Welding in new motorcycle swing arm/engine mounts?

[peejay75]

I need slightly wider mounts for a custom project.

Once the old mounts are cut out, would you weld in new mounts that have no thru hole, then use some sort of contraption to drill through both mounts to make sure the thru holes are aligned with each other?

Or weld in mounts that have through holes already in them and be confident in your welding skills that you will be able to line up the holes?

(And how would a weekend warrior do this vs. a paid professional, and is there a difference?)

 

[G1K]

Use mounts with a hole already and a bar to connect the two (to ensure they are concentric) when you weld them to the frame.

 

[The Cobbler]

then use some sort of contraption to drill through both mounts to make sure the thru holes are aligned with each other?

that would be called line boring .

And how would a weekend warrior do this vs. a paid professional, and is there a difference?

unless you're very sure of your welding skills, it may be prudent to get a professional , you don't want a failure there , in my opinion...


and I agree with above poster, use a straight bar and carefully line everything up . lots o f tacks so it can;t move and hope for the best

 

[peejay75]

Use mounts with a hole already and a bar to connect the two (to ensure they are concentric) when you weld them to the frame.

I like that approach, thank you!

 

[peejay75]

that would be called line boring .


unless you're very sure of your welding skills, it may be prudent to get a professional , you don't want a failure there , in my opinion...


and I agree with above poster, use a straight bar and carefully line everything up . lots o f tacks so it can;t move and hope for the best

Line boring, thanks for the knowledge boost!

And I agree with you, this is probably one best left for the pros!

 

[Beerhippie]

Line boring, thanks for the knowledge boost!

And I agree with you, this is probably one best left for the pros!

Yeah, I mean, the rear wheel mount of a motorcycle... what could possibly go wrong?

 

[M.Brane]

Actually the rear wheel alignment on a bike is not that critical. Rigidity is the important part. Ask anyone with an FL HD or a ST11-1300.

Is this a tube frame bike? I would do what is stated above: line up your points with known straight material/jigs, and weld a little at a time moving to opposite sides while the other side cools. If you can make good welds you'll be fine. If in doubt about your ability to get good penetration without porosity then farm it out.

 

[Beerhippie]

Actually the rear wheel alignment on a bike is not that critical. Rigidity is the important part. Ask anyone with an FL HD or a ST11-1300.

Is this a tube frame bike? I would do what is stated above: line up your points with known straight material/jigs, and weld a little at a time moving to opposite sides while the other side cools. If you can make good welds you'll be fine. If in doubt about your ability to get good penetration without porosity then farm it out.

I was thinking more along the lines of keeping it attached to the rest of the bike... at 100 MPH.

 

[M.Brane]

I'd rather be doing 35+ MPH in a 15 MPH curve than 100 MPH in a straight. That's where the cops hang out.

 

[Beerhippie]

I'd rather be doing 35+ MPH in a 15 MPH curve than 100 MPH in a straight. That's where the cops hang out.

Who says bikes can only go 100 in the straightaway?

There's a paved road out of St. Helens (or was it Rainer?), OR that actually has marked 5 mph turns. It was designed for logging trucks, but is for bikes. The Old Logi Trail. Ride it sometime--you might even see metal I left on those turns long ago.

 

[whateg01]

..., and weld a little at a time moving to opposite sides while the other side cools.

Sounds like a good way to get to "cold-welds-ville" unless TIG welding it

 

[M.Brane]

Sounds like a good way to get to "cold-welds-ville" unless TIG welding it

Is that like cold solder joints?

 

[Chris_Hamilton]

I would do what is stated above: line up your points with known straight material/jigs, and weld a little at a time moving to opposite sides while the other side cools.

Full disclosure I'm not fully visualizing what the OP's setup is but I think I get the gist.

I would only want to do that with the initial tacks. To counteract any shrinking or pulling that may occur and throw it out of alignment. If it's jigged I would be less worried about that. Do one side (fully) , come back do the other, if it's jigged it should be still aligned. Multiple tacks or spots would actually affect your alignment more at least that has been my experience. And like was said above depending on the thickness of the material, you are going to play hell having full penetration on those tacks/ spots. You actually will get more heat variation (HAZ) that way and warping, or more correctly pulling, out of alignment. And you've got a funky looking likely low penetration weld bead when finished.

Jig it, weld one side, cool, come around to the other side using the same settings, bevel of material ( if any) and try to duplicate what was done. If you have even or very similar HAZ's around both welds then it's all good. They will cancel each other out in terms of "pull". A good looking HAZ in this situation is one that is nice and level across the length of the weld. You don't want to see peaks and valleys in the HAZ. Or variations in color in the peaks and valleys. Don't know if that makes sense or not. Hopefully it does.

 

[M.Brane]

Who says bikes can only go 100 in the straightaway?

There's a paved road out of St. Helens (or was it Rainer?), OR that actually has marked 5 mph turns. It was designed for logging trucks, but is for bikes. The Old Logi Trail. Ride it sometime--you might even see metal I left on those turns long ago.

Done 170 on a corrected speedo, but it was in NV. Bike was happy. I had a little adrenaline rush goin'.

 

[Beerhippie]

Done 170 on a corrected speedo, but it was in NV. Bike was happy. I had a little adrenaline rush goin'.

Never pushed it that far--nor had a bike that could. 120 was my top--in the wilds of West Texas, with a loose swingarm on a shaft-drive bike (thanks, Yamaha).

 

[ArcIndWeld]

I need slightly wider mounts for a custom project.

Once the old mounts are cut out, would you weld in new mounts that have no thru hole, then use some sort of contraption to drill through both mounts to make sure the thru holes are aligned with each other?

Or weld in mounts that have through holes already in them and be confident in your welding skills that you will be able to line up the holes?

(And how would a weekend warrior do this vs. a paid professional, and is there a difference?)

100% i'd use a pre drilled mounts with a most likely ground shaft at the correct diameter from MCmaster or similar to hold the two concentric the whole way through. It can be done other ways but this is how i'd do it.

 

[peejay75]

100% i'd use a pre drilled mounts with a most likely ground shaft at the correct diameter from MCmaster or similar to hold the two concentric the whole way through. It can be done other ways but this is how i'd do it.

That seems to be the concentrus, er, consensus!

 

[peejay75]

Gulp, ok, here's a pic roughly showing what I'd be up against. Cut out the old mount(s), and weld the new ones in.

 

[Chris_Hamilton]

Is the swingarm mount one piece? Meaning does it go across the backside of the tube there and also encompass those mounting holes on the other side of the tube?

 

[Chris_Hamilton]

If so then I would want to reinforce the extension piece in some way or make the entire mounting plate which would add some complexity to the job. Hard to tell from the pic if that mount is one piece or not. If it is not then simply fabbing that section with the holes in the correct location should be sufficient. Reinforcing it afterward would be a good idea if possible. If it's one piece it gets some of it's strength from being attached to the tube (frame) in multiple welded locations. I would want to add on to the existing piece (including filling the hole) to get the swingarm fitting then reinforce it with something like several fishplates

Maybe some of the other guys might have a different or better solution.

 

[Chris_Hamilton]

Should also go without saying but regardless of the equipment you are using (MIG,TIG,etc) get some scrap material (same thickness) and orient it in the same way and get your settings correct. You want full penetration. Do some destructive tests if possible with your scrap material of the same thickness.

More I think about it more I would leave it alone at the factory welds, and simply add on to the existing mount (**** weld) then make two small fishplates to go on either side of the mounting hole. That would be the simplest way. Jig it with rod like has already been mentioned. Clamp everything so nothing can move. Get everything as clean as possible.

 

[Chris_Hamilton]

You can use any number of materials to make templates for the new pieces. 1/4" MDF would be my choice. You can sand it and get the templates to fit the exact profile. Trace out your profile onto steel and cut out. Cleanest way would be plasma or even something like laser or water jet. In a pinch a jig saw would work. Might have to sand the piece to get a tight fit after cutting with a jigsaw though. No biggie.

Just be sure to get a nice tight fit. If using a MIG slight bevel on both pieces. (Assuming it's around 1/8") More bevel if thicker.

 

[RoninB4]

Gulp, ok, here's a pic roughly showing what I'd be up against. Cut out the old mount(s), and weld the new ones in.

-Ok I'll ask the question: Why are you even considering cutting out the old one? What doesn't fit?

 

[Chris_Hamilton]

-Ok I'll ask the question: Why are you even considering cutting out the old one? What doesn't fit?

The swing arm mount. He needs to move it to fit his new setup.

 

[RoninB4]

The swing arm mount. He needs to move it to fit his new setup.

-Well thank you for the reply but what specifically isn't right? Moving the swingarm back a few inches doesn't really change much besides the fender alignment and the chain length. It will affect the handling but it seems a fair trade-off to cutting out a proven weld on factory brackets for new brackets of dubious weld, alignment to the frame, and tracking. Resetting the fender would be less critical than a swingarm.

 

[whateg01]

I need slightly wider mounts for a custom project.

Once the old mounts are cut out, would you weld in new mounts that have no thru hole, then use some sort of contraption to drill through both mounts to make sure the thru holes are aligned with each other?

Or weld in mounts that have through holes already in them and be confident in your welding skills that you will be able to line up the holes?

(And how would a weekend warrior do this vs. a paid professional, and is there a difference?)

-Well thank you for the reply but what specifically isn't right? Moving the swingarm back a few inches doesn't really change much besides the fender alignment and the chain length. It will affect the handling but it seems a fair trade-off to cutting out a proven weld on factory brackets for new brackets of dubious weld, alignment to the frame, and tracking. Resetting the fender would be less critical than a swingarm.

His first line seems to spell out what he needs, I thought

 

[MOS3522]

Tagged for the 6 month and 1 year follow up. Can't wait!

 

[RoninB4]

His first line seems to spell out what he needs, I thought

I must have missed the "wider" part, thank you. One wonders just how much wider is needed. Numbers would help that.

 

[Chris_Hamilton]

I'm assuming wider was a misspeak. I think he meant longer. In the pic he posted above you can see the swing arm where I'm assuming it needs to be versus where the mount is. My guess is he's using longer/different swing arm off a different bike.

Now if it's something different then I guess I wasted alot of my time replying.

 

[whateg01]

.

Now if it's something different then I guess I wasted alot of my time replying.

As did i

 

[peejay75]

I'm sure I would lock my computer up if I attempted to multiquote all the good comments here, but I will point out to @Chris_Hamilton that I knew somebody was gonna suggest cutting and welding onto the existing mount!

Well, the mount ideally needs to be wider between "the ears" to accommodate the new ('94) swingarm which is wider than the factory' (87) swingarm. How much wider you ask? Don't flame me, but...2mm (on each side). I know, I know! But let's just humor me some more!

My plan was to have the new brackets made with a CNC service.

Here's a different view of the current setup and a ROUGH mockup of what would be the new mount(s).

Oh, @Chris_Hamilton, I never considered that the mount could possibly go through the frame, thanks for that can of worms! I assumed it was welded just to the "front" of the frame, but maybe I can ask some dirt bike/suzuki aficionados to find out for sure.

 

[RoninB4]

Now if it's something different then I guess I wasted alot of my time replying.

-I won't say that the OP is not deserving of some help but something else should be noted. The OP wanting to cut and weld onto a motorcycle frame is the same person that couldn't figure out the solution to transfer existing holes in a stair stringer onto a new tread. Not knocking this person but if the stairs project is difficult how is cutting/welding new tabs going to go? Says that new tabs will be CNC milled, as if that's going to compensate for lack of skills/experience and machinery.

My advice to the OP is if the stairs project is at the edge of your ability then the frame tabs will not end well if you do any of the work yourself. Good luck.

 

[whateg01]

-I won't say that the OP is not deserving of some help but something else should be noted. The OP wanting to cut and weld onto a motorcycle frame is the same person that couldn't figure out the solution to transfer existing holes in a stair stringer onto a new tread. Not knocking this person but if the stairs project is difficult how is cutting/welding new tabs going to go? Says that new tabs will be CNC milled, as if that's going to compensate for lack of skills/experience and machinery.

My advice to the OP is if the stairs project is at the edge of your ability then the frame tabs will not end well if you do any of the work yourself. Good luck.

Maybe he's a professional welder and weld inspector like the guy at our local makerspace! Seriously, though, I do know some people who are great at assembly but couldn't design a trash can.

 

[Chris_Hamilton]

@peejay75 So if I'm understanding correctly the issue is that the new swing arm is too wide for the mounting area? How much wider is it? If it's minimal I think I would look at shaving (narrowing)the swing arm itself in the mounting area. Provided it's not too drastic that would be the best solution. Cut it down on the inside, perhaps removing and replacing that steel bushing with a thinner one. Looking at that pic I don't like the idea of cutting and widening in the mount area as that is a high stress area and the design of the frame spreads that load out. If you cut and widened, much of that load and stress would now be on the welded area. Hope that makes sense.

​

 

[Chris_Hamilton]

If you did cut and widen it, you would need to spread the load out similar to how it is now on the tube. Mimic the plate that is there now. Cut out the section so that you can get enough clearance but don't cut out that whole section. Only the minimal amount. Make your new piece(s) and lay it over the existing and make the weld against the frame like it is now. Important that your new piece mimic the shape and length of the existing mounting plate and your weld seam is roughly the same length. Use something fairly thick. .187 or better IMO. Weld to the frame, like the existing mount, drill holes in your new piece (before) and plug weld (rosette) in places to the existing mount as well. Important that you do that as that will strengthen it and allow the existing piece underneath to provide some strength/support. I would want to see at least 2 holes on top and bottom of the bolt hole. As large as possible. Ideally 3/8" but I don't know if you have room for that. Min 1/4" for each hole which should be doable. Wouldn't hurt to also weld the edges of the pieces as well.

For it to survive, penetration is going to be extremely important. Be sure you have the equipment to weld that effectively. Will take some amperage to do so.

To be clear, doing this and doing it effectively and correctly is going to be fairly involved. It's going to take some planning, a lot of fitting and a significant amount of welding which will need to be done correctly for everything to survive and function as intended.

 

[peejay75]

To be clear, doing this and doing it effectively and correctly is going to be fairly involved.

Yer killin' me, Chris! But I know you're right...if that spacer/pad was sanded down, the new swingarm (4mm wider overall, to the best of my measurements) would probably fit.

I'll see if there are some pros in the area that would be willing to tackle it, just wanted to get an idea of what I'd be up against, I appreciate all your comments, I can at least practice on some scrap for future situations such as this!

(Stick is a no-no?)

 

[whateg01]

...

(Stick is a no-no?)

Stick will likely be the least pretty weld, but it's also, along with TIG, the least likely to have insufficient penetration.

 

[peejay75]

I won't say that the OP is not deserving of some help but something else should be noted. The OP wanting to cut and weld onto a motorcycle frame is the same person that couldn't figure out the solution to transfer existing holes in a stair stringer onto a new tread. Not knocking this person but if the stairs project is difficult how is cutting/welding new tabs going to go? Says that new tabs will be CNC milled, as if that's going to compensate for lack of skills/experience and machinery.

My advice to the OP is if the stairs project is at the edge of your ability then the frame tabs will not end well if you do any of the work yourself. Good luck.

Busted! My approach to these projects is  slowly getting better (I hope). The stair problem, I didn't measure twice, cut once! But the old me would've just left it...oh, and not sought counsel on GJ first!

 

[Chris_Hamilton]

Yer killin' me, Chris! But I know you're right...if that spacer/pad was sanded down, the new swingarm (4mm wider overall, to the best of my measurements) would probably fit.

I'll see if there are some pros in the area that would be willing to tackle it, just wanted to get an idea of what I'd be up against, I appreciate all your comments, I can at least practice on some scrap for future situations such as this!

(Stick is a no-no?)

Well I wish you good luck Sir. I'm just trying to give some advice that will ensure you have sucess. Stick has it's place but I wouldn't really feel good about it here. Unless you have years of experience stick welding, it will be the hardest option IMO. If you feel confident stick welding it could be done I guess but honestly if you are not super experienced I wouldn't.

Look first at narrowing your swing arm. If that's not doable then perhaps a happy medium would be to design your pieces, get it mocked up and then farm out the welding. If you want to tackle it I would highly recommend that you get some scrap in appropriate sizes and practice and do destructive testing. It's going to take a good deal of power (amperage) to weld that effectively over the existing surface.

This is a dirt bike right? If it's a street bike then most certainly have a Pro weld it for you. Dirt bike you've slightly less chance of killing yourself if things go awry. But keep it in mind, if it fails you could hurt yourself pretty badly.

 

[peejay75]

a happy medium would be to design your pieces, get it mocked up and then farm out the welding.

I believe the saying is "this is the way".