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All about dynos

October 21st, 2013

Andy Marcer

A motorcycle mechanic using a dyno in Houston

A dynamometer can only measure actual power at the output location. Actual power produced AND delivered by an vehicle will be highest if measured at the engine’s crankshaft, lower at the transmission output shaft and even lower, but more meaningful, still, at the rear wheel.

The power that you use is the power at the rear wheel.

Dynamometers are used to measure the power output of your motorcycle. The power is expressed in terms of torque and horsepower. In short, torque is the rotational force and horsepower is a specific measure of how much work the rotational force is doing during a given amount of time. The formula is Horsepower = (Torque X RPM) / 5252.

Although manufacturers like to quote horsepower at their engines’ crankshaft because it is the highest number, most shops measure the power from the rear wheel using a chassis dynamometer. The reason is cost. To measure the power at the crankshaft, the engine would need to be removed and special adapters machined to fit the dyno’s input shaft. The downside of using a chassis dynamometer is that transmission, drive train, and wheel/tire weight differences all make a significant impact on the final reading. Throw in the need to adjust for weather conditions such as humidity and air pressure; and you can start to see why comparisons between different motorcycles (even the same make, model, and year) can be misleading.

If that is not enough, the two most popular types of dynamometers used for tuning measure the power output in significantly different ways and generate dramatically different totals. The most popular is the inertial dynamometer, such as the Dynojet brand. The reason this dyno is so popular with many shops is that it is relatively inexpensive and dyno runs only take a few minutes. Using the inertial dyno, the motorcycle’s rear tire spins up a roller drum with a known inertial mass while in top gear at full throttle. A complex version of our basic formula is then used to derive the horsepower and torque the rear wheel should have been delivering to accelerate the roller drum as quickly as it did. Unfortunately, all of the variables used in the formula also introduce the potential for error and the opportunity to fudge the numbers. Incidentally, the typical inertial dyno numbers are inflated by 10% – 15% in the 100 HP range vs. our second type of dynamometer.

The next type of chassis dyno is the brake dynamometer and can actually vary the load or resistance of the roller drum, often using a device similar to an electric motor (eddy current) to precisely apply the load. The brake dynamometer is used for research and development because, rather than implying the horsepower from a complex mathematical formula using acceleration rates, inertial mass and other variable; the power is actually measured via the load being applied by an eddy current brake, as is the case for the Metric Motorcycle’s Pro Factory eddy current dynamometer. This provides a true, repeatable measure of horsepower.

The chief advantage of Metric Motorcycle’s eddy current dyno over cheaper inertial dyno is that we can run a motorcycle at a steady state RPM for an extended period with a known load applied to the rear wheel. Instead of simply sweeping through an RPM range from idle to redline, our eddy current dynamometer allows us to hold a specific RPM and throttle position (partial or full) while we make air/fuel adjustments to maximize horsepower. This also provides the time needed to stabilize the exhaust gases so that an accurate analysis can be made of its composition (CO, CO2, O2, unburnt fuel, etc.) to confirm that we are building a optimal, but safe map. So, when building a custom map for your motorcycle, we can perform a “stepped run”, whereby we stabilize the engine at each adjustment point (throttle position/RPM/gear) of your fuel/air computer.

It is also common for dynamometer companies to add to the power readings by adding transmission and primary gear/chain losses back into the measured power readings. Some companies make a concerted effort try to measure frictional losses and, optionally, add the power to the measured readings. Other companies – some that would surprise you – say that it’s not important and give a blanket, single factor for frictional losses in every engine. That includes some $25,000-$35,000 dynos.

How does this benefit you? For most riders, the vast majority of engine operating time is at less than full throttle. So when we develop a custom map for our customers’ motorcycles, we are able to focus on how the engine is behaving at any combination of throttle setting, in any gear, and at any RPM. The goal, of course, is to deliver useable power in a linear fashion so that when you pick that throttle up at mid corner, you get smooth, predictable power all the way through your motorcycle’s power range.

Given our serious methodical approach to tuning, the Pro Factory eddy current brake dynamometer’s ability to stabilize RPM and exhaust gases at any throttle position and anywhere your engine’s operating range far outweighs the additional cost over the cheaper inertial dynos, such as the Dynojet.

Our dyno room is not a marketing gimmick. It is a serious diagnostic and development tool which, when combined with our knowledge of building racing engines, separates us from the other shops. We have experience with most of the aftermarket computers, such as the TuneBoy, Power Commander, and Bazzaz.

Proper oil pressure on a GSX1300 drag bike engine

October 19th, 2013

Andy Marcer

Suzuki Hayabusa specialty maintenance

One of our customers needed to obtain the correct oil pressure reading for his screamingly-fast GSX1300 Suzuki Hayabusa. In particular, he needed an accurate reading for the highly-customized and tuned engine’s connecting rods—the goal being to ensure they were correctly lubricated during its brief, but highly punishing, runs.

The typical approach has been to tap into the hydraulic cam chain tensioner lubrication point. After some study, however, we determined that the oil pressure here is bled down by the oil feed to the transmission and heads. Therefore, the reading wouldn’t be sufficiently accurate for this application.

An alternative was to tap into the bottom access hole closer to the connecting rods. Unfortunately, this machine’s particular configuration would force electrical wiring into its sidewinder exhaust. At this point, we could try calling all of the hydraulics distributers we know, explaining that we have an 18.0 X 1.5 mm access hole and need a 90 degree angle to a 1/8 NPT standard thread; all within an overall length of 50mm. But that option was basically out of the question because no one was going to have those parts lying in inventory.

One could say that I have too much machining tools on hand, but I prefer to view my equipment and knowledge of how to design and create with them as allowing me to formulate options where none existed. In this instance, I added some billet alloy and made the necessary part. Here’s a few photos to show how it went.

Timing belt tension is critical for Ducati engines

October 19th, 2013

Andy Marcer

Belt deflection meter used to tension a Ducati timing belt

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.

Proper diagnostic equipment

October 17th, 2013

Andy Marcer


Although the equipment does not make the technician, even a top-notch technician needs the right equipment to diagnose problems on the modern motorcycle and ATV. Let’s face it, many dealerships may have the factory-mandated diagnostic equipment, but their service staff skills may be lacking. On the other hand, you may like the idea of an independent shop who does not have to protect the manufacturer; but so few will commit to purchase and learn the equipment needed to properly diagnose and repair your machine.

At Metric Motorcycles and ATVs, we have top-of-the-line diagnostic equipment, a machine shop, and a development dyne. The dyno room even has its own dedicated air conditioning system to eliminate the chance of overheating your expensive motor without having to shut down in mid-run.

We rely on the TEXA diagnostic computer and system. Its software is up-to-date and interfaces with American, European, and Japanese machines. Here’s a real story to illustrate how we work a complex problem to resolution; and how even the factory diagnostic equipment won’t overcome poor technician skills.

A Ducati was brought in with issues of running rough, eats batteries, and lack of power. Our customer had brought this machine to dealers several times over a significant time span. Every time, he was charged for service, with either a promise of the problem found and fixed or with the explanation that the dealer found no problem.

However, we found 3 key unresolved problems. First, the temperature sensor fault which our TEXA picked up was being cleared by the dealers’ technicians when they viewed the temperature gage on the rider’s console as within the normal range. However, there is a second sensor in the rear cylinder which tells the fuel injection system to richen the fuel-air mixture for a cold start. This sensor was driving the fault code. The engine had been running rough because the mixture was being varied from lean to rich, depending on what signal the faulty sensor sent to the injection system.

Second, after replacing the rear cylinder sensor and during our normal post-repair testing on the development dyno, we found that the engine was now running very lean. This engine had been running so poorly for so long, that the intake manifold tubes had warped, thus allowing air in at the cylinder head. Having our own machine shop allowed us to machine the surfaces for a perfect fit, thus eliminating leaks. Now this engine was running as the Ducati factory intended. Sweet!!

The electrical issue (the third problem) was exposed by our diagnostic equipment while we had the machine on the dyno for the second post-repair run. By keeping the TEXA plugged into the Ducati during our dyno test runs, we found that although the voltage of the charging system was within the manufacturer’s stated tolerance when the engine was cool; after getting the engine up to full temperature, voltage began to waver well outside anyone’s tolerance for a 12-volt system.

Upon further investigation, we found defects in the alternator’s insulation which was revealed only after it was up to full running temperature. The dealers’ technicians had simply put a voltmeter to the motorcycle’s electrical charging system, read 13.5 volts, concluded that the battery or owner (infrequent use) was to blame and cleared the stored faults. A new alternator from the dealer came with a stunning price tag. After conferring with our customer, we sent the alternator to one of our reputable vendors for a rebuild at fraction of the cost.

For the first time in years, our customer has his wonderful Ducati running perfectly and his restored confidence allows him to take it on trips with the knowledge that it will get him home again.

Our independence puts our loyalty with our customer, not the manufacturer. Our investment in state-of-the-art diagnostic equipment, machine shop, and dyno room; as well as the experience and knowledge to use them properly; gives you a shop which can find and repair any problem you bring to us.