Leading link forks, advice needed

Reposted due to fuckwit at keyboard...





So, I've got a set of leading link forks from ebay.

http://www.flickr.com/photos/8963323@N05/2409782962/

They look to be about the right size to fit on the front of a K100
(which I'm fitting a sidecar to).

However... the fork tubes are 34mm whereas the K100s are 41mm. Speaking
to the manufacturers they weren't really interested since every set are
different and they'd recommend I had a new set built (at over a
grand...)

So I seem to have three[1] options:

1. Make up two sleeves which runs between the yokes, OD 41mm, ID 34mm
and with a slot in them so they squeeze the forks when squeezed by the
yokes.
2. Get someone to make replacement tubes to the same pattern but in 41mm
tubing with the bottoms squished down to 34mm to fit in the 'swing arm'
piece. Get new clamps for the 41mm forks top suspension mount.
3. Get replacement yokes made to take 34mm forks



Looking at my three options

1. Seems to be the easy choice and probably not too difficult or
expensive. But it seems like a bodge.

2. Seems to be the most obvious way to approach it but...
- Will the tube be weakened by squeezing it to an oval profile?
- Any ideas where I could get this kind of fabrication done in the
south-west?

3. Seems to be relatively straightforward but again I've never had
custom stuff like this made (but I suspect it just involves throwing
money and a set of yokes at someone)


What's the option least likely to result in me riding an outfit and th
front end falling off?





[1] Get some fucking sense and don't piss about with sidecars isn't the
advice I'm looking for...

 

My first thought was are the new ones going to be strong enough for a
K100 and sidecar?
There is a lot of weight there, add in rider and passenger, and you have
probably double the forces on the front end compared to a solo bike with
its larger diameter forks.
Or maybe leading link forks are a better design to cop with the extra
stresses invloved?
Alan.

 

Either secure the sleeves with high strength retainer (Loctite 638 or
similar) or have them made so you can shrink them on by using a bit of
heat. I can work out the allowances for doing this but you need to get
the sleeves machined by someone with a bit of a clue...

I think you'd have more luck if you got someone to cut off the top
part of the forks and weld on new 41mm items but you'd need to give
them an old pair of yokes to use as a jig.

It's that spending bit that's so wrong.

3b. Ride it on standard forks.

3b.

 

Well, 3b is the default and I have a horrible feeling that if 3b feels
ok that neither 1, 2 or 3 will take place.


BR

 

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=160225448158
"leading link front end ideal for trike what you see in the picture is what
you get bought for project not needed know sow must go"

There's a clue in the description.

Who knows what world of pain these could lead to.

Are the wheel bearings OK?
What about the calliper?
Is it compatible with your master cylinder?
What pads does it take?
What rating are the springs?
What are the dampers set to?
How much rake and trail would you get?
What ride height?

Can (will?) the manufacturer tell you what bike the setup was originally
supplier for? Might give some clue regarding the weight.

Nige it back on ebay and hope *someone* will give you more than the £160 you
paid.

 

I'd assess the tubes. If the 34mm ones are significantly thicker wall than
the 41mm ones, then they should be strong enough. However, they look like
they're off an off-road outfit which is likely considerably lighter than a
K-brick-plus-chair. If they seem strong enough, option 1 is the best bet;
I'd get sleeves made with a flange, myself, so they have a flange under the
yoke.

If they aren't going to be suitable, then option 2 is better. Don't fancy
option 3 at all, and besides, it offers no engineering advantage over option
1.

Option 1 is the easiest machining job.

 

Yes... they were being sold by someone who planned to build a trike.
He'd seen them advertised as that in BSH some time back.

Can be replaced.

I've seen them before, not sure.

Am sure they can be rebuilt.
Pads I'm sure I can identify.
Compatible with master cylinder; details, details.

"adequate I'm sure"; adjustable Konis

Well, a visual inspection suggests the ride height would be similar; had
them measured before I bought them.

No. Completely unhelpful.

No. Have a plan and insist on the opportunity to **** up properly.


Thanks for all your help by the way; fwiw I'd considered most of the
above questions, with the exception of the rake and trail. I'd also
thought "where could I get replacement disks from"?

I'd also considered/planned measuring up a set on a K100.

 

Would it be a fucker to use a pair of yokes from another bike that uses 34mm
stanchions? The steering stem won't be much different (I imagine) and
spacing/sleeving for bearings is a damned sight less "dodgy" than a
stanchion sleeve.

Just a thought.

Or a little bit of money at a bike breaker.


--
Beav

VN 750
Zed 1000
OMF# 19

 

There are two reasons for converting to leading links - they're stronger and
better able to take the side loads than those slidey telescopic things, and
they're generally built with decreased trail to lighten the steering. I
suspect that, despite the tubes being of a smaller diameter, the overall
structure will be at least as strong as your conventional forks. You may
have to consider a different handlebar setup whether you change forks or
not.

What I think you should do is:

First, fit the chair, and see how it feels with the original forks.

Then, if you think there's room for improvement, fit the LLs. Sleeve them
up to fit the standard yokes. Take the plot out and rag **** out of it. If
they're an improvement, and they don't break, game on. Sorted.

If you don't like them, put the originals back on.

 

You're my role model.

 

I feel soiled.

 

Don't feel too bad about it.

 

They look like Unit leading links almost identical to the ones I had on
the Mille and RS3. Can't remember what diameter the tubes were on that.
Not massive IIRC - Sweller might know. The Mille wasn't exactly light
but not as lardy as a brick I suppose.

I'm with Platy. Though if you can use Andy's demon precision methods to
get a really tight fit for the 'shims'[1] do much the better.

The only problem I can foresee is the amount of trail provides by the
bend in the tubes IYSWIM. Though similar ride height suggests it may not
be miles out. That presumably was set to suit the steering head angle of
the bike they were built for.

I have ridden an outfit with telescopic forks and LLs (though not the
same bike). The one with telescopics (AJS 31CSR) was light by today's
standards, but the LLs on the Mille were a relevation after them.

If you can get them set up near enough and the shims don't allow things
to start twisting I don't think you will want to go back to telescopics.

[1] I think something a bit thicker and specifically engineered than a
piece of beer can is called for.
--
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On Sun, 13 Apr 2008 19:00:32 +0100, Pete Fisher

snip>

I've emailed him on the anti-clique list with a couple of suggestions
and I'm confident we can put something together that will do the job
properly. It might involve him begging to Eaton Engineering but I'm
sure the man in question would be able to hit the sizes if he had
enough tries.

 

Using the patented Mavis Beacon "Hunt&Peck" Technique, Andy Bonwick

Sho 'nuff.

Two or three hundred goes, no worries.

I'll be wanting a full disclaimer signing, natch.

 

That's "sizes", not "sides".

Can we watch?

 

I think you may have the makings of a rudimentary plan. Probably with a
'temporary fix' sleeve. And if it seems ok then something better.

 

Item 130213680303 would seem to have potential as "something better".

 

I like that. I wonder if he'd consider a swap for an old K100 and a
Wessex sidecar?

 

If your supply of round tuits doesn't run out first. Which it will.

Ron Robinson