TY175 Fork Stiction Reduction

[mcman56]

Once I used the lightest oil I could find, my TY175 forks felt pretty good as far as spring rate and damping was concerned.  However, there is still a lot of stiction and the forks are not very compliant over little bumps.  A friends TY with 250 forks looks and feels much more compliant on small stuff.  Are the 250 forks more compliant for some reason.  (They are hard to find.) Can the 175 forks be improved in this area?  My fork tubes were a bit scratched up but repaired with JB Weld and much polishing.  They do not leak.  I was advised to get the "green" fork seals but could not find them in this small size.  Has anyone tried fitting bushes in the lower legs?  How difficult is it to set the legs up on a lathe?  It does not look like an easy task.  Are modern Teflon coated bushes available to fit the tubes?  I could not find any.        

[trialman]

the ty175 has a sleeve on the r/h side of front spindle! always bounce the forks before clamping r/h leg up....if you still have stiction you need to have the fork tubes checked to make sure they aren't bent,you could do this on a plate glass sheet or you need v-blocks with a dial gauge.for fork oil in mine I use atf fluid its about an 8 grade

[mcman56]

I pulled them apart and measured straightness.  Do you know how straight they need to be to perform OK?  I turned them on V blocks with the lower legs still installed.  One tube is 0.020 inch TIR and the other is 0.006 inch  TIR.  The axle itself is 0.015 inch TIR.  I wonder what other 45 year old bikes are like. 

 

 

Edited November 3, 2022 by mcman56
spelling

[feetupfun]

If there are slight bends in your tubes, align the bends fore and aft with both bends the same way and you will minimise the friction.

A good test for if you want to tell if you are making an improvement in alignment is to make an axle spacer to replace the wheel, suspend the bike, remove the oil, fork seals, springs, mudguard/fork brace and assemble the front end without them and move the axle up and down by hand.

There are left field things to consider as well such as on one TY175 I bought had a fairly twisted lower yoke that was causing alignment issues. When assembled, the tubes looked fine but if you slid one tube down out of the upper clamp while the other tube was still in the other side, the bent yoke became very obvious.

Another TY175 had a bent fork brace which was pushing the sliders away from each other (causing friction).

Another way to look for the cause of friction is to look for areas on the tubes that are more shiny than others.

Another cause of sticky forks is dents in the sliders. This is easy to test for by feeling for stickiness with the spring out and cap off and the fork slider disconnected from the fork brace and the axle.

To answer your first question, TY175 forks working properly have very little friction and TY250 forks working properly are no different.

I'm unsure if polishing the tubes is a good idea because the standard ground finish is intended to hold oil to lube the seals and to lube where the tubes rub against the sliders. Polishing the tubes may make the seals feel sticky and may also overheat the seals if you ride along a corrugated dirt road.

[mcman56]

It is interesting that you mentioned polishing because I did a quite bit of that.  When I got the bike there were quite a large number of deep gouges and burrs on the tubes so the seals would not seal.  I filed burrs, filled big gouges with epoxy, filed and polished smooth.  I don't remember the sand paper roughness but they look pretty shiny.  It was done in a lathe.  The entire fork action felt very stiff until I went to the thinnest oil I could find.  After that I just felt stiction.  Is there a way to reproduce the original ground finish?  With the right paper it seems like you could create something like the honing finish in a bore. 

Are all old forks likely to have issues?  I'm a little tempted to buy new tubes but hate to do that and find no change.   I may try straightening.  

The yokes have a machined surface on the bottom that looks perpendicular to the bores.  They sit flat on a surface plate so are straight.  The fork brace is not perfect but seems close.  Is there a way to get a perfect fit?   

Pushing on the assembled forks off the bike seems OK.  If anything, I may feel a little uneven damping sort of like cavitation of the oil at times.  That makes no sense to me.  I'll try without springs and oil.  

 

 

 

  

[feetupfun]

15 hours ago, mcman56 said:

It is interesting that you mentioned polishing because I did a quite bit of that.  When I got the bike there were quite a large number of deep gouges and burrs on the tubes so the seals would not seal.  I filed burrs, filled big gouges with epoxy, filed and polished smooth.  I don't remember the sand paper roughness but they look pretty shiny.  It was done in a lathe.  The entire fork action felt very stiff until I went to the thinnest oil I could find.  After that I just felt stiction.  Is there a way to reproduce the original ground finish?  With the right paper it seems like you could create something like the honing finish in a bore. 

Are all old forks likely to have issues?  I'm a little tempted to buy new tubes but hate to do that and find no change.   I may try straightening.  

The yokes have a machined surface on the bottom that looks perpendicular to the bores.  They sit flat on a surface plate so are straight.  The fork brace is not perfect but seems close.  Is there a way to get a perfect fit? 

Pushing on the assembled forks off the bike seems OK.  If anything, I may feel a little uneven damping sort of like cavitation of the oil at times.  That makes no sense to me.  I'll try without springs and oil.  

 

 

 

  

Yes you can replicate the original cross hatch finish with fine paper.

Old forks only have issues if there is something wrong.

Checking the yokes: Fit one tube and do the clamps up. Slide the other tube through the bottom hole and up to the top hole. If it lines up it's likely that the bottom yoke is straight on that side. Do the same again but insert the tube through the top clamp towards the bottom clamp. If it lines up, it's likely that the top yoke is straight on that side.

As for the fork brace, it's made of thin mild steel so should be pretty easy to shape it to fit perfectly.

[mcman56]

I did some more investigation.  One fork moved pretty well without oil and spring but when checked over full length had 0.030" run out.

The other side would stick intermittently and the tube was 0.006 TIR.  It must have been the one with the cavitation feel and has a pretty nasty gouge inside the slider near the top.  I can't even imagine how it got there, maybe previous owner maintenance.  It is not an interference fit because the tube can at times slide freely through.  It feels more like like the right combination of oil and air in the gouge creates a vacuum and sort of attaches tube to fork leg.  Have you ever fixed anything like this?  I found some 30 mm bushes but suspect the fork leg would be very challenging to set up on a lathe. 

https://www.amazon.com/RockShox-Bushing-02-05-Duke-30mm/dp/B001CK0LTM/?_encoding=UTF8&pd_rd_w=UqY3c&content-id=amzn1.sym.8cf3b8ef-6a74-45dc-9f0d-6409eb523603&pf_rd_p=8cf3b8ef-6a74-45dc-9f0d-6409eb523603&pf_rd_r=7DAET5N6F5TCJWQKNRW9&pd_rd_wg=ab5En&pd_rd_r=65ff88f9-e798-4544-bed9-97c475955d64&ref_=pd_gw_ci_mcx_mi    

Picture is attached but not that great as the site is only allowing me 18.46 kb.  Seems odd.

 

  

 

 

 

[tony27]

Had the top of my 250 forks sleeved, previously they'd been worn enough that you can feel movement & fork seals didn't last for long. 

A steady was used to keep the top running true during machining, I think the fork tubes were fitted at full compression for clocking up the 4 jaw chuck then removed

 

[feetupfun]

13 hours ago, mcman56 said:

I did some more investigation.  One fork moved pretty well without oil and spring but when checked over full length had 0.030" run out.

The other side would stick intermittently and the tube was 0.006 TIR.  It must have been the one with the cavitation feel and has a pretty nasty gouge inside the slider near the top.  I can't even imagine how it got there, maybe previous owner maintenance.  It is not an interference fit because the tube can at times slide freely through.  It feels more like like the right combination of oil and air in the gouge creates a vacuum and sort of attaches tube to fork leg.  Have you ever fixed anything like this?  I found some 30 mm bushes but suspect the fork leg would be very challenging to set up on a lathe. 

https://www.amazon.com/RockShox-Bushing-02-05-Duke-30mm/dp/B001CK0LTM/?_encoding=UTF8&pd_rd_w=UqY3c&content-id=amzn1.sym.8cf3b8ef-6a74-45dc-9f0d-6409eb523603&pf_rd_p=8cf3b8ef-6a74-45dc-9f0d-6409eb523603&pf_rd_r=7DAET5N6F5TCJWQKNRW9&pd_rd_wg=ab5En&pd_rd_r=65ff88f9-e798-4544-bed9-97c475955d64&ref_=pd_gw_ci_mcx_mi    

Picture is attached but not that great as the site is only allowing me 18.46 kb.  Seems odd.

 

  

 

 

 

To start with, I would just tidy up the gouged section to make sure nothing was sitting proud.

Once that was sorted, I would test the fit again, checking for wear and tight spots

[mcman56]

5 hours ago, tony27 said:

Had the top of my 250 forks sleeved, previously they'd been worn enough that you can feel movement & fork seals didn't last for long. 

A steady was used to keep the top running true during machining, I think the fork tubes were fitted at full compression for clocking up the 4 jaw chuck then removed

 

What type of sleeve was used?  Was it a pressed in or loctited bronze bush?  Bicycle bushes look like modern split motorcycle fork bushes.  They may fit but are probably 1 mm thick at max and would need some kind of metal retainer.  

[tony27]

Solid bronze bush, couldn't find a modern type bush available in 34mm