1964 G12 CSR roadholder forks sticking

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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tony54
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Location: Leicestershire UK

1964 G12 CSR roadholder forks sticking

Post by tony54 »

Hi. Have just rebuilt (following Mick Hemmings' guide) the forks with new stanchions, full bush and seal kit, damper tube caps and valves (all from Andover Norton) Everything went together ok and nothing appeared too tight. When I put the front brake on the forks compress and do not recover. I have released the front wheel spindle and fork brace, pumped the forks and tightened them up again but to no avail. Can anyone advise what the problem might be please.
Many thanks.
Mick D
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Location: Aberdeenshire

Re: 1964 G12 CSR roadholder forks sticking

Post by Mick D »

Hi

Did you slacken the pinch bolts on the lower yoke, have you fitted the dust cover / spacer on the LH side of the hub, did you torque the spindle nut before you nipped up the slider pinch stud?

Regards Mick
tony54
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Location: Leicestershire UK

Re: 1964 G12 CSR roadholder forks sticking

Post by tony54 »

Thanks for your reply Mick.

Yes hub is as it should be. Slackened off spindle, brace and lower yoke, pumped forks and tightened spindle, pinch bolt, brace and lower yoke. Feels a bit better but still not recovering fully without tugging the handlebars, feels a bit 'lazy' Will see if they settle in with a bit of use.

Regards Tony
tony54
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Location: Leicestershire UK

Re: 1964 G12 CSR roadholder forks sticking

Post by tony54 »

Hello Mick.

When I said that the hub was as it should be I had put it back as it came off, which meant that I was reliant on the previous owner doing it correctly (why I don't know considering the bodges I have found elsewhere) My manual gives scant info and I cannot find any drawings online.

Have stripped the forks out again and discovered that the pinch stud slider has been welded (couldn't tell from the outside but crack still evident on the inside of the spindle hole) I take it that the slider should float on the spindle and be held in place by the pinch, due to the poor repair it does not float.
Could you also advise whether the smaller diameter of the spindle should pass fully through the brake side slider or is the outside of the spindle hole reduced in order to prevent this.
Finally, you mentioned a spacer along with the dust cover. The dust cover has a recessed washer pressed into it but I appear to be missing the spacer, could you advise the part number for this spacer please?

Thanks for the help

Regards
Tony
Mick D
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Re: 1964 G12 CSR roadholder forks sticking

Post by Mick D »

Hi Tony

I think you've solved it - the spindle should be free to move laterally in the slider when the pinch stud is slackened. The larger diameter of the spindle bears against the dust cover, (which also acts as a spacer), and clamps it to the bearing when the spindle nut is tightened.
You need to dress the hole in the LH slider to allow the spindle to slide in it - this should fix your problem.
Front Spindle.png
Regards Mick
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tony54
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Location: Leicestershire UK

Re: 1964 G12 CSR roadholder forks sticking

Post by tony54 »

Thanks Mick, much appreciated.

Regards
Tony
tony54
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Posts: 16
Joined: Fri Apr 26, 2019 3:28 pm
Location: Leicestershire UK

Re: 1964 G12 CSR roadholder forks sticking

Post by tony54 »

Slowly going mad now. Off the bike each fork leg compresses smoothly and recovers fully without any sticking or binding. Forks back into the bike, without mudguard/brace/wheel, and the spindle now slides freely into both sliders and I can turn it easily by hand. Fit the wheel, tighten wheel nut, using a small lever I can see that the pinch slider floats on the spindle, connect brake cable, off stand, bung the brake on and forks compress and stick!!!!! I have to heave on the bars to get them back up.
Slacken wheel nut, slacken lower fork brace, pump forks, tighten everything including pinch stud and they still stick.
All ideas, suggestions gratefully received.
Tony
Mick D
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Location: Aberdeenshire

Re: 1964 G12 CSR roadholder forks sticking

Post by Mick D »

Hi

Are you expecting too much extension? off of the stand the forks will be compressed due to the weight of the bike. Sticktion will allow you to extend them a bit by heaving up on the bars.

The other thing to confirm is that your springs are correct length and gauge.

Regards Mick
mdt-son
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Re: 1964 G12 CSR roadholder forks sticking

Post by mdt-son »

Your lhs slider may have suffered deformation induced by welding. Repair of sliders should be left to the experts. Norvil used to offer a repair service - they may still do. The fact that the slider binds in the compressed state when the bottom bush approaches the slider bottom tells me something is wrong with your slider bore.

Did you check slider travel without springs fitted?
Is there any visible slider movement transverse to back and forth, or vice versa? When sliders ovalize, they shrink in one direction and expand in another.
Straightness test performed on new stanchions by rolling them on a table?

Good luck on your fault finding.

-Knut
Last edited by mdt-son on Mon Mar 13, 2023 6:11 pm, edited 1 time in total.
tony54
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Posts: 16
Joined: Fri Apr 26, 2019 3:28 pm
Location: Leicestershire UK

Re: 1964 G12 CSR roadholder forks sticking

Post by tony54 »

Have just noticed that I failed to reply to the last two posts, apologies.
Off the bike, and with the springs (correct for the bike) removed, the forks had a nice smooth action. Much shining of light down the slider bores eventually revealed a slight bottom bush sized depression in the rear face of the repaired slider bore. It would appear that, when fitted, the deflection in the forks was causing the bottom bush to jam in the depression. A new slider restored full function. :)
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