Author Topic: Shortening fork tubes (Read 14025 times)

Flying J · « **on:** April 28, 2010, 04:46:19 PM »

I swaped my rusty 550 fork tubes for a set off a 78 750F. Now i want to lower the front end a little. I think im going to go with the brat style on this bike. So, the 750 forks are an inch over stock and i think im going to drop it 2 inches lower than stock so i have to lose close to 3 inches of fork tube. I could order a set from franks for 250 but that is to much. so i took it to my local machine shop and he said he could cut and thread them for $35 a leg. So i think thats what im going to do.
Is there any reason not to do this? I havent seen any threads about it.

OldSchool_IsCool · « **Reply #1 on:** April 28, 2010, 05:07:51 PM »

I can't speak to the shortening of forks, but I recently swapped 750K1 forks onto my 550K3. No biggie as long as you also swap the brake components too.

Flying J · « **Reply #2 on:** April 28, 2010, 05:11:17 PM »

I didnt swap the lowers just the tubes.

754 · « **Reply #3 on:** April 28, 2010, 07:38:37 PM »

I have cut many down.. Its a good thing.

You may have to shorten your springs..

Flying J · « **Reply #4 on:** April 28, 2010, 08:07:52 PM »

I plan on shortening the springs. I was also thinking about tempering the springs since i have some to spare. Anybody try that? I might have some connections to some big tempering ovens.

754 · « **Reply #5 on:** April 28, 2010, 09:01:34 PM »

Why, do you want to temper them...?

bucky katt · « **Reply #6 on:** April 28, 2010, 09:05:40 PM »

i cut down the forktubes on a friends 750 on a lathe to be sure of getting a nice true cut, then tapped it while it was on there, worked perfectly.

borzwazie · « **Reply #7 on:** April 28, 2010, 09:14:46 PM »

curious, what tap do you need for that? is it feasible to do it by hand?

754 · « **Reply #8 on:** April 28, 2010, 09:29:28 PM »

You also have to cut the O ring surface, with a good surface finish, then cut the threads.. I thread them on the lathe, dont use a tap..

I am sure someone will come along and say they tapped a set with pipe thread with a tap.. but I prefer to keep it looking like a bike...

Flying J · « **Reply #9 on:** April 28, 2010, 10:13:49 PM »

I was thinking of tempering the springs if they were to spongy and worn out. Just a thought.

Duke McDukiedook · « **Reply #10 on:** April 29, 2010, 09:28:09 AM »

If they are spongy and worn out you need to replace them, tempering could potentially make them brittle or more spongy and you won't be able to predict the spring rate it would create any way.

kabuki · « **Reply #11 on:** April 29, 2010, 09:29:04 AM »

What's the best way to shorten the springs?

I just put new progressives into my 550 forks and installed the adjustable compression valves from MikesXS at the same time. Now I have about 1.5" of spring preload and I'm worried I may have too stiff of a setup (haven't put the forks back on to test yet)

Nikkisixx · « **Reply #12 on:** April 29, 2010, 09:30:20 AM »

I am no metallurgist, but I've found spring steel does not play well with heat treating. If they are that saggy, will they work in the shorter tubes? Just a thought.

MCRider · « **Reply #13 on:** April 29, 2010, 09:33:52 AM »

Quote from: Nikkisix on April 29, 2010, 09:30:20 AM

I am no metallurgist, but I've found spring steel does not play well with heat treating. If they are that saggy, will they work in the shorter tubes? Just a thought.

If you put a full length spring in a shorter tube, you'll run into coil bind at some point. But on chopper/bobber style bikes does anyone care?

754 · « **Reply #14 on:** April 29, 2010, 09:49:35 AM »

You can check for coil bind before you install, either wooden fixture on drillpress or lathe.. or a screwthread to push it.

It may be tricky to re heattreat at home..

To cut, cut as square as you can, bout 1/4 inch longer than you want to end up..
Thin cutoff wheel or chopsaw should work. You can then heat and reform the last coil so it looks more like the end used to. the re square up the end on a grinder or sander.

Unless you get this real good, best to cut upper end of spring as pushing against steel cap will do less damage than the aluminum leg..

swellguy · « **Reply #15 on:** April 29, 2010, 10:59:13 AM »

found this article which makes it seem pretty simple:

http://www.hondachopper.com/garage/shortening_forks/shortening_forks.html

Flying J · « **Reply #16 on:** April 29, 2010, 11:11:02 AM »

Thats not a bad way if your just loosing an inch. As far as tempering goes im not sure how good or bad the springs are. Tempering them was just a thought. My dad used to work for a company that built spring for almost anything. I could call his engineer buddy who works there but i figured with all the brains on this forum id get a pretty good idea weather it was a good move or not.

Wisconsin Jeff · « **Reply #17 on:** April 29, 2010, 11:13:53 AM »

I found this the other day.

http://www.hondachopper.com/garage/shortening_forks/shortening_forks.html

Has anyone else tried this? I know they make similar kits like these for drag bikes. Not sure about street ride-ability.

754 · « **Reply #18 on:** April 29, 2010, 07:40:50 PM »

Heat treating under the correct conditions.. not a problem..

But I am thinking they are quite fatigued.

BTW usually stuff is hardened then tempered.. Not sure in spring steel if procedure is same and it varies with different alloys. So when someone throws part of the term ot there , I assume they will not do it correctly..

Flying J · « **Reply #19 on:** April 29, 2010, 09:32:29 PM »

No, if i was going to have it done it would be by people who do it for a living. I like to do things myself but i usally do lots of research before i dive in. I was was just tossing out a random idea that popped in my head.
So what is the most you think i can cut down these tubes? Im going to take a ratchet strap and max out the fron suspension to see the clearce of the front wheel ass well as how close before i hit the triple clamps. I guess what i want to find out is what the max travel of the wheel is. My guess is 4 inches or so. Maybe 5.

754 · « **Reply #20 on:** April 30, 2010, 08:03:21 AM »

Easy to check travel with springs out.

You can probably cut out a few inches, choice of fender may limit travel, smaller wheel can give more room. Spring preload and stiffer fork oil can prevent bottoming if you want to severly ower it..

swellguy · « **Reply #21 on:** May 05, 2010, 03:14:31 PM »

Quote from: Wisconsin Jeff on April 29, 2010, 11:13:53 AM

I found this the other day.

http://www.hondachopper.com/garage/shortening_forks/shortening_forks.html

Has anyone else tried this? I know they make similar kits like these for drag bikes. Not sure about street ride-ability.

Sorry to bring this thread back but I was going through this hondachopper post and found the part where he says:
"Now the piston. i got two 2" bronze bushings 1" od and 3/4" id at the local hardware store. Install on piston as shown"
and there's this picture:

What are they for? Are those the things sitting at the bottom of the piston? There's no mention of inside diameter.

People talk about going into Home Depot or Lowes and buying bushings. Here, the guys at Home Depot have no idea exactly what I'm asking for which is correct.

I've shortened Harley forks before and always used PVC tubing. Is this the same thing?

vorhese · « **Reply #22 on:** May 05, 2010, 04:00:54 PM »

He put spacers on his damping rod. Doing that sucks the damping rod higher into the fork tube, eliminating the length of the spacer in total fork travel, but equally lowers the forks. It's an old old trick. I've done it to my Triumphs. The Triumphs have different fork components, but the idea is the same.

You can get copper pipe fittings in the plumbing section. I'd love to know if there's a better option. I had my pops make my Triumph spacers.

For a CB the spacer will be INSIDE the tube sitting between the damper rod spring and the top of the damper, over the damper rod itself. As long as you aren't dirt jumping you should be ok.

Flying J · « **Reply #23 on:** May 05, 2010, 05:38:41 PM »

home depot doesn't ever have what you need. try looking at OSH.

swellguy · « **Reply #24 on:** May 05, 2010, 06:14:28 PM »

Quote from: ffjmoore on May 05, 2010, 05:38:41 PM

try looking at OSH.

Wish we had them in Canada, thanks.

News:

Author Topic: Shortening fork tubes (Read 14025 times)

kabuki