Those of you who look at the Real World
Solutions web site and their latest photos may recall seeing a photo
titled "Congratulations, it's a boy" which shows coolant squirting into
the air from my overflow tank. Photo taken at Charlie's fly
in. That was pretty good evidence of a coolant leak between
combustion chamber and coolant galleys and supported by the fact that I
had notice my coolant pressure increasing on the flight to Charlies by
approx 11/2 psi per hour of flight. It started at a normal 10 psi and
had increased to18 psi by the end of the flight.
Well, by the time I had flown another two
hours to Louisiana in and out of rain showers, etc, back-tracking, I
finally made it to my destination. There I found that the number 1
(front) rotor would shoot coolant out of the removed spark plug hole
like old faithful when I pulled the prop through. Clearly, had to
fix the problem. Upon opening up the engine I found two
things
1. One of the triangular pieces of
the apex seal was missing - I first though it had fallen out on
disassembly in my brother-in-law's garage, but concerted search
failed to locate it.
2. There were two "hot" spots
(metal discolored to blue) on the front rotor side housings opposite
each other. One about the size of a half dollar coin was on the
side of the missing piece of the apex seal. the second spot on the
opposite housing at the same location was smaller about the size of a
quarter. It was clear looking at the "O" rings that the heat
had compromised their integrity. The appearance of the "O" rings
at that spot was as if they had shrunk in diameter. Elsewhere the
"O" rings were slightly proud of the surface of the side housing
indicating good sealing.
Someone on the list suggested that the
missing piece of the apex seal might have gotten wedge at the end of the
rotor and caused the problem. At first, I was inclined to dismiss
that hypothesis but failure to find any other explanation leads me to
the following conclusion.
At this point, it appears that one
of the triangular pieces of the apex seal (could not find it anywhere)
left its proper position (undoubtedly during my assembly) and got lodged
at the end (apex) of one of the rotors. May have been held their by some
combination of the corner and side seal. In any case, it appears that
one area of the rotor housing was slightly narrower than the rest (some
area has to be {:>)). Every time that rotor with the wedged piece of
apex seal passed that area it created tremendous friction and heated the
side housing hot enough for the blue discoloration. The large Hot spot
was on the side of the rotor that the piece of apex seal would normally
have been. I think the smaller Hot spot on the opposite side housing was
due to the rotor being pushed to that side by the wedged piece on the
opposite side of the rotor. So the brunt of the heat occurred where the
wedged piece was rubbing the side wall – but, at that same spot in
rotation, the seal piece forced the opposite side of the
rotor into the opposite side wall creating a smaller hot spot – but
still sufficient to overheat the "O" ring.
The wedged piece probably
accounts for the initial tightness of the engine and after two hours of
running it had either disintegrated or dropped out of the housing
causing the engine to loosen up. Of course, by that time the damage to
the "O" rings had been done and the results was the slowly increasing in
my coolant pressure and of course the resulting "Congratulations, it’s a
boy" photo.
The main point is that several folks
(including Bruce T) expressed concern when I reported the initial
tightness after reassemble from my apex seal failure on way to Sun &
Fun. However, I was in a hurry to get my aircraft off that
derelict airfield and talked my self into the notion that I had just
rebuild a really "tight" engine. Clearly, I paid for that by
having to open up and correct the situation. This time there was
no tightness and the compression was even better (guess the missing apex
seal piece could account for less compression as well).
Fortunately, having friends like Laura and
Tracy Crook really helps. Laura was practically reading my mind in
shipping the parts I needed to get the engine back together. The
longest time line was simply the time required to get the parts I
needed. No local source within 60 miles was found.
As always, I aim to share my experience in
hopes it will preclude someone from making the same mistakes I
made.
Between the brake failure/fire and the
engine rebuild in no-rotary land during the heat and humidity of a
Louisiana summer, its been one long month - but finally home and glad to
be doing "Honey Dos"
Best Regards
Ed