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rexjan(at)bigpond.com
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 Posted: Thu Jun 15, 2006 5:36 pm Post subject: Re pump mounting |
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Hi ! Guys,
re which way to mount the pump I'm not going to stick my neck out here and pretend to be an expert but I do know from experience racing two strokes in Karts years ago that those diaphram pulse pumps can cause lean running mounted flat. We always assumed it was the weight of the fuel getting bounced up and down in sympathy with engine vibration causing ineficient pumping. We certainly also found mounting ignition modules flat that they soon broke off but if mounted vertically they never did. This seems to support the idea of the weight of fuel getting bounced up and down.
Somewhere and I'm pretty sure it was from Rotax I read that little breather hole in the pulse line inlet elbow was to let any oil dragged in from the crankcase drain. I don't remember any further comment but it would therfore seem logical to mount the pump flat with that drain hole down and perhaps this is why it has been done. However we are left with a conflict here so perhaps the best idea is as has been suggested to mount the pump vertical, block the existing drain hole, drill a new one down low in the pulse chamber, have the fuel outlets up so the air gets out. Sounds good to me.
Incidentally I'm pretty sure Rotax are the only ones using that vent hole. Makes you wonder if there is any real need but I guess the minute loss in efficiency does not warrant playing aroung without it.
Rex Shaw.
PS
just before posting this I have looked up the Rotax Installation Manual and it says, " The fuel pump should be installed in a cool place [ not on the engine itself ], with the small drain hole near the impulse connection towards the bottom. This hole drains oil condensate from the pump diaphram chamber."
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Mark.Napier(at)sciatl.com
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| Posted: Fri Jun 16, 2006 6:55 am Post subject: Re pump mounting |
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Hey Rex,
That is how mine is right now. The pump was originally installed
vertically according to the builders' manual. When I rebuilt the pump I
plugged the hole at the elbow with thread lock and drilled a new hole
very low in the chamber with the same sized drill. I've got a set of
very small PCB drills.
I didn't do it for any good engineering reason other than not wanting to
have to relocate the pump and wanting the weep hole at the bottom. It
has worked for the 85 hours I have on it so far.
When I opened up the pump I did see some varnish low in the chamber.
But I would point out this airframe had sat up for nearly six years so I
was surprised that there was no corrosion. Every thing seemed fine with
the hole in the stock location.
Draw your own conclusions....
It's time for condition inspection so I'm going to put in a new kit into
the pump.
FWIW,
Mark Napier
Time: 06:36:20 PM PST US
From: "Rex Shaw" <rexjan(at)bigpond.com>
Subject: Re pump mounting
Hi ! Guys,
re which way to mount the pump I'm not going to
stick my neck out here and pretend to be an expert but I do know from
experience racing two strokes in Karts years ago that those diaphram
pulse pumps can cause lean running mounted flat. We always assumed it
was the weight of the fuel getting bounced up and down in sympathy with
engine vibration causing ineficient pumping. We certainly also found
mounting ignition modules flat that they soon broke off but if mounted
vertically they never did. This seems to support the idea of the weight
of fuel getting bounced up and down.
Somewhere and I'm pretty sure it was from Rotax I read that little
breather hole in the pulse line inlet elbow was to let any oil dragged
in from the crankcase drain. I don't remember any further comment but it
would therfore seem logical to mount the pump flat with that drain hole
down and perhaps this is why it has been done. However we are left with
a conflict here so perhaps the best idea is as has been suggested to
mount the pump vertical, block the existing drain hole, drill a new one
down low in the pulse chamber, have the fuel outlets up so the air gets
out. Sounds good to me.
Incidentally I'm pretty sure Rotax are the only ones using that vent
hole. Makes you wonder if there is any real need but I guess the minute
loss in efficiency does not warrant playing aroung without it.
Rex Shaw.
PS
just before posting this I have looked up the Rotax Installation
Manual and it says, " The fuel pump should be installed in a cool place
[ not on the engine itself ], with the small drain hole near the impulse
connection towards the bottom. This hole drains oil condensate from the
pump diaphram chamber."
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