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Old 28-01-18, 02:53 PM   #1
Tomcatracing
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Default A question about fork tubes

2002 curvy with standard 41mm tubes.

Due to the usual problems of pitting and corrosion I looked at options, coming to the conclusion that replating was probably the best one. So I sent them off and eventually they have come back. The finish on the running surfaces is fine but what worries me is down the bottom end, at the groove where the bottom bush sits in. It seems to me that to prepare the forks for plating they ground the entire length of it to remove the old chrome. Unfortunately in doing so they have also ground back the lands either side of the bush groove, to the extent that the depth of the groove is just 0,28mm (about 7 thou). To me this is dangerously inadequate as minimal wear in the bush and/or slider could allow the bush to jump out of its groove and jam the forks.

The question I have, that I'd be very grateful if someone could assist me with, is what is the diameter of the lands either side of the groove on a new fork tube? I suspect it's the same as the running surface of the leg but I'd like that confirmed before I go back to the company demanding they do something.

For info on my legs the replated tube diameter is 40.90mm and the diameter of the groove lands is 40.63/40.66
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Old 31-01-18, 05:56 PM   #2
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Default Re: A question about fork tubes

Nobody? Come on guys....
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Old 31-01-18, 11:29 PM   #3
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Default Re: A question about fork tubes

It's ages since I last saw that end of the stanchion so I really don't remember mate. Best I can do is show you a pic of a curvy stanchion with the bushing in place.

http://www.bluepoof.com/motorcycles/...s/351_5187.JPG

http://www.bluepoof.com/motorcycles/...s/351_5192.JPG
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Old 01-02-18, 01:56 PM   #4
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Default Re: A question about fork tubes

Thanks Dave but it's the dimensions I need. This is a bit of a saga so bear with me. I sent the forks to Brooks Suspension who input it into their system on 1 December, finally returning them after 2 chase-up messages on 27 January. One leg looked fine but the other had a massive step in the chrome, see pic.



I suspect this is an area where the bushes and seals don't run but I brought it to their attention, since it looks like the step is asymmetrical in any case. That got me looking at the rest of the fork tube and raised my suspicion that the bush groove lands had been ground down as part of the process. If this is the case then it would only take a small amount of wear in the bush or slider bore for the bush to be able to jump out of the groove and jam the fork.

I've measured both tubes and although only one has the big step in the chrome both have similar groove land dimensions.

I contacted Brooks Suspension almost a week ago but they have not responded, so before I start taking any action against them I'm looking to get as many facts as possible in place.
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Old 01-02-18, 02:21 PM   #5
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Default Re: A question about fork tubes

Sorry can't help with dimensions. Hopefully someone here will have a stanchion lying around who can help.
That does look like a shoddy job though.
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Old 02-02-18, 08:55 AM   #6
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Default Re: A question about fork tubes

I've not seen anything like this before. If they have ground away the stantion too much and it's not safe then I'd bin it.

Take them to the small claims court if you get no response.

Pretty sure you can get replacement stantions at Wemoto.
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Old 02-02-18, 10:18 AM   #7
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Default Re: A question about fork tubes

Yes you can.
From an Italian firm and very good quality

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Old 02-02-18, 04:41 PM   #8
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Default Re: A question about fork tubes

i would suspect that brooks sub contract the chroming out as there are very few places that do hard chroming.

the 'step' is a crack that would have been there before the work commenced.

TBH the work looks very shoddy.

good luck getting it sorted.
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Old 10-06-18, 02:13 PM   #9
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Default Re: A question about fork tubes

Update: after much pestering Brooks took the tubes back and sent them back to their subcontractor. The final result I am pleased to say is excellent, and they have also reclaimed the bush land height that was lost after the first attempt (to the same diameter as the rest of the tube). If only they'd have done all that the first time round.
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