March 2015 Issue
Starter Replacement: Consider Weight, Hot Starts
When it’s time to replace a starter, good choices abound. New starters have unprecedented reliability - so long as the pilot doesn’t crank too long.
Master switch—on. Mixture—rich. Fuel pump—on until pressure registers, then off. Ignition key—start.
Fortunately that result is rare. Almost invariably, when we turn the ignition key to start or hit a starter button on a piston-engine airplane, the starter engages and the prop swings with vigor. Over the past 20 years, new technology has made aircraft starters remarkably reliable—the newer ones should last beyond the engine’s TBO, if not abused. So, when there’s a big silence on hitting the start switch, the chances are that the problem is not with the starter itself. Nevertheless, the time does come when the starter slips its mortal coil and must either be replaced, rebuilt or overhauled.
We’ll talk about how to make your starter last, a little about troubleshooting problems and what options are available when it gives up the ghost.
The one thing a pilot absolutely needs to do to maximize starter life is to keep from overheating it—that means rigidly following the duty cycle limits.
The process of spinning a small, electric motor to turn over a larger piston engine means that heat is going to build up in the motor quickly. Each starter has a published duty cycle limit—the starter may be operated for a maximum number of seconds and then must cool for a minimum period of time. Tim Gauntt, Director of Product Support for Hartzell Engine Technologies, told us that the one way to almost certainly assure that you damage a starter is to operate it beyond the published duty cycle limits.
Hartzell and Sky-Tec duty cycle limitations call for no more than 10 seconds of turning the starter per attempt before letting it cool/rest. That’s it, 10 seconds. B & C Specialty allows 30 seconds, but then the starter must cool for two minutes.
For all Sky-Tec starters, the rest time after a 10-second start attempt is 20 seconds. The start/rest cycle can be repeated a maximum of six times.
For Hartzell Engineering Technology heavyweight and lightweight Magnaflite (formerly Kelly) starters, the rest time after each 10-second attempt must be 60 seconds. The cycle can occur three times before a 15-minute cooldown is required.
For Hartzell’s lightweight E-, X- and M-Drive (formerly Kelly) units, the cooldown/rest time is 20 seconds and the start/rest cycle may be repeated 20 times before a 10-minute cooldown is required.
We think those duty cycles are perfectly reasonable. If the engine doesn’t start within those times, something is wrong with the engine that needs to be rectified.
If you turn the key or press the button and the prop doesn’t start turning or only goes to the next compression stroke and stops, don’t assume the starter is the problem. Most likely it’s an electrical system problem. Rich Chaffee of Sky-Tec told us unequivocally that the first step of troubleshooting a starter problem is to pick up a voltmeter. That was echoed by Tim Gauntt of Hartzell. The websites for Hartzell and Sky-Tec have clear guidelines for troubleshooting starter issues—just follow them. Our compliments to both companies for websites that provide a great deal of information in a user-friendly manner. We, unfortunately, can’t say the same about B & C’s website due to its lack of info.
Aircraft starters were not designed to be forced backward. If the engine kicks back during a start, there’s a good chance the starter will be damaged.
Kickback is caused by mistiming of the engine’s starting system or a problem with the mags that allows a mag that shouldn’t be firing to do so during the start. If a cylinder fires before TDC it will develop from 20 to 50 HP backward against the 2-HP starter motor. The starter loses. Kickback can even break teeth on the ring gear of a Lycoming engine.
There is nothing in a pilot’s starting technique that can cause kickback except for cranking the engine with the mags on BOTH when the POH calls for cranking on one mag—such as on many American Champion aircraft.
Newer starters are designed to break internal components so that no teeth are broken on the ring gear—it’s cheaper to replace a starter. Hartzell and Sky-Tec offer models of their starters that are protected against kickback.
Starter warranties generally do not cover damage due to kickback. The only one we did find that did so was on Hartzell’s E-Drive series.
In the real world of hot starts, renters grinding the starters of 172s until the battery goes flat and less-than-perfect ignition systems, we got all sorts of responses to the question of starter life. Scott Ward of T & W Electrical Service, a company that has been overhauling starters for decades, told us that they routinely get heavyweight starters that have lasted 800-1000 hours, “depending on how hard the airplane starts.”
Derek DeRuiter of Northwoods Aviation in Cadillac, Michigan, told us he typically gets from 1000-1500 hours out of a starter, and referred to a nearby Part 135 operator that primarily makes 15-minute flights from the mainland to an island in Lake Michigan as one who sees near the low end in starter life. However, we also got word that the newer lightweight and heavyweight starters will last more than 2000 hours.