bent fork stanchions

Helpful information and requests for assitance and advice
Locked
Invicta
Member
Posts: 171
Joined: Mon Jan 29, 2018 9:42 pm
Location: Kent , England

bent fork stanchions

Post by Invicta »

Having cleaned up and polished my fork stanchions, I decided that they would be OK to use, but then I checked them for being straight, (should have done this first) They are bent to 0.045" in the middle. New stanchions for 1949 shuttle valve type forks are no longer available anywhere, and fork repair companies want silly money to straighten them,( over half the cost of a new set of stanchions). has anyone had any success with straightening slightly bent stanchions without the use of a hydraulic press ? i know that I can buy some of the cartridge type stanchions if all else fails.
Mick D
Posts: 2886
Joined: Mon Mar 24, 2014 5:44 pm
Location: Aberdeenshire

Re: bent fork stanchions

Post by Mick D »

Hi

Whilst 45 thou is not desirable it's not going to be visible to the naked eye when in use. Do the forks function OK at the moment? if so I'd consider refitting them with the stanchions orientated with the concave side facing forward, (of course, give them a good inspection for cracking using a 10 or 15 power magnifying glass).

Straightening the stanchions, with or without a hydraulic press, risks local deformation and binding in operation.

Regards Mick
SPRIDDLER
Member
Posts: 8541
Joined: Wed Sep 01, 2004 1:00 am
Location: WEST SUSSEX UK

Re: bent fork stanchions

Post by SPRIDDLER »

I go along with MickD. In fact I wouldn't be surprised if the new factory ones weren't 100% perfect.

Following a collision Carole Nash sent a (hopelessly out of his depth) engineer to inspect my bike. He glanced casually at it for about ten minutes and wrote the bike off reporting that the frame was bent. C Nash then wrote that I had to provide an official Destruction Certificate and return my V5c to them whereupon they would settle with a payment of £500 to reflect its PRE-ACCIDENT value.
Marigold collision damage 23 Aug 2010 (720x540).jpg
I took it to Motoliner frame specialists at Maidstone who jigged it........
In jig LH side (720x540).jpg
and using the swing arm pivot casting and headstock as reference points could only find a 2.5mm vertical twist/misalignment in the frame.......(The vertical red line is the zero defect datum).
2.5 mm twist marked (720x540).jpg
I sent C Nash photos (from the book 'Working at AMC) of the factory's very basic frame brazing shop arguing that the 'misalignment' was as originally built. After 14 months of countless emails and frustrating phone calls with their impenetrable call centre and 'experts' they finally agreed that I could rebuild it and sent me £1000 in settlement.
Hope I haven't bored y'all (and gone too far off topic, Mr President ;) )
You do not have the required permissions to view the files attached to this post.
'There is a tide in the affairs of men
Which taken at the flood............'
User avatar
ajscomboman
Member
Posts: 3963
Joined: Mon Jan 01, 1990 12:00 am
Location: HAMPSHIRE UK

Re: bent fork stanchions

Post by ajscomboman »

SPRIDDLER wrote: Hope I haven't bored y'all (and gone too far off topic, Mr President ;) )
No, I'll let you off Nev, just don't make a habit of it!!! ;) ;)
alanengineer
Member
Posts: 1175
Joined: Wed Oct 12, 2005 10:45 pm
Location: KENT UK

Re: bent fork stanchions

Post by alanengineer »

45 thou isnt much. i would do as MickD suggests and get them to be bent facing forwards. in time they will straiten themselves out. I have bent many sets of stanchions straight using a simple fly press and a DTI. If you go to the rechromers, thats their first operation.
Not seen a stanchion fail due to being rebent yet. But if its really bent like Marigold's, then you cant bent them straight
User avatar
clive
Member
Posts: 5657
Joined: Mon Jan 01, 1990 12:00 am
Location: LONDON UK

Re: bent fork stanchions

Post by clive »

I rode my 49 G80 for many years and possibly 80,000 miles with stanchions that needed to be set so the bend in each was aimed forward. Not sure if it was an impact or just use over the years with a 1 1/8 forks. I would go for refitting them after the inspection suggested.
clive
if it ain't broke don't fix
g5wqian
Member
Posts: 220
Joined: Wed Nov 18, 2015 7:43 am
Location: wiltshire
Location: near swindon wilts

Re: bent fork stanchions

Post by g5wqian »

flat heavy steel bench required with some pieces of softwood to sit ends of forks on above bench .
7lb sledge hammer and short piece of softwood on top of stancion and hit it where necessary .
roll the stancion on a pair of vee blocks or over a surface table to see if straight , well thats if you have an eye to see if things are straight or not .

you can also roll the stancions on the surface table and look for light under them as you roll them .

rather than a hydraulic press it would perhaps work better using a fly press with a block of wood or alloy in the centre and some wood or alloy blocks spaced apart for stancions to sit on , you can get a better feel with this than a hyd press ..

you can make a rolling jig up by using 2 ballraces each end on a fixture which you can place the tubes on to roll them freely to inspect them ..
alanengineer
Member
Posts: 1175
Joined: Wed Oct 12, 2005 10:45 pm
Location: KENT UK

Re: bent fork stanchions

Post by alanengineer »

Thats the way it was done in the old days
Andy51
Member
Posts: 741
Joined: Thu Mar 31, 2005 1:00 am
Location: BERKS UK

Re: bent fork stanchions

Post by Andy51 »

Hi, when I rebuilt my '54 18S a few years ago, I found the front forks were very stiff when everything was tightened up. After several goes at loosening the axle mounts and bouncing the suspension a la handbook, I realised one or both stanchions were bent (should have checked at an earlier stage!). I took them both off, found one was bent by rolling on a flat surface (lathe bed at work). Helped by another classic biker at work, we straightened the stanchion using a hydraulic press, measuring straightness using a 24in steel rule. Put forks together, they worked beautifully smoothly and have provided excellent service for the last 10 years. I didn't measure the 'bentness' but it wasn't enough to show at a glance, so probably about the same as yours. I suggest you straighten them to a similar standard and use them - so long as the forks work smoothly they are good enough. Hope this helps, Andy
Locked