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fourex

Sherpa T mod 183 bent swingarm.

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As above, my newly acquired mod 183 ('76 350) has a slightly bent upwards swingarm on the the left side just forward of the brake stay fixing point. I will attempt to have it straightened but would then like to leave it as original because it still has all the original brackets and clips in place for the stop lamp switch and its cable, which I don't need at the moment but would be nice to keep in place.

Basically, I'd like another swingarm to install for some actual Twin Shock competition which won't bend,  what would people suggest please?

My thoughts are......

1). Source another 159/183/191 swingarm on ebay or wherever and weld gussets along the the top similar to the 199A swingarm.

2). Source a 199A swingarm, but I don't know if they are compatible with model 183?

3). Find someone that makes replica swingarms,  preferably in alloy.

How top riders like big units like Martin Lampkin back in the day managed with these spindly swingarms is beyond me, works bikes with different swingarms I guess.

 

 

 

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7 hours ago, fourex said:

How top riders like big units like Martin Lampkin back in the day managed with these spindly swingarms is beyond me, works bikes with different swingarms I guess.

 

 

 

That's the great advantage "works" riders have, they can change absolutely anything on their bike without worrying about the costs.

Back in the day, a bike would be taken back to the factory or to Comerfords and completely rebuilt for the next event, noting what changes the rider wanted. If new bit 'n pieces became available from the factory,  it would be a case of try that during the week and let us know if you want it on the bike for the next event.

Edited by model80
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On my M199 I had to buy a swing arm off eBay as it had a nasty bend in it. The first one I bought I could'nt use as whoever sold it had done some great photography so the bends were unseeable. The next one I bought was okay. A M199A one will probably fit on but you would need to check the length to be certain. I can have a look on Monday for you Fourex. I'm assuming a M159 would be the same as a M183. Graham.

Edited by bullylover
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All swinging arms from 158/159   250/325  onwards will fit. They were lengthened from 182/183 onwards [about 10 - 15mm] The shorter ones have a triangular rear shock mount and the longer ones have a rectangular shock mount. I am pretty sure a 199A arm is just the earlier one with a gusset welded on, which wouldn't be difficult to copy. I rode Bultacos for years in competition, and still do, and never bent or twisted a swinging arm and I would think I you are going to restore the bike and ride it in the occasional event a standard swinging arm would be fine. I have however seen a couple of bent ones and I was thinking it may have happened if the bike was ridden with one bent rear shock, causing one side to 'bottom out' before the other. Bent shocks back in the day were very common and some riders would continue to ride the bike in this condition, particularly if the binding/bend didn't occur until close to full compression, as this was difficult to feel. The original Betors were very good when new but did not last very long and were very easy to bend. The bike you have bought looks very good and original and should prove to be an easy and enjoyable restoration.

Cheers Greg

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Thanks all, Greg that's good info about triangular verse rectangular shock mounts regarding how to pick the different length swinging arms, mines rectangular. Reason for it being bent is anyone's guess really, previously bent shock as you have suggested is a possibility as it came fitted with some unknown brand of Mexican made mx shocks whereas the rest of the bike seems very original right down to the battered alloy mudguards and 860mm wide heavy steel handlebars.

Graham, also many thanks, I'm going to explore the aftermarket alloy swingarm avenue at this point, your experience buying from flea-bay has turned me off that option.

Robido's suggestion is what I'm currently exploring. After much googling I think I have found who Robido was referring to, I believe it is Berry Gamelkoorn who trades as AJG Twinshock Specials. Just waiting for a email response from him in the next day or so.

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I would at first give away the bent swing arm to a good car body workshop which do too restaurations. So they can restore the right geometric numbers aka straigthen the swing arm.

Then take a closer look at craiglists in Europe and too eBay for a donor swing arm.

Bultacos never had aluminium swing arms it will look a bit strange.

 

 

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Wasn't it Newton that said...   'Give me a long enough lever, and I will move the Moon.'

So just clamp it under the wheel of a car, and then use a ten foot lever to get it back to straight.  As long as the axis of the swinging arm bushes are parallel to the wheel spindle you should be Ok.

I once dropped a Bultaco 350T from the top of a Volkswagen at an arena trial, it landed on its crossed up front wheel, and bent the frame.  That took a lot of unbending with the long lever.     If you use some heat in the right place, you can take most bends out.

.

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Hi, reference "unbending" frames.

My Model 191 has had a  heavy impact lower left frame tube: that now fouls the Mag cover on the engine. Fairly common I believe.

Chrome moly tube frame: will heat require annealing to bring back the metal strength? I can live with the deformed tube, and have removed engine and will fit dummy bars in the frame to "lock the geometry" like a jig, to ensure engine fits back in. 

I would like to finish up with the frame to be true with wheels in line. Any advice most welcome.

 

Thanks Guys 

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If that is the Bash-plate area, it is likely that the bend has moved the frame lugs apart.  So if you hit it back with a wooden hammer, to give a 10mm clearance, then the engine lugs should be back where they started..   Any slight mis-alignment in location of the holes (~1mm.) could be eased by using the right size drill, cos you don't want to stress the engine castings too much.

.

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Thanks for the photos,   aaarh yes I remember it well.  You can see where the tube has been rubbing on the engine.   They are not the best of Bash Plates for hitting rocks at any speed.... Try to keep the front wheel in the air next time  !

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Hi all.

And another issue. Removing swinging arm looks so simple, however. .....

The bushes appear to be rubber bonded type, no doubt similar to Series Landrover suspension bushes with steel collar and sleeve. So, sleeve rusted to swinging arm spindle, and spindle rotates to frame stop, and then bonded bushes flex to give more travel. 

Presumably solution is to burn bushes out, and re-fit new bronze with steel sleeves, or nylon?

Any input will be appreciated.

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Jonjeans, your Sherpa should not have rubber bushes in the swingarm. I don`t know why anyone would fit them. They are supposed to have bronze bushes with a steel inner and have seals from the outside of the bush hole to the steel inner on the inside of the swingarm.

 

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