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ChrisX
ChrisX
Lake Macquarie NSW Oz
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Swing arm spacer question
#673654 11/07/16 12:00 am
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When I dismantled my B50MX swing arm, I may have done it incorrectly. The long center spacer seemed to have some washer "shoulders" on it. Well, those are pretty banged up now. I don't see these in the parts diagram. Just gives a part number for the whole center spacer. What function do these serve and what's my remedy?


1971 BSA B50MX
1971 Moto Guzzi Eldorado
1994 Moto Guzzi California 1100i
1978 Kawasaki KZ750B
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Re: Swing arm spacer question
Steve Davis #673737 11/07/16 9:30 pm
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The center spacer / distance piece keeps the needle bearings in place on the outer ends of the swing arm. The spacer has shoulders on the ends. I could likely turn up a good used on if you need to replace yours.

Peter


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Re: Swing arm spacer question
Steve Davis #673781 11/08/16 12:16 pm
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Wow !! B50s had needle bearing swing arms?? Why didn't BSA do that years ago on the A group...... Didn't know this.


Down to 1 BSA, 2 Triumphs, 1 '56 Chevy
1 '65 XLCH, Hernia Gift, on the way to Japan!
Re: Swing arm spacer question
Steve Davis #674164 11/11/16 10:01 pm
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OK, so that center spacer that has the shoulder "washers" to keep the needle bearings in place. How far from the outside edge of the spacer are these "washers" placed?


1971 BSA B50MX
1971 Moto Guzzi Eldorado
1994 Moto Guzzi California 1100i
1978 Kawasaki KZ750B
Re: Swing arm spacer question
Steve Davis #674228 11/12/16 1:32 pm
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Steve,

I just tore apart a 1971 OIF swing arm to double check the internal bits since what you describe doesn't seem to match the parts book or what I recall.

The center spacer tube is just that. A plain tube 5-1/16" long. No bevels on the ends. So I was wrong on that. It is the same diameter as the two outer bushings that ride inside the needle bearings. The swing arm spindle rotates in all of that. The tube just keeps the outer bushes in place.

So starting with a bare swing arm you insert needle bearings, insert the central spacer tube, then insert the two outer bearing bushes. On the outer edges of the swing arm there are plastic/nylon seal holders that hold the oil seals. Lastly sitting on the ends of the seal holder are stepped steel thrust washers. You insert this stacked assembly back into the frame and insert the swing arm pivot.


check out: www.bsaunitsingles.com
2500 BSA part numbers with inventory in stock just for the unit singles!
Re: Swing arm spacer question
Peter Quick #674240 11/12/16 2:42 pm
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Thanks Peter. Still a little confused because the parts breakdown clearly shows a "shoulder" near the edges of the center spacer and I ended up with 2 "rings" or "washers" that look to have possibly fit snug on that spacer. They got a little mangled somehow during removal. I was not gentle on the stuck needle bearings. Ha ha. But, by your description, I suppose I don't need those 2 mangled pieces anyway.


1971 BSA B50MX
1971 Moto Guzzi Eldorado
1994 Moto Guzzi California 1100i
1978 Kawasaki KZ750B
Re: Swing arm spacer question
Steve Davis #674246 11/12/16 4:00 pm
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The parts books are notoriously wrong on many pages in 1971. A variety of incorrect illustrations. A great example is the page on the gear cluster which drives folks crazy as the diagram is for a B44 not a B50. The timing side end has the wrong parts pictured for the kick ratchet mechanism all the way to the wrong lock washer. In the last week I have disassembled two OIF swing arms and the center spacer was the same - not shouldered. But as BSA was spinning apart at about this time anything is possible. Like your MX frame with a kick stand lug. The day yours was to be assembled and stamped they likely didn't have any frames without kick stand lugs so they grabbed a regular frame stamped it and assembled your bike. Stuff like that was super common.

I have lots of conversations with folks who get confused by BSA spares books illustrations. They need to be taken with a grain of salt. The part number is usually correct but the diagrams are often wrong. Sometimes even the part number is wrong. Typos with flip flopped numbers or just wrong numbers. Then you notice that the number has been corrected in a later years spares book. Secrets of the trade!

Peter



check out: www.bsaunitsingles.com
2500 BSA part numbers with inventory in stock just for the unit singles!
Re: Swing arm spacer question
Steve Davis #674263 11/12/16 5:23 pm
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The plastic 'shoulders' on the spacer tube are used to center the spacer tube within the swingarm so that the swingarm spindle can be relatively easy to install. Once the swingarm spindle is in place those plastic shoulders serve no additional useful purpose and just go for a motorcycle ride.

On my B50MX I broke the plastic 'shoulders' as well. I machined out aluminum 'shoulders' as a replacement. However, you could just simply remove those broken 'shoulders' and then pack a lot of grease around the outside of the spacer tube and that will hold the spacer in position when you install the spindle.

I hope this is of some help,
Peter Joe

Re: Swing arm spacer question
Peter_Joe #674279 11/12/16 8:13 pm
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Could you not make a spacer out of anything somewhat rigid like, say, cardboard?

Re: Swing arm spacer question
Peter_Joe #674755 11/17/16 11:48 am
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Originally Posted by Peter_Joe
The plastic 'shoulders' on the spacer tube are used to center the spacer tube within the swingarm so that the swingarm spindle can be relatively easy to install. Once the swingarm spindle is in place those plastic shoulders serve no additional useful purpose and just go for a motorcycle ride.


Now I get it!! Ha ha. In the previous replys referring to "centering", I was think that meant left and right in relation to the bike. If that were true, I was thinking that centering was probably pretty important. Now I realize that those pieces are there to simply center the spacer in the swingarm tube to ease the install of the spindle. Mystery solved!! Thanks!!

Last edited by Steve Davis; 11/17/16 11:49 am.

1971 BSA B50MX
1971 Moto Guzzi Eldorado
1994 Moto Guzzi California 1100i
1978 Kawasaki KZ750B

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