Richard Condy at Sky-Tec was kind enough to school me in the possible failure modes and history of our starters, and the symptoms were consistent with a failing solenoid due to a loose internal connection. He offered to overnight-ship a replacement, but fortunately after a couple of hours everything cooled-off enough that I was able to start the engine.
Absolute Aero in Hayward (close to home) had a rebuilt starter and completed the repair in an hour. So the overall delay was mercifully short! Though the Rockies crossing was now pushed into the afternoon.
After spending time in the Sky-Tec booth at OSH, here is a summary of what I've learned about Sky-Tec starters. Hopefully this will be helpful to others.
Chris
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For reference, four Sky-Tec starters are currently certified for the Lycoming IO-360 M1A.
Three were on display at OSH:
Here is the fourth:
NL/ec
Sky-Tec’s generally recommended starter for 24V Lycoming 360-powered aircraft is the “NL/ec”(extended crank). This uses a series-wound field, will crank without complaint until the battery dies, and has field-replaceable shear pins in case of kickback. Spares are attached to the mounting plate:
The NL/ec is Sky-Tec’s most robust starter for the Lycoming IO-360 and perfect for flight schools. For an extra pound (0.5 kg) this seems like a great choice! But physically it will not fit in the DA40 due to the throttle linkage and hoses positioned directly behind the starter.
LS
The LS is the OE starter for the DA40 (the PM is simply an LS model with the solenoid on the opposite side). As noted in a prior DAN thread (link), the earliest castings were specifically designed to break in an effort to protect the flywheel ring gear in case of backfire. But having starter parts drop out the bottom of the cowling was understandably unpopular! So in late 2007 Sky-Tec reinforced the casting and also changed to a stronger alloy. The trade-off is that a bad kickback can damage the ring gear, and repairs require prop removal.
The primary failure mode of the flyweight starters (LS/PM/XLT) is over-cranking. Eventually the armature overheats and fails. Sky-Tec starters ship with the following operating limitations on a self-adhesive sticker:
A cumulative 60 seconds of cranking should be sufficient to hot-start an IO-360 with reasonable technique. But if the engine floods, open the throttle and go take a break! Or plan to buy a replacement starter.
Solenoid improvements are the other major change in the LS. Pre-2014 models used a rivet to connect the internal wiring to the solenoid binding post. This rivet can sometimes work loose and fail. ‘Click’ but no motion is generally an early symptom (and should trigger prompt investigation!). This was the problem with my starter (and my "fix" was equivalent to simply jiggling loose wires!). Starting in 2014, Sky-Tec replaced the rivet in new and refurbished starters with a more robust through-bolt:
FWIW, there are actually two solenoids to “Position” and “Hold” the pinion gear. My “new” (rebuilt) starter not only properly engages the pinion gear, but also cranks noticeably faster. Presumably the failing connections in the solenoid limited current flow to the motor. The faster crank enables much easier starts.
XLT
The “XLT” is essentially a refined and lighter version of the LS, PMA approved (link) for the Lycoming IO-360 M1A.
The remarkable 28% improvement in weight is due to design improvements, not cutting corners. Comparing the LS and XLT side-by-side reveals a number of sometimes subtle changes. While slightly smaller, apparently the motor is – if anything – more durable than the LS. The most visually obvious change is the recessed void at the mounting plate:
Sky-Tec recommends the LS for the DA40 mostly because it’s Diamond’s OE starter. But the XLT would be my first choice for an owner-operated DA40 unless you have an aft W&B problem.
HT
Like the NL/ec, the HT uses a series-wound field that will crank until the battery dies. An internal clutch absorbs several severe kickbacks before needing factory service. So the HT is marketed for helicopters, which are apparently much more susceptible to kickback.
Generally the HT fits in the same spots as the LS, but nobody at Sky-Tec knows - for sure - if the HT will fit in the DA40. But Sky-Tec would be happy to work with an interested owner or shop to find out. Note that Sky-Tec will accept *any* model core in exchange for a refurbished starter (e.g., refurbished HT or XLT in exchange for an LS core). So the only risk for experimenting with the HT would be extra shipping costs and potential delays.
Assuming the HT physically fits, this would probably be the best choice for DA40s in club or flight school environments. Or owners looking for help with aft W&B issues.
