Fork Tubes

[double diamond]

Never seen a chromed original 31.5mm tube, but it is certainly plausible that it’s been done post-factory. Since new tubes from Tarozzi are $168 and hard chroming an original tube costs $100, if I had an original tube in otherwise good condition, I’d certainly consider hard chroming. Anyone know what the Frank’s tubes go for these days? I recently disassembled an Aermacchi fork that had obviously been straightened. There were marks in the tubes from the V-blocks and the tubes were cracked at the inside of the bend. Got a couple Ducati and Betor tubes in similar condition. I’ve straightened many fork tubes and don’t have a problem with it if the bend is only a few degrees. But, if after straightening there is any sign of the metal tearing, it’s a throw-away. After many years and miles, the original fork tubes on my BMW cracked just below the triple clamp and had never been straightened. I only noticed it because they started to leak fork oil. Steel has a fatigue life. After a certain number of cycles, a tube will fail. If it’s been compromised by straightening after a severe bend, it will fail sooner.
You’re right, Amartina, greasing the tubes does have a down-side but the fork is shrouded (although the shrouds just make the fork something of a leaky air pump) so grit accumulation is impeded. Another unfortunate consequence of the Ducati fork is that the external springs rub on the fork tube and will actually wear the tubes. There goes your nice hard chrome. It is possible to install internal springs. I’ve been told early Ducati’s (175?) used internal springs, and Aermacchi used internal springs in a 30mm fork.

[amartina75]

You don't use V-blocks to straighten fork tubes. That and other user error is probably to blame for your damaged fork tubes.
Here is a picture of the push block i made to straighten my tubes, i also made support blocks out of oak to match the profile of the tubes.
look at this link to see how the pro's do it http://www.framestraightsystem.com/Motorcycle%20Fork%20%20Repair.htm

image.jpg

Here is the reciept for the two sets of tubes i bought from Franks I'm pretty sure all their tubes cost the same, so you are looking at just under $300 shipped for a set which is cheaper then the tarozzi tubes

image.jpg

[tobydmv]

So are the Franks tubes chrome plated and do they transfer the damper piece over to the new tubes? I cant figure how to get that piece out.

[double diamond]

There’s a wire clip holding the damper valve in the fork tube. To remove the clip, make a hacksaw cut from the end of the tube to the retainer groove. Then rotate the clip to where it’s over the cut and you can pry the clip out. Obviously this procedure is only for tube that will be discarded. For tubes that will be re-used, grind a notch in the fork tube at the open end of the clip. Only make the notch big enough to get a little pick in there to pry the clip out.

[amartina75]

Toby,
You haven't reported on the condition of your tubes or posted any pictures.
Have you decided they need replaced? Is the travel area clean? What is the max. gap you see with
the tube on a flat surface?

[Rick]

I've never been able to straighten bent tubes with Vblocks- they leave marks and distort thinwall tubes. I build rocking saddles that I place on each side of the bend, with the crown facing up, and can press tubes straight as accurate as my straightedge.

tube press.jpg

This pictures shows the top die as a straight concave, but it still left little footprints at the ends since I had to overbend to allow for springback, so I made another top die with radiused ends- it worked perfectly- can't find it now.
I use this type of die set to make small, but very accurate, bends also, using a segment of a bending die.
Rick

[Jordan]

Wow, I'm impressed with the press tools shown in this thread.
I recently was given some centres, that were used to check fork tubes at the main Honda distributor in Sydney. I don't know how essential they are, but they clearly were used a lot.
The info on avoiding V-blocks for this work is good to know.

[Moto Chuck]

Not to hijack Toby's thread but I was wondering how much corrosion is acceptable on the old 31.5mm fork tubes? Every set of these old forks I have ever disassembled has had corrosion or galling on the tubes. While polishing may clean up the tubes it will also reduce the diameter of the forks.

On the other hand I have seen several vintage racers that are using 31.5 tubes with visible rust or corrosion on the fork tube. I always winced at the idea of getting on track with rusty fork tubes.

Has anyone rebuilt a set of 31.5 forks with less than perfect tubes and what were the results?

[DucRedux]

I'd like to offer another source for service: Framestraight.

http://www.framestraightsystem.com/Moto ... Repair.htm

My NC 250 forks were bent from racing when the bike was purchased. The chroming was in acceptable condition and I was assessing all the other expenses involved in the ongoing rebuild, so I put a more expensive full fork reconditioning off for later. My experience found Framestraight offers a pleasant responsive service at a reasonable cost.

[tobydmv]

Toby,
You haven't reported on the condition of your tubes or posted any pictures.
Have you decided they need replaced? Is the travel area clean? What is the max. gap you see with
the tube on a flat surface?

Hey thanks for reminding me. I'll have a pic tonight for you. I'm not sure if I mentioned it but this bike was in an accident. Appears to have ran into something head on. I think the frame is bent slightly too. It was hard to remove the motor and the gusset under the top tube is kinked. The fork tubes are bent badly. You dont need a straight edge to judge them. I'm leaning towards new tubes for safety sake. But I would like to hear if these can be salvaged.