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Feckin Eejit!
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Discussion Starter · #1 ·
So heres a shot of the subframe for reference with some perspective for wall thickness of the square tube



I want to connect heim joints to that square tube and have concerns about reliability and safety.

I started looking at some sort of bracket and found these 2 styles.




Any opinions on either style?
I'm leaning toward the bottom style made of steel. If you think aluminum would be strong enough... please share.
Then I'm not sure if I should bolt thru the tube or just the first wall. I can fit a small (10mm or 11mm max) box wrench in the tube and fasten them to just the bottom wall of the square.
 

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lɐʇuǝɯᴉɹǝdx&#4
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Would the threaded section of the heim be going to the tube, or are you trying to bolt the head to the tube? And if so, why?

Without really understanding the application, I'd agree with the second choice looking good. Seems similar to mounting a shock. I'd want to see it welded to the subframe, not bolted as the sample item is.

How big is the hiem, and what is it intended to be doing? Aluminum can be strong enough, you just use more of it, and distribute the forces on it more evenly. ;)
 

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Feckin Eejit!
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Discussion Starter · #4 ·
Inspiration was this, support tube will be like it. Heim at either end to eat some of the force. Bolted to the subframe. In my application the top bit is stock aluminum subframe, shortened, Heims/tube as the support.


I'm going to support myself with thick walled carbon tube...

I know noone with a tig welder.

edit: I'm working off of 300lb load. Me, ATGATT and a backpack loaded for a weekend.
 

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Is my bike ok?
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edit: I'm working off of 300lb load. Me, ATGATT and a backpack loaded for a weekend.
300lb + pothole at speed = 600 lb+

Just saying....

That second style clamp you posted would be ideal , I think, but I'd want it out of steel. The weight difference would be negligible ,but the strength difference would be huge.
 

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Oops, forgot to add...

Make slugs to slide inside your square tube. Thread them for your heim. Just drill and bolt. 8mm IMO would be sufficient.

Most bikes with twin shocks have 1 8mm bolt at the s-arm. Four holding a subframe should be stout.

What exactly is the wall thickness of your tubing? If it's thick enough to allow you too use a countersunk fastener tap your slug, rather than a thru-bolt with a nut. Like Seb's lower control arm , creates a very strong, zero slop connection.
 

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Feckin Eejit!
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Discussion Starter · #7 ·
F=MA
6" of drop, 300lbs, inflate 1.5x for safety. Looking at about 1000lb of force in a worst case scenario. But thats spread across the 2 supports... 500lbs each. The tube I'm looking at doesn't start to deform in any direction till 3000lbs or so (iirc). Bonding heims to carbon with an epoxy that has a touch of elasticity, shear strength in the 5k-10k rpm range. Heims will mitigate some of the force applied to them as well.

Weak spot will be the ears the heims are bolted to.

I'm REALLY liking the idea of using a steel slug inside the tube.

I could coat that fucker in epoxy before it goes in to eliminate galvanic corrosion, make it a non conductive epoxy thats good to at least 500f, repeat for the bracket, then I could powder coat the whole thing and noone would be the wiser.
:cfrocks:
 

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lɐʇuǝɯᴉɹǝdx&#4
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Make slugs to slide inside your square tube.
This. Keeping the forces through the Hiem all lined with the center axis of the tube is part of what makes the example you showed work. Go messing about with brackets and such that get the forces off-line, it just makes it weaker.

I think aluminum threads should be plenty strong, if you wanna weld the slugs in. Otherwise the steel slugs w/ epoxy sound like a good call. I dunno about just bolting them in, seems better to bond them.
 

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Actually, I was thinking al for the slugs. Plenty strong and much easier to work with.

And after thinking some more, heim joints can be rattly. Especially the ones that aren't urethane bushed. Also, since your sub tubes are converging, and there's no rear pivot, adjustability is NOT something the heims will give you anyway.

If it was me I'd incorporate your rod ends as just an extension of the slugs. Just one solid piece. Make and mount the uppers. Make the lowers and slide them in to place. Adjust tail angle then drill them.

Not saying it's the "right" way, just tossing it out there.

Heims are spendy anyway.
 

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Feckin Eejit!
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Discussion Starter · #11 ·
What exactly is the wall thickness of your tubing?
My shit plastic ACO 'micrometer' says it's a touch over 2mm so probably 14ga. Theres already a nutcert 3" or so from the end of the subframe. I could drill that out and reuse that hole...

so the heims piece will replace the bottom support rail?
For reference on what I'm planning.


Nutcert is at about the hole labeled "1". If I lean back to stretch, all my weight will be on the rear seat support above "2". During normal riding it'll probably be by "1"

I'd cut a larger/longer bracket to match the angle the heims rod will be attaching to the top rail at, and move the heims as close as you can to the rail, so you have the smallest lever possible.
This. Keeping the forces through the Hiem all lined with the center axis of the tube is part of what makes the example you showed work. Go messing about with brackets and such that get the forces off-line, it just makes it weaker.
The above pic is if I bolted directly to/thru the slug. My first reaction is that it would cause torsional stress to the tube over time and transfer that stress to the ears the subframe mounts to at the top.

This design

puts all the stress on the heims without torquing the aluminum.

Actually, I was thinking al for the slugs. Plenty strong and much easier to work with.
Good. I like aluminum more...

And after thinking some more, heim joints can be rattly. Especially the ones that aren't urethane bushed. Also, since your sub tubes are converging, and there's no rear pivot, adjustability is NOT something the heims will give you anyway.

If it was me I'd incorporate your rod ends as just an extension of the slugs. Just one solid piece. Make and mount the uppers. Make the lowers and slide them in to place. Adjust tail angle then drill them.
Not sure what you're saying. Thread a heim into the back of the slug where it pokes out the back of sub?

2 heims bolted to each similar to the bike I got the idea from?
 

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Feckin Eejit!
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Discussion Starter · #13 ·
Oh. Heim the bottom, get good measurements and drill the slug at an angle and tap that. Use threaded rod to connect the carbon tube to the slug. I could do that... I've never successfully drilled a hole at an angle and had it come out as desired :p
 

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lɐʇuǝɯᴉɹǝdx&#4
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I like the looks of the one with the heim under the bar. It resolves the torque, and keeps things tucked out of the way. A heim might not be strictly needed, but the look good and are easy to work with. Also potentially gives you some adjustment in seat angle. I don't know about rattle. Sure hope not, my whole front suspension and stearing is full of em.
 

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Feckin Eejit!
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Discussion Starter · #15 ·
I think I'm liking that one too. Gets the support moved forward a bit as well. Aesthetically pleasing to tuck that support as far forward as possible without turning it into a pivot point and doesn't torque the front ears the subframe mounts to or the square tube.

My only worry then is galvanic corrosion at the bolt into the aluminum slug. Not exposed to the elements at all so it just doesn't corrode?
 

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Is my bike ok?
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Oh. Heim the bottom, get good measurements and drill the slug at an angle and tap that. Use threaded rod to connect the carbon tube to the slug. I could do that... I've never successfully drilled a hole at an angle and had it come out as desired :p
LMAO! I have no clue what you are describing.

Sorry. I suck with words. I'll be back in a bit....
 

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Ok. Let's try again. :D

I just meant something like this:



Or:



^^^ From this build here.

Seb, as far as being rattly. Sorry, wasn't the best term to use. If an entire component is suspended/supported/built on ALL heim joint it can get sorta sloppy or floppy. Unless the rods are triangulated or working against each other to prevent lateral movement.

Like a GM triangulated 4 link.


Otherwise, they need some sort of lateral stability. Since all of his subframe tubes are running fairly close to parallel, and they are pretty close together, using all heims might require something like they use on 3 & 4 link drag car setups

Like:


Or:


From personal experience, the 3 link that was on the back of my old drag car was a little rattly WHEN EVERYTHING WAS UNLOADED. Of course, I couldn't use urethane bushed heims for that application as they would have been too squirmy. No need to explain why that is a no-no for any susp. But, with the diagonal link nice and snug it kept the slop out of everything and all was happy.

Basically, I just kinda think if an entire subframe was attached solely with heims it might have the notion to sway back and forth.

If you really want the look/ need the adjustability of heims, you can buy solid vs spherical.



Or is you are really concerned with isolating your bum from engine vibes





Sorry for being totally unclear before fells. Phones, ya know...
 

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Feckin Eejit!
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Discussion Starter · #19 ·
The front of the top rail is static.

Frame has these thin ears that I hear aren't the sturdiest things...


The only heims I was using are at either end of the support. A static rod end at the top is probably not a bad idea. After looking at the geometry of a triangle...
Support length somewhere in the neighborhood of 13", difference in width between the bottom mounts and the top rails is roughly 1", or slightly less. A^2+B^2=C^2, ~13.5, makes the angle less than 4°.
I could probably use static rod ends at both ends and just shave em a tiny bit to get that 4°
 
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