ChinaRiders Forums - TT250 steering head

After the correct bearings arrived yesterday I made this evening's project getting them installed. That, and changing the fork oil. I already had most of it apart from a few evenings ago when I found out the part number 22-1021 bearing kit doesn't fit a TT250. The bearings that do fit from All Balls are the 99-3516-5 for the upper and 99-3517-5 for the lower. Both bearings came with seals.

The seals are a bit of a quandary as their O.D, is correct, but the I.D. of both seals was the same and larger than the ID of either of the bearings. So you don't have to go back to an earlier post I made in this thread, the top bearing is a 22.5mm I.D. and the bottom bearing is a 24mm I.D. Both outer races are 41mm O.D. This is no issue with the top seal as it can be installed in the "normal" direction and centers on the outside portion of the inner bearing race. It also causes no issue because the upper bearing race sits just proud of the top of the steering stem so no spacer is required between the inner bearing race and the seal. Good thing too, because I didn't exactly feel like fabricating a spacer since none came with either bearing. Also, since the assembled height of the tapered roller bearings is a couple mm greater than the assembled height of the original ball bearings, you're already separating the upper and lower triple clamp from each other a bit anyway. No sense in making that difference more than absolutely necessary. When we move on to the lower bearing we end up with a bit of an issue. Since the lower outer race seats well up into the steering head, installing the seal in the "normal" direction would require a spacer or the seal would get chewed on by lower edge of the roller cage. As luck would have it, the depth that the lower race seats into the steering head is such that there is no issue with simply installing the seal "upside down". Since the seal has lips that face both inward (to keep the grease in) and outward (to keep the dirt and water out) there really is no "wrong" way to install them. It's just more about making them fit the application that you're applying them to. In fact, installing a spacer would make the outward facing lip of the seal dangerously close to the bottom edge of the steering head and may compromise its ability to keep swarf and water out.

This left the concern of ensuring the seal was properly centered when pressing the lower bearing inner race onto the stem. As a solution, I found a suitably thin cross section O-ring in my handy stash of extra bits that made it over the lower portion of the stem with just a bit of a stretch. It nicely occupied the extra space created by the I.D of the seal being too large. The O-ring did sit just proud of the flat surface of the seal but that's no matter since the I.D. of the inner race is tapered in that area. I'm quite confident it compressed nicely and ensured the seal was centered as the bearing was driven home on the stem.

As for the process of removing the old races, the outers were both dispatched handily with a long brass drift and a hammer. Just go a bit at a time, side to side and back to front, and they come out without much ado. The lower bearing inner race on the stem was bit more of a bugger as I don't have a proper puller with thin enough jaws to fit the small space between the lower race and the triple clamp. A bit of patient tapping with a sharp chisel around the race's periphery, after having applied some heat with a heat gun, had it off without too much trouble. I did stop to have a refreshing beverage after that little success though.

For installing the outer races I used the time honored process of freezing the races and heating the steering head. Nothing too crazy with the heat, just whatever my heat gun puts out. Too hot to comfortably touch for more than a brief moment is about what I'd call it. I had a socket on hand that I'd preselected as a driver since its O.D. was just shy of the I.D. of the steering stem. The upper race went a bit over halfway into place just from the temperature difference and was driven home with just a few whacks on the aforementioned socket with a medium-sized brass hammer. I once again heated the steering head and then it was the lower outer race's turn. It was a bit more fussy than the upper race, but not unduly so. It took a few more whacks but it finally gave the solid shudder through the frame that indicates it had found the limiting edge of its machined bore. A quick inspection and wipe-down to ensure no sharp metal bits were hiding above or below either race was next and all was well.

I also had the steering stem in the freezer while all this was playing out. The seal and the O-ring I mentioned earlier were freezing away as well. I heated the lower inner bearing race on an electric hot plate while monitoring its temperature with an infrared thermometer. It's best not to heat bearings much beyond about 250-300 degrees F for purpose of installation. The rule of thumb I've heard is generally at least a 150 degree F difference between the cold part and the hot part and I had quite more than satisfied that. The race slid down over the stem and fell into place like it knew where it belonged. Well, all except for the difference in thickness between the O-ring and the seal's flat surface. Lacking a piece of tubing of suitable size to drive the race, I had on hand my smallest brass drift and an appropriate hammer. Several well-placed taps later the race was home.

I proceeded to pack both bearings with Maxima waterproof grease, the blue stuff. I'm sure any good waterproof wheel bearing grease would suffice but I'm a bit partial to this Maxima stuff. It really holds up well in applications such as this, as well as swingarm and linkage bearings, brake pedal pivots, footpeg pins, etc. While my otherwise surgically clean hands were all greasy anyway I gave a thin smear all along the steering stem and inside the steering head just to help ward off any rust that might try to form.

On to the installation and adjustment... I slid the stem and inner lower bearing up through the frame and the upper bearing and seal. I threaded the adjusting nut with its attached shield into place and gradually snugged it with a proper spanner while working the lower triple clamp back and forth.

This is the point where people may have different methods but I followed the tried and true method I've followed for lo these many years. Since I didn't have a socket to engage the four spanner notches with which I could actually torque the adjuster nut to fully seat the bearings, I approximated 35 lbs ft while continuing to work the lower triple back and forth. All remained quite smooth but, of course, the effort to move it increased significantly. Well satisfied that everything was as seated as it's going to get until it's ridden, I then backed off the adjusting nut a half turn at which point the lower triple clamp moved quite freely. I then slowly tightened it to the point where it could still just fall to either stop of its own weight.

This is where it gets a bit a tricky. I put the upper triple clamp in place and lightly snugged the bolt that threads into the center of the steering stem. The key thing to understand here is that when you tighten that bolt to its final torque, 50 lbs ft in this case, it will tend to take out any slack in the threads of the adjuster nut (the one you turn with a spanner). This will make the final preload on the head bearings tighter. I start with that spot on the adjuster nut where the steering falls to either side of its own weight, then torque the upper triple clamp bolt to spec and reevaluate how much force is required for the steering to move to the stops. With used bearings that I'm just servicing, I'd like them to take just a "touch" more force than their own weight to fall to either side. With new bearings, such as is the case here, I like just a "touch" more than that. It's such a small difference that it's probably inconsequential and almost too light to be measured as rotational torque with an lb in torque wrench. It's a "feel" thing. As I recall reading in a 1960's Jensen-Healey factory workshop manual many, many years ago, when describing a circumstance similar to this, "A torque value is no substitute for the feel of a well-trained fitter." In any event, if you have any doubt about your "feel" err on the side of being ever so slightly loose than than ever so slightly tight. A too-tight steering head imparts unintended forces to the chassis that can upset a bike's road manners. This process does require loosing the torqued upper triple clamp bolt, removing the upper triple clamp, making a small adjustment the adjuster nut (the one that takes a spanner), reinstalling the upper triple clamp, and retorquing the upper triple clamp bolt to evaluate your adjustment. It can be a little time consuming but if done well it will result in the best possible adjustment and a good handling bike with bearings that will last a long, long, time.

This is already a novel, so I'll close it out before I ramble any more. I didn't take that many photos as the lighting wasn't great and I had oily (when working on the forks) and greasy hands for a substantial portion of all this. I figure there are enough youtube videos on changing out steering head bearings (I'm sure with both good and bad advice) that I don't need to detail every little step. I'm not much of the step-by-step tutorial maker type. That said, I don't mind sharing my experience for those that may find it useful. Here are the handful of pictures I did take.