The manufacturer is not always right. You have to understand my background to even get a partial idea of how signifcant it is, this statement. I have made my living all my life in the powersports industry, and much of it on the inside, as it were, on the dealer/manufacturer/tech school side. Fifty percent of my 40-year career has been with the manufacturer's corporate office and with the industry's number one technical school, Motorcycle Mechanics Institute. In addition, I worked many many years in the metro dealer service department "trenches.". Thus I was one of the most indoctrinated folks you could ever find. The manufacturer was a god who could do no wrong. But eventually I learned. It just took me longer than most. So here's a little irreverant poking of fun at the manufacturers.
In describing their then-new Concours 14 's variable intake cam timing system to dealer techs, Kawasaki once got advanced and retarded timing backward. Bombardier, the maker of (the world's largest selling) Sea-Doo personal watercraft, Ski-Doo snowmobiles and the new Can-Am Commander side-by-side (as well as many little-known ventures such as the Lear jet), once declared in a technical training PowerPoint "Hp is the amount of work done by the engine," a fallacy as any first semester physics student knows. Hp is the *rate* at which work is done, not the amount. Honda once described in Euro tech training materials grounded ignition coils on their 1980s road bikes. This is plainly erroneous. DC ignition coils do not need a ground, a fact I was pleased to demonstrate to my students every new training term when a votech instructor. Kawasaki made the same mistake ten years later. One of the Big Four in a dealer technical training video decares that liquid-cooled engines run smaller clearances than air-cooled ones. An odd statement inasmuch as any first semester tech school student knows that the piston-to-cylinder clearances, for example, of these engines are often double and even more, larger, than those in their air-cooled counterparts.
Yamaha, in its industry leading online mechanics training, Yamaha Technical Academy (YTA) describes engine crankcases that separate left to right as "horizontal split," while the rest of the industry calls this vertical split, and those that separate up and down as "vertical split," while the rest of the industry refers to these as horizontal split. Yamaha also has a hard time keeping things simple in the electrical area, commonly referring for example to a permanant magnet alternator as a "magneto" alternator, terms reminiscent of ignition systems. Speaking of magnetos, all but one or two of the powersports industry's many OEMs fail to distinguish between energy transfer and magneto systems, referring to both as magneto. Energy transfer is a 3-coil rising field system most common on off-rroad motorcycles, magneto is a two-coil collapsing field system found mostly on stationary engines.
Another mistake some factory service manuals make is encouraging folks to test for steering bearing tension by wiggling the fork assembly back and forth (front to back). While I submit this might help you identify bearings that were so loose they were about to fall out of the frame, first, there is a much better test for that, and second, this is not the correct way to check steering bearing tension, and it should not be presented as such. For really loose bearings (which actually would make themselves felt and heard long before one suspected the need for the wiggle test) the best test is the hand on the top clamp while pushing front suspension down technique. As for bearing tension, Honda and BMW for their part show the right perspective when they specify the spring scale method of tension measurement.
Here's a common one. Granted, many manufacturers no longer include brake system rebuild instruction in their authorized service manuals for liability reasons. And not all manufacturers made this mistake when they *did* include system rebuilding. But the "technique" of removing brake caliper pistons by using compressed air is so dangerous it is unbelievable. In most mechanics schools doing this will get a student noticed in all the wrong ways. Do NOT remove brake caliper pistons using compressed air! There are special tools for doing this.
Most manufacturers regularly err in their service and owner's manuals, referring for example to octane in motor and research terms instead of pump, relying heavily on volt and resistance measurements in troubleshooting, listing tool part numbers available only in certain markets, assuming a familiarity with the product that is unrealistic, and are famous for using ivory tower engineering verbiage instead of language the common person will understand. One well-known example of a manufacturer error is the frequent specification of 9~12 foot pounds of torque for a 6mm bolt. There are two things wrong with this. First, no 6mm bolt, regardless of its type, when threaded into aluminum, should ever be tightened that tight. It's insane. The standard in the industry is 90 in-pounds, which is equal to 7.5 foot pounds. The other thing wrong is no one has any business using a ft-lb torque wrench on so small a bolt. At that setting a ft-lb torque wrench is going to be very inaccurate, as it is too close to the beginning of its range. Moreover, it is interesting to note that Yamaha and Kawasaki have each issued corrections to their MX bike manuals which originally specified this same unrealistic torque spec for those bikes' cam holder bolts, in response to deslers experiencing seizure of the cams in their holders. Lastly, manufacturers have a reputation for covering up their mistakes by blaming their customers and their dealers (the 1st-generation Honda V4 cam debacle is a prime example).
So they're not perfect. Heck, just a look at an Internet manufacturer's recall database should set the matter straight. Major league OEMs have dozens of recalls each year. The point of all this is, the manufacturer, while they usually get things right, and when they do, do it better than anyone, having the best service manuals, the best training, the most up-to-date information on their product, the most timely and effective dealer resources, well, they don't always. They're not the infallible organizations we would like to think they are.