Tech Questions & Answers

Colonel Qlink
I have a 2007 QLink Legend 250. (QLink Motors is the manufacturer). It's a nice cruiser and when I bought it, had only 395 miles on it. When I get up to 50mph, I get a buzzing vibration in the footpegs and a little in the handlebars. If I pull in the clutch at this speed, the vibration stops. This leads me to believe that it's not the balancing or the tires causing this problem. I've checked the motor mounts. Could it be a loose chain? Any ideas?
Jeff R
Detroit, MI

Jeff, what I know about QLinks is exactly nothing. That being said, small-bore engines tend to be buzzy (especially ones made by off-brand manufacturers), and typically any vibration is felt through the pegs and grips, which are after all two of the three main points of contact between you and the bike. My guess is that what you're feeling is entirely normal, especially since it disappears when you disconnect the engine.

Chain me up...
I recently discovered that a "silent chain" was just another name for what typically drives camshafts in autos. So, why do you think this type of chain drive has not been used much (at all?) in modern bikes? It seems like it would be much stronger than your typical bike drive chain, quieter, and require less maintenance. (In my experience, almost anything, including the wreck of the Hindenburg, would be quieter than most chain drives).
Richard
Via e-mail

While using a Morse "HY-VO" style chain as a final drive chain might have advantages when it comes to noise reduction, and would theoretically be slightly more efficient at transmitting horsepower, any advantages would be offset by several disadvantages. First is the width; manufacturers don't want to offset the sprocket from the rear wheel or the tranny any more than they have to, and Hy-Vo style chains are considerably wider than the conventional roller- style chains now in use. The width of the HY-Vo also makes it heavier for a given length than a roller chain. The increased weight is undesirable mainly because it adversely affects the rear tire's rate of acceleration, which in turn affects how hard the bike accelerates. This isn't so important in a cruiser application, but would be detrimental to something like a sport or dirt bike.

Secondly, the Hy-Vo chain has a lot more moving parts than a roller chain, and all of them need periodic attention. Don't forget that when used in a cam timing or automotive primary drive application, HY-Vos run submerged in oil. Exposing one to the elements would actually increase maintenance, particularly since the design isn't conducive to the O-ring technology most conventional chains use.

The third disadvantage is the big one-expense. Both the Hy-VO chain and the sprockets needed to accommodate it simply cost more to produce than their roller chain counterparts. Hy-Vos have been used as primary drive chains before; the original Honda CB750 used one, though I can't think of any bikes that used them for their final drive, and no, the Benelli 900 with its twin row roller doesn't count.

I'd also point out that the cogged rubber final drive belt, which has become so popular in cruiser applications, is essentially a development of the HY-Vo chain, though it's cheaper, quieter and requires less maintenance. It's why they've become so ubiquitous, despite their width, and the expense of machining the sprockets.

However, the bike has a nasty tendency to "flop" into a turn. What I mean by that is, as you enter a turn, the bike tends to suddenly drop in at a certain point, which dramatically increases the turn - more than desired. I find I have to consciously be prepared for this action, and either ready to supply resistance with my inside hand, or better, counter it by pulling with my outside hand.

My question is, what factors of frame geometry would cause such performance? I have brand new OEM tires and no modifications except steel brake lines and such, that I wouldn't imagine would have any effect.

My own guess is that the bike has a very high center of gravity, especially with a full tank of gas. Can you comment on what might cause the "flop" I'm experiencing, and if anything can be done to fix it?
Cordell Clarke
Calgary, Canada

Cordell, your "flop" is caused by something called steering head drop; if you sit on your bike and turn the handlebars from left to right and see that the steering head rises and falls as the fork rotates, the distance it falls is called 'drop'. It's accentuated by rake, so the more rake a bike has-and cruisers typically have generous amounts-the greater the drop.

As the fork drops, it tends to steer, or as you so accurately described it, "flop" the bike into the turn. It also makes you work a little harder to pick the bike up again as you exit the turn, because you must lift the mass against the portion of the bike's weight supported by the steering head. The effect can be (and usually is) exacerbated when the bike has high center of gravity, simply because the weight acts like a pendulum.

As far as frame geometry, lots of rake and/or a high steering head (which, as an aside, is sometimes necessary just so the handlebars can clear the fuel tank) are the prime culprits but, unfortunately, without a cutting torch or modified triple clamps, there's not a whole lot you can do about either.