Jampot Outer Tube - Too Far Gone? (1955 18CS)

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Jampot Outer Tube - Too Far Gone? (1955 18CS)

Postby Halfwhelk » Tue Oct 15, 2019 3:20 pm

Hi,
I'm rebuilding my Jampots.
They were as expected, completely empty of oil and the piston has been grating up and down the outer tube and left a nice lot of aluminium filings at the bottom.
Please have a look at the picture attached. Is this outer tube too worn to reuse?

My feeling is that this wear is going to reduce the smoothness of the action and some oil is going to leak past, reducing the effectiveness of the damper, but not actually leaking to the outside.
Given that replacements are £40 each, I'm thinking I'll rub down the high spots with fine emery paper, rebuild them (with new bushes and seals) and see how it goes.
What does the voice of experience say?

Further to my earlier posts, which were a bit downhearted, The engine is back together with a bottom end rebuild, new cylinder liner, NOS wirewound piston.
Its great! Starts first kick and sounds like a sewing machine. I'm very pleased and fired up to continue the restoration.
Thanks for your help and advice.

Cheers
Matt
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Re: Jampot Outer Tube - Too Far Gone? (1955 18CS)

Postby Andy51 » Wed Oct 16, 2019 7:00 am

Hi Matt, never had this problem but they do look bad inside! By the time you have smoothed those scratches down I would have thought that the bore would be too large. As they are easy enough to remove and rebuild, you have nothing to loose by trying, but perhaps in the meantime you should start looking for a cheaper pair of replacements at autojumbles? Andy

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Re: Jampot Outer Tube - Too Far Gone? (1955 18CS)

Postby SPRIDDLER » Wed Oct 16, 2019 10:12 am

Yes, they do look pretty well corroded rather than worn. However, they are 'only' dampers and are of fairly quick action over bumps etc. and not providing any continuous suspension so perhaps they'll still function well enough.
I expect that my Jampots have been dry for years but I never seemed to 'Pogo stick' after encountering bumps.
I've never had a unit apart so I'm ignorant of the details but perhaps refill with a thicker oil than standard....... :?
I poke badgers with spoons.

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Re: Jampot Outer Tube - Too Far Gone? (1955 18CS)

Postby Halfwhelk » Wed Oct 16, 2019 11:12 am

Thanks for the replies.
I made a sort of honing tool with some tube and emery paper and they don't seem too bad now. The worst of the problem was alloy flakes friction welded to the steel lower bush, which cleaned off OK.
AMC classic spares have a pair of secondhand tubes, which I have purchased. Doesn't seem to be worthwhile going overboard on the refurb as everyone says as suspension units they're not much good even when new.
I have enjoyed working on them and building the tools needed to disassemble them. Pity they don't fulfil the promise of their intricate design.

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Re: Jampot Outer Tube - Too Far Gone? (1955 18CS)

Postby SPRIDDLER » Wed Oct 16, 2019 1:25 pm

I'm probably wrong but I don't think there were so many potholes and crumbling roadsides back in the day.

Making special jigs and tools has also been a large part of my satisfaction when fixing bikes.

Halfwhelk wrote: Pity they don't fulfil the promise of their intricate design.

:rofl: That's what one of my ex-wives used to say about men.
I poke badgers with spoons.

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Re: Jampot Outer Tube - Too Far Gone? (1955 18CS)

Postby 56G80S » Wed Oct 16, 2019 6:23 pm

I rebuilt my jampots a very long time ago. They may have no oil left in them but I've never noticed leaks.

These were probably disguised from the oil leaking forward of the jampots and covering the rear of the Matchless!

If "bounced" when stationary there does seem to be some residual damping.

"AMC classic spares have a pair of secondhand tubes, which I have purchased." Does this mean that the "originals" are not being re-used? I'd keep them anyway.

Johnny B

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Re: Jampot Outer Tube - Too Far Gone? (1955 18CS)

Postby Halfwhelk » Wed Oct 16, 2019 9:20 pm

Johnny,
Please let us know the condition of the bearing surface of your secondhand tubes when you get them. As a newly self-appointed 'expert', I think I can state two truths:
1) All Jampots leak (by now).
2 Any Jampot run for <5000 miles without oil will be scuffed to hell.
Therefore all Jampots are scuffed.

I'll be happy to be proved wrong.

I have found Tru-Blu PTFE liquid thread sealant. (£3.50 from Toolstation) I'm going to try to stop the oil leaking from the threads (at least) when I reassemble mine.
Matt

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Re: Jampot Outer Tube - Too Far Gone? (1955 18CS)

Postby 56G80S » Thu Oct 17, 2019 1:39 pm

Hi Matt

I was quoting your thread. I shan't be looking at my jampots for a while. Fixing the timing side bush more important at the moment.

Cheers

Johnny B

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Re: Jampot Outer Tube - Too Far Gone? (1955 18CS)

Postby Guille » Thu Oct 17, 2019 2:31 pm

Halfwhelk wrote:Johnny,
Please let us know the condition of the bearing surface of your secondhand tubes when you get them. As a newly self-appointed 'expert', I think I can state two truths:
1) All Jampots leak (by now).
2 Any Jampot run for <5000 miles without oil will be scuffed to hell.
Therefore all Jampots are scuffed.

I'll be happy to be proved wrong.

I have found Tru-Blu PTFE liquid thread sealant. (£3.50 from Toolstation) I'm going to try to stop the oil leaking from the threads (at least) when I reassemble mine.
Matt


I put thread sealant when I rebuilt my jampots last year. New seals, bushings, o-rings and new oil.
Not a single drop leaked ever since.

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Re: Jampot Outer Tube - Too Far Gone? (1955 18CS)

Postby bitza » Sat Oct 19, 2019 3:47 pm

How about fitting girling type inserts. They still look original but with improved damping

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