Swingarm extention basics

I get a lot of people asking me alot of questions about extending there swingarm, And after reading Leons post about tripple clamp stem swaping I thought maybe I should do a write up on the basics of extending a swingarm, maybe it will answer some of the questions and help some of you guys out. This is not a how to or the only way but more of a guide or just my way of doing it. I will be doing a first gen hayabusa arm with the top brace removed and a new under brace added. Lazt night I went ahead and cut the top brace off and cut the factory adjuster blocks out. As you can see in the pics the factory adjuster blocks do not go inside the arm more than a 1/4 of an inch or so. I like to make my extentions go inside the arm at least an inch with a very tight fit.

Today I started making the new swingarm ends. I am going to cheat a little and use a cnc to do this but they can be done on a manual mill, I have done them many times on a bridgeport but now I am lazy and time is money so cnc it is. I know and understand that everyone does not have a cnc or mill or access to one but you can cut the arm your self and make a 2-d drawing of what you need and have the pieces machined by a local shop. The aluminum I used is 2.0 X 3.5 t6 6061 extruded flat bar found just about anywhere.

The busa arm is a little differnt than most arms because it is angled 5 degrees from the center of the arm to the top and bottom so you need to match that angle or it will look like crap.


When I know the arm is going on a bike that will truely be at the dragstrip, I will pocket out the back side of the inserts to reduce some of the weight and it keeps me from drilling and taping into a blind hole for the adjuster screw.

You dont have to do this it just helps with the weight after all they ar solid blocks. Tomorrow I will set up and finish the ends,drill and tap the adjuster holes and get ready to weld it up.

Awesome post. Thanks for taking the time to detail the steps. I know full well that this really slows down progress.

I'm surprised that the adjuster blocks don't fit further into the arm than 1/4". I guess it works. You don't see rear wheels falling off Hayabusas. Not too many bikes that can put 'em to a test more than a Busa.

testarossa wrote: Awesome post. Thanks for taking the time to detail the steps. I know full well that this really slows down progress.

I'm surprised that the adjuster blocks don't fit further into the arm than 1/4". I guess it works. You don't see rear wheels falling off Hayabusas. Not too many bikes that can put 'em to a test more than a Busa.

Thanks Josh, hopefully this will answer some questions or help the guys who have the skill level but just aren't sure of all that is envolved.

You would be shocked at some of the welds that are on factory arms and what they let go on the assembly line.

I would have never thought about the angle. And I too would have thought the factory ones went in further than 1/4 inch.

I would assume that if you where doing a whole arm that you wouldnt worry about that angle.

I would have never thought about the angle. And I too would have thought the factory ones went in further than 1/4 inch.

Ok so today I finished machining the ends and taping the holes for the adjuster screws and made some axle adjuster blocks ,as much as I hate to put standard bolts in a metric bike,I like to beef up the adjuster screws with 3/8-16 bolts instead of 8mm.





After that I started the final prep work on the swingarm, this is a very important because the arrm must be clean clean clean!!!! I start off buy washing the swingarm extentions with simple green or dawn dish washing soap this will remove any oils left from the maching process, then I check to make sure the swingarm legs are the same length,an easy way to do this is to stand the arm on end and lay a strait edges or something flat across the top and measure to it from the floor up.


Then I start grinding the champer on the edges of the swingarm ends, I grind at least 1/4 back on about a 45 degree until you get a knife edge on the end of the arm.



Then you can fit your extention ends into the arm, you want a tight fit this helps hold the ends square and true to the arm.


Then I use a s.s. wire brush on a die grinder this will strip off the factory anodizing on the hayabusa swingarm and it leaves it clean for a good surface to weld to.


Once you are sure everything is good install the extentions in the arm and clamp one side of the swingarm with some c clamps and some thick flat steel. Now you can do this arm and most of the suzuki arms like this because both sides of the swingarm legs come out of a bend and go strait back unlike most of the other sportbike arms out there. You wil need a fixture or a jig for most of the kawasaki's yamaha's and honda's but the suzuki's are pretty easy.



Now you are ready to start welding,first you will need to preheat the swingarm extentions and only the extentions with a torch evenly because of the thickness of the swingarm verses the extention blocks this will make them flow together even.



Then tack the arm while it is clamped up in 4 places and weld across the bottom,then remove the top clamp and block and weld the top and repete the process for the outside of the arm and the inside.


Then do the other side the same way and you should be good.

Ok once the arm is all welded up you can start your underbrace and make the plate to cover the big hole in the top of the swingarm. I use 1 inch .083 wall tubing for the underbrace and 3/16 plate for the top of the arm. I bend the tubing in a JD square bender, I have a peice that I bent as a jig so I dont have to measure all the time I just bend 1 90 and the just lay the bending jig on top and mark it off with a sharpee.



I bend the tubing on the exhaust side 60 degrees and then 30 degrees this gives me clearence for a sidewinder pipe that most of these guys are running, once you have your brace bent and your top plate made you need to preheat the extention blocks again so the blocks will flow at the same rate as the tubing when welding the two together.

And that is just about it, you should have something that looks like this when done.

Nice work! Nothing like a true machinist, craftsman.
Brings back memories of "Puppet" in his shop, making his own parts. Before CNC machines
Nice bead of weld too!
Your gonna get a lot of guys PM ing you for work.

I like it. However, I have one question. 6061-T6 is heat treated as we know. When you weld it it, don't you ruin the heat treatment to some extent? How do you combat this? Or do you feel it's necessary?

T_Dub wrote: I like it. However, I have one question. 6061-T6 is heat treated as we know. When you weld it it, don't you ruin the heat treatment to some extent? How do you combat this? Or do you feel it's necessary?

I have never had any problems. But I will say this years ago I was welding most all my swingarms with er5356 filler rod but I was fighting porosity and some cold cracking, Then I spoke to a rep at a welding supply house in orlando and he told me to try er4043 And it worked out real well for me 4043 has a little less tensile strength but it flows better and you get better penetration, and it is not as prone to cold cracking.