rear engine after rain storm

rmorris · #1 09-26-17, 01:32 PM

My plane is almost always outside in the weather. One thing I noticed as a pattern - after a really heavy rain storm, the rear engine is hard to start.

I thought it might be the engine...but I have a practically new engine now, and it still does the same thing....starts super easy most of the time, but if I go to the plane after a heavy rain event the rear engine takes literally minutes of cranking to get going.

this happen to anyone else?

kilr4d · #2 09-26-17, 02:53 PM

Mags getting wet somehow?

JimC · #3 09-26-17, 03:43 PM

Minutes of cranking? How are your starters holding up?

I'd lean towards wet mags as well.

JimC · #4 09-26-17, 03:44 PM

And it's possible that only one mag is getting wet, but the other is already weak and you just haven't noticed.

rmorris · #5 09-26-17, 07:29 PM

Obviously could be a bad mag, but doubt it
this was a symptom of the 'old' engine...but now I have an engine with 40ish hours on it doing the same thing, and the mags were definitely overhauled.

I was thinking that maybe the air filter was getting a bunch of water in it from the top scoop, then sucking it into engine

basically engine starts immed, but then dies out after about 5 seconds or so...and then takes many minutes of cranking (with small rest period for starter).
yes, tough on starter, which is why I was wondering if others are seeing anything similar.

kilr4d · #6 09-26-17, 07:34 PM

Quote:

Originally Posted by rmorris

basically engine starts immed, but then dies out after about 5 seconds or so....

That sounds like loss of fuel?

Do you have fuel flow gauges? Have you tried leaving the boost pump on low?

Does it spit unburned fuel out the cylinder drains while you're cranking?

JimC · #7 09-26-17, 09:07 PM

Most starters specify the max cranking period in seconds and the min rest period in minutes, not the other way around. I'd start flying with a spare from now on.

hharney · #8 09-26-17, 09:57 PM

Robert
Could there be water in the fuel? Right side is always selected for the rear engine. Have you noticed any water when you sump the tanks? It would probably take a lot of water but this would be unrelated to the new engine

rmorris · #9 09-27-17, 11:53 AM

Herb - yep, I had same thought, and after heavy rain storm I do extra sumping just to make sure, no evidence of any water in fuel at any of the three points (main, aux, engine dump)

a combustion engine is pretty simple, so it has to be spark, fuel, or air....I think I am going to figure out a makeshift plug for top scoop to eliminate water coming into compartment that direction, and see if that helps any....

kilr4d · #10 09-27-17, 12:24 PM

Quote:

Originally Posted by rmorris

I think I am going to figure out a makeshift plug for top scoop to eliminate water coming into compartment that direction, and see if that helps any....

https://www.aircraftcovers.com/337#15

Kim Geyer · #11 09-27-17, 09:48 PM

Think your mag switch might be getting leaked on?

rmorris · #12 09-28-17, 09:38 AM

if you are talking about the switch to turn on mags up front...no, I don't think so

also, if it was mags related - I think (and again, this is all conjecture) that it wouldn't start right up and run 5-10 seconds then shut off....Herb's thought it is fuel related was my first thought, so I went to extraordinary sumping after big rain events. my current theory that it is water drippng in top engine inlet onto top of air filter and saturating it (again, only after heavy rain event)...so it starts up, but then begins sucking all that water from air filter into engine...then it takes a bit before it clears out.
that's my working theory

when I say minutes of cranking, I literally mean many minutes (doing it in cycles to let the starter cool down)

I think I may try the following experiment:
- soak the plane through that top scoop at a washing bay, then see if the engine displays the problems.
- assuming it does (which reinforces my theory), then put some sort of cover over the scoop (yes I saw link for the $150 cover, but think I may be able to ddo something more along the lines of a camping style rain fly that is much more lightweight to carry around)
- the try to resoak and repeat test
my guess is that I will get to doing something like this in the next month or so

skymstr02 · #13 10-01-17, 09:01 AM

Other things to consider, check the grounding cable from the engine to the airframe and the power wire to the rear engine starter. Sometimes reinstalling these after an engine change gets missed.
You may not be getting a full 24v to the starter because of a weak contactor or corrosion in the starter wire, or the grounding cable may have a voltage drop due to poor connections.
If the engine is not spinning fast enough, the impulse couplings may not be engaging.
Check the resistance from the starter motor mounting stud to the rear cowling mount flange, and check the voltage to the cable stud on the starter motor. It shouldn't be a volt or two below battery voltage.