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O-470 Hot Start Problems, now dies when hot

sj

sj

Staff member
Northwest Arkansas
I have a real %$#@& of a time starting the O-470-J when she is at all hot. When it is cold, starts like a champ. Today, upon landing after a quick turn trip to way too muggy Arkansas (delayed about 40 minutes to get the plane started, which involved a battery charger) it died when we turned off the runway and would not restart. Never had a CARBURETED plane do this kinda thing, but I am sure somebody else has!

It really acts like a thermal problem, but something is going on and any advice that would save time on the troubleshooting would be greatly appreciated!

Thanks!

sj

P.S. When it died, it acted like it was out of gas, but it was not, in spite of my checkered past.
 
How old are the coils in the mags. I had a PA12 that wouldn't start hot but would when cold---coils were bad.
Marty
P.S. must be that ethanol fuel you're burning----just kidding!!!!
 
Throttle

Where do you set the throttle during the hot starts? One of my planes would only easily start, when hot, w/the throttle completely closed initially.
 
This is somewhat of a new behaviour, and I believe I have the original Bendix mags (which apparently are notorious for this). I have tried throttle and mixture in all kinds of positions, but cooling off is the thing that makes it work best so far.

Geeze, didn't want to honk out $1500 on new mags... ugggh.

sj
 
I guess the coil gets weak when it gets hot or some such.

BTW, here is another retarded question (get it, mag, timing, retarded...). Is the "left" mag on the left side of the engine when you are sitting in the plane, or standing in front of it?

sj
 
Steve, On an O 470 both mags have impulse couplers to retard timing. A few years ago there was a deal where you had to check and make sure the coils were red. There is something about heat that makes a coil weak---I think the coating on the wire that wraps is breaking down.
Marty
 
Thanks, Marty and everybody. I figured it was probably just sparking on the left mag on start, but if it has IC's on both maybe both coils are shot?

sj
 
You also mentioned it was muggy. Hot and humid are the conditions when weak coils will show themselves. You are probably doing it anyway, but if not, try hot starting with the mixture out and shove it in when it starts to fire like you would with FI.
 
Boz,

I tried every combo of mixture and throttle and primer and carbheat and holding my tounge in different positions I could think of. I am pretty sure it is mags, but I also need to check to see if the fuel line is close to the exhaust, which could cause fuel vaporization when not moving. I am going to tear into it today. Pretty confident it is the mag coils, but we shall see...

Thanks!

sj
 
The plot thickens, as I have SLICK mags in this beast (can't find them in the logbook, must have been added at some overhaul over the years). So I have decided to do the smart thing and let the mechanic tear into it, rather than just try to troubleshoot it myself. Seems like I will come out ahead in the long run.

Meanwhile, I wish I had had a camera. I thought the vents in the wagon were a little weak, so I cleaned out about five pounds of mud dauber nests (one of which was still active) from the vent tubes and my guess is the ventilation will be MUCH improved! Time to pick up some Chore Boys for sure!

sj
 
Check the spark plug gap. Many a flight school airplane has been stranded here because it wouldn't hot start. Pull the plugs out and the gap is .025" or better. Regapped and they are gone. Of course I only take cash from flight school airplanes. :evil:
 
Well folks, I always like it when folks come back and give us the skinny on what the problem was or how it was solved so I will do the same here.

As it turns out, the biggest problem was that the aircraft was improperly timed. Continental has a BIG SB that covers all their engines explaining the approved method for timing them, and listing all the timings. The "J" model engine that I have is one of the few where the timing is 20 BTDC. Most of the other models are 24 or 26 BTDC. Of course, mine was timed at around 24+. There was also 1 bad plug, and a couple others that needed gapping and a cracked inlet manifold tube. However, the timing change has decreased my EGT's by over 100 degrees in all cases. I thought the EGT's looked high (digital), but folks kept saying "SJ, don't worry about EGT, just watch your CHT" - which was always nice and cool (which surprises me now).

Plane runs smoother, seems to have more power, and in the time I had for a quick test, it hot started just like it should.

I also took a minute and installed a "stop lock" on my seat rail to keep the seat from flying back. After reading how many many skywagon owners this has happened to, it seemed like a prudent thing to do.

sj
 
SJ, glad you got it going again.

Next time it starts idling rough, have your mechanic check the intake risers for leaky gaskets. The A and J -470's don't have 4 bolts holding the intake risers to the head like the later model -470's. This leads to leaky gaskets, often found because of a rough idle.

FYI .

DAVE
 
Steve,

So it was just a matter of timing, and your mags were fine?
I just had my annual on my 170, and this was a squawk going in. The old C145 was running rough at full power, and while timing it, we discovered the wrong gasket had been used on the right mag. It was super tight and wouldn't allow full rotational adjustment. The old mechanic just shined it and got it as close as he could. We replaced that and set it to the proper 26 deg advance, now much smoother.

It's so nice to find out that your problems can be solved with an adjustment, and not a replacement. :)
 
Yep no new mags needed. He checked all the intakes and stuff and fixed a cracked intake tube, but the timing was for sure the deal. Now having said all that I have not made a 3 hour X-C in it yet which is when it heats up.

sj
 
Steve, I guess I can go eat "crow" for suggesting coil problems. What I find interesting is that the O 470A is timed 26 degrees BTC and the J is 20. Both use the same cylinders except maybe the smaller case through bolts on the older A like I used to have. Oh, I guess my old A wound up to 2600RPM's vs. 2550 on your J.
Marty
 
Marty,

You were in EXCELLENT company with sugguesting the coils. I got 25 emails sugguesting that was the problem. Of course, everyone ASSUMES that a plane is timed correctly, but this must have been wrong done at the last annual before I bought it.

sj
 
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