Why do we want rare, complicated stuff?! Amp forks kupput

[dyna-ti]

When I renovated my F4 BLT it needed amongst other things a spring, as one was missing.
I phoned a couple of spring makers who quoted prices for progressive custom wound this and that and were asking close on £200 each.

While out and about I happened on a small engineering workshop and brass necked walking in to find 3 guys in oily overalls sitting round a giant teapot. They had me leave the spring i had with them and said to come back in about a week.
So I return a week later and they've made me a couple of springs the same stiffness as the one I gave them. They charged me 30 quid

Custom spring makers are used to making fancy springs, and have big expensive machines, and are wearing clean overalls. Small down to earth engineering firm are probably just as good if not better in many ways, and just as experienced and knocking out something like a small spring probably took them 10 minutes.

There should be a thread on here somewhere about the renovation process for my F4. it would be about 2008

I brass necked my way into another firm, this one produced machines for making plastic injection mouldings and one of their younger workers was a bike rider - I spotted a bicycle when I went in and spoke to him.
My fork had pivot points missing and the rest were all cracked
He replaced all the pivots and made them in T6 alloy, knocked out the old oil impregnated bushings and refitted them, made new collars for the springs, and a spring clip that holds them on and also made a jig to compress the springs with in conjunction with an engineering vice, which was also lined in nylon to protect the spring collars, and a holding clamp to grip the shafts of the dampers should you need to service them.

I think he charged me £110 or about that amount, but it was clearly a wee lunchtime project for him, and he was quite taken by the look of the fork, despite being a cyclist he'd no idea such types of forks existed.

I've a pic somewhere showing the condition of the fork when I first got it, though many of the pics have long vanished, so the ones of them before and after i dont have any more.
Before and after, all polished up


After

 

[Ren Rawbor]

edit- reply is re using a rear shock spring... A possibility if it did seat but be aware that whatever the quoted weight of the spring, removing coils to shorten makes it effectively stiffer.

Speaking of which, if the original spring was on the soft side for you (and assuming it won't compress to the point of coil-bound, and is not seriously weakened by rust) couldn't you square off the broken end & add an alloy spacer to take up the lost length?

 

[Thias]

Oh, I forgot. Did you write, what version of fork you have? The one shown above or the older version with just one spring inside the parallelogram? I somehow thought you had the latter.

Shortening a coil doesn't change the stiffness. It just reduces the travel. Unless it's a progressive spring where the wire width changes from top to bottom. But they are very uncommon. Using a spacer to make up for the missing section will do the same. Might be workable, if the coil didn't loose too much lenght. Rubber spacer might be better than alloy though. For some top out protection.

 

[enigma]

edit- reply is re using a rear shock spring... A possibility if it did seat but be aware that whatever the quoted weight of the spring, removing coils to shorten makes it effectively stiffer.

Speaking of which, if the original spring was on the soft side for you (and assuming it won't compress to the point of coil-bound, and is not seriously weakened by rust) couldn't you square off the broken end & add an alloy spacer to take up the lost length?

Hi, I dont think this is an option will take pics later.

 

[enigma]

Oh, I forgot. Did you write, what version of fork you have? The one shown above or the older version with just one spring inside the parallelogram? I somehow thought you had the latter.

Shortening a coil doesn't change the stiffness. It just reduces the travel. Unless it's a progressive spring where the wire width changes from top to bottom. But they are very uncommon. Using a spacer to make up for the missing section will do the same. Might be workable, if the coil didn't loose too much lenght. Rubber spacer might be better than alloy though. For some top out protection.

I dont think theres anything useful about the remains, other than id correct one, its a single spring up in the head of the fork.
I am uncertain what that makes it, from what I had understood prior to buying it , its likely a mongoose labelled basic one that the decals have come off.. I found an fleabay listing for spares which had charged £10 each for a red or a black spring for a fork like mine, sadly sold.. but it means that when I find one it needn't be extortionate, its not a lost cause its another patient rise to fruition I think.

 

[dirttorpedo]

Ya, that sucks. This is one reason why I tend to target fully rigid vintage bikes. The other is that early suspension was terrible.

 

[enigma]

Ya, that sucks. This is one reason why I tend to target fully rigid vintage bikes. The other is that early suspension was terrible.

I tried conventional low end suspension from rst ,and a short and very dissatisfying flirtation with the nonsense of cannondales headshox as a teen, and did not take to any of it, mainly as so heavy I preferred to ride rigid bikes.. I had a Whyte prst1 for a while twenty years ago because I got it cheap, and it did not ride like a suspension bike the poise and difference was amazing, but sold it.. now have a last of the line prst 4 as it was an itch when I got back into bikes, but the idea of the Amp was no real weight gain, very little travel as I just want to lower minor bumps and trail buzz on my aging body and the bike an old lava dome.. now, and I am better financed at my age and wanted some because I think they look kool!
One day it will be so, I do not expect miracles from this fork, just a little comfort without a big weight penalty, spring breaking aside, it appears to be of excellent quality in engineering terms.

 

[focomat 1c]

It appears that you have a pair of AMP F1 forks . These have a single centrally positioned compression spring backed up by an
elastomer plug which stops the spring from coil binding at full travel . The F2 version is similar albeit with slightly changed geometry .
The F3 and F4 variants have external springs fitted around the shocks on each side . Looking at an F1/2 spring we have the following
dimensions : wire diameter - 5.5mm spring o/diameter - 28.5mm spring length - 52mm no. of coils - 5
This is a ' black ' painted spring , which I believe is for the heavier rider , I have a ' red ' spring with a slightly reduced wire
diameter fitted to my bike which I presume to be for the ' average weight ' rider ? I don't know if there were any other spring
options . The F1 has tubular steel fork legs joined together by a steel bridge piece , under braking it is possible to see the brake pivots
twisting apart under load ! once you have seen this a brake booster plate becomes quite high on your shopping list !!!!
The F2 version is an all alloy variant with the tubular forks bonded top and bottom into the bridge piece and dropouts , resulting
in a much stiffer assembly .
It should be possible to find a suitable spring from the lists of standard compression springs to be found on Google ?
Hope this helps

 

[just jacques]

I can recommend flexosprings,

https://www.flexosprings.com/stock-springs/compression-springs

 

[youngsspeed]

Still ride a F4BLT and it is fantastic.
Definitely worth finding a spring