Swing arm (swingarm) swap help

[Doubledown]

This may be a shot in the dark though search has not helped me much. I have a project bike that I want to do a swing arm swap on to move from steel to aluminum while adding a few inches in length. All the models I have come across for sale are too long by at least 3". (yz125 and 250s finding 23-24"s)

My current arm is 16.25" from pivot to end. And the pivot mount width is 6 5/8".

I would like to have an arm from any make/model as close to 21" as possible and a pivot mount width as close to the original (6 5/8") as possible or have enough meat on the ends that I can mill off to make it fit. (I am still up in the air on chain adjuster style, I will have to make some items in either case so is there any better system than others?)

Just avoiding lengthening the stock or trimming a longer aluminum as I don't have an aluminum welder.

Any help or direction is appreciated.

[TheLetterJ]

Are you planning on using the matching wheel/brakes with whatever "new" swingarm you come up with? Does your bike currently have drum or disk brakes? Does your bike currently use linkage on the rear shock? Is it even mono shock? What about the width inside-inside on the frame end of the swingarm? There are a ton of variables that could change depending on what you can/cannot modify on your own, a bit more information about what bike you are trying to fit it to may make it easier for other's to help you. I'll go check measurements on my smaller bikes and post up if anything is close to your 2 dimensions.

2003 suzuki drz125 (14"rear wheel with drum brake and shock linkage mounted under swingarm)

steel swingarm (drz125l is the same but 1" longer, kx100 is 2" longer, aluminum and set up for disk brake)

1) pivot bolt to end of swingarm = ~20 1/2"

2) outside mounting width at frame ~8 3/8"

3) inside mounting width at engine cases ~4 1/4"

2003 suzuki rm85 (14" rear wheel with disk break and shock linkage mounted on top of swingarm)

aluminum swingarm

1) 21"

2) ~6 5/8"

3) ~2 5/8"

Edited May 17, 2011 by TheLetterJ

[Doubledown]

Are you planning on using the matching wheel/brakes with whatever "new" swingarm you come up with? Does your bike currently have drum or disk brakes? Does your bike currently use linkage on the rear shock? Is it even mono shock? What about the width inside-inside on the frame end of the swingarm? There are a ton of variables that could change depending on what you can/cannot modify on your own, a bit more information about what bike you are trying to fit it to may make it easier for other's to help you. I'll go check measurements on my smaller bikes and post up if anything is close to your 2 dimensions.

This is actually going on a YSR50 and I will be using the factory wheels. The brakes are drum, for now, and I will be having the brake stay point welded on and make some spacers to center up the wheel/hubs. I will also have a shock mount welded to the top to fit the ysr spring as well. I am trying to limit the difficulty/time of the aluminum welding as it is a friend of a friend that will be doing it and stretching or shortening the arm is pushing the favor a bit far. As for width at the rear, as long as it is the stock ysr 7.25" or wider it will be fine. I am guessing any dirt bike swing arm wont be too wide as it won't look weird with a 130 or 140 tire.

[TheLetterJ]

I edited my above post with more measurements, the rm85 looks damn close.

[Doubledown]

I edited my above post with more measurements, the rm85 looks damn close.

First off, thanks for the super fast checking/post.

that Rm is dead on.. depending on chain adjustment that will give me 4+" extension..

Couple questions on that RM.

I am looking on ebay at arms and they are listing "big wheels" is yours the big wheel model that I need or is there a standard?

Do you know the distance back from the pivot mount that the shock mount is? (if that lines up or is even close I am golden)

Looking at pictures I am seeing different chain adjuster types for the same year as well..one is internal with little bolts poking out the back that pull the adjusters back. The other is the bolt on the side type where it pushes the adjuster plates back (which i'd prefer for fabrication ease) ist his also a "big wheel" vs standard thing?

[TheLetterJ]

mine is the little wheel (14" rear) version. The bigwheel (16" rear) version is 1" longer overall. I'll try to get some pictures and the rest of the measurements for you, but it might not be until tomorrow.

[Doubledown]

mine is the little wheel (14" rear) version. The bigwheel (16" rear) version is 1" longer overall. I'll try to get some pictures and the rest of the measurements for you, but it might not be until tomorrow.

Awesome , much appreciated.

[TheLetterJ]

frame end (pic is deceiving, mount is on the money at 6 5/8"):

top mounted linkage pivot to swingarm pivot (right at 6 1/2"):

chain adjuster:

upper link mount (2 1/4" inside width):

hopefully this helps, let me know if you need any other measurements:cheers:

[Doubledown]

frame end (pic is deceiving, mount is on the money at 6 5/8"):

top mounted linkage pivot to swingarm pivot (right at 6 1/2"):

chain adjuster:

upper link mount (2 1/4" inside width):

hopefully this helps, let me know if you need any other measurements:cheers:

Perfect! I owe you a beer. I was looking at some OEM parts sites for the swing arms and it looks like there is the RM85 and RM85L (which I am assuming is a big wheel) and each of those has 4 models of swing arms for the same years. Some look like yours others look like the external one I was speaking of before. seen here http://www.partsnewandused.com/servlet/Detail?no=36809. I just bought one of the external ones on ebay, 30 dollar gamble on if it matches your measurements, if not I will look for one just like yours on ebay.

Thanks

[TheLetterJ]

As for width at the rear, as long as it is the stock ysr 7.25" or wider it will be fine.

D'oh! I just checked the width inside the swingarm at the rear axle and it is also 6 5/8". Maybe you could just shorten your wheel spacers?

[Doubledown]

D'oh! I just checked the width inside the swingarm at the rear axle and it is also 6 5/8". Maybe you could just shorten your wheel spacers?

yea I can, but the worry there is tire rub or the 520 chain sprocket fitting.. .. the ysr swing arm is short so the 120 tire on there now is very close to the tapper.. so hopefully this being longer the tapper will be wide enough where the wheel will be to fit the 140 I want..

[Doubledown]

frame end (pic is deceiving, mount is on the money at 6 5/8"):

top mounted linkage pivot to swingarm pivot (right at 6 1/2"):

chain adjuster:

upper link mount (2 1/4" inside width):

hopefully this helps, let me know if you need any other measurements:cheers:

Thanks again for all the measurements.. ended up with this 2004, seems the same except for the axle adjusters.

[TheLetterJ]

Very cool! Glad I could help. Have you put any thought into hooking up the rm85 disk brake? I'd imagine that a simple adaptor could be made that fits inside of the YSR drum/hub that you could bolt a stock rm85 rotor to, might be less work than hooking up your current drum?

[Doubledown]

haha right on the same page.. I dont have the rm85 brake setup though I will definitely NOT be cutting off those mounts just in case I can come across those cheap to look into making something that will work with the ysr hub.

[Ki4bhg]

can you tell the difference between the long and short swing arm by the tensioner?