Thorp Air Command - T18.net

Greetings All,

The following is a long post. Please forgive my long-windedness.

N89ER has a 160Hp O320-B3B. The engine has 1,100 hours SMOH and
has been a good performer for the three years and 300 hours that I have flown it.

Two days ago my wife and I flew about 30 minutes to have lunch and when we returned to fly back home (after about 30 minutes of sitting) it simply would not start. It never fired a single time. At the time I thought that I had flooded the engine. The battery and starter did an amazing job of cranking the engine for many, many tries.

A couple of experienced pilots attempted to help and we did all of the things that should help a flooded engine. No joy. We let the engine sit. We turned it backwards to clear the excess fuel. We tried starting it with the mixture pulled. We tried using starter fluid sprayed into the air intake. No joy.

Next we disconnected the P-leads to see if the mags were being unintentionally grounded. That made no difference.

Next we looked at whether there was spark getting to the plugs. First I pulled the mixture to prevent additional fuel from going to the engine. The first test was to pull a spark plug lead and crank the engine to look for a spark. The lead happened to be from the right mag and the guy who was watching could not see a spark. This makes sense though as the impulse coupling is on the left mag.

This is when it got strange. On the second attempt to look for spark from the lead that came from the right mag the engine fired for the one and only time that it did all day. It seemed as if it was going to start and come up to full speed. However, since the guy checking for the spark was right next to the engine/propeller, I shut it down with the ignition switch. We put the lead back on and tried to start again. No joy.

Then we moved to a lead from the left mag. The guy looking for spark said that I had a good spark from the left mag when we cranked the engine. What I am uncertain about is whether the spark is delayed properly by the impulse coupling or not. I can definitely hear the impulse coupling snapping as the engine goes past TDC.

Finally gave up and towed the plane to a borrowed hangar. Found a ride home and came back the next day. Tried my standard cold start technique, though at 60F it was not cold. No joy.

I did not add fuel after I landed. The fuel from the sump looks good. When I attempt to start after a bit I can smell fuel, so it seems that it is getting fuel.

At this point the only thing that I can think to try is to replace the left mag and see if it will start.

Any suggestions, theories, things to try would be appreciated.

Thanks in advance for your help.

Regards,

Mark Russell

Mark,

Two possibilities, fuel or spark.

Safe to say if you sprayed started fluid and got nothing then its not a fuel issue.

First I'd find a spare mag to troubleshoot with.

Second, I'd put a mag synchronizer on what you have and verify the timing didn't shift. This can and does happen (especially if you use the wrong gasket underneath the mag or didn't use good lock washers). The mag sync should also tell you a little about the health of the left (and right for that matter) mag too.

Third. I'd put the loaner mag on (don't forget to time it) and see what happens.

Sounds to me like your left mag is feeling low and you got lucky once (when the guy was holding the lead).

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

I had a simular situation several years ago. It would not start. Had spark on both mags. You indicated that the left mag was un-coupling, mine too. Problem was the impulse spring was broken and the mag was out of time. The spring broke in such as manner that the spring would snap the impulse.

If they are Bendix mags some have a spring in the case that keeps the mag grounded when the P lead is removed a test plug has to be inserted or the back removed to unground them. Check the P lead to the switch for continuity and possibly a bad switch or a grounded wire. Ed

*** admin posted for Ed Torbett ***

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Forum Administrator

Another problem was the mag switch. The switch had a start position and when in the "start" position the switch was shorted, same as the switch in the off position.

Mark,
I had the exact same thing happen after my first flight 11 years ago. Turned out to be a rusted/pitted impulse coupling. No problems since replacement.

*** admin posted for Cubes ***

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Forum Administrator

easy to check the mag switch, just simply put the mag synchronizer timing box onto the p leads ,disconnected from mags of coarse, and check each switch position while watching the lights .Only works on the old buzzer type.Or use a mega ohm tester even Betta.The switches these days have a diode in them , some times this can give a fault.

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James Ball

Are the impulse mag spark plug electrodes wet or dry when you pull the plug out?

Mac nussey

Gentlemen,

Taking your feedback in the order received:

Lee: I have a replacement magneto with an impulse coupling on the way. I am planning to get some assistance from an A&P and install it on Friday or Saturday. As I didn

Mark,

Check the cam drive. Pull a spark plug and crank the engine with a finger
over the spark plug hole. Feel the pressure changes. You can also remove one
of the valve covers to watch the valve action vs. the piston movement. You
may have a failed or slipped cam drive. It has happened before just as you
described the problem.

Good Luck, Les King

*** admin posted for Les King ***

_________________
Forum Administrator

Hi Mark:
Are you sure you are getting fuel up into the cylinders for a cold start. We had an 0320 that wouldn't start and we found the primer injectors were completely blocked.

Mac Nussey

Good afternoon All,

N89ER is back in the air! It turns out that the impulse coupling was clicking, but not producing a spark. Tested all of the leads from the left mag to see if I could get them to spark while manually turning the prop. No joy. Once I put the new mag on, presto! spark on all cylinders from the impulse coupling.

Timed the mag to spec. and when I tried to start the engine, it fired on about the third blade past. No drama, just an easy regular start.

Thanks for the suggestions and support. It has certainly been learning experience.

Now, I can go back to just flying it for a bit.

Regards,

Mark