Service

SERVICE

Paul Dean

Lead sled F-Zed

I own a 1990 Yamaha FZR1000 that is very sound mechanically and has just 15,000 miles on the odometer. It’s a dream to ride in the canyons, but during freeway-type riding, the throttle-side clip-on has a vibration that puts my hand to sleep after about 20 or 30 miles. I’ve ridden numerous other machines and never felt this kind of vibration. I realize that my bike isn’t a leadwing tourer, but I feel it could be fairly livable on the open road were it not for this annoying problem. Should I consider an after-market clip-on? Is this an inherent problem with FZRs or is something else causing it? Mike Hankel Missoula, Montana

The vibration you describe is not exclusive to the FZR1000. Many motorcycles that emit high-frequency vibration, inline-Fours in particular, buzz more through the right-side handlebar than the left. The reason is simple: The left handgrip is securely affixed to the handlebar, whereas the right grip fits around the hollow plastic throttle tube, which is a loose fit over the handlebar. Consequently, you effectively grasp the left handlebar directly while riding, which allows the weight and mass of your left hand (and, to a certain extent, your wrist and forearm) to damp out most of the vibration. But because your right hand grasps only the hollow throttle tube, the right handlebar is free to vibrate practically unabated inside of the loose-fitting twistgrip.

You can’t completely rid the FZR of its throttle-side vibes, but you can move their peak point to a different rpm and road speed by changing the natural frequency of the bar. The easiest way to do this is to fill the hollow interior of the bar with a heavy metal-lead, most likely, since it is so easy to work with. You may have to experiment with different amounts of weight, but you should be able to shift the worst of the buzzing out of the rpm range you use for freeway riding.

Making this modification on your Yamaha is a bit more difficult than it is on most other clip-on-equipped sportbikes. The screw that secures the bar-end weight threads into a non-removable steel insert built into the batnear its outer end. That insert blocks access to the hollow interior of the bar, so it must be removed, either by drilling or machining, to allow placement of additional weight inside the bar. Then, after the lead has been installed, replace the original insert with one of the removable, expansiontype inserts that are standard on some Honda and Kawasaki sportbikes fitted with bar-end weights. When you 're finished, your FZR will have become a “lead ” wing after all.

No idler threat

I own two 1975 Kawasaki Z-ls. One is a high-mileage (120,000 miles) daily commuter, the other a lowmileage (18,000) running rebuild. Both have suffered the same failure with their two cam-chain idler gears. On one bike, the needle bearings have separated from the molded rubber; on the other, the gear teeth have detached themselves from the rubber. There was no catastrophic failure, just a lot of rattling that alerted me to the problem. Is there a replacement available that is solid steel, with no rubber between the teeth and bearings? The local Kawasaki dealer knows of none, and at S65 apiece (times 2 per engine), it would be an expensive pain to replace these gears every few years to ensure they wouldn’t fail in use. Rich Sullivan Bradford, Massachusetts

In all fairness, Rich, I don 't think you can describe gears that have endured for nearly two decades-and in one engine, for 120,000 miles-as needing to be replaced “every few years.” Many entire engines won 't even last that long. Spending $260for parts that might not need replacement until the year 2013 doesn ’/ sound like a bad deal.

As far as I know, no one currently makes solid-steel cam-chain idler gears for the Z-l. And even if they did, you might not want them. The rubber helps cushion the impacts that result from normal fluctuations in cam-chain speed and directional loading of the chain. These fluctuations are caused by the individual cam lobes first forcing open their respective valves (which tries to slow down the cam and push it bacfo\'ard) and then allowing them to close (which tries to speed up the cam and push it forward). So, the rubber medium not only reduces cam-chain noise, but to a small extent also extends the life of the chain-which, I assume, is as important to you as the lifespan of the idler gears.

Bogus black box

Regarding Michael Iczkowski’s Service letter (December, 1993) about his 920 Virago’s poor idle and backfiring just off of idle, your advice about the carburetor mixture-screw settings was right-on, but change the Transistor Controlled Ignition unit (black box) to fix this one. My ’83 920 also started missing intermittently just off idle on one cylinder, particularly after a long coast-down. After cleaning the carbs several times, checking the fuel valve, the fuel filter, the air filter, etc. to the point of near-insanity, a new TCI unit cured the problem completely. Unfortunately, these units are quite expensive ($400 in Canada), but check your local salvage yards. The Yamaha parts books lead you on a merry chase through all the superseded numbers, only to end up specifying a 1982 750 unit as the replacement. That TCI unit’s harness plug is wired differently, however, so be sure to check and change wire positions to achieve the correct color match. I’ve fixed three more bikes that had this very same problem, all of them 920s, with this cure. The only bright side to all of this is that by the time you’re done, you usually have the cleanest carburetors in town! Oliver Burr Truro, Nova Scotia, Canada >

Clueless in Cleveland

I’ve read articles in several magazines, including your Service department, about whether or not cam chains can be changed on certain bikes without completely disassembling the engine, but I’ve never seen anything that told when to change the chain. None of the service manuals for the last three bikes I’ve owned has given this information, and the mechanics at the shops around here don’t seem to have a clue, either. Most of them just say that when the chain starts rattling, it needs to be replaced. Aside from noise, are there other risks inherent in running with a worn-out cam chain? Steve Colella Cleveland, Ohio

One very significant danger is that a badly worn cam chain is more likely to either jump a tooth or break altogether-both of which can result in bent valves-especially if it has stretched to the point where it constantly rattles loudly. The rattling usually is an indication that the tensioner has reached the end of its adjustment range and is no longer able to keep the chain taut.

Even if these worst-case scenarios don’t occur, though, a worn cam chain still has adverse effects on engine performance. On an engine with a “normal’’ direction of crankshaft rotation (clockwise when viewed from the right side), for example, the cam timing is determined by the front chain run as the crankshaft uses the chain to “pull ” the camshaft through its rotation. Since the tensioner takes up slack only in the rear run of the chain, any stretch in the chain causes the cam timing to be retarded. By the time the chain reaches the end of its useful service limit, overall engine performance will have noticeably deteriorated, especially in the higher rpm ranges.

It is possible to determine if a cam chain is worn beyond its serxice limits by measuring the distance between a certain number of links and comparing the measurement to that of a new> chain. But you have to remove the chain from the engine to do this, because there aren’t enough exposed links in the cambox area to allow an accurate measurement. If, however, you can lift the chain farther than about i/8-inch off of the cam sprockets with the tensioner relaxed, the chain is worn enough to warrant its replacement. □