Aluminuim swinging arms?

[ronan]

Years ago i done the roof on JMC swing arms....Army of Tig machines and lads all making wonderfull braced arms,Still my favourite arm of all time the old classic braced JMC Ime actually on the hunt for one to go into my Bandit.

Could you not sneak one out in your lunch box .

 

[roofman]

Could you not sneak one out in your lunch box .

I done the roof in the late 90,s...dont even know iff there still there on an industrial estate outside Liverpool (Kirby)

 

[Chris Stevens]

*facepalm*
GIA use 7020, irrc jmc used a 7000 series alloy and I think from memory spondon used to use 7020 too. Its a sod to work, has to be worked cold or you wreck the temper and it has to go for heat treat and lots of people use 6082 as an alternative. If the 6082 arms are bending its a design fail not a material one as you increase section to deal with lower material strength. Or more likely its not even real 6082, nobody seems to check material certs or saws lumps of the delivery and sends it off to a lab for analysis. There is a lot of fake materials in the supply chains and that's without people putting it on the sales ad and deliberately misleading. I've seen the material grade dandan moto in china calls aircraft grade alloy and I wouldn't ride something that had his headlight brackets on, let alone a clip on or something structural. Really, I know someone who went to cut a coupon out of it and he found a big void in the sawcut area and I know people that have had clip ons from the same and they've just fell off pushing the bike round the shed. Thing is 99 handlebars might be fine, but one crappy one so the internets say theyre ok to use, but there's no qc or material certification chain involved so its the gamble of cheap price and hope you didnt buy a loosing lottery ticket...

Alloy swingarms might be majority cast now (though I have my doubts at even that), but its not how they were always made. I can go in the shed and lay my hand on about 5 different oem alloy arms all welded up from box and tube assemblies from honda, kawasaki, suzuki and yamaha. Bimota used to make all of their frames and swingarms from standard box welded to machined from raw stock castings at the swingarm and headstock by hand by little old italians in a little factory because they couldnt justify casting stuff, and there are some that might suggest they knew a bit about how to make a rigid well handling bike too. Castings have become de rigeur because theyre cheaper to make on a mass production line and you can get them to into funny shapes to make packaging easier. I've also seen a lot more stress fractured cast frame and swingarms than I have welded together from extrusion and machined stock ones. As a reference point I have a "new" z1 swingarm here (ie the modern watercooled one, not the original 70's one) and that's a welded from stock extrusions assembly and thats what, 2007 I think. I also sent a piece of it off for analysis and it came back close enough to 6082 for me to be comfortable with welding shock mounts onto it so I could use it on a twinshock bike.

As a material its possible to get a significant increase in torsional rigidity for a lighter weight, and that's why you don't see tube swing arms not fashion. My gpz1100 would tie the oem steel tube swingarm into bendy spaghetti going hard into a corner because its a fat overweight overpowered for its running gear old behmoth, I've followed my kawasaki gt750 with watsonian adult double adult sidecar into a bend with someone else riding it and you could visibly see the stock steel arm bending enough to be clearly able to see from another vehicle let alone feel it on the bike, but the modern deep box welded alloy one the 1100 has now doesnt and it weighs significantly less than the original.

Thanks thats very useful info. Tried to get JMC to make some swinging arms for me about 10 years ago, but they were a nightmare to deal with, and in the end struggled to even get the pattern had sent them returned. Think you are 100% on the 6082 arms bending due to a design flaw. The material is thinner than required to keep the weight below the OE steel part, and is probably good enough for most purposes. However when used very hard in serious competition, they do bend as they are too thin. On balance though probably fine for almost everyone.

Ideal seems to be rectangular extrusion, with an internal rib across the middle, which is what Honda used on HRC swinging arms for the trials machines. Cast swinging arms fitted to things like Gas Gas, are relatively heavy, and have been known to snap in extreme situations, and would agree the use of castings has a lot more to do with cost than them being better than fabricated. Spoke to Gavin at GIA about swinging arms, and he was very helpful, and told me some of the guys from Sponden are now working for Norton at Donnington.

I guess the way to go with this is to see if there are any 6082 sections with central rib available, and if not make some arms in different thickness and give them some serious testing (big drop offs should be a good way to test)? Not had any problems welding shock mounts onto OE aluminum swingarms though, but they are too long for TS bikes.

 

[Chris Stevens]

http://www.diagnosis2012.co.uk/vtwinspecials.html

^ some serious home engineering on old bikes, much better than sending off mail order to get an overpriced shiny bendy swinging arm in the post.

Very interesting, and good to see some very nice home made motors.

 

[daleyd]

I guess jmc had loads of business with bikes up to the late 80s vintage with their flexi frames, but once the manufacturers got their act together (late 80's ie the first delta box fzr's)with their chassis then their business must have dried up somewhat...

 

[Chris Stevens]

I had one on my TLR250 out of necessity, the original on my bike was rotten; though as Chris says I'm not sure it would have stood up to much punishment, fortunately I only ride soft southern mud...

Think the arm you have is fine for almost anything but an extreme rider doing British championship events. There is no proper Brit twin-shock championship next year though, and the guy who bent his alloy swinging arm has packed in now anyway.

 

[MrFluffy]

Thanks thats very useful info. Tried to get JMC to make some swinging arms for me about 10 years ago, but they were a nightmare to deal with, and in the end struggled to even get the pattern had sent them returned. Think you are 100% on the 6082 arms bending due to a design flaw. The material is thinner than required to keep the weight below the OE steel part, and is probably good enough for most purposes. However when used very hard in serious competition, they do bend as they are too thin.

Ideal seems to be rectangular extrusion, with an internal rib across the middle, which is what Honda used on HRC swinging arms for the trials machines. Cast swinging arms fitted to things like Gas Gas, are relatively heavy, and have been known to snap in extreme situations, and would agree the use of castings has a lot more to do with cost than them being better than fabricated. Spoke to Gavin at GIA about swinging arms, and he was very helpful, and told me some of the guys from Sponden are now working for Norton at Donnington.

I guess the way to go with this is to see if there are any 6082 sections with central rib available, and if not make some arms in different thickness and give them some serious testing (big drop offs should be a good way to test)? Not had any problems welding shock mounts onto OE aluminum swingarms though, but they are too long for TS bikes.

Are you making one or planning to go into production as a better mousetrap than the 6082 arms that are failing?
If the former, you can go a long way by slitting the weld and disassembling an original built up arm and making up new end plates for more length or a different/better axle location scheme, or cutting the arm extrusion section shorter. I'd rather slit the end off and make a long end plate and either weld it on myself or if I wasn't confident in my skill level to get someone who is to, than run with those silly bolt on drag slot extensions you see people wanting a longer arm but worried about modifying arms with on.

Another interesting factoid, the Petronas FP1 superbike used 5083 for frame and swingarm, that sort of makes sense as 5083 h14 after welding in comparison to welded 6082 t6 will have a higher proof stress, more elongation before it reaches its yield point and a higher tensile strength unless you can somehow post weld assembly heat treat the entire arm back to T6 temper. And it has a better fatigue life...

 

[MrFluffy]

If you haven't read it, I can recommend "the racing motorcycle" by john bradley. Its about a inch thick and packed with detail about what works where and what doesnt. The 5083 snippet above was from it for a example.
I don't build race bikes (well not ones that have to go round corners during the race anyway), but I think its a valuable book to read and digest for anyone that builds modified bikes...

 

[ronan]

I guess jmc had loads of business with bikes up to the late 80s vintage with their flexi frames, but once the manufacturers got their act together (late 80's ie the first delta box fzr's)with their chassis then their business must have dried up somewhat...

I knew a lad with a 70's kawasaki 3 cylinder 2-stroke, everytime he went out on it was a new adventure , he couldn't face riding it anymore in the end and sold it.

 

[ronan]

If you haven't read it, I can recommend "the racing motorcycle" by john bradley. Its about a inch thick and packed with detail about what works where and what doesnt. The 5083 snippet above was from it for a example.
I don't build race bikes (well not ones that have to go round corners during the race anyway), but I think its a valuable book to read and digest for anyone that builds modified bikes...

I seen that book in a bookshop in town, it was expensive i seem to remember, i would have bought it but didn'thave the money that week.

 

[hotrodder]

The main problem with 7020 (aka 7005) is getting hold of the stuff... effectively it doesn't exist as extruded sections* or sheet unless you pay a mill to extrude you a few tonnes which is a shame as it 'recovers' from welding far better than the 6xxx series which are typically what virtually all 'off the shelf' extrusions are made from; 6063 & 6082 being the two common flavours and always in T6
Scott0031 doesn't post much these days but used to be involved in making swingarms (from 6082-T6) alongside various other motorcycle bits and pieces and has a lot of pics in the albums section

2007 aluminium is not suitable for welding and has very poor formability. It's a free machining flavour

Unless they were already annealed ALL flavours of ally are softened when welded. Strain hardenable flavours like the 1xxx, 3xxx & 5xxx series are locally annealed, heat treatable flavours have a more complex HAZ containing partially annealed and 'overaged' areas. Unless it's properly overheated best case scenario for 6082-T6 is properties similar to 6082-T4 if left in the 'as welded' state. The nice thing about 7020 is that it natually age hardens after welding and unlike the 6xxx series doesn't need putting through a solution anneal (quench from near it's solidus temp) and artificial aging treatment. It can be put aside to age harden naturally or, for better results, artifically aged by baking for half a day at lowish temps; Eastern 7005 bicycle tubing for example is ~ 6 hours at 90ish °C followed by another 4 at 160°C while their 6061 tubesets needs quenching from 527°C and then straightening before aging at 176°C for 8 hours
As said 5083 can match/beat the 'as welded' properties of many of the heat treatable grades. Good formability, excellent weldability used a lot in shipbuilding and for storage vessels along with various other structural things. Doesn't extrude well, usually only available in the H111 and O (annealed) tempers as shate & plate from your average stockholder and doesn't like high temperatures like many of the other AlMg alloys with >3% Mg; above 65°C stress corrosion cracking is a possability, more so if it's been welded

* with the exception of a few sources (most in Eurpe IIRC) in a very limited range

 

[Chris Stevens]

Are you making one or planning to go into production as a better mousetrap than the 6082 arms that are failing?
If the former, you can go a long way by slitting the weld and disassembling an original built up arm and making up new end plates for more length or a different/better axle location scheme, or cutting the arm extrusion section shorter. I'd rather slit the end off and make a long end plate and either weld it on myself or if I wasn't confident in my skill level to get someone who is to, than run with those silly bolt on drag slot extensions you see people wanting a longer arm but worried about modifying arms with on.

Another interesting factoid, the Petronas FP1 superbike used 5083 for frame and swingarm, that sort of makes sense as 5083 h14 after welding in comparison to welded 6082 t6 will have a higher proof stress, more elongation before it reaches its yield point and a higher tensile strength unless you can somehow post weld assembly heat treat the entire arm back to T6 temper. And it has a better fatigue life...

Thanks. The 6082 arms arent failing, just that one used by a serious rider in Brit championship series events, tended to bend. Probably fine for less able riders in easier events. Going to see a producer next week who uses 5083, and has extrusions with ribs in the centre, and from what you say seems more suitable then 6082. Mate of mine made the tanks for Foggy Petronas road bikes.............but I dont think very many though!

 

[Chris Stevens]

The main problem with 7020 (aka 7005) is getting hold of the stuff... effectively it doesn't exist as extruded sections* or sheet unless you pay a mill to extrude you a few tonnes which is a shame as it 'recovers' from welding far better than the 6xxx series which are typically what virtually all 'off the shelf' extrusions are made from; 6063 & 6082 being the two common flavours and always in T6
Scott0031 doesn't post much these days but used to be involved in making swingarms (from 6082-T6) alongside various other motorcycle bits and pieces and has a lot of pics in the albums section

2007 aluminium is not suitable for welding and has very poor formability. It's a free machining flavour

Unless they were already annealed ALL flavours of ally are softened when welded. Strain hardenable flavours like the 1xxx, 3xxx & 5xxx series are locally annealed, heat treatable flavours have a more complex HAZ containing partially annealed and 'overaged' areas. Unless it's properly overheated best case scenario for 6082-T6 is properties similar to 6082-T4 if left in the 'as welded' state. The nice thing about 7020 is that it natually age hardens after welding and unlike the 6xxx series doesn't need putting through a solution anneal (quench from near it's solidus temp) and artificial aging treatment. It can be put aside to age harden naturally or, for better results, artifically aged by baking for half a day at lowish temps; Eastern 7005 bicycle tubing for example is ~ 6 hours at 90ish °C followed by another 4 at 160°C while their 6061 tubesets needs quenching from 527°C and then straightening before aging at 176°C for 8 hours
As said 5083 can match/beat the 'as welded' properties of many of the heat treatable grades. Good formability, excellent weldability used a lot in shipbuilding and for storage vessels along with various other structural things. Doesn't extrude well, usually only available in the H111 and O (annealed) tempers as shate & plate from your average stockholder and doesn't like high temperatures like many of the other AlMg alloys with >3% Mg; above 65°C stress corrosion cracking is a possability, more so if it's been welded

* with the exception of a few sources (most in Eurpe IIRC) in a very limited range

Thanks. I have spoken to a producer who used to have 7020 extrusions, but they are gone now. Can get 7020 sheet, from my alloy supplier, which is sourced from Germany, but its £800 for a smallish sheet, so is a non starter, unless it was for a £3K race arm.

Going to look at possibility of having 5083 arms made, but get the feeling that 6082 will probably work fine, especially if I can find extrusion with a central rib.

 

[hotrodder]

Yeah, as said if arms are bending it's a design problem more than a material one

 

[addjunkie]

I knew a lad with a 70's kawasaki 3 cylinder 2-stroke, everytime he went out on it was a new adventure , he couldn't face riding it anymore in the end and sold it.

This is called charchter, i love these bikes, even though you can feel the frame flex accelerating through corners. regret selling the last on i had.

Now all this ali stuff blew my mind... So much info out there do we confuse ourselves!

 

[Hyper22]

Thanks. I have spoken to a producer who used to have 7020 extrusions, but they are gone now. Can get 7020 sheet, from my alloy supplier, which is sourced from Germany, but its £800 for a smallish sheet, so is a non starter, unless it was for a £3K race arm.

Going to look at possibility of having 5083 arms made, but get the feeling that 6082 will probably work fine, especially if I can find extrusion with a central rib.

Hi chris how is it going with your swing arms?
Did you go with 6082 T6 or did you go 5083 ??

 

[Chris Stevens]

Hi chris how is it going with your swing arms?
Did you go with 6082 T6 or did you go 5083 ??

Producer with 5083 extrusion wanted more than the arms would retail for. I think 6082 is feasible, but would need some specially made extrusions with an internal rib, as otherwise not strong enough for serious off road use (there is someone making them from 6082, but they bend when bikes used hard!).

 

[Pete.]

Do a google image search for 'grudge bike swingarm'. You'll see that box section does quite well on very powerful bikes.

 

[Chris Stevens]

Road bikes have a very easy life compared to trials. The 6082 arms seem fine for gentle club events, but bend in Brit championship level competition.

 

[blenkie1]

Personally I think modern Triton looks hideous, and that its pretty silly trying to make an old Brit something its never ever going to be. Alloy swinging arm does look good on trials bikes though, and here is one of the ones which are now being sold for £600.

Lovely bikes by the way. Were they proper works bikes or the ones HRC were selling to the public? Was at Penrith last year at the world trials championship, had a great day out with the kids. Still see they wear Montessa badges