Weird starter problem

by Deane Williams in 2 Stroke Technical Questions 8 years ago

I have an Apis self-launch glider powered by a Rotax 447. Yesterday I launched and climbed normally but when I shut off the engine I could hear a loud sound like an electric motor was running. The engine stopped normally and I folded it in but the electric motor kept running. Soon I was getting notifications that my battery was low and slowly the sound died down as it killed the battery. I landed with a dead battery, unable to extract the motor to look at the situation.
The only motor in there is the starter unless the alternator that charges the battery can act like a motor. Has anyone ever had this happen to them? How can the starter turn without causing the Bendix to engage?? Is the Bendix defective or broken? How can the starter turn? It must be that the relay contacts have welded so they are always supplying power to the motor. I can fix that.
Why did both things happen at the same time??
This is just too strange. Any ideas welcome. PS - if the Bendix is bad can I just replace that part?

Re: Weird starter problem

by Kevin Kane » 8 years ago

Kevin Kane

1 32 24

Deane,

It sounds like your starter solenoid is faulty, or the start switch in the cockpit is bad. Check the solenoid first for continuity between the battery cable posts. I would suggest disconnecting the cable that leads to the starter from the solenoid. With the start switch in the relaxed position there should be no continuity between the terminals. With the start switch engaged there should be continuity between the terminals and you will usually here a "click" when the start switch in engaged. The other issue may be the start switch in the cockpit, if it is not actually disconnecting power to the solenoid then you've got a problem.

To answer your question about how the starter could turn, and the bendix gear. I'm assuming you have an E gearbox, the starter on that gearbox does not have a bendix gear, it uses a sprag clutch to engage the starter. It can turn while the engine is running and you wouldn't even notice, except of course for the sound of the starter spinning.

Sounds like an easy and cheap fix. Please let me know if you have any more questions. I am very experienced with Rotax engines and operate a full mobile repair business.

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Re: Weird starter problem

by Deane Williams » 8 years ago

Deane Williams

1 1 0

Hi Kevin,
Thanks for your posting. I really needed some expert help here.

I have more facts now. I removed the starter and the starter relay.
The relay is definetly welded closed and it measures an ohm where it
should be open. I am going to replace it with something with more current
capacity. It is a Bosch 80 amp relay. I see Trombetta makes some 200 amp
starter relays I can get locally.

I put the starter on the bench and connected 12 Volts. The starter turns and
the gear immediatly extends and then retracts slowly over the next second. The
motor continues to run. This explains why the starter was able to run without
engaging the engine when the relay stuck. I am betting that this is the normal
mode of operation. The gear extends and starts to crank the engine. The force
on the gear holds it in the engaged position. When the engine fires then the
load on the starter is reduced to zero and the gear retracts.
(This Rotax has no gearbox.)
So is this normal operation?

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Re: Weird starter problem

by Kevin Kane » 8 years ago

Kevin Kane

1 32 24

Deane,

Sounds like you found the culprit. It's hard to say for sure what happened with the bendix gear because there are so many types of starters for 2 stroke Rotax engines, but your thoughts sounds right to me.

I would still suggest you check the start switch and make sure it is not providing voltage to the solenoid unless the switch is engaged. The frozen solenoid could be a result of the start switch not cutting power to the solenoid.

Let me know if you have more questions.

Kevin

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