Jampot plastic bushes

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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AJS_Chris
Posts: 28
Joined: Thu Mar 16, 2017 7:45 am
Location: Wiltshire

Jampot plastic bushes

Post by AJS_Chris »

Morning all,
This has probably been covered before but a search didn't throw anything up. The rear end of my 1951 18S is very stiff, pressing down on the rack would give little or no movement then, 'clunk' it would compress and then release with a similar clunk. I removed the Jampots and found the swing arm to be free. If I pressed down on one of the Jampots against the bench it would compress but 'stuttering', this is the best description I can give. Pressing down on the other Jampot gave no compression at all.
I've stripped the first Jampot, the very stiff one, and discovered all of the resistance is between the inner tube and plastic bush, so much so I had to use a drift to tap the inner tube out. My guess is the other Jampot will have the same problem.
I wondered if the outer tube was oval and therefore deforming the plastic bush but measuring the outside diameter of the outer tube in the area of the plastic bush only shows a few thou variation around it's circumference. I don't have a suitable tool to measure the inside diameter to see if it is oval.
Assuming for a moment both inner and outer tubes are OK is there any history of the plastic bushes swelling over time, perhaps because an unsuitable oil has been used? I can rebuild the Jampots easily enough but I'm uncomfortable with what I've found and would like to know why this has happened before proceeding.
When rebuilding the Jampots do I just go for 85cc of 20W or is a heavy fork oil preferred these days?
Any ideas or thoughts would be appreciated.
Thank you in advance,
Chris.
AJS_Chris
Posts: 28
Joined: Thu Mar 16, 2017 7:45 am
Location: Wiltshire

Re: Jampot plastic bushes

Post by AJS_Chris »

Update....
With the bush removed from the outer tube it slides freely on the inner tube so the outer tube must be compressing and/or deforming the bush.
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Pharisee
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Location: Lincolnshire UK
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Re: Jampot plastic bushes

Post by Pharisee »

Machined bronze replacement bushes are available from AMC Classic Spares. I've used them on two sets of Jampots with complete success.
I'm from the Fens.... Gimme six.
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Chazzyb
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Posts: 553
Joined: Tue Apr 08, 2003 1:00 am
Location: Suffolk UK

Re: Jampot plastic bushes

Post by Chazzyb »

The bushes swell. I had the same problem with my forks some years ago. Bronze bushes from our friends at Falcon Rd sorted it out
Charles
AJS_Chris
Posts: 28
Joined: Thu Mar 16, 2017 7:45 am
Location: Wiltshire

Re: Jampot plastic bushes

Post by AJS_Chris »

Thank you Charles. Confirmation of the swelling is reassuring and explains the problem.
Regards,
Chris.
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