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Leading Link designs

 
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Bandit Bill



Joined: 31 Jan 2005
Posts: 202
Location: Hamilton, Ontario, Canada

PostPosted: Tue Feb 08, 2005 1:56 am    Post subject: Leading Link designs Reply with quote

This isn't really an HPS question, as LL front ends are considered somewhat marginal in the handling dept. as compared to more HPS oriented center hub steering setups - but i imagine we've got a reasonable pool of experience here to lend some advice on the design of such a front end.

While i await my Charnwood motors car tire rim, i've been wracking my brain on my final leading link setup. As it sits right now, i'd settled on a custom fabricated bearing block utilising a needle roller bearing of 27 mm OD, 20 mm ID, and a 26 mm width, with an inner spacer of 30 mm width, sleeving it down to a 12 mm shouldered bolt. This is the same bearing as used on the rear wishbone suspension mount to the motorcycle frame on the Suzuki Bandit - My rational at the time of choosing it was that if it is up to the task of suspending the rear end of the bike, two of them utilised as the swinging arm pivot bearings should be up to the task of holding the front end up. I've noted also, that most commercial front ends seem to have the pivot bearing on the ends of the downtubes, with the pivot bracket mounted to the swingarm - in my case, i'm doing the opposite to this, one of the reasons being that the downtubes are going to be 44 mm in diameter, and if i mounted the pivot bearing i intend to use, the fork tubes are going to run into an interference issue with the pivot brackets.

Am i on the right track for my choice of suspension, or am i travelling down a hazardous path?

comments, alternative suggestions?
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zentime



Joined: 22 Jan 2005
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Location: Massachusetts USA

PostPosted: Tue Feb 08, 2005 3:46 am    Post subject: Reply with quote

It doesn't seem like there would be any inherent reason why the bearing couldn't be mounted to the swingarm instead of the forks. I wonder if you're going to build in any means to adjust the trail? In that case it seems like it would be better to mount the bearings to the fork. One time I built a LL using 1/2" rod ends screwed into plugs that I welded into the fork tubes. An unacceptable amount of play developed pretty quickly in the rod ends so I removed the spherical ball bushings and replaced them with standard bushings. Not sure if any of this helps but that's my input.
Bill
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Bandit Bill



Joined: 31 Jan 2005
Posts: 202
Location: Hamilton, Ontario, Canada

PostPosted: Tue Feb 08, 2005 3:59 am    Post subject: Reply with quote

zentime wrote:
It doesn't seem like there would be any inherent reason why the bearing couldn't be mounted to the swingarm instead of the forks. I wonder if you're going to build in any means to adjust the trail? In that case it seems like it would be better to mount the bearings to the fork. One time I built a LL using 1/2" rod ends screwed into plugs that I welded into the fork tubes. An unacceptable amount of play developed pretty quickly in the rod ends so I removed the spherical ball bushings and replaced them with standard bushings. Not sure if any of this helps but that's my input.
Bill


I considered Rod ends - but then i've seen just how sloppy the hiem joint on the end of my steering dampner has gotten in a single season of usage - and that wrote off rod ends as an option. As i envision it, the custom fabbed bearing block i'm considering, would be the adjustment method, basically in an adjustment range of 1 - 1 1/2" total fore and aft, using a slotted base that is bolted to the swinging arm. See the below picture of Robert Graur's rendition of this, which had sparked my decision to further refine the design. I'm using needle bearings on the advice of my machinist, who has said (in theory, anyway) that solid delrin type bearings tend to wear oval with heavier loads placed on them, and are more difficult to remove and replace cleanly out of aluminum. I'd also have to make the shock mounts range adjustable, using this method, but the shocks i'm using are length variable to compensate.


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zentime



Joined: 22 Jan 2005
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Location: Massachusetts USA

PostPosted: Tue Feb 08, 2005 4:06 am    Post subject: Reply with quote

Seems like a nice design to me. Great way to adjust the trail. Clean and simple.
Bill
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swaybar2002



Joined: 26 Jan 2005
Posts: 380
Location: Central Pa.

PostPosted: Tue Feb 08, 2005 5:17 am    Post subject: Reply with quote

Bill,
As I had mentioned when you first shared that pic a while back it certainly looks liek a nice desigh. The adjustable trail is a very nice feature too.
I am curiou sif you have settled on mounting the calipers direct to the swingarm or creating a floating caliper design. ('floating' in this case meanintg the caliper would be secured by a link and a 'pivot' at the fron axle.)
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Claude Stanley

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Bandit Bill



Joined: 31 Jan 2005
Posts: 202
Location: Hamilton, Ontario, Canada

PostPosted: Tue Feb 08, 2005 5:27 am    Post subject: Reply with quote

swaybar2002 wrote:
Bill,
As I had mentioned when you first shared that pic a while back it certainly looks liek a nice desigh. The adjustable trail is a very nice feature too.
I am curiou sif you have settled on mounting the calipers direct to the swingarm or creating a floating caliper design. ('floating' in this case meanintg the caliper would be secured by a link and a 'pivot' at the fron axle.)


Definitely floating, with the bracket being attached to the axle spacers, and tied off of the down tubes via adjustable hiem joints. To mount the calipers direct to the swinging arm introduces undesirable braking lift of the swinging arm.. If i'm going to all this bother to construct a LL .. i might as well take this 1 step further and do it right Smile
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swaybar2002



Joined: 26 Jan 2005
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Location: Central Pa.

PostPosted: Tue Feb 08, 2005 5:36 am    Post subject: Reply with quote

Sounds good Bill!
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Claude Stanley

Founder: Internet Sidecar Owners Klub
http://autos.groups.yahoo.com/group/SCT/

2007
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bmcsheehy



Joined: 22 Jan 2005
Posts: 972
Location: Massachusetts USA

PostPosted: Wed Feb 09, 2005 6:27 pm    Post subject: Reply with quote

Bill Strong,
Just re reading some post here. Who does you fabrication work, they did a nice job. Really looks neat and clean. Motorcycle Happy
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Bill
High Performance Sidecaring... ...There is nothing "HACKED" about it.
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Bandit Bill



Joined: 31 Jan 2005
Posts: 202
Location: Hamilton, Ontario, Canada

PostPosted: Wed Feb 09, 2005 7:24 pm    Post subject: Reply with quote

Hi Bill

The photo I put up in the proceeding post of the swinging arm/bearing block assembly is NOT of my work - it is of Robert Graur's custom BMW/sidecar rig he's put together. I've simply decided to borrow his design and adapt to my own setup. The machine shop that i lean on to do what i cannot, does do similar quality work - for the right cash / no receipt price, however.

http://www.canadianbron.ca/
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