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Author Topic: Steering stem bearing replacement ('14-'17, all models)  (Read 190 times)

rayivers

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Steering stem bearing replacement ('14-'17, all models)
« on: February 04, 2018, 09:14:56 PM »

During my recent fork-revalving work I noticed very serious detenting of the steering bearings, to the point where the bars would snap into the detented positions like they were spring-loaded.  The last thing I needed was the added work of a steering bearing install (especially at < 5K miles) but this just had to be done.  NOTE: To replace steering bearings, you'll need to fully support the front end of the frame while leaving the steering area clear, and also hammering on it both up & down.  If you decide to take it to a dealer - which IMO is not a bad idea - I'd suggest supplying your own bearings (see below).  You might want to get all the bearings while you're at it - I've now replaced every bearing/bushing on the bike at least once.

The OEM bearings in my bike were Koyo 30x55x17mm SAC3055-1 angular-contact caged ball bearings, used on all '14-'17 (-'18?) Zeros.  These are decent rotary-shaft bearings & are well suited to assembly lines as they go in quickly with the proper tools & require little set-up, but are poor choices for this limited-rotation high-loading application. My vintage ICE bikes use 21 uncaged BB-sized balls each end of the steering stem, and go 8-10K dirt miles before exhibiting mild detenting; the Zero bearings use a smaller number of larger balls, concentrating force more heavily in fewer locations.

For replacements, I used Timken 32006X tapered roller bearings (mine were $18/ea. on eBay; the OEM bearings above were $40/ea. fm Zero).  The 32006 races' taller 55mm-OD sections kept them straighter in the bore during installation, unlike the thin OEM races which behaved more like machined-edge washers & cocked/jammed repeatedly in the soft frame aluminum during removal.



I started by lifting the bike with my usual MX-type stand, putting a brick under the rear tire, then running a tie-down thru the rear spokes with both ends running back behind the wheel flat on the floor.  I then put a car battery on top of the tie-downs, weighting the rear of the bike down onto the brick to prevent it from popping up &  pitching forward later (I also drove thin wood wedges under the front of the skid plate & stand as back-up).  I removed the bar riser bolts & dash-bracket screws, then suspended the bars/risers & dash unit w/tie-downs from a ceiling hook to lift them up & away from the triple clamps, protecting everything with soft rags / tape / small bungee cords etc.  Once the front wheel and fork tubes were removed, the bike remained stable under hammering with OK stem-area accessibility.  Bear in mind this is a lightweight FX, a bigger Zero may well need more support.

Removing the top triple-clamp nut was difficult, even with an impact gun.  I protected the powder coat as always, but this nut was really on there & took over 45 seconds of bearing down on the gun to get off, so the finish got chewed anyway (a large nylon ring washer would be ideal, like Non-Ferrous Fasteners' NF20600 or NF26802).  My YZ manual specs 105 ft/lb - 142Nm of torque for its top TC nut, which is about as tight as it gets on a dirt bike.  The threaded-collar bearing retainer underneath the TC came right off with a small curved spanner I used on my vintage twin-shock preload adjusters.

Here's a steering-stem replacement video from All Balls which is very similar to the procedure I used:



It's a fairly straightforward process if nothing goes wrong.  :)  The Zero has front & rear channels cut into the steering-tube I.D. to allow access to the outer bearing races for tapping; these are fairly wide to allow tapping left and right of center (I used a long flat-tipped punch).  My advice is to use whatever works, regardless of L/R orientation.  After a few false starts with the easily-cocked OEM bearing, I drove it back in completely, put anti-seize on the pocket wall, then used only the far-RH side of the channel to drive it down about 2mm or so, then drove it out the rest of the way using the entire perimeter of the race. The top bearing is obviously tapped out from the bottom up, which was much easier as the pocket is shorter and a slightly looser interference-fit, on my bike at least.  The bottom bearing's center race is not pressed onto the steering stem, which is unusual but makes things easier.

Installing the Timkens wasn't hard at all. I put them in my freezer first for several hours, then heated the frame tube with a heat gun alternating hi-lo.  I tapped them in with a double-face tapping hammer and then a short flat punch, bottom one first (a bearing driver close to the frame tube I.D. would've been ideal, but I took my time with the punch and it worked fine). I don't usually use anti-seize when installing bearings, but after the galling episode with the Zero wheel bearings I wasn't taking any chances on screwing up my frame. There was still plenty of resistance driving it in, but it went in straight and steady & seated perfectly, as did the top one.  I then worked synthetic grease carefully into each and every bearing roller on the center races, making sure every last mm was coated.  The seals rotate, so I greased them along with their mating surfaces.  I put both bearings in and retained them with the seals, cleaned both bearing I.D.'s, then put in the triple clamp. Move quickly, as the lower bearing center is heavy-ish and the seal won't hold it in forever. You can also install the bearing & seal on the TC first as in the video, but I didn't want to chance folding over the seal lip on the frame recess.

The procedure Yamaha recommends to tighten my YZ's steering bearings is 1) tighten the bearing threaded collar (ring nut) to 27 ft/lb - 38Nm, back it off 1 turn, then retighten to 5.1 ft/lb - 8Nm.  To use this procedure you'll need a special socket - just go to the Motion Pro site and use the drop-down menus to find it (JUST KIDDING!  you'll have to get it custom made, or figure out what year and model of ICE bike uses the exact same thread / tooth pattern / collar depth, then try and find one of those).  I went with Plan B; I tightened it until it started to bind, then backed it off maybe 2mm of rotation (from the info I've found online it's far better to have it a little too tight than at all loose, as with any bearing it will loosen up slightly during break-in & a loose bearing = greatly reduced life / sketchy steering).  I've got two rides on it now and it's just the same, but I'll keep checking it to be sure.  I put on the top TC and tightened the hex nut to 70 ft/lb - 94 Nm; I guess it should be more than that, but it seems bone-crushing tight to me - maybe someday there'll be a manual with the proper spec in it, but till then it's the usual Zero guesswork / needless Web-detective BS.

The first ride after replacement was a real eye-opener.  I was all over the place, oversteering with the rear end sliding around, etc. At first I thought the bearing was loose, but it was fine.  I think the main center detent was acting kind of like a friction steering damper, requiring more steering input and also reducing & self-centering frame pivot around the steering axis (the 2nd ride was fine, I adapted quickly to proper steering behavior ;) ).  I've wanted a steering damper for a while now & this actually makes me want it more, strangely enough. 

Ray

« Last Edit: February 05, 2018, 07:12:35 AM by rayivers »
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'14 Zero FX 5.7 (now 2.8, MX), '14 Zero FX 2.8 (street), '08 YZ250F, '82 RM250Z, '75 MR175, '74 CR125M (175cc)

Keith

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Re: Steering stem bearing replacement ('14-'17, all models)
« Reply #1 on: February 04, 2018, 09:46:21 PM »

A nice write up, thanks for this. Maybe someday I'll do this or more likely pay a shop to do it. I think my bearings are ok but I have a lot of trouble with the forks twisting on tip overs. I wonder if my steering nuts are not torqued correctly. No amount of torque on the fork tubes seems to help.
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2016 Zero FX, 2014 KTM 1190

rayivers

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Re: Steering stem bearing replacement ('14-'17, all models)
« Reply #2 on: February 04, 2018, 11:07:45 PM »

Thanks !  I wonder if the Showa fork 41mm tube diameter might have something to do with the flex thing.  It's hardly a scientific test, but I just tried holding the front wheel with my knees and pulling medium-hard on the bars in both directions on all my bikes: the vintage forks (31mm stanchions) were a wet-noodle joke by modern standards, the RM's (38mm stanchions) were much better but still flexy, the Zero 43mm USD sliders moved a bit L to R and then went very stiff, and the YZ's 48mm sliders felt super stiff at first and then nearly rock-solid.

Here's an interesting concept - a carbon-fiber USD fork brace:



Ray
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'14 Zero FX 5.7 (now 2.8, MX), '14 Zero FX 2.8 (street), '08 YZ250F, '82 RM250Z, '75 MR175, '74 CR125M (175cc)

Keith

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Re: Steering stem bearing replacement ('14-'17, all models)
« Reply #3 on: February 04, 2018, 11:43:58 PM »

Yeah, I'm not a fan of USD forks. My old two strokes, a '96 KTM 360 and '86 YZ490 both have conventional and never gave me any trouble. I bent a lot of handlebars too. Inverted might flex in some way that's good on the track, but it means the seals get dirt in them and the tubes get dings from rocks. And it means the clamps can squeeze the internals if they are too tight. All bad, I think, for my rocky trail, crash it on a hill climb riding style. All to save a few ounces unsprung.
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2016 Zero FX, 2014 KTM 1190

MrDude_1

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Re: Steering stem bearing replacement ('14-'17, all models)
« Reply #4 on: February 05, 2018, 07:30:49 AM »

after the first snug down of the bearings, I move the tree back and forth lock to lock several times.. this rolls the bearings and forces the grease around so that the hydraulic "lock" they were snugged into dissipates.  then reset it to the proper preload.
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