Potential out-of-round frame at steering stem bearings

[Joe Garfield]

I was about to install new steering stem bearings and noticed that, when I install the bottom race, the bearing has a little 'wobble' side-to-side but not front-to-back. Hopefully I can write the rest of this post without any more hyphens. In other words, if you put a bearing on a table and sit the race on top of it, you can put your thumbs on either side of the race, and as long as there is some pressure the race should stay centered on the tapered bearing.

The race is round to a tighter tolerance than I can measure. The bearing fits fine on the bench but wobbles once the race is installed. The upper bearing is fine on the bench and installed in the frame.

I sort of dry-fit (dammit) the steering stem together and didn't feel any play, but I don't feel good about leaving it as-is (I have no control) - I don't feel play now but I don't want to find it at 65mph over a pothole (or is it pot-hole? Ha.)

It appears to be pinched in the front/back (safe) since the play is sideways, but I am having a tough time measuring the inner diameter since it's sort of rough in there (like someone had a hard time removing the lower race?). I will note that the lower tree was bent and the forks have been recently rebuilt, so I am guessing the bike was in a crash. When I test-drove (game over) the bike, it had a little bounce in the front wheel when making somewhat tight turns. I figured it was maybe just fork oil, then later figured it was just the lower tree, but now wondering if the frame is actually bent.

So what the heck do I do with this? Searching online turns up 'get a new frame' results, but I know the people in this forum are a little more resourceful than that. I don't have many serious machining tools, but one idea is re-boring the lower ID, maybe it can be done at home with a special order tool and some proper fixturing. Maybe there is a suggestion for a better way to measure the ID, and hit it with a simple rotary grinder to remove some stock or something.

Please help

 

[chuck hahn]

Put it together, set the tension and then ( with the front wheel off the floor) gently climb on and sit like riding and feel the bars and action for anything notchy. If OK..then ride it and feel for the same things. If ok..ride the snot out of it.

 

[Rob S.]

Put it together, set the tension and then ( with the front wheel off the floor) gently climb on and sit like riding and feel the bars and action for anything notchy. If OK..then ride it and feel for the same things. If ok..ride the snot out of it.

Be sure to re-fill the snot! (Or is it refill?)

 

[bwringer]

Put it together, set the tension and then ( with the front wheel off the floor) gently climb on and sit like riding and feel the bars and action for anything notchy. If OK..then ride it and feel for the same things. If ok..ride the snot out of it.

Kinda what I was thinking, honestly... even if there's some minor issue, with weight on the bike and the bearings loaded, I suspect it won't matter one jot.


Joe, it's common when some thumbfingered PO has been at work that there's a chip or ding in the frame that prevents the bearing race from seating completely. Make sure this isn't the case.



Here's a little story I'm going to tell. Don't take this as advice; just a musing on possibility...

Long ago, a friend raced an FZR400 -- a wee Yamaha with an aluminum frame and an eager little 400cc inline 4. He wasn't a very good racer, and neither were any of the poor little Yammie's previous owners. As the closest thing he had to a chief mechanic, I became pretty good at improvised crash repair and frame alignment.

Anyway, we once noticed a front-back "click" when we pushed the bike and applied the brakes. To shorten a very long story, we finally discovered that the "cup" in the frame where the lower steering stem race seated was actually oval-shaped from some past frontal impact, and the race could move back and forth a few mm. Basically, someone had hit something hard enough to stretch the frame "cup" and then replaced the demolished forks and continued racing.

Having nothing much to lose, we located some quality epoxy putty (some sort of "titanium putty"), cleaned everything, applied a bead of the putty to fill the gap at the back, then improvised a contraption using all-thread to apply pressure to the bearing races. We removed the contraption the next day after the putty had set and had no more trouble with this issue. Didn't make a noticeable difference in his crash rate, of course.

 

[Joe Garfield]

Thanks guys. I appreciate that the bike can be put back together and ridden with little chance of the lower race causing anything other than the bike feeling like a 30+ year old motorcycle, if anything. Yesterday it seemed like a necessary problem, today it seems like a repair choice.

bwringer, that's basically what I was wanting to avoid (front/back or side/side click) and that same repair idea has crossed my mind a few times. I'm going to get myself and the bike in a good position and light to get under there and get a good look at what's going on, and figure something out. I don't like race getting squeezed out of round: I don't want to have to regularly tear down my front end to change bearings, and I really don't want to be distracted by front end movement when I'm on the road in traffic.

Hopefully there is a tight spot that can be relieved. If I grind it down and find it was actually bent, it will end up oversized and in need of a 'shim' - epoxy or other.

 

[Steve]

Wow. All that and only ONE hyphen? :-\\\

.

 

[chuck hahn]

WELL!!! Whats the outcome of this one???

 

[Weapon]

could be someone gouged the metal inside with a chisel. A burr inside there could push the race out of round once its in place.

 

[Joe Garfield]

I can't believe it's almost been a year. I've had so much going on and no time to look at the bike until now. I'm going to get back to it within the next couple of days, maybe tonight. I will keep the thread updated as I really need to get through this hurdle.

 

[Joe Garfield]

Dogma brought up a good point that the race may not be seating fully. I've been looking for burrs around the sides of the stem but haven't focused on the lip that the race seats against. There are plenty of scrapes and gouges in there so I feel like that could be the culprit.

Can you guys suggest the right tool and method for easing burrs inside the stem, both around the sides and against the stop lip? A dremel with a round stone is an obvious approach for the sides but I'd prefer something either a bit more precise, or something a little more gentle. For example, the right sized disk wrapped in sandpaper...

Any suggestions would be appreciated. I will see what I can come up with, but I'm balancing a bunch of projects this week along with the bike, so I'd like to use my time wisely. And as usual, thanks to all of you for the advice and encouragement. I've learned a ton from you guys and am continuing to do so.

 

[JamesWhut?]

Anyway, we once noticed a front-back "click" when we pushed the bike and applied the brakes. To shorten a very long story, we finally discovered that the "cup" in the frame where the lower steering stem race seated was actually oval-shaped from some past frontal impact, and the race could move back and forth a few mm. Basically, someone had hit something hard enough to stretch the frame "cup" and then replaced the demolished forks and continued racing.

Actually what you had was one of the super rare FZR400RS with variable headstock angle.


Out of round (not gonna do it) is less of an issue because when the bearing races are tightend to spec, the outer races are seated aganst the inner lip of the head stock "cup", keeping the bearings and steering stem shaft in proper alignment. As long as they haven't been mutilated so badly that the ID of the cup is bigger than the OD of the bearing race (as was apparent in the above hapless FZR), its a non issue steering geometry wise.

 

[Joe Garfield]

I guess I had 2 threads on this topic. I thought I was finding play in the steering stem bearing, but apparently the race wasn't pressed in all the way. I don't know if it was using a different tool, or the last little bit of filing down burrs that did it, but eventually it seated nicely.