Dog Bones

Pulled the rear shock out today, expected to see it covered in oil and rattle like the Salvo's cup at the local pub. However it was as clean and as functional as it was when I installed it, piston pretty hard to push down and comes back under it's own steam, even mechanic at the local Suzuki dealer agrees with me that the shock appears ok. BTW the spring is in good nick as well, but I will be looking for a heavier duty replacement.

The issue was the dogbones, in particular the left one, it had snapped, and the right has a bend in it near the bottom end probably due to it taking all the load.

When I was installing the Busa shock I was toying with getting new dogbones made. As I needed to gain an extra 6mm length to drop the rear down to the pre-busa height I didn't think filling and redrilling would have been wise as it pit the mounting holes too close to the end. The engineering shop I took them too said they could cut & reweld and it would be as strong as the originals, so I took that option - as I had arranged a barter and swapped them a set of adjustables for the work, everyone seemed happy.

I believed the dogbone broke near Port Campbell on the GOR, that's about when I noticed it bottoming out and thought to myself the shock had blown a seal and lost its oil and/or nitrogen.

I haven't take a photo of it yet, but interestingly the break wasn't where it was cut but a couple of millimeters closer to one end away from the weld, its a jagged tear rather than a clean snap, the other side's weld appears to be ok. Strange the symptoms all pointed to a stuffed shock, you could sit on the bike and the suspension would sag but not return when you got off, however you could lift the rear of the bike up by the pannier holders and it would come up and stay up until you hopped back on again.

Here's hoping that it is only the dogbones and no other damage has been done by riding the final 200 road kls to get her home.

barry_mcki wrote:Pulled the rear shock out today, expected to see it covered in oil and rattle like the Salvo's cup at the local pub.  However it was as clean and as functional as it was when I installed it, piston pretty hard to push down and comes back under it's own steam, even mechanic at the local Suzuki dealer agrees with me that the shock appears ok.  BTW the spring is in good nick as well, but I will be looking for a heavier duty replacement.

The issue was the dogbones, in particular the left one, it had snapped, and the right has a bend in it near the bottom end probably due to it taking all the load.  

When I was installing the Busa shock I was toying with getting new dogbones made.  As I needed to gain an extra  6mm length to drop the rear down to the pre-busa height I didn't think filling and redrilling would have been wise as it pit the mounting holes too close to the end.  The engineering shop I took them too said they could cut & reweld and it would be as strong as the originals, so I took that option - as I had arranged a barter and swapped them a set of adjustables for the work, everyone seemed happy.  

I believed the dogbone broke near Port Campbell on the GOR, that's about when I noticed it bottoming out and thought to myself the shock had blown a seal and lost its oil and/or nitrogen.  

I haven't take a photo of it yet, but interestingly the break wasn't where it was cut but a couple of millimeters closer to one end away from the weld, its a jagged tear rather than a clean snap, the other side's weld appears to be ok.  Strange the symptoms all pointed to a stuffed shock, you could sit on the bike and the suspension would sag but not return when you got off, however you could lift the rear of the bike up by the pannier holders and it would come up and stay up until you hopped back on again.

Here's hoping that it is only the dogbones and no other damage has been done by riding the final 200 road kls to get her home.

Sounds to me like metal fatigue caused by the heat from the adjacent weld. Weld obviously strong enough, but dogbone weakened by the heat.
Can you not get suitable ready made dogbones?

Not that I've found so far MM, the length I'm after is 186mm between centres however most aftermarket suppliers only tell you they raise/lower by "x" inches. And a lot of aftermarket dogbones are made of aluminium, hence why I thought a cut and shut welded by the shop would be okay. I was a little surprised with the break, but you're probably right with the fatigue diagnose.

I'm getting a set plasma cut by the engineering shop so hopefully they will be fine, and the money I was going to spend on a shock rebuild will now go towards a heavy duty spring.

Yeah mate, M.M has nailed exactly what has happened.

I usually make my own out of 6mm 304 Stainless. Only cause I can get my hands on it.

When you do that kind of thing,  you should stress relieve it by heating it up slowly, and very slowly letting it cool .

I`m glad nothing serious happened.

It may be very vigilant for you to thoroughly check, ALL the connection points for signs of cracks,
due to the off set forces, from being supported from one link only, and not two, as engineered.
As the dog bones, connect from the swing arm to the pivot arm, there will be a lot of uneven force been applied to the pivot arm. This will cause twisting and side loading on the pivot arm, and as the other one is bent, tells me the forces on those connection points aren`t traveling two dimensional any more.  

That "could", not saying it "will",  cause premature fatigue on the weaker parts of the pivot supports, mainly, the frame mounts for the pivot arm, but also the pivot arm itself, and some on the lower shock connection to the pivot arm.

While its apart, better to be safe than sorry.

The engineering shop obviously misunderstood you when you asked them to work on your dog bones.  
They didn't realise just how big your dogs are, or they would never have modified your stock ones, but manufactured some diamond coated carbon/kevlar re enforced titanium jobbies.

Hi Barry,

I purchased new dog bones for the Strom for around $80

A friend of mine measured them and made his own for about $5

He used 32 x 6 bright steel flat bar and drilled the 12mm mounting holes with a cordless drill.
He didn't even bother to make them the original dog bone shape but just left them as flat bar, square ends with holes drilled.

I see in the catalogues the next sizes up are 40mm wide and 8mm thick which would fit the Strom, I cannot comment on the Bandit.

If the dog bones are the weak link then this would fix it.

I also made a set out of flat bar to get the right size for my setup (186mm between centres), yep about $5.  

But having seen how one welded side broke and the other side bent using the OEM steel I think the flat plate pieces are staying in the garage to be used for setup purposes only.  Here is the broken side, you can see the metal has been torn apart:




The stainless steel laser cut pair will cost between $50 and $80 depending on how long they take to cut out, I feel a lot safer with these than my homemade temps.

That's been cracked for a long time mate. The welding has crystallised the parent material. 
Too late now but heat treating the whole bone after welding would have worked. 
The dog bones on my VFR look like they're stainless.

2wheelsagain wrote:That's been cracked for a long time mate. The welding has crystallised the parent material. 

Correct

Personally I wouldn't weld any steering or suspension component but if you really couldn't avoid it, something like this would have been structurally much better than a weld across the dog bone

After welding where you did to join the 2 halves, lay another piece of similar dimension steel over the arm and weld along the sides, don't weld the ends or you'll have 2 compromised locations on the arm

Chook wrote:

2wheelsagain wrote:That's been cracked for a long time mate. The welding has crystallised the parent material. 

Correct

Personally I wouldn't weld any steering or suspension component but if you really couldn't avoid it, something like this would have been structurally much better than a weld across the dog bone

After welding where you did to join the 2 halves, lay another piece of similar dimension steel over the arm and weld along the sides, don't weld the ends or you'll have 2 compromised locations on the arm

You would think the engineering shop would have know better.

These were made and installed 3 days prior to going to Phillip Island, I didn't noticed any slump in the rear end until the 2nd Tue after the races, photos I took over that next week and a half didn't show any slouching of the rear end, though it was soft but that's due to the spring. With the weight I'm carrying it was probably always on the cards it was going to break, but I still reckon it was the 30km of very corrugated dirt road I hit in SA that caused it to fail when it did, and over the next 400km it broke all the way through. Normal riding probably would have seen 12 months or more before it let go.

I don't think sandwiching the cut/weld would leave enough room for them to fit, maybe if the weld was on the bottom section, but as it gets up the top they come close to the swing arm mounting section.

Aftermarket dogbones are usually made from aluminium, hence why I thought a cut & shut at an engineering shop would have been sufficient strength-wise, live and learn, and as Chook says, don't weld suspension parts.

I spoke to a friend of mine who is a retired boilermaker.

He told me that stainless steel does not have the same strength as regular (high tensile??) steel.

I found this table which I think supports his statement.

Tensile Strength Comparison Chart

Tensile Strength is the maximum tension applied, as loading, that a fastener can support prior to, or coincidental with, its fracture.

Imperial	lbf/in2	Mpa	Metric
		1200	Class 12.9 (AS1110 High Tensile Steel)
		1100
SAE Grade 8 (AS 2465 High Tensile Steel)	150,000	1034	Class 10.9 (AS 1110 High Tensile Steel)
		1000	Stainless Steel Class 100 (e.g Bumax 109)
		900
SAE Grade 5 (AS 2465 High Tensile)	120,000	827	Class 8.8 (AS 1110 High Tensile Steel)
Stainless Steel Class 80 (e.g Bumax 88)	116,000	800	Stainless Steel Bumax88 (e.g A4-80), Duplex 2507 (UNS S32750) Yield 550 MPA
Stainless Steel (304 & 316) 1/4 to 5/8 dia	100,000	700	Stainless Steel Class 70 (e.g A2-70, A4-70)
		620	Duplex 2205 (UNS S31803) Yield 448MPA
Stainless Steel (304 & 316) 3/4 to 1-1/2 dia	85,000	600
		550
		520	Class 5.8 (AS 1110)
		500	Stainless Steel Class 50 (e.g No Markings)
		450
BSW Mild Steel (AS 2451)	62,000	427
	58,015	400	Class 4.6 (AS1110), Mild Steel (AS1390)

1000 PSI (lbf/in2) = 6.8948 Mpa 1 Mpa = 145.038 PSI (lbf/in2)

Thought #1 is that the "dog bones" do not need to be shaped as such and can just have straight sides.
Thought #2 is why not increase the metal thickness from 6mm to 8mm (a size increase would fit the Strom, I expect the Bandit would be the same).
Thought #3 does the sidecar introduce a new force not normally encountered on a regular bike.

BanditDave wrote:I spoke to a friend of mine who is a retired boilermaker.

He told me that stainless steel does not have the same strength as regular (high tensile??) steel.

I found this table which I think supports his statement.

Tensile Strength Comparison Chart

Tensile Strength is the maximum tension applied, as loading, that a fastener can support prior to, or coincidental with, its fracture.

Imperial	lbf/in2	Mpa	Metric
		1200	Class 12.9 (AS1110 High Tensile Steel)
		1100
SAE Grade 8 (AS 2465 High Tensile Steel)	150,000	1034	Class 10.9 (AS 1110 High Tensile Steel)
		1000	Stainless Steel Class 100 (e.g Bumax 109)
		900
SAE Grade 5 (AS 2465 High Tensile)	120,000	827	Class 8.8 (AS 1110 High Tensile Steel)
Stainless Steel Class 80 (e.g Bumax 88)	116,000	800	Stainless Steel Bumax88 (e.g A4-80), Duplex 2507 (UNS S32750) Yield 550 MPA
Stainless Steel (304 & 316) 1/4 to 5/8 dia	100,000	700	Stainless Steel Class 70 (e.g A2-70, A4-70)
		620	Duplex 2205 (UNS S31803) Yield 448MPA
Stainless Steel (304 & 316) 3/4 to 1-1/2 dia	85,000	600
		550
		520	Class 5.8 (AS 1110)
		500	Stainless Steel Class 50 (e.g No Markings)
		450
BSW Mild Steel (AS 2451)	62,000	427
	58,015	400	Class 4.6 (AS1110), Mild Steel (AS1390)

1000 PSI (lbf/in2) = 6.8948 Mpa 1 Mpa = 145.038 PSI (lbf/in2)

Thought #1 is that the "dog bones" do not need to be shaped as such and can just have straight sides.
Thought #2 is why not increase the metal thickness from 6mm to 8mm (a size increase would fit the Strom, I expect the Bandit would be the same).
Thought #3 does the sidecar introduce a new force not normally encountered on a regular bike.

Grade 8, and grade 5 are structural grades, are they not, not mechanical grades. There is a diffenence
If your going to those extents, yes Bright Steel, but you want 4140, or 4340 as high tensile mechanical grade.

High tensile steel will be harder and have less chance of bending but may have a greater chance of cracking than mild steel

exactly right.
it must be durable , not brittle.

I spoke to my friend , the retired boilermaker again today who agreed with the points made by others on this thread.

As a general rule high tensile steel has a higher tensile strength than stainless steel which is higher than mild steel.

I have seen some alloy dog bones but we agreed they were not made from aluminium but probably some high strength alloy from the aviation world that looks like aluminium.

One thought that came from our discussion is that most of the force on the dog bones on a solo motorcycle are in the axis of the dog bones. The introduction of a sidecar, with a little dog included may be creating a force not along the dog bone axis but maybe in a different direction.

I'm not a boilermaker nor a mechanical engineer, just a cute and lovable retired radio technician, so a lot of this discussion is outside of my field of expertise.

This isn't about the material but it is a good read non the less

http://www.promecha.com.au/leverage_linkages.htm

What an interesting article. I thoroughly enjoyed it and hope there is not an exam attached.


So............ is it possible to determine from the photos of the dogbone failure, if it fractured as a result of longitudinal forces (wow, that was a big word !!!!!!) which I assume would exist with a solo motorcycle, or are there other forces which are contributed by the sidecar (and small dog!)

Is this dogbone failure something that has not been previous documented? I have not heard of such a failure but that does not mean it hasn't happened before.

That is a good article chook, explaining mechanical leverage.

I still think the achilles`heel was the process itself, of extending the link, not the grade of the link, as Barry has had his bike for a long time, fully laden, on multiple trips.

Whilst this last trip probably put more strain on the rear suspension than any previous, I agree the main problem was with the cut&shut process more than any other factor. I haven't heard of anyone actually extending the bones this way, there is probably a reason for that

I might give the (new) engineering firm a call tomorrow and ask about stainless verses high tensile for this application and see what they reckon.

Barry, I`ve been using 6mm x 32mm 304 stainless flat bar for just over 9yrs. I have shaped them to the dogbone shape, as if I didn`t, it would interfere with mechanical workings.

I mark my mine out, and cut the basic shape with a 1mm cutting disc, then match drill the holes, as this is also important. 
I don`t ever put undue heat into them when making them.    I have never had a problem!!!!

I`m not a metallurgist, but am a boilermaker, and have been for 30yrs.

I don`t see a problem using 6mm 304 stainless.    I do realize you have a sidecar, which does chuck other mechanical engineering properties at the equation, but the load is also being distributed to the side car, not solely on the bike. If you had any concerns, you could go to 8mm material, but you will have to look at the length of the pivot bolts, when reassembling, as you must at least have 3 threads showing after tightening.   This is rule of thumb with bolting anything.
But if your engineering shop hasn`t started on them, and he has mechanical engineered grade metals at his disposal, then you may as well go straight for that, as he should have his trusty bible of elements book, to guide you both in the right direction. 
There is a lot of options of material you can use.
I guess another important thing you can do, is to tune the suspension, so the bike and cart, are acting as one, so you would have to know the weight bias between the two, to work out what the cart needs to be in harmony with the bike, and vice versa.  That alone would be stopping undue stress on the whole mechanical operation.

Another scenario is when your towing a trailer by car, you should only have a rated down force on the toe ball, if you`ve got to much, it hasn`t been set up right, the same would go with a sidecar in some respects.

And yes, I do understand that the weight bias can easily be changed on a trailer, through load transfer, as opposed to a sidecar, that has a fixed attach point.

Thanks MT, I thought about making my own but didn't think my artistry with the 1mm cutting disc was good enough to do a proper job. This new shop I'm using has proper laser cutting equipment so I'm hoping the end product is as good if not better than OEM.

All this concern about dog bone length started because the Busa shock lifted the rear end of the Bandit by a little over 1". Prior to this there has never been anything really that wrong with the setup other than my concern that under full load I could be carrying an additional 200 - 300kg on the standard rear shock. By some rough calculations and then trial and error I worked out the length required to bring the rear end down to where it was pre-Busa, hence the need for an additional 6mm to the bones to shorten the ride height.

When I was in Geelong Peter Stephens talking to the parts rep he mentioned the shock itself could be shortened to go back to the standard Bandit height, would have been nice to know that before this all started.

barry_mcki wrote:Thanks MT, I thought about making my own but didn't think my artistry with the 1mm cutting disc was good enough to do a proper job.  This new shop I'm using has proper laser cutting equipment so I'm hoping the end product is as good if not better than OEM.  

All this concern about dog bone length started because the Busa shock lifted the rear end of the Bandit by a little over 1".  Prior to this there has never been anything really that wrong with the setup other than my concern that under full load I could be carrying an additional 200 - 300kg on the standard rear shock.  By some rough calculations and then trial and error I worked out the length required to bring the rear end down to where it was pre-Busa, hence the need for an additional 6mm to the bones to shorten the ride height.  

When I was in Geelong Peter Stephens talking to the parts rep he mentioned the shock itself could be shortened to go back to the standard Bandit height, would have been nice to know that before this all started.

You wonder how they shorten a shock, I hope its not by the cut-shut method

Interesting read all this

I put the question of preferred material to use to one of the Chartered Professional Engineers the SA Government use to assess vehicle modifications etc.
I explained it was now a side car, not a solo as originally built, this was his response

It is very hard to say exactly what to use without looking at it, taking some measurements and doing some calculations. We have never had such a problem so we have nothing to compare to. However doing a quick search online, there are aftermarket dogbones available which would most likely be standard mild steel. If the standard Suzuki units were aluminium, then if he had his new items cut from a base grade 250MPa steel of the same thickness as the original aluminium units, I would say that would be sufficient.

How did you go Barry..all sorted???

Did you use common sense, or go to NASA to re-engineer the wheel?