1952 sun challenger forks

[darloman]

Hi all, can someone give me instructions on how to replace springs in the forks of a 1950s Sun challenger. This may sound a bit mad but it looks as though the bottom tube as been re- chromed to far up the tube and so not sliding far enough into the top tube. Is this the case or do you think  its a bit more simple. As you have probably gathered by now it is my first attempt so any help would be a bonus.
 
Many thanks.
PS  Can you tell me what a neoprene rod is ??

[R]

Without knowing those forks personally, they usually have a nut on the top and/or at the base that keeps them all together.
What happens when you undo them - or have you already tried this.
Unless the Sun is something different, they need to be well greased inside, since thats all they have for lubrication.

Neoprene is a form of synthetic rubber/plastic.
How does this rod come into it ?
Hopethishelps.

[33d6]

Sun generally used MP (Metal Profile) forks on their 50's range and I assume that is what you have. Finding info on these forks can be difficult as my mate and I found when I rebuilt the forks on his mid 50's Sun Cyclone. All we ever found were annotated free hand sketches in the VMCC Library and had to work from there.

The forks were only held together by the springs. These were screwed onto a short threaded device top and bottom and worked much like those novelty Chinese finger handcuffs kids play with. You know the things. You slip a finger into each end with no effort but when you try to pull them out they tighten up The harder you pull, the tighter they get.

This was the same idea. The springs were easily screwed in place by MP when new but just got tighter and tighter the more we tried to remove them. Luckily the previous owner had made such a mess of trying to get them apart we had no qualms about using a hack saw and making the lot from new.

I suspect you are running into much the same problem. I would strongly suggest you get as much info as you can about the forks as you can before charging in as MP didn't seem to make their forks with any thought of later maintenance in mind. Once assembled they can be difficult to get apart without damage.

I had to machine away a section of one of the sliders for us to find out their construction. They were so worn they were dangerous so I had to make new anyway. I think my mate may still have this sample and I could take a photo for you if he has.

The final frustration was MP's trick of fitting grease nipples to the oil holes. The instructions advised use oil sparingly  but of course the previous owner had used a grease gun on the nipples and filled everything up with grease which doesn't compress and makes the fork action rather tricky. This particular Sun was a one owner bike but owned by the one family and had gone down from grandfather to son to grandchildren so we have photos of it from new-with grease nipples in the oil holes.
Have fun, cheers,   

[darloman]

Fantastic, thanks 33d6 you were spot on with the chinese handcuffs,the forks are now totally apart with no damage. All very dry and a bit of rust but nothing to worry about. A good clean and a bit oil and put them back together (fingers crossed). Have found a few pages of a Sun maintainance and instruction book, if it is any use to you for your collection i would be only too pleased to post a copy to you. At the moment they are with my brother who will post to me in a few days time. Do you have an email address? Will try and put a photo of the forks on here. Once again many thanks and happy new year.

[R]

Happy New Years to all !

If these forks use oil, not grease, then how do they get any damping.
The grease at least supplies a modicum of damping, in similar type forks.
With oil, they'd be like pogo sticks ?

You didn't explain the neoprene rods.
Is this some sort of addition or modification, to give damping ?
Or bump stop ?

[33d6]

You're quite right R, they didn't have any damping. They were just pogo sticks. This was common in British lightweight teles of the time.
Have a look at the original BSA Bantam forks, the first Francis Barnett teles and James first own make teles and you'll find the same story. Proper hydraulic damping on British lightweights came years after it did on larger machines.
Norman had an early go with an upside down system where the oil sat on top of the seals with the airspace in the sliders below. The seals slowly leaked of course and the forks then locked solid as the bottom airspace filled up with oil. Norman didn't change the design. They merely changed the advice in the later owners handbook about the quantity of oil required. Later advice was to add a few drops only for lubrication with no talk of damping.
Grease doesn't supply any damping. If there is an excess present the suspension just goes solid.
As for the neoprene rods, the Cyclone forks I rebuilt didn't have any. They were designed along the same lines as the Challenger but were slightly different. If they were present I would imagine it would be as you say, some sort of bump stop. They would need to be firmly attached at each end to have any damping effect.
In the late 1940's Dunlop offered a proprietary lightweight fork with an internal long thin rubber cartridge attached top and bottom as a suspension /damping medium. James used them for a short time before making their own undamped fork. A local club member has a James fitted with these forks and in a rush of blood to the head had a local rubber company extrude some replacement rubber for him. He swears it's impossible to remove and replace the rubber without losing at least two fingernails in the process. The owners handbook maintenance instructions are the opposite to the usual and make great emphasis on NOT getting oil anywhere near the rubber.
From the above you can certainly guess what I like to play with can't you. I rode these things as an apprentice because I couldn't afford much else. Now I'm very content with them.   
Exploring the world of British lightweight suspension in the 40's and 50's is a hoot. It's one of the reasons I love'em so much.

   
 

 

[wetdog]

in 1953 MP trapped a piece of rubber within the spring this was to dampen the movement , not sure if it worked and was all done to a very tight budget id say , this maybe a retro fit if you think the forks need it

[darloman]

Thanks wetdog, here is a page from a maintainance book that i came across and the spring stripped down. 33d6 hit the nail on the head.

[wetdog]

no rubber mentioned ? will did out what I have and scan , maybe they changed there mind , or more like it made no difference so stopped it . I have nothing at the moment with these forks fitted , but I do have my kids old Honda Z50R and they look to be the same setup and have worked well for many years over my garden and fields near by