O-360 no start

V

VA Aviator

Pre-takeoff checklist
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VA Aviator
I recently joined a flying club with 172 equipped with a Penn Yann O-360. Nice, well maintained airplane.

However, we seemed to have developed a problem with starting.

First time I flew it was on a demo flight before joining the club a few months ago. Started up no problem.

The next time was a bit more problematic, and it managed to start before the battery crapped out completely. Turns out the battery had a dead cell and was replaced.

Tried to fly the other night and had zero luck over a half hour period. I was with another club member and both of us tried everything we could think of - normal starts, flooded starts, normal again, a few things we made up on the spot, etc. No sign of ignition, period. The good news is that the battery held up and we gave up before it did.

A few of the other guys have had the same type of problem, and the shop on the field has looked at the problem and has discovered none - fired up for them first time, every time.

I have a theory. The ignition switch has a dead spot to the far right in the "Start" position to where the starter will only engage in the first 1/2 of the "start" arc. My guess is that the switch is going bad in that position on the left mag, too.

Another theory is that the impulse coupling is going bad.

Any other guesses?
 
A few of the other guys have had the same type of problem, and the shop on the field has looked at the problem and has discovered none - fired up for them first time, every time.
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You are using the same technique as the shop, correct? Just asking.



Anyway, are you saying that when you are trying to start the starter will cut out sometimes (dead spot) in the switch?
 
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If they can get it to start, I would double check your procedure with theirs. I own a Mooney and the start procedure (especially the hot start) I use sometimes won't work on other Mooneys.
 
flyingmoose said:
You are using the same technique as the shop, correct? Just asking.



Anyway, are you saying that when you are trying to start the starter will cut out sometimes (dead spot) in the switch?
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To my knowledge, everyone is using the POH cold start method. That's what we started with the other night, even though the pre heater was plugged in for a short duration (OAT about 30 degrees F, pre heater on for 30 minutes max, no temperature reading on temp gauge)

Correct with the switch. The starter will engage in the first 1/2 or so of the "start" position. If you turn it too far or go to the stop, the starter will stop. To keep the starter going you have to hold it just right. I've attached a poorly drawn image to illustrate.
 

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Time for a new switch, if it is cutting out the starter it also may be grounding out the mag.
 
Marauder said:
If they can get it to start, I would double check your procedure with theirs. I own a Mooney and the start procedure (especially the hot start) I use sometimes won't work on other Mooneys.
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Multiple other members have had the same problem, and it is a recent phenomenon. Perhaps I've cursed it in some way by being the new guy, but I'm not alone.

The guy I (almost) flew with the other night was telling me he has never had an issue until recently. The only change has been the addition of an engine pre heater. I doubt that has anything to do with it.

I'm mostly curious if anyone is familiar with the mag switch and if there is a common failure mode.
 
Skylane81E said:
Time for a new switch, if it is cutting out the starter it also may be grounding out the mag.
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The mag-shorting plates get a long ways from the mag contacts during start. I would expect that the switch is shot, alright, but the mags themselves are possibly way past due for inspection. I'd expect to find worn points and the internal timing (E-gap) way off. It doesn't take much to weaken the spark.

Dan
 
VA, the switch has moving parts and they do die from time to time. Yours is broken and needs to be replaced. It might not help the starting problem, but it IS broken and needs to be taken care of so you may as well start there.
 
Dan Thomas said:
The mag-shorting plates get a long ways from the mag contacts during start. I would expect that the switch is shot, alright, but the mags themselves are possibly way past due for inspection. I'd expect to find worn points and the internal timing (E-gap) way off. It doesn't take much to weaken the spark.

Dan
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Yep, and another I've seen is the p-leads crossed on single impulse coupling set ups so that the engine is trying to start on the mag without an IC. It usually will if everything else is just right.
 
I know you probably don't know, but if its a ACS switch SB92-01 might be helpful. Im with Duncan, either way you probably need to have them look at the switch. It shouldn't cutting out during start. Hopefully that fixes your other problem too.
 
Unsure on the switch. It used to be a bendix, it was replaced to avoid having to comply with the AD, but I'm unsure what it was replaced with.

The last magneto inspection was 2 1/2 years and about 250 hours ago.

Thanks for the suggestions everyone. I think we can all agree that intermittent failures just plain suck.
 
Both ACS and Bendix switches have ADs against them. They're the two most common switches. The ACS AD applies even to a brand-new ACS. They must be opened up every 2000 hours, inspected for burned contacts and relubricated. A diode must be installed on the starter solenoid to shunt the voltage spike when the key is released from the start position. Without the diode, the start contacts in the switch burn out real quick. The traveling contact in there is a really thin metal cup.

http://rgl.faa.gov/Regulatory_and_G...B8ABD56539B4684886256A3E00759DBF?OpenDocument

Dan
 
That Bendix switch AD only applies to a few part numbers, even if you have one, it is a real PITA to comply with by turning the engine off by the switch once every 100 hours and entering it in the logs as AD complied with.

Yep it is really some thing to avoid .
 
N801BH said:
ha..........

Why would anyone put a used switch bought off Ebay into a plane??:confused:
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Because they never wear out and are vary easy to clean and repair.
 
Lycoming/Cessna manual primers are great....

Which do you have? A system that primes 1/4 or 3/4 cylinders? :goofy:

Honestly, I don't use them anymore because it seems like I just frost the plugs when I do.

Also, most of these 4 banger lycoming only have one impulse. It's not uncommon to see them struggle to start in the winter.
 
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Skylane81E said:
Yep, and another I've seen is the p-leads crossed on single impulse coupling set ups so that the engine is trying to start on the mag without an IC. It usually will if everything else is just right.
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THIS!

If you have a heater blanket stuck to the accessory case someone might have reversed the P leads...

Chris
 
For anyone that cares (or happens to google across this page with the same problem) the problem was....

The plug driven by the left mag on the only primed cylinder was fouled. Not sure if it was completely or partially fouled but a little cleaning took care of that issue.

Two hours of pre heating with the installed pre heater, a single shot of prime and it started up after 4 blades for me tonight! (OAT about 15 degrees F!!!)
 
VA Aviator said:
For anyone that cares (or happens to google across this page with the same problem) the problem was....

The plug driven by the left mag on the only primed cylinder was fouled. Not sure if it was completely or partially fouled but a little cleaning took care of that issue.

Two hours of pre heating with the installed pre heater, a single shot of prime and it started up after 4 blades for me tonight! (OAT about 15 degrees F!!!)
Click to expand...


Looks like I was on the right path in post #21 when everyone else was ready to replace stuff... :D
 
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