October 19th, 2013
Metric Motorcycles uses a belt deflection meter on your Ducati. What the heck is a belt deflection meter? Is timing belt tension really that important?
A belt deflection meter, also known as a belt tension meter, is a sophisticated device that will accurately measure how much a belt can be deflected with a given amount of pressure. Since the Ducati factory provides the exact specifications for this measurement, the belt deflection meter allows our technicians to set your new or used timing belt perfectly to those specifications. This article explains why that is so important to you as a Ducati owner.
So why does Metric Motorcycles use a belt deflection meter? For a thorough answer to that (and you want an accurate and detailed answer, don’t you?), let’s cover the most frequently stated fears that Ducati owners have about the timing belt. For those a little hazy on its purpose, the timing belt transfers torque from the crankshaft to the cam shafts. The camshafts open and close the intake and exhaust valves which allow air to flow into (intake) and out of (exhaust) an engine’s combustion chamber.
Any internal combustion engine is effectively an air pump. The more air it moves in a given span of time, the more power it will produce. Superchargers, turbochargers, more aggressive camlobe profiles, and higher reving engines are all commone devices engineers use to increase the volume of air an engine of a given displacement can move. The Ducati engine uses a desmodromic valve operating system combined with the interference motor design; each design brings its own unique tuning and maintenance challenges.
With the Ducati design, when the valves are fully open, they project deeper into the combustion chamber than do free running engines. By opening the valves further, the Ducati engine can effectively move more air (intake and exhaust) through the combustion chamber than a free-running engine of equal displacement. The benefit is a lighter engine and the potential to achieve a greater power-to-weight ratio.
The reliablilty challenge is that when the valves are fully open, they will contact the piston head, if it is at top dead center. Thus, if a timing belt completely fails, the valves will collide with piston head, destroying the valves, piston, and valve guides—a very costly repair.
Maintaining the proper belt tension minimizes wear and helps ensure that your timing belt will perform properly thoughout its full useful life, as determined by the Ducati factory. Avoiding this catastrophic failure is reason enough for some to recommend replacing the belt more frequently, which is an effort to overcome poor maintenance. This approach can significantly increase ownership expense, and—as we will see—it’s not the panacea one might think.
Another oft-cited problem caused by improper belt tension is fluctuation in cam timing. Of course, this would cause your engine to deliver poor and erratic power. However, this issue isn’t as common as some would have you think. Thanks to the desmodromic design, the valve train has very little frictional loss; thus, the pulleys and belts aren’t subject to the resistance caused by the valve springs found in other motors.
So what else creates the need for precision when setting the timing belt tension in a Ducati engine? The answer is more subtle compared to the previously discussed points, but it can make a huge difference in your Ducati ownership pleasure and experience. Let’s take a look at ignition timing.
Proper timing belt tension is critical to the timing of the Weber Marelli ignition system on your modern Ducati. The Weber Marelli uses a magnetic pick-up on the cam pulley shaft to trigger the exact instant of ignition to the fuel/air mixture. There’s a gear-to-gear contact in the drive; therefore, there will be (as any engineer will tell you) some gear backlash. By keeping the timing belts tight, fluctuation in the timing of ignition is eliminated. With accurate ignition timing, your engine will generate the power it was intended to produce. It’s a small detail, but oh so critical to your engine’s potential. After all, you didn’t buy the best machine only to have it run below its potential.
Ducati knows the criticality of the timing belt and has provided detailed and exacting specifications regarding the proper tension for this key component, both new and used. If your mechanic has the proper equipment, knows how to use it, and will take the time to set the tension correctly; a new belt will actually wear in and be set correctly over its lifespan. And since the factory provides settings for a used belt, even an improperly set (and stretched) belt can be tensioned properly—so long as it has not experienced undue wear.