172 starting issues

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UngaWunga

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UngaWunga
Over the last month, my 172 has been a little hesitant to start. First crank the propeller will turn a half turn, then stop. I'll let go of the key for 10-15 second, then crank again. Normally it'll start then. But after flying back from VT last monday, it wouldn't start when I got home. Lucky I was home.

Concorde battery, btw.

Mechanic at the field said the battery was a little low. He charged it and it load tested fine. He put it back in, but still was weak to start.

Now he's thinking it may be the starter or something in between.

Suggestions?

If I do need a new starter, suggestions on which one to get? Go with a lightweight starter to drop a few pounds from the plane?
 
UngaWunga said:
Over the last month, my 172 has been a little hesitant to start. First crank the propeller will turn a half turn, then stop. I'll let go of the key for 10-15 second, then crank again. Normally it'll start then. But after flying back from VT last monday, it wouldn't start when I got home. Lucky I was home.

Concorde battery, btw.

Mechanic at the field said the battery was a little low. He charged it and it load tested fine. He put it back in, but still was weak to start.

Now he's thinking it may be the starter or something in between.

Suggestions?

If I do need a new starter, suggestions on which one to get? Go with a lightweight starter to drop a few pounds from the plane?
Click to expand...


What engine? Huge difference in starters....
 
If it's still slow to start ,you might want to try a light weight starter.
 
0-320-D2G

He's looking into it this afternoon. I'm trying to stay outta his hair so he can sort it out.
 
More than a few years, and no. Which is why I'm leaning towards battery.
 
I wouldn't just lean, I'd go buy a new Concorde. Those little battery's don't last much over three years, especially if your alternator isn't putting out correctly or it sits a lot.
 
Check the voltage across the battery terminals while cranking the engine. If it drops below 9 volts (18 if a 24 volt system) the battery is suspect. If it stays above that, check the voltage drop from there to the starter. If that's good check the ground side. Corrosion is the enemy of electrons.
 
all battery terminals and contacts and wire terminals need to be shiny bright. That black stuff is an insulator
 
UngaWunga said:
Over the last month, my 172 has been a little hesitant to start. First crank the propeller will turn a half turn, then stop. I'll let go of the key for 10-15 second, then crank again. Normally it'll start then. But after flying back from VT last monday, it wouldn't start when I got home. Lucky I was home.

Concorde battery, btw.

Mechanic at the field said the battery was a little low. He charged it and it load tested fine. He put it back in, but still was weak to start.

Now he's thinking it may be the starter or something in between.

Suggestions?

If I do need a new starter, suggestions on which one to get? Go with a lightweight starter to drop a few pounds from the plane?
Click to expand...

Solenoid contacts get pitted and carboned up and create a lot of resistance, that's a pretty typical cause if the battery is good.
 
I like to start with the easy stuff 1st, before going down the costly options.

The easy things would be a strong battery, not real old, fully charged. Check connections. If you have any aluminum cables on that 172 give this a thought as well, copper cranks much better.

I had solenoid problems a few years back, but then I got zero crank.
 
Jimmy cooper said:
I wouldn't just lean, I'd go buy a new Concorde. Those little battery's don't last much over three years, especially if your alternator isn't putting out correctly or it sits a lot.
Click to expand...

Mine made it well over 3 years, considerably over 3 years.
 
James331 said:
Mine made it well over 3 years, considerably over 3 years.
Click to expand...

Some do, some don't. Depends on how it's used. A gill usually lasts less than a Concorde in what I've flown. They are all little for a reason which adds to their short life span.
 
Stewartb said:
Tighten ALL the terminal connections at the starter. carefully
Click to expand...

Important addition above.

Note I have never wrenched on an aircraft starter. But I have wrenched on a large marine diesel, where the power connections to the starter are made out of copper for better conductivity. Copper is soft and it is easy to twist the copper lugs off the starter. Ask me how I know..... :sigh:
 
Like Henning said, those solenoid contacts get burned and/or oxidized.

There are vast numbers of batteries and starters replaced because of bad contactors. There seems to be a real lack of understanding of Ohm's Law among mechanics, so they just shoot new parts at the problem.

First, do like someone suggested and measure battery voltage while cranking.

Then put that voltmeter across the big master contactor terminals. Postive to the battery side and negative to the other. Crank and see if it indicates voltage. An old analog meter is best for this. If it shows any voltage at all, that contactor is shot. Current will only flow through the meter and make it read if the contacts have a bit of resistance. The more current, the bigger that voltage drop across the contactor.

Then do the same thing to the starter contactor, the meter's negative on the starter's terminal and positive on the battery side. It will show 12 volts or whatever and then it shoud drop to zero while cranking. Anything above zero (like half a volt) indicates a bad contactor.

Ohm's Law says that voltage is equal to resistance times current. So take a contactor with a hundredth of an ohm's resistance in its contacts and try to run 400 amps through it. One hundredth times 400 is a four-volt drop, which is a BIG problem for your starter.

Aircraft electrical systems are designed to offer no more than a 0.5 volt drop. That's a cumulative total: all the terminals, wires, crimp connectors, contactors, everything.

Contactors are way cheaper than batteries or starters.

Maybe it's a bad ground. A broken engine ground strap, or a loose or dirty one. You can burn throttle/mixture/prop control cables that way. They become ground paths.
 
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