Sticking forks

[b.walker5]

What would cause a fork to bind? For the last couple of months I have been putting my bike back together, after a mishap earlier in the year, and today I was refitting the forks, and aligning them when I noticed the left one was stiff to move. I took wheel off, removed the cap and tried to work the fork up and down, and found that it is sticking at about half way and completely jams up at about 3/4 travel. First thought was a bent fork so I dismantled and took it down to work where we have a "flat" table for precision welding work. It rolled perfectly on the table and shows no sign of being bent. Inspection of the leg, and the tube shows no signs of wear or kinks etc and nothing looks out of place, except the spindle which looks like this..





I cant see any reason for this and I cant see why the fork is binding. I'm almost certain it's not the result of falling off, and if its been that way for a while then it explains some interesting handling problems I've been having.

Any thoughts, anyone..??

[fredintoon]

What would cause a fork to bind? - - - nothing looks out of place, except the spindle which looks like this..
I cant see any reason for this and I cant see why the fork is binding. I'm almost certain it's not the result of falling off, and if its been that way for a while then it explains some interesting handling problems I've been having.
Any thoughts, anyone..??

Hi Brian,
that looks like #16 "oil lock piece" in my Clymer's book and no, it should NOT look all marked up like that.
My best guess would be "foreign body entrapment" AKA
"you got some big chunks of sh1t in there."
I'd say tear down both fork legs and wash out everything with acetone then take a good squint down inside
(Your place got a boroscope?) for debris.
I dunno if you dressed those parts up they'd still work or if you'd need to make new ones.

[b.walker5]

Thanks Fred, both forks are in as many pieces as I could get and have been thoroughly washed down and out. No boroscope but my internal Mightylite on a stick inspection shows nothing. Your right about the part ID but for the life of me I cant figure out what caused the marks, (I was thinking PO until I remembered I stripped and cleaned the forks shortly after buying the beast 10 years ago), however it sits at the bottom of the fork and the fork bolt goes through it before screwing into the inner cylinder, so it shouldnt affect the fork tube until it bottoms out and my trouble is before bottoming occurs. I've tried swapping tubes but it makes no difference, it still binds, I've tried swapping legs but it makes no difference. I'm no fool when it comes to mechanical "stuff" but this one's got me stumped.

[bikerphil]

Try sliding the stanchion in the fork leg without the damping rod in the fork. If it is still binding, the fork leg might be distorted from being placed in a vise. Are these Standard or Special (leading axle) forks? Another place to look is the bottom edge of the stanchion tube. It can become worn and develop a sharp edge and cause friction on the inside of the fork leg. Standard forks are more prone to this because of the lack of a lower Teflon bushing. This sharp edge can be sanded down to ease the sliding action. HTH

[mxmikie]

if you need them i have this part and the damping rod

[b.walker5]

Try sliding the stanchion in the fork leg without the damping rod in the fork. If it is still binding, the fork leg might be distorted from being placed in a vise. Are these Standard or Special (leading axle) forks? Another place to look is the bottom edge of the stanchion tube. It can become worn and develop a sharp edge and cause friction on the inside of the fork leg. Standard forks are more prone to this because of the lack of a lower Teflon bushing. This sharp edge can be sanded down to ease the sliding action. HTH

Thanks Phil, I've tried the stanchion with as the rod as you've suggested and it made no difference. The forks have never been in a vice while I've owned the bike (10 years +) so i dont think it's out of round. I havent looked at bottom for the sharp edge you speak of, and thats worth checking out. I'll do that tonight after work. It's a Special fork (leading axle) but there's a metal bush at the bottom of the tube, not teflon as you refer to. Should it be teflon? Last night I removed the bush, thinking that it might be the cause but it made no difference.

[b.walker5]

if you need them i have this part and the damping rod

Thanks, I'll keep that in mind, but the freight to New Zealand might be fairly scary. I've asked Andreas if he has any also.

[bikerphil]

That lower bushing should have a Teflon coating on it. I've seen a few where the Teflon coating has worn off some, but the stanchion still moved freely. Make sure the bushings are coated with oil as they might bind if dry. What is the condition of the oil seal? Is it the right size (37X48X10.5)? Maybe try the stanchion from the other good fork to see if it still binds?

[crazy steve]

That part (shown as 'spindle taper' in my book) also works as the lower stop when the forks are bottomed. The spindle is supposed to fit into the end of the fork tube and the taper is to prevent from hammering any sharp edges on anything. But yours looks like it's been driven in too far, so I wonder if the end of the tube has been slightly flared out? Filing all the raised edges off the gouges should fix the spindle. You'll probably have to use a micrometer to check if the tube end is flared, making sure the diameter is the same all the way down.

If the 'mishap' was the cause of the damage to the stop, then I would suspect you have a bent tube, bent fork lower, or both. If one fork lower/tube doesn't bind, and any mixed combination of parts between the two does, then both are bent. It doesn't take much either; while Yammy doesn't give any allowable tolerances, I've seen as little as .005" make a big difference on other forks. These really are precision pieces. Easy way to check is to lay both tubes next to each other (assuming one is straight) and roll them together. If you see any gaps while rolling at all, one's bent.

Good luck....

'78E original owner

[b.walker5]

Okay, it appears that I have a bent leg?? or something. I had the stanchion tube "trued" and mic'd (36.97mm from top to bottom) at a precision engineers shop tonight and after getting a little "forceful" with sliding the tube up and down in the leg i've noticed a "rubbing" point about 3/4 of the way down, inside the leg, between the caliper mount and the axle. It looks like an internal high spot that woud be caused by a dent on the outside but there are no visible marks I wonder if it got "twisted" somehow when the bike went down ?. The only scenario where I think that could happen is if the left end on the axle took a hit and bent, twisting the fork between the axle and the brake caliper, which would be held rigid by the disk, especially if the brakes were hard on. Problem is, the axle isnt bent and there are no visible marks to support this hypothesis. The plot thickens.

[jmnjrpa]

There is the remote possibility of a fracture in the tube. You might want to have it dye tested for cracks. All this may be more expense than is warranted. Could be cheaper to just replace and forget.

[b.walker5]

[QUOTE=jmnjrpa;239604] Could be cheaper to just replace and forget./QUOTE]

I wish. If you think it's tough finding good parts for 30 year old bikes in the US, try down here. This far south of the border, parts like that are harder to find than rocking horse _hit (insert s) and when/if you do find them you need a second mortgage to buy the bloody things. Getting stuff out of the states is my only option but the freight costs on big items is horrendous, often twice or thrice the value of the part in USD, then converted to NZD. 100US at the moment is around 150NZ, and thats good, normally its around 200 and the prices of goods in the two countries isnt that much different.

I know a guy in an engine recon shop just down the road from work and i think they have dye testing gear. I'll call on him at lunch time and beg a favour. Good thought, thanks.

[crazy steve]

If both your fork tubes are straight, then you have a bent/damaged lower. If it's bent or distorted out-of-round, it's toast and you better start looking for another one, or start considering which late-model front end you want to adapt to the XS. If you only have a localised internal 'dimple', you may be able to hone that away. Just don't go too far; do just enough to allow free movement.

But from the way you describe the symptoms, I think that lower is done..... sorry.

'78E original owner

[b.walker5]

Had the leg dye tested, no cracks. Spent 20 minutes last night with a brake cylinder hone attached to 3 feet of threaded rod and a drill, no difference . Ordered a replacement set from Andreas today. Problem solved. (as long as some freight jockey doesnt bend them on the way, I've seen the way they throw freight around in a cargo hold)

[andreashweiss]

Small box just enough room for them to be in there. Each fork is wrapped in an entire old bed sheet,let the mail do there best, they should arrive just fine. through in a complete front axle as well, bonus part,no charge. thanx andreas