Fork chassis, axles, friction: burnishing, chassis alignment, etc...

Because you probably greased the dust wipers and added oil to the foam rings at the same time. Its like blowing on your nintendo* cartridge - its not blowing on it that does anything, its the taking it out and reinserting the pins properly that helps. Or greasing cassette splines - that does nothing, but retorquing the lockring afterwards does

Too much grease was a problem nearly 10 years ago now in early 35mm pikes and 36's but since then negative chambers got MUCH bigger, and the amount of grease also dropped to about 25% as much. to the point that it makes a negligible impact on neg volume. Any less and they run dry and cause too much friction (ask me how I know!)

A few 34SL forks possibly have too much, but they also only have one seal on the neg plate which allows bath oil in very quickly which is equally to blame. They are also an XC fork that sometimes includes negative spacers so its less of a problem there too. 36, 38's, lyriks and zebs etc all come with completely acceptable grease quantities for a long time now

Was thus hub a cup and cone variant? I can't imagine the width of a decently high quality hub with cartridge bearings vary in width more than a tenth of a milimeter... You have to have very precise width of the inner ring seats for the bearings to axialy preload the anyway, so having a similar tolerance for endcaps shouldn't be a problem as well. 

With cup and cone bearings, since the nuts are a lot more "industrial" and hubs are adjustable, the variance in width should be a bit higher. 

But yeah, width variance should affect alignment negatively. A floating axle should help, but as pointed out, if the fork is misaligned from the getgo, it won't help. 

I figured I would bump this thread as I had two recent significant improvements in forks in my fleet of bikes by clearancing the bushings.  I have a tool, sourced from oliver at blue liquid labs that I use for this purpose.  I have two heads of each of the 3 major sizes of forks that I still mess with; 35.07, 35.10, 36.07, 36.10, 38.07 & 38.10.  I have been messing with the bushings of my forks since 2019 and have nothing but improvements from the process.  I am willing to admit that there is a fair bit of risk while playing with this, but I have yet to screw up a set of lowers.  Obviously, there is only so much (read: mostly nothing I can do) I can do about stanchion alignment and lower alignment both with regards to stanchions being aligned with each other and aligned with the bushings in the lowers.  I would say that the improvements that I get from this process, have far outweighed the potential risk of screwing up 350 dollars worth of lowers.  It will happen to me someday, I'll end up destroying a bushing, but until then, nothing but improvements.  To date, I have only created bushing knock with this process once, and the one time it occurred was with a very old 2019 grip 2 36.

From my anecdotal experience, I have had quite a few 2019-2022 Zeb's that were mine, and also friends that have had some pretty bad bushing issues.  Everything from stanchion alignment not being quite parallel, to lowers with bushings that seem off kilter.  Some of them would feel like crap until you put a hub into the lowers, some felt like crap no matter what.  Recently, I had one particularly bad sample that no matter what I did, had a lot of friction and would really only feel good for 2-3 rides after a lower service and then would feel like crap.  Other than that, I've had really good luck with the recent zeb's and really all RS/Fox products across the board have been quite good for the past couple of years.  

I digress, onto the most recent experience.  I typically handle the process like this:

-Get new fork, ride for 4-6 months and 2 lower services without touching the bushings.  

-On 3rd lower service, remove the dust wipers and check the sliding friction of the uppers/lowers with no dust wipers installed.  If the sliding action is sticky... I'll clearance the bushings using the .07 over tool head and re-check the clearances.  Typically, this nets an improvement and I re-assemble the fork and repeat the cycle 2-3 lower services later.  

-On some forks, I'll go right from the .07 to the .1 oversize head and re-install after breakin and stick with that.  

Recently, I had both a 2023 fox 36 grip 2 and a 2025 fox 38 grip x2 that I had completed the .07 clearancing process on.  I had re-assembled the 38 (which has a smashpot) and noticed that there was a distinct hitch in the operation of the fork about half way down.  Upon noticing this, I tore it back down and clearanced the bushings with the .1 oversize tool head.  The tool head didn't have a significant amount of friction... no where near as tight as the 2020-2022 Zebs had and really didn't take much effort to push it through.  That being said, I gave each bushing about 6-7 passes and did see an improvement in how easy the tool passed through the bushings.  I reassembled the 38 and honestly, I'm blown away by how much better the fork is performing after the enlarged clearancing.  

So... long story short, I don't see a ton to lose in performing this as a home mechanic.  You are for sure reducing the lifespan of your suspension products as a result and you do stand a chance of screwing things up.  That being said, I haven't experienced anything other than improvements from performing this modification .

Perhaps he’s doing it because the bushings lose their perfect roundness over time?

This is something I have been curious about because I’ve heard other people say it. They claim bushings deform due to the fore and aft forces the chassis exerts on the bushings. 

My limited experience with bushing burnishing hasn’t yielded a mind-blowing effect yet, and I agree that other variables discussed here previously matter more. 

But still, what do you guys think, do bushings lose their shape over time? I feel like none of this was ever a concern back in the day. We just rode our bikes.

Depends on how they are specced, what the loads are like and if there is any wear. But it is for sure very possible they deform a bit. Likely is a different question, but technically possible. 

Burnishing them, other than making them larger overall, won't help that though. Might get them round but you will still have the celarance from before. And once loaded, the contact pressures (due to the larger diemeter) will be higher so you'll be accelerating the wear. If they are worn/deformed, at least they fit the shape of the stanchion and the contact pressures are low. 

Whoops, sorta forgot about this thread and forgot to respond to @Digit Bikes many moons ago.  I digress.  I start with a .07mm die head for my own forks because I am not aligning the bushings from one side to another as I am doing this.  I am purely clearancing them to a given size.  Because of this, I like to sorta sneak up on the clearance that works best as I have found a few fork chassis that are well aligned, but with tight bushings and a few that are not as tight, but not aligned well.  I have found that some forks will have bushings that function well in isolation, which I check by just sliding one side of stanchion in at a time and they are aligned well in a single side, but not aligned well with the CSU and eachother.  These forks tend to take a .1 oversized head to keep the right clearances when assembled.  

Most of my buddies that bring their forks to my garage for this, just get straight to the point and we do a .1 oversize.  I haven't created bushing knock by doing this (yet) and most people don't have the patience to slow roll and work my way up to the .1 oversize.  Honestly, that's what I would advise anyway as the .1 always makes a measurable performance difference, and I haven't seen any un-desirable effects yet.  

Interesting. So, have you had any of these forks long enough to see if there are negative effects long term after the .1 oversizing, as @Primoz is suggesting above?

Usually a 0.07mm tool is enough but 0.10 is good for larger stanchion forks or anything with slight misalignment. It's still within acceptable tolerances for a sliding parts like that. If the 0.1 tool is hard to push through I would step back and start with a smaller one, you can actually peel the teflon lining off the backing metal if you get greedy. Which is why some of the massive tools (~0.15) on the market make me nervous - they will do some damage if they get forced!

They also spring back a certain amount, depending on the difference between the current size and the size of the tool. eg if there is 0.03 mm clearance and you ram a 0.1 tool through straight away it might spring back to 0.7, whereas if you work your way up in a couple of steps the final clearance might be 0.08 or 0.09. If you kept going with the 0.1 it would eventually reach the same point after several passes but there is more risk of damage doing it that way. Then they still creep back out over time, either through squishing out at the points of pressure or just trying to return to the original state but they are noticeably tighter after a couple of years. Probably not the same as new but definitely a change.

I have for sure had several of these forks in my fleet long enough to speak to detrimental effects.  I haven't yet had one develop bushing knock from burnishing, that is in any way noticeable in any way shape or form.  Specifically I mean that there is no bushing play in the fork if you have it off the bike and are messing with it, no bushing knock or play with it installed in the bike and messing with the bike in the shop and no perceivable impact while riding the bike.  One fork in particular (that I mentioned above), was a 2019 fox 36 grip 2 which I had for 5 years and lived in 3 different bikes, with the final bike being my orbea rise, which I put 4k miles.  Looking back at my gear in strava... that fork seems to have had about 8,000 miles put on it.  It only developed bushing knock in the last 3-4 months of my ownership of it... I can't honestly say that it was from burnishing the bushings... I think it really just wore out in general.  

Revisiting your previous comment regarding this not being a mind blowing effect.  I personally am pretty impressed with the results of doing this.  I would say that the performance increase in some forks is as significant as putting in smashpot in it or doing a lower leg service.  Some forks don't benefit as much as others, and the impact can simply be that the improvement from a lower leg service seems to last longer, instead of only being for a few rides.

One last thing... The last few fox forks I have done 2 very new 38's, and a new/current generation fox 36, have all had vastly improved off the shelf bushing tolerances compared to what I used to see a few years ago.  A few years ago (call it the grip 2 vvc era), even a .07 head would take at least some notable amount of effort to get through on the first couple of passes... the last few fox forks I've done, the .07 head dropped straight through, and even the .1 head just needed maybe 4-6 passes and it was good to go.  

This is all so interesting. Thanks guys! Our shop got the burnishing tool not too long ago (hence my limited experience) because it’s trendy, but I’ve been a bit skeptical especially considering all the alignment variables. Super glad I stumbled upon this thread, and the discussion regarding alignment. 

I’m curious about what Diaz is doing but don’t use Insta so I guess I can’t watch any of his vids. But I feel like I have enough info from this thread to do a bit of an experiment. 

Been thinking about how to test alignment, and how to create a tool for it. Then I realized my frame builder buddy has an alignment table! I’ve watched him measure frame misalignment using fixed points and sliding blocks. He then manually flexes the frame where he thinks it needs to go and re-checks. He almost always fixes the frame in place by the bb shell, then checks the seat tube for squareness, then goes to the head tube and dropouts. 

I might go see him and try to figure out a way to fix a set of lowers with a dummy hub, then check how square/perpendicular things are, and maybe attempt some “manual alignment”. The uppers I think would be even easier because they can just be placed down on the perfectly flat surface and checked in various ways using blocks. 

I think it would also be interesting to test hub spacing intolerance on a known, well-aligned fork, by deliberately adding those 15mm ID shims to make it wider, as well as flat-grinding one of the end caps to make it narrower. 

Recently I started riding a Super Z for curiosity and am surprised at how excellent this fork is considering how budget it is. The faces of the dropouts are completely painted over! Meanwhile people are using shims!? Lol

Also curious if any of the manual adjustments would actually last, or if the fork would just spring back to its natural (original) state. I guess we’ll have to try and see. 

Some of you guys mentioned manual adjustments earlier in the thread. Anyone care to share and elaborate more specifically about your approach?

 

I recently purchased some (relatively new) air Z1's from a mate who remarked I should burnish the bushes as they seemed a bit harsh/wooden. 

They were set to 170mm so but need ~150mm so I cut the 170mm shaft to make them 155mm and drilled a new hole for the piston dowl pin. 

Whilst I had them apart I did burnish the bushes with my newly made 36.08mm burnishing head. I found the air spring side was pretty good and the damper side was a little tighter. 

Assembled back together and I've found the sweet spot at 115psi and 2 tokens (17% sag and maybe 80% travel use bouncing as hard as I can on the forks). 

I was surprised as I have another set at 170mm and only running them at 105psi with no tokens (granted I haven't burnished those ones).

It's pretty typical to run less pressure with more travel so those numbers are in line with what I would expect anyway

This is what I was going to say. It's not apples to apples because when you change travel, the positive chamber volume at full height and at bottom out have both changed, your sag in millimeters should change, and lower leg volume has changed, too (which serves as a sort of second positive spring chamber/pneumatic bottom out chamber).

Similar to why you might need a 450 pound spring when you run a 75mm shock and an 850 pound spring when you run a 38mm stroke coil shock.

Yeah, definitely aware of the need to run more pressure for a lower volume of air (to achieve similar bottom out characteristics). 

These are the only 2 Marzocchi(Fox) forks I have run since the coil 36 and 40 on my Reign X1 and TR450 respectively (with the exception of the Z3 Bomber on my ATX 860). 

I was just surprised how close to the recommended maximum pressure for the Z1 I am, considering how far away from the recommended maximum pressure I was for the Revelations I had on previously. 

Just going to share my own experience, batch of exactly 1, well sort of 2.

I had a stock Mezzer Pro that was always pretty sublime but I had damaged the stanchion so just saved it for parts. Then I bought a new Mezzer Expert on sale to send to Avalanche for a hybrid kit.

The Mezzer Avy Hybrid never tracked well or felt very good. I swapped the bath oil 2x and both times it was incredibly dark, so I assumed it was breaking in, and maybe it did a bit.

At this point after about a year, I was ready to give up on the fork and order an Intend but a forum peep kindly offered to send me a Mezzer burnishing tool.

A few things I found:

1) my old Mezzer lowers, the one that worked well, was much better than the Expert I used for the conversion from a bushing tightness standpoint.

2) I had no alignment issue at all; it was all in the individual bushings. I'm not sure how flexing the lowers would make much difference anyways considering it's going to settle at hub width once tightened down unless you have a floating axle.

3) Placing the wheel on a scale I'd have to push down the fork with around 14#s to get the fork to initiate movement with all internals removed but seals in place. Post burnishing it was a bit less than half that, about 6#s as I recall.

4) Burnishing helped both lowers, but the new Expert lowers were never as good as the Pro lowers. I still run the Expert lowers because they were way less scratched up. When burnishing the Expert lowers got much better, where-as the Pro lowers only got a bit better.

5) If I had, had the next size up burnishing tool, I would have tried it, at least on my old lowers. Cause they honestly still felt a bit tight to me.

6) I tried some other tricks including placing the lowers in my deep freeze and the tool in the hot TX sun. Although this made it really hard to get the tool in, once everything went back to room temp I could tell no difference in how the uppers slid through from after burnishing but before the temp trick.

7) It made a hell of a difference in fork performance. Like the fork is a solid 8 now (1-10 scale). Before it was like a 5.

8) The spring does rattle inside the fork, a known issue with the Hybrids. I just added shrink wrap to the spring (not recommended by Craig) to try and quiet it down as the rattle is just more than I can take. On the neighborhood test ride this totally worked at reducing rattle. I'll report back even though this has nothing to do with the point of this thread. Edited: The shrink wrap around the spring definitley reduced rattles dramatically, highly recommend. I can feel no difference in suspension performance.

I believe there was a known bushing fit issue with certain Manitou forks at some point in relation to a change in bushing/stanchion clearance spec. Personally I have not had much experience with Manitou and have never seen a case. Users have warrantied them for this reason, and Mantiou seemed very supportive in making it right.

As you found out @Suns_PSD , the bushing fit and/or chassis alignment can play a significant role in overall fork performance. While the bushing fit can break in to some extent (it really shouldn't as it's a clearance fit by design), chassis alignment does not which is why it is important that every fork be checked. Especially if the fork is new, it is good to know what state it is in before changes to damping, spring rate, etc are made as a means of compensating for a poor bushing fit or alignment.

I have seen riders go up in pressure by 10psi or more and increase compression damping after a bushing fit or alignment issue was corrected, and they are amazed at the change in performance. "It is so much smoother and supportive at the same time". 👍

While we’re on the topic of burnishing bushings. My local suspension shop Dirtlabs started offering that as a service recently so I thought I would try it since my Fox 38 Grip X2 was in for its first seasonal rebuild. They said my bushings weren’t that bad but they were able to use the 38.06" tool, which was the smallest they had. 

It made a noticeable but not life changing difference, mostly on fast square edge hits. I have a local trail thats fast and all square edge hits and thats where it made the biggest difference. On steeper, slower trails with bigger impacts I didn’t notice as much. Im not sure how much of that was “fresh fork feel” but Im pretty good about keeping up on my service intervals.