Vintage Aluminum Swingarm Question

mx400bee
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mx400bee
Edited Date/Time 8/27/2014 6:21pm
Was there a company named U.S. Sports that manufactured swingarms in the 70`s?
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newmann
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newmann 11/11/2010 6:09pm
11/11/2010 6:09pm
Yes. Think they were in Houston if not mistaken. Their swingarms had a cast aluminum front section and cast axle dropouts connected by round tubing down the sides. Pretty easy to spot. I think they also produced them for T&M and PDI. They will have the logos cast into the front section.
newmann
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newmann 11/11/2010 6:12pm
11/11/2010 6:12pm
Vintage Factory has an old T&M catalog on their site. Here is their version.

mx400bee
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mx400bee 11/11/2010 6:40pm
11/11/2010 6:40pm
Thanks Newmann, I bought one years ago for my DT2 not knowing who made it. It`s identical to the pics but with a full length gusset on top of the tubes and a half length gusset next to it with three mounting holes for changing the bottom shock location.
slowvet
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slowvet 11/12/2010 5:56am
11/12/2010 5:56am
I always liked the CrossUp Incorporated swingarms.

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xnationalwrench 11/12/2010 11:25am
11/12/2010 11:25am
slowvet wrote:
I always liked the CrossUp Incorporated swingarms.
I worked for both CrossUp & Thor, to be honest Thor's arm were stronger and lasted longer not to menton was designed to use the stock axle and chain adjusters
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slowvet
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slowvet 11/12/2010 3:07pm
11/12/2010 3:07pm
slowvet wrote:
I always liked the CrossUp Incorporated swingarms.
xnationalwrench wrote:
I worked for both CrossUp & Thor, to be honest Thor's arm were stronger and lasted longer not to menton was designed to use the stock...
I worked for both CrossUp & Thor, to be honest Thor's arm were stronger and lasted longer not to menton was designed to use the stock axle and chain adjusters
That is surprising to me anyways, I always thought the extra bracing inside that swingarm was indestructable. I didn't know about not being able to use the stock axle on the CU swingarm.
tydog
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tydog 11/13/2010 6:42am
11/13/2010 6:42am Edited Date/Time 11/13/2010 12:36pm
About a year ago, I had a Cross Up for a RM 125. It used special axle adjusters that were recessed into the arm. In my opinion, it was not nearly as well built as a Thor arm. I was going to check the alloy of it but a friend needed it pretty bad so I sent it to California. I am a machinist by trade, and I just was not real impressed by some of the construction techniques that CU used. The extrusion looked to be a good design with the internal rib but I am not sure about the wall thickness and the alloy they used.
The current Thor that I have on a RM 370 takes unique axle and adjusters also. I am sure that if Xnationalwrench says that they made units for stockers, then they did, I just have not dealt with one.
xnationalwrench 11/13/2010 12:16pm
11/13/2010 12:16pm Edited Date/Time 11/13/2010 12:17pm
tydog wrote:
About a year ago, I had a Cross Up for a RM 125. It used special axle adjusters that were recessed into the arm. In my...
About a year ago, I had a Cross Up for a RM 125. It used special axle adjusters that were recessed into the arm. In my opinion, it was not nearly as well built as a Thor arm. I was going to check the alloy of it but a friend needed it pretty bad so I sent it to California. I am a machinist by trade, and I just was not real impressed by some of the construction techniques that CU used. The extrusion looked to be a good design with the internal rib but I am not sure about the wall thickness and the alloy they used.
The current Thor that I have on a RM 370 takes unique axle and adjusters also. I am sure that if Xnationalwrench says that they made units for stockers, then they did, I just have not dealt with one.
Thanks for the vote of confidence Tydog. I still believe that Richard (Thor Racing) used the stock chain adjuster but that was in the mid 80's (30 years or so) so my mind can get a little fuzzy. I did see a lot more of the CrossUp arms fail than Thor arms but both were many times better than stock. Richard was a perfectionist and checked and rechecked all his arms with jigs to be sure everything was correct from start to finish and were quality pieces.
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tydog
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tydog 11/13/2010 12:50pm
11/13/2010 12:50pm
xnationalwrench wrote:
Thanks for the vote of confidence Tydog. I still believe that Richard (Thor Racing) used the stock chain adjuster but that was in the mid 80's...
Thanks for the vote of confidence Tydog. I still believe that Richard (Thor Racing) used the stock chain adjuster but that was in the mid 80's (30 years or so) so my mind can get a little fuzzy. I did see a lot more of the CrossUp arms fail than Thor arms but both were many times better than stock. Richard was a perfectionist and checked and rechecked all his arms with jigs to be sure everything was correct from start to finish and were quality pieces.
Richard was a pefectionist; wasn't he the one that told some of the OEM engineers (while they were visiting his shop) that he was going to sell a lot of his arms to replace their broken ones, due to the fact that they did not stress relieve their early aluminum arms after welding? Do you know what is educational background was?
As for the adjusters on the 370; the stock Suzuki arm is 10mm (.392") thick at the axle plates, the Thor is exactly 1.0". The 78 C2 and then the later 79 and 80 extruded arms were a little thicker at about .550". The adjusters on Richard's arms are the only piece that was not quite up to speed, in my opinion. They were made from a very thin mild steel and a little flimsey, I am sure this was due to production costs. I just finished a set for my Fox bike out of titanium, a little overkill, but cool nonetheless.
xnationalwrench 11/13/2010 12:59pm
11/13/2010 12:59pm
Tydog, I'm not sure what education backround he had but his dad owned a bike shop in the 70's and he was in the Navy as a SeaBee. LOL Tosh from Suzuki brought over some Engineers from Suzuki Japan and Richard asked that question about the stock aluminum swing arms and how they were heat treated, they replied they used heat treated aluminium so they didn't need to be reheat treated. I know for a fact that Richard would rejig the arms 1/2 way thru the heat treated process and CrossUp didn't. The alunminum from Japan had a different heat treat to them than Richard, to all my knowledge all his arms were made from 6061 and were heat treated to T-6.
tydog
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tydog 11/13/2010 1:22pm
11/13/2010 1:22pm
10-4, thanks for the reply. Heat treating, even if just a mild stress relieve, is crucial on some alloys and so many people totally disregard it.
newmann
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newmann 11/14/2010 4:48pm
11/14/2010 4:48pm
All the Thor arms I have for the early CR125's and 77 RM125 use a special axle (longer than stock) and Thor chain adjusters. All special stuff for the wider axle slots where stock used pate steel.
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L SNORE
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L SNORE 8/27/2014 5:48pm
8/27/2014 5:48pm
slowvet wrote:
I always liked the CrossUp Incorporated swingarms.
xnationalwrench wrote:
I worked for both CrossUp & Thor, to be honest Thor's arm were stronger and lasted longer not to menton was designed to use the stock...
I worked for both CrossUp & Thor, to be honest Thor's arm were stronger and lasted longer not to menton was designed to use the stock axle and chain adjusters
Yeah it's an old thread I know but do you recall what year the Thor arms were first available to the public?
xnationalwrench 8/27/2014 6:21pm
8/27/2014 6:21pm Edited Date/Time 8/27/2014 6:21pm
slowvet wrote:
I always liked the CrossUp Incorporated swingarms.
xnationalwrench wrote:
I worked for both CrossUp & Thor, to be honest Thor's arm were stronger and lasted longer not to menton was designed to use the stock...
I worked for both CrossUp & Thor, to be honest Thor's arm were stronger and lasted longer not to menton was designed to use the stock axle and chain adjusters
L SNORE wrote:
Yeah it's an old thread I know but do you recall what year the Thor arms were first available to the public?
I believe he first started them out in 1975/76. He first started out as a repair/fab shop and then went from there. Actually he sold THOR RED air filter fluid and Radical Richard's Racing Wrap 1st.

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