Service

SERVICE

Paul Dean

Covert tire change

Both of the tires that presently are on my bike are of the same brand. The rear tire is ready to be replaced but the front one is not, and I am thinking of putting a different brand of tire on the rear. Will putting two different brands of tires on the same bike have any negative effect on the handling? Both tires would be of the same type and speed rating, but not made by the same manufacturer. Jorge A. Sanchez

La Jolla, California

Gee, Jorge, if you would have tried just a little bit harder, you might have given me less information. You didn’t tell me what kind of bike you have, which brand of tires currently is on it or which brand and model of tire you are considering for the rear replacement. This kind of input is critical, because no tire behaves in exactly the same way on all motorcycles, and no motorcycle responds in the very same way to all tires.

For this reason, it is virtually impossible for anyone to predict exactly how any given combination of tire brands will behave on any given motorcycle— unless, of course, that particular combination has actually been tried and

evaluated on that model of bike. But I can tell you that you generally don’t want to mix radial and bias-ply tires on the same machine; that combination has been known to result in some genuinely evil handling characteristics.

Self-healing hydraulics

My Honda VT1100 Shadow has always made a valve-adjuster noise. Yes, I know, the adjusters are hydraulic, but as a car mechanic with 35-plus years of experience, I’ve heard many engines make a similar “clacking” sound with no valve problems. A couple of shops checked out my Shadow’s engine and said they found nothing “out of the ordinary.” The bike has always run great, and I say that with 40 years of riding under my buns. But a strange thing happened the other day: While cruising at around 65 mph, the bike suddenly felt like a V-Max that just went into “V-Boost,” and accelerated at an astonishing rate. Not only that, it also stopped making the lifter noise. So now, with 38K on the clock, the VT runs better than ever. My question is, has this thing been running all this time with a lifter or lifters that were not operating properly? Have you ever heard of such a thing?

John Isenberg Kinston, North Carolina

First, understand that the hydraulic valve adjusters in your Shadow’s overhead-cam engine are not “lifters ’’ in the conventional sense. Lifters are used in overhead-valve engines in cars and Harley-Davidsons, and they move upand-down with the pushrods. The hydraulic adjuster mechanisms in your Shadow’s engine are similar to lifters, but are stationary devices that control valve clearance by keeping constant pressure between one end of the rocker and the cam lobe, and the other end of the rocker and the valve stem.

This illustration shows how the system works on your Shadow. The cam pushes up on one end of the rocker, the other end of which then pushes down on the valve stem. The rocker pivots on an eccentric shaft that can rotate a few degrees, and the hydraulic adjuster pushes against the eccentric so there always is zero clearance between the cam lobe, the rocker and the valve stem. On some other overhead-cam motorcycle engines with zero-lash hydraulic adjusters, the cam sits atop the middle of the rocker arm, with the hydraulic adjuster at one end of the rocker and the valve stem at the other end. The constant upward hydraulic pressure exerted by the adjuster maintains zero clearance between cam and rocker, and rocker and valve stem.

Until its sudden burst of newfound power, your Shadow no doubt had a partially inoperative hydraulic adjuster. Most likely, something was preventing the small ball-check valve in the adjuster from seating properly-perhaps a tiny metal chip left over from the manufacturing process, or a burr on the ball seat. This would have prevented that particular valve from opening fully and at the proper time. When that obstruction got knocked loose, the ball-check valve was able to function properly, allowing the engine to realize its full performance potential.

Roll your own

Will the single-crankpin version of Honda’s 1100 V-Twin engine (Shadow ACE and Aero) fit into the chassis of the offset-crankpin Shadow Spirit? If so, are many modifications required?

I want that Harley sound in a factory custom frame but am too impatient to wait two years for a Harley Dyna.

MEH563

Posted on America Online

Although I don’t know anyone who has performed such a swap, those two engines are similar enough externally that the installation should be pretty straightforward. You may have to improvise with a few small pieces here and there, but I doubt you d encounter anything that would make you wish you hadn’t attempted the exchange.

But if a Harley-Davidson is what you really want, why don’t you build one? The Motor Company is now selling Twin Cam 88 engines and transmissions, and stock Harley frames are easy to find these days, because so many people are replacing them with custom frames. And with the endless variety of H-D equipment available in the aftermarket, you could whip together a real Harley custom fairly easily. That sounds more interesting than sitting on your hands for two years.

Stick it where?

What is a “carb stick?” I’ve been told that the carbs on my 1994 Yamaha FZR600 need balancing, and that it is done with a carb stick. I’ve heard of balancing carbs with gauges, but not with some kind of stick. Brad Burstyn Elmhurst, Illinois

What you ve described is a carburetor-balancing tool whose actual product name is Carb Stix, not carb stick. Synchronizing multiple carburetors involves adjusting each carb individually until they all are pulling an equal amount of intake-manifold vacuum at idle. This is done using any of several different tools such as the gauges you mentioned, which are dial-type analog instruments, or another type called a manometer, which consists of four long glass tubes partially filled with mercury. A small hose connects each tube of mercury to its corresponding cylinder’s intake manifold. Intake vacuum causes the mercury to rise in the tubes, and the more vacuum, the higher the mercury level. Adjusting the carburetors raises or lowers the mercury, and the carbs are balanced when all four mercury levels are equal.

Carb Stix is simply a variation on a mercury manometer. It, too, uses four long glass tubes, but each tube has a steel ball in it rather than mercury. The intake-manifold vacuum has the very same effect on the balls, however, causing them to rise and fall according to intake-manifold vacuum.

One gear too many

In the April, ’99 Service letter from Robin Richards (“The Dogs of Wear”) regarding his Suzuki RF900’s transmission jerking in second gear, you were correct in your conclusion that the second-gear output gear and its mate were the offending parties. But if these gears magnafluxed okay and had no tooth irregularities, they could be remachined by undercutting the engagement faces of both gears. You were wrong, though, in stating that the RF900 gearbox contains 12 gears; the RF has a five-speed gearbox, not six, so its transmission has 10 gears (actually, just nine individual gears, since first gear on the input shaft is integral with the shaft). Mark Doucette

R&D Motorsports Clearwater, Florida

Oops.