Service

SERVICE

Dark passage

Paul Dean

Any time I'm riding my '91 Honda VFR750, all of its lights randomly flicker between normal brightness and slightly dimmed. Most of the time, though, they're dim. The problem isn't bump-related because it happens on smooth or rough roads, and it happens during the day as well as at night, although it's not as easy to notice in the daylight. Based on my description of the symptoms, the local Honda dealer thinks the problem is most likely the stator, but I thought stators rarely go bad. I’ve gone through three brandnew Yuasa batteries in less than two years of riding the bike about 300 miles a week, and I’m thinking the battery consumption is related to the flickering lights. I’ve done all I know how to do by changing the air in the tires and staring for long periods of time at some of the more mysterious-looking parts on the bike, but nothing seems to help. Any suggestions? Rick Jones

Huntington Beach, California

VFR75ÖS of 1990-93 vintage often have problems with their solid-state voltage regulator/rectifiers, usually after a few years of use. In some cases, the unit will fail suddenly and completely, cutting off all charging current to the battery; in other cases, it functions intermittently, sometimes giving the battery a full charge, sometimes giving it either a weak charge or no charge at all. Your VFR is exhibiting the latter symptoms, which > would explain both the often-dim headlights and the frequent battery failure. The regulator/rectifier is easily accessible beneath the right-hand plastic sidecover, and the replacement units have been redesigned to eliminate these charging problems.

In wheel despair

I’m having problems with the frontwheel bearings on my FZR600 Yamaha. About a month ago, I replaced the bearings, and when I tried to reinstall the wheel, I couldn’t tighten the axle nut all the way or else the wheel would get hard to turn. As soon as I’d loosen the nut, the wheel would turn easily. I couldn’t figure out what was going on, so I tightened the nut just enough that it wouldn’t fall off, but not so tight that the wheel wouldn’t turn. After I took the bike on a short ride, I checked the nut; it had loosened a little bit and the wheel was easy to turn. I snugged it up, but that also made the wheel harder to turn again. I went through this tighten-loosen-tighten procedure quite a few more times until the wheel bearings failed again with less than 150 miles on them. I replaced them but had the same problem when trying to tighten the axle. So, the bike is now sitting in my garage, front wheel off, until I can find a solution. Any ideas?

Gregg Erson Baytown, Texas

Only two possibilities seem plausible: Either you’ve forgotten to reinstall the spacer tube that fits between the wheel bearings, or the bearings aren’t fully seated in their mounting holes. Either way, tightening the axle nut would force the inner races of both bearings to be drawn toward each other, causing misalignment with their respective outer races. The inevitable result is binding of the bearings, followed by complete bearing failure.

If you haven’t forgotten to reinstall the spacer, you then must ensure that the bearings are fully seated in their mounting holes. Even a seemingly insignificant little burr of aluminum or a small amount of residual dirt in the hole can prevent the bearing from being inserted all the way. So, remove the bearings you just installed-yes, the brand-new ones-and throw them in the trash; you fatally damaged them during the axle-tightening routine you went through right after you installed them. Then thoroughly inspect and > clean the bearing-mount holes. Once the holes are squeaky-clean, install the bearings by tapping them into place with a hammer and a drift pin, hitting the bearings only on their outer races; hitting or applying any force to the inner race will destroy the bearing.

After the bearings are installed, poke your finger through the inner race of one of the bearings and see if you can move the spacer tube. If the tube rattles freely from side to side, one or both of the bearings is not fully seated; if the tube does not move or has just a barely perceptible amount of side-to-side play, the bearings are fully seated. You then should be able to tighten the axle without any binding.

Thumb do, thumb don't

I hope this question doesn’t sound dumb, but why do ATVs have thumboperated throttles and motorcycles have twistgrip throttles? Seems to me that twistgrip throttles are easier to use, so why aren’t they standard on ATVs? And if there’s something superior about thumb throttles, why aren’t they used on motorcycles?

Charlie Miller Salesville, Ohio

The reason has to do with the low levels of skill needed to operate an ATV as compared to riding a motorcycle. ATVs are like automobiles in that they don’t fall over when left to their own devices; as a result, the operator doesn’t have to know how to balance the vehicle. This makes it quite easy for someone with no previous riding experience or training to just sit on one and make it go.

But that utter simplicity of operation also can make it easy for a complete neophyte to open the throttle accidentally—such as when bouncing around on rough terrain, or as his upper body is slung backward when he’s trying to climb a hill or cope with an inadvertent, unexpected wheelie. But when the same thing occurs with a thumb throttle, any rearward thrust of the rider’s torso tends to close the throttle.

In principle, a twistgrip is better for all-around throttle control, which is why many experienced ATV riders and racers convert their machines from thumb to twistgrip operation. But for ATVs that are likely to be operated by absolute beginners, the thumb throttle trades a little convenience for a larger margin of safety. □