type is a proper material for high stressed parts unless it is hardened, even then there are better choices. If rust is the only reason for using stainless I would prefer some sort of plating on proper steel parts. Just my opinion.

Part of the reason of the migration to stainless is that plating is expensive now and the cad plating isnt the same, it seems
soft to me. So polished stainless is cost effective and longer lasting.
It isnt original factory issue but unless you are putting it on display so what.

I also agree with Madass

it is not an issue of the material specifications as the stock rear axles are also prone to sheer ,But a poor design especially on the Cush drive hubs

I have fitted two piece stainless axles and had no issues , but do check wheel bearing condition and the fit of the bearings is critical these can often work loose in the hub and apply leverage to the axle under load
causing premature fractures normally where the stub joins the main spindle , also check cush pads are a good fit worn rubbers also add stress to the spindle assembly

the Madass solution of fitting a 1 piece axle is a great idea as it removes the stress point where spindle / half spindle join

To say nothing of doing away with the questionable stock cush hub completely.

This issue of stainless fasteners seems to come up regularly on the forum. With a bit of effort with the search function one can find the other discussions. A couple of the significant conclusions are the following:

1. There are very high strength and toughness stainless fasteners available. We have used them in military and aerospace for decades to hold air and space craft together. A look at the specs for stainless fasteners in the NAS standards (or NASM for the metric minded) will provide plenty of proof for that statement. Plenty of 180,000+ psi stainless fasteners holding the engines in our fighter jets together. In the motorsport community common fastener sizes are available in stainless alloys with 170,000+ psi tensile strength from suppliers like ARP. CNW offers fastener sets specifically for Commandos sourced from ARP. I don't know of any fastener that needs it on a Commando, but if you want higher strength (at higher cost) you can find stainless alloy fasteners at even higher tensile strength that still have high toughness and low notch sensitivity, but that's really overkill for our old bikes. I've seen specs for stainless fasteners used in missiles with tensile strengths well above 225,000 psi.

2. There are also plenty of stainless fasteners available at your local hardware store that are relatively low tensile strength, and probably not suitable for high strength applications. You probably wouldn't want to use the stainless bolts from an unknown Chinese supplier to replace Commando head bolts. On the other hand, cap screws from A286 and 17-4 PH are readily available from industrial suppliers, and have tensile strength in the 130,000+ psi range, about the same as common high strength grade 8 steel fasteners, and stronger than most of the original equipment fasteners on a Commando. Even the common cap screws in 316 stainless are good for 70,000 psi, more than enough for most of the chassis fasteners.

It's not really correct to say that 300 series can not be hardened. It can't be hardened by heat treating, but is commonly hardened by cold working. This is the process used by ARP to make 304 series fasteners with 170,000+ psi tensile strength.

Plenty more info on the subject if you google "high strength stainless steel fasteners" and spend a couple hours reading. This is an issue that was sorted out long ago by the military and industrial designers and suppliers.

Ken

I fear I'm feeling the need to pontificate even more, so back to the subject of stainless rear axles.

The comments about shear strength are a bit of a red herring, I believe. The shear strength of most steels, including the stainless varieties, is generally estimated for design purposes at 60% of tensile strength (UTS). Specific tests and analyses have shown that to be accurate to within a couple percent for typical bolts. That means that a stainless axle with the same tensile strength as a carbon steel axle will have the same shear strength.

In fact, I doubt if any Commando axle has ever failed in shear. The typical failure is a break at the start of the threaded part of the main axle, and is a result of bending stress, not shear. Under normal loads, the two piece axle wants to bend at the junction of the main axle and the stub axle. The ones I've seen (and I've had two of them break on my own race bike) have a break that starts at the beginning of the thread, where the stress concentration is the highest. The original two piece axle design is probably fine for normal use, as long as everything is aligned and tightened properly. The combination of over or under tightening, not having the axle exactly perpendicular to the swinging arm, as well as hard usage like racing, can overstress the joint and result in failure. After one of my failures, I determined that I had put the axle out of line when adjusting it to align front and rear wheels. That put a severe bending stress on the joint, further compounded by sticky race slicks and high speed cornering. I didn't determine the cause of the other failure, but I think it likely that it had a similar cause. After the second failure, I replaced it with a one-piece axle. I eventually broke that one too, but I think that was also my fault. I had crashed the bike several times, so the frame was probably not straight, and I think I again place the axle in a bending stress by adjusting to keep the wheels aligned. I'm clearly a slow learner. I also didn't take enough care to make sure that the threaded ends were outside the swingarm plates, making the start of the thread more highly stressed. I eventually sorted it all out, and never had another axle break.

Judging from my own experience, you might just conclude that the major problem with the 2-piece axle design is that it isn't idiot proof.

Looking at the pictures of Madass' axles, I can't see how you could make it any better. In any case, I think it's clearly safer than the original 2-piece design. And for sure it's not going to fail in shear (unless maybe you get rear ended by a semi truck).

Ken

lcrken said:

And for sure it's not going to fail in shear (unless maybe you get rear ended by a semi truck).

Ken

Click to expand...

Never rule this possibility out. !
(Not that I am sure that it is a totally needed quality in an axle.)

This one - a one piece axle - was removed from a plunger frame dommie.
Before my time, so I don't know what happened, but it could have been important that the axle didn't disintegrate...



We diverge a little from stainless and Commandos...

Ouch! Whatever happened to that bike, it probably wasn't a real pleasant experience for the rider.

Ken

Don't know.
Since the wheel was out loose, someone replaced it...

madass140 said:

Its not so much the grade of stainless but the design of the axle as to its strength, look at a Norton front axle 17mm in diameter, its never going to shear. The rear will break whether its original or stainless, many here know the original ones break because its a very poor design.
<...> One piece axle (stainless) there is no threaded part of the axle residing between the 2 swingarm plates therefore there is no vulnerable point on the axle, I cant imagine what abuse a Norton would take for it to shear a solid piece of 9/16" round bar, regardless of what grade of stainless it is.

Click to expand...

Hi Don,

If the axles fail, it will be in bending mode, not shear.
I made a quick calculation to end the guesswork. Assuming the rear axle has to take the load of the entire bike, I have assumed 350 kg divided by two bearings positioned at L/4 and 3L/4, L being the length between the s/a supports. In spite of an accurate size, I scaled your picture and got L=0.257m.
Axle diameter 9/16in = 14.29mm yields A=160 mm2 and Iy=2045.5 mm4 for the second moment of inertia (or area). Between x=0.25L and 0.75L, the bending moment is constant and yields a maximum, M(x) = 112 Nm. The shear force is constant between x=0 and 0.25L, and between 0.75L and 1.00L.
The shear force is V(x) = Vmax = 350*10/2 = 1750 N in rounded figures. Stresses are 391 MPa for bending and 11 MPa for shear.
According to Eurocode these stresses superimpose in a certain fashion but the resulting stress will clearly be close to the bending stress.

As for selecting a suitable material, a safety factor has to be added. Since the axle is a critical component, let n=1.5 .
The required YIELD stress us therefore Sigma-y >= Sigma-b *n = 391*1.5 = 587 MPa.
So, it is advisable to seek a material having a yield stress greater than 587MPa.
Yield stress of EN16-S (tempered state S) comes a little short having 585 MPa but can probably be tweaked a little.
Yield stress of AISI 303 falls short with a yield stress of 310 MPa only. This alloy should clearly not be used, as mentioned in another comment above.
Yield stress of AISI 403 is clearly a well suited alloy, performing a yield stress of 655 MPa in the anealed condition.

I hope me using SI units doesn't cause too much distress!

Don: I hope the alloy you are using is AISI403 or something similar!

-Knut

dennisgb said:

Aluminum and stainless have significantly different expansion rates. Trying to find a stainless that will expand at the same rate as aluminum for head/barrel bolts is a folly and makes no sense at all.

Click to expand...

That's right. I don't want to capture this thread by discussing head bolts but may I point at Peter Bejbom's article in The Roadholder, i think it appeared Dec. 1999. He used high tensile stainless bolts successfully. I can send you a scan if interested, please request by a PM. Calculation of head bolts is a topic of it's own.

-Knut