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Lower steering stem bearing installation

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Hello everyone :)

Just a quick question, to install the lower steering stem bearing you either need to use a press or some sort of metal pole to hammer the bearing to the bottom of the stem. Where the hell do you get a metal pole that is the required size to fit snug over the stem and not damage the bearing? Or if not a metal pole then what else can be used?

The bike is a 2008 crf250 if that helps, and I'm in the uk

Thanks in advance :)

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Any metal or plastic pipe of the right ID should work… as the bearing doesn't take much force to install.  I would try a plumbing supply store and find a metal pipe with the right ID. 

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measure the inner race diameter then go to depot and get a 2 foot length of pvc with an i.d. that is close. freeze the stem/lower clamp then drop the grease packed bearing onto the stem, place the pvc on the stem over it, flip the whole thing over and drive the pvc down onto your driveway or shop floor with a bit of force. the bearing will go flush to the lower clamp with just a few hits. easy peasy.

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You can also put the bearing in the oven at 300ish degrees for twenty minutes.  Work quickly and it will drop onto the stem without any hammering or metal pipes.

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having replaced my race bike 250cc honda steering stem bearings, and those on Suzuki DR350, many times, I never had a problem seating them or getting them off, maybe I am the lucky one?  Even so, after bearing is off, when you re-assemble the triple clamps, and torque them to specs, that seats the  bearings just fine.  I also over tighten all my steering head bearings to stop head shake, there is no need for an expensive dampener. With bike on stand, push against the bars on one side hard, if it bounces back from the stop more than two inches it is too loose.  I have yet to find a bike steering stem set up properly, they are all too loose in my opinion.  If you say, this wrecks the bearings, SO WHAT... they are so much cheaper than a dampener, you can replace them once a year or more for tons of money less.  Mine never showed wear or failed, when I replaced them, I really did not have to.   

good luck

gary

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Your are lucky.  Press fit bearing tolerances are usually +0 to +.001" for a shaft that size.  So at 0 the bearing will drive on by pressure from the nut but if you do have a .001" interference you will not be able to drive it on by the nut.  Also, for a bearing on a shaft you never want to drive it by the outer race (which using the nut  does).  So guys bake 'em in the oven keep them under 350F they fall right on, no damage is done.  If you don't get it hot enough and it locks up you can drive it on the rest of the way with a piece of pipe or anything that fits.  If you're good you can even run it on with a drift if you are good.

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Where the hell do you get a metal pole that is the required size to fit snug over the stem and not damage the bearing? Or if not a metal pole then what else can be used?

 

Lacking the correct driver to use in pressing or driving the lower bearing down, and assuming that you are replacing it, cut the cage off the old bearing with a pair of diagonal cutters ("dikes"), dump the rollers, and turn the inner race upside down on the top of the new bearing.  A piece of common pipe down on top of that, and you have a good workable driver that will contact only the inner race of the new bearing, leaving the cage and rollers untouched.  You can even open up the inside of the old bearing a bit with a hand grinder to make it easier to get back off, but generally, between the fact that it won't go onto the bearing seat very far, and the fact that it's upside down, it won't take much to remove it.

 

Preloading tapered roller steering bearings not only doesn't damage them, it's required.  On most typical setups, there is a ring nut below the top clamp that gets snugged up to around 5-10 ft/lb, then the crown nut is cinched up to a much higher value, often 100 ft/lb or more.  That presses down against the ring nut, taking all the slack out of its threads, and adds more preload to the bearings.  On a stand, they should be tight enough to hold the steering in any position it's placed in without it falling over against the stop. 

 

What damages head bearings the worst (besides water and lack of grease) is clearance.  If you don't squarely and completely seat the bearings or races on the stem or in the steering head, they may settle during use and loosen the preload.  Then, every little bump drives the rollers into the races like a hammer, and they'll be full of dents in no time, rough as a cob.

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The 0.0-0.001 interference fit can be modified by using a Dremel drum sander to remove about a half thousand from the bearing ID. I wrap the bearing with vinyl electrical tape to protect the rollers from possible grit contamination.

 

As other have said tapered roller bearings are designed to run with a pre-load rather than no pre-load like ball bearings, car wheel bearings are an example. And if you over torque the nut you can fell the extra drag in turning the bars (on a stand).

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The tapered roller pinion bearings in automotive rear drive axles (that spin continuously for hours at 2000 RPM or better, not just back and forth once in a while) are preloaded to the point that the shaft requires 20-40 inch/pounds to rotate it.   More if it's a 3/4 ton or larger.

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