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Fitting a triumph fork
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Gnarak
Posted 2005-04-17 6:04 PM (#6288)
Subject: Fitting a triumph fork


OK, let's make a long story longer....

I've used pics from the Yamaha parts site, and draw some in them.

Gonna try to explain:

What we want to do: Replace silly old fork, with a better (modern) fork. The one thing we don't want to do is mill in the stock triple tree. So, we have to use the tree which belongs to the fork we are going to fit. We also want to keep the stock Yamaha rim.

First we have to make sure the fork + triple tree can be fitted to the frame and rim. There is two things we need to know. First, the length between the fork tubes (center-center) can not be smaller than the stock fork. It's simply not possible to make the rim thinner, right? We can always 'make it wider' by using bushings and washers.... Second, we can not use a triple tree which has too short tube/pipe on the lower tree, it has to reach through the headstock in the frame... If it's too long we can make it shorter, right?

Anyway, look at picture

http://www.yamaha-triples.org/photos/show-album.asp?albumid=87&phot...

It's a picture from the stock parts but i use them for explanation purposes.
The distance 'A' and 'B' may not be less than the distance on a stock fork. You also have to make sure the outer diameter on bearing 'green' and outer diameter on bearing 'red' is the same as the stock bearings. The parts 'yellow' (dustcover) and 'purple' is of no concern as they will be disgarded and you have made sure they come with the new fork...ok

If all those diameters and distances are the same as on the stock fork, go ahead, fit it. It will fit like a stock fork... If the don't..... Well.... In my case, with the Sprint 43mm fork, the both distances 'a' and 'b' were taller and wider. 'b' concerns the wheel, we'll ge there later but 'a' concern the mounting to the frame, and we don't want to modify the frame, right?

I had to put the lower tree up in a lathe and lathe a new seat for the upper bearing, cause it could not get down on the tube far enough, there were a play of an inch... Should be next to nothing ;-) Slow rpm on the lathe cause the tube isn't detachable from the lower tree so to get as little vibration as possible when lathing i did it like i do it with the wife...... Slowly but without any chance to escape ;-)

Take a look at picture

http://www.yamaha-triples.org/photos/show-album.asp?albumid=87&phot...

and you can see that the red part of the tube is about an inch lower, right?

Now, the only problem we may have is that the threads on that tube will go up and above the upper tree to far, so the nut wont lock them together, but in my case i only had to add another washer about 1mm thick...

Now then, the tree is fitted and next on to the wheel, what about the distance 'b'? Is it the same as stock? Fine, but what's about the wheel axle? Will it fit the clamps in the bottom of the tubes? Are the holes in the bottom of the fork legs the same as stock? They are? Go fit the damn thing and be happy, if they are not.... Silly old fool. Take measurements and go back to the lathe...

In my case, the holes in the fork legs were 34mm and the wheel axle is 16mm? (not sure if i remember correct) also the hole in the opposite tube leg, where bigger then the inner diameter of the wheel bearings.... Damn.... Should have kept the stock fork and rebuildt that one ;-) I basically had to have a wheel axle looking like this:

http://www.yamaha-triples.org/photos/show-album.asp?albumid=87&phot...

Now that's simply not possible to push through... So i made it like this instead:

http://www.yamaha-triples.org/photos/show-album.asp?albumid=87&phot...

Two parts, going in from each side... Push through the axle-part, threaded in the outer small end, all the way so all you see on the other end is the threaded thin part and push the bushing over it, the bushing has a washer-part making it look like a washer from the outside, and also makes it possible to center the wheel in the middle beteen the fork legs... Measuring the required length of this part whas a PITA, big time. I actually made it out of wood, and fitted it, checked clearence between tire and lower leg on
both sides, grinded it a little and fitted it again, and again, and again.... Thus eventually i had the correct lenght and made one out of steel in the lathe.

http://www.yamaha-triples.org/photos/show-album.asp?albumid=87&phot...

Red is the axle and yellow is the bushing, barely visible.


Fitment of the brake calipers is a completely different thing. Look at this picture:

http://www.yamaha-triples.org/photos/show-album.asp?albumid=87&phot...

Thickness of the adapter plus shape is all dependent of the fork and how the brakes are fitted on that one, but i hope you get the genreal idea. Don't use stainless steel, use some sort of dural alu, it flexes a little, but keeps it's shape. Doesn't bend like steel or brake like castings... Then there is fitment of the instruments, handle bar, steering stop, headlight, flashers... Yaddayadda....
Hey, do i have to tell you how to do everything???


Well, now the fork is fitted.... Lot's of ramblings but hopefully you can
make any use from it.

As always, any message from me generally causes more questions to rise than it answers ;-)
But feel free to ask me direct anything you want further explained or doesn't understand...
I'm probably very unclear to you, but to me it all makes sense.

Finished it looks like this:

http://www.yamaha-triples.org/photos/show-album.asp?albumid=87&phot...

H./

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