Headshake: front tire wear or steering head bearings?

'86 700, 20K miles

Recently I've been getting some odd feedback from the handle-bars when in tight, slow turns and when in 35mph-ish turns that are downhill & decreasing radius, or where I'm otherwise lightly engine-braking in the turn.

I think what I'm experiencing is head-shake.

It started a month or two ago, mainly on the 35mph down-hill, decreasing radius turns (not terribly leaned over, but lots of weight on the front tire). But my forks were super soft, and I almost immediately thereafter found the right fork seals blown, so they went in to Lindemann for the rebuild.

Now, with the stiffer springs, when it's happening, it's more pronounced, and I'm also getting it on some very low-speed maneuvers that I don't do very often.

I'm trying to decide if this is a tire-wear problem or a problem with the steering stem bearings.

The tires (Dunlops) are, if I'm reading the date-codes correctly, 4 years old, and now have roughly 3000 miles on them. My daily commute ride involves Hwy 9 in the SF Bay Area, so I spend about 30-35 miles a day riding mtn twisties, most of that leaned over for a turn. 9 doesn't have a lot of straights in it. As such, the tire-wear is centered halfway between the center and the edges, and has a peculiar flatness to the profile, turning what should be a smooth arch into a bit of a trapezoidal shape (flat on the center, and flat on both sides where it's leaned over in turns).

So, I've got an obvious wear item that's well-worn, and with what appears to me to be an odd wear pattern, so that's one possible cause. Also, at 20K miles, it wouldn't surprise me if the steering stem bearings are getting loose, or maybe just need to be tightened up (??).

Or, is it possibly something else?

Thanks.

 

YOU'RE READY FOR 20K SERVICE :: remove, clean, inspect, regrease and install or REPLACE upper and lower steering bearings.



The Service Manual calls for this inspection and adjustment periodically





Use a magnifier to find flat-spots on your :tongue::tongue:balls.
and races.....:smile::smile:

 

When the forks were off, I noticed that the steering turns amazingly smoothly, although with almost no drag at all from the bearings (it would just flop from side to side with ease). That made me suspect the bearing pre-load, but it's completely free of all notchiness.

Given the current budget, I'd rather diagnose it to the problem before digging into replacing things, and I don't have all the specialized bearing tools (would be nice, though).

 

Before I take the top triple off, what is the special socket for bearing pre-load like? Is it a toothed socket, or just a particular size?

Currently, I've been able to isolate it to the bike being leaned over, and the frequency of the wobble changes with road speed, and tire pressure (more pressure ups the frequency for the same road speed).

Usually only happens when leaned over about half-way, downhill, and decelerating (I ride on curves that should just not be accelerated through if one wants to not go off the edge of the cliff).

I can also reproduce it in a flat parking lot doing a larger, faster version of the MSF figure-8 box. It's worse when turning left than right.

 

Looks like its about time for a new tire too....

 

Definitely getting time for a new tire, especially before it starts getting wet. Thinking the Pirelli Sport Demons. I just don't know if I'm doing the rear as well or not. The rear tread is nice and deep, and very evenly worn (no chicken stripes, but I haven't abraded off the base of the nubs at the edge of the tread, either.

I'm not sure that I push it hard enough to worry about unequal grip, although I do lean it over a ways (getting better about leaning off a bit so I'm not scraping pegs while seated, but still WAY not smooth at that).

 

Ok Here goes, To check if the head bearings need to be tightend get your front wheel off the ground (with a bike jack) grab your front forks from the front of the bike at the axle area lightly push and pull DO NOT SHAKE THE ENTIRE BIKE if there is of movement your bearings are loose, tighten head bearings. And as far as the tool needed for that year I'm not sure but i think an ajustable spanner wrench is what you need.

 

Already done that, as well as the other tests in the service manual, if it's the bearings, then it's a miniscule amount of movement.

 

If it is any help, my 1993 VFR steering stem bearings were replaced w/ tapered roller bearings when it was new (It's just my old habit to always put in tapered rollers)
When the front Dunlop gets worn, the front wheel will start to shake side-to-side at low speeds, even w/ properly adjusted tapered rollers.

I would like to try some other tires someday, but not sure what to get.

But I'm accustomed to the signals it is sending me "buy a new front...", so
It's not really a problem, more like a communications event.

 

LOL, I like that view on it. I'm definitely getting the front tire replaced soon.

 

i would say replace the tire first and see if the problem goes away

 

im running michelin pilots on mine love them put nitrogen in them as well instead of air

 

ANOTHER thing:

test the upper and lower fork bushings for excess play or wear

 

Squirrel, just had the forks rebuilt by Lindemann Engineering. All new seals/bushings/springs.

It was doing this before, and still is after. My current plan is to replace the front tire with a Pirelli Sport Demon, and then see where this is at.

 

Unless you're looking to get body work done as well, quit rolling off the gas, engine braking and/or coasting thru turns. I can 100% guarantee you that this is NEVER a good thing. This is one of the most simple things I teach in my Sport Bike classes yet is one of the hardest things for the students to accept. I could go into a long drawn out explanation of why, but I will shorten it & say that rolling off the gas in a turn has the tendency to overwhelm your front contact patch.

KC-10 FE out...
lane: :usa2:

 

It's a 3-4 turn S, at a pretty hefty downhill grade. Slowing enough to be able to accelerate through the turns means I'm hammering back on the brakes to slow back down as I switch back left/right.

For the record, this turn EATS sport bikes who try to go fast. Looks like it picked up a couple more this weekend.

I putt down it like I'm on a cruiser. Traction isn't even a remote worry, at least not for another 10-15mph (I've taken it at those speeds, I just usually don't, because frankly, I'm not usually that dumb).

This is the set of turns:
Google Maps

Uphill, it's a blast. Downhill, it's a lot of pucker at anything other than the posted 25. At 35, it starts getting REAL interesting.

Now, if the road's level, I'm on the throttle the whole way through. (and even on these turns, I'm not fully closed up, just not enough throttle to accelerate through the turn).

 

I didn't say anything about speeding up. I said quit rolling off the gas. If you need to negotiate a series of turns off the power, make sure you keep off the gas the entire time. The goal being to not upset the bike.

KC-10 FE out...
lane: :usa2:

 

Ok, I misread what you meant. Thanks, KC.

 

Changed my dunlop d220 with 3500 miles on it for a used metzler M1 ....no more head shake

 

KC, turns out I can go through those turns with braking/leaning/turning/roll-on/straighten/braking/leaning/turning/etc....

Hell of a lot of work, and lots of concentration. Aside from coming out of one of the turns hotter than I expected, definitely more in control than when off throttle (especially with the lean angles involved).

I do see people take these deep into the throttle, but they've got knee pucks down when doing so. I don't like to play that game (at least, not on the street, but looking forward to doing it at a track school).

Funny how MSF instructors always seem to be right about this stuff. :smile: