Aluminuim swinging arms?

[Chris Stevens]

Wonder if anyone on here has ever made an aluminium motorcycle swinging arm? Noticed a Triton in "Classic Bike Guide" this month, fitted with alloy arm, which is made from 6082 rectangular extrusion.

Is 6082 a good material to use I wonder, and is it likely to be weakened by the welding process?

 

[cocker]

Wouldn't it be better to get one from a breakers ?
I guess I would be good to make your own but if your back end lets go it could get messy !

 

[Chris Stevens]

They are specialist parts for off road bikes. Was interested if anyone had used 6082 to make a swinging arm, as it doesnt seem that suitable a material to me.

 

[ronan]

I think the problem with aluminium swingarms is that to get the strength of steel, it has to be so heavy in section that you wind up with very little weight saving. Most of the racing manx nortons etc were made of lightweight accles and pollack or reynolds tubing, light and strong.

 

[Chris Stevens]

Yes quite right, but people are paying £600 for 6082 swinging arms for Honda trials bikes that bend when bikes get serious use, and was curious if anyone had used this material at all?

Harris swinging arms costing £3K were made from 7020 sheet, and stronger and lighter than steel, but according to Steve a nightmare to make, needing heat treatment etc...............maybe they will now do one for Royal Enfield?....................lol

 

[ronan]

Yes quite right, but people are paying £600 for 6082 swinging arms for Honda trials bikes that bend when bikes get serious use, and was curious if anyone had used this material at all?

Harris swinging arms costing £3K were made from 7020 sheet, and stronger and lighter than steel, but according to Steve a nightmare to make, needing heat treatment etc...............maybe they will now do one for Royal Enfield?....................lol

Also Chris, do they look right on classic bikes ? Imho no. I see tritons and specials with twin front discs and alloy swinging arms, look completely out of place, again imho.

 

[Chris Stevens]

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.

 

[ronan]

I find that boy racers and people like that always want the newest and latest upgrade, even if that overpriced upgrade has little or no advantages over what it is replacing.

 

[Chris Stevens]

I find that boy racers and people like that always want the newest and latest upgrade, even if that overpriced upgrade has little or no advantages over what it is replacing.

Of course they do, hence paying £600 for a swinging arm which bends if bike is used in serious competition!

 

[ronan]

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.

 

[jordan1]

Aluminium swinging arms are mainly cast like this Gull arm. http://www.ebay.co.uk/itm/Honda-CBR...835856?hash=item51b66b4b10:g:rKgAAOSw9N1VsezT
Difficult to fabricate one of sufficient strenght at home I would imagine.

 

[ronan]

I've seen some cast aluminium japanese swinging arms off sports bikes, they weren't light, but i suppose with bikes making well over a hundred hp they have to be built to handle the power.

 

[MrFluffy]

*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.

 

[chunkolini]

MrFluffy knows his onions.
And his swing arms.

 

[brightspark]

eat a few less pies loose weight and no need for all this fancy stuff

 

[addjunkie]

MrFluffy knows his onions.
And his swing arms.

mr flurry sure does, but his reference to face palm confused me. My xjr 1300 has an extrusion fabricated swing arm too.

And i am one of those heretics the rivett counters hate, why only today i have been considering butchering whoops i meam modifying a t140 with a box ali arm, among a few other things.

 

[MrFluffy]

Heres a few commercial examples of specified as 6082 in use for this application too :-
Riccardo Pierobon's F042, which is a frame/swinger kit for ducati engines :-
http://www.duccutters.com/pierobon-F042.tpl

CCM GP450 Adventure has a 6082 frame and swingarm though I think they actually glue this together not weld.

You can find more if you search hard enough, for most people "aircraft" or "billet" is the magic stuff things need to be made of so spec's and heat treatment can be a bit hard to come by at times.

Face palm was at the talk of alloy arms are just fashion for people with more money than sense and 6082 produced bendy arms when it was the design at fault.

 

[Mick Annick]

I find that boy racers and people like that always want the newest and latest upgrade, even if that overpriced upgrade has little or no advantages over what it is replacing.

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...

 

[roofman]

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.

 

[ronan]

Face palm was at the talk of alloy arms are just fashion for people with more money than sense and 6082 produced bendy arms when it was the design at fault.

They are for classic bikes like old tritons and tribsa's and other british specials though, never liked them. As i said they just don't look right, like disc brakes on a bike from the 50's or 60's.