I did a measurement today
for the resistance from the starter flange at the re-drive plate to the copper
tube, which is my ground bus going from engine compartment back to the batteries
that are in the nose of the Velocity. The ground
strap from the engine is from the bottom right corner of the front cover. So
this is the measurement through the engine (20B), back to front, and after the
two connections – cover to strap, strap to bus.
The resistance
measurement was really too small the get a good reading on the Fluke; say less
than a milliohm. Then measured the voltage drop while engine cranking –
about 10 milivolts. Clamp-on ammeter suggests about 50-60 amps draw to
the starter after first surge. The math says resistance is about 0.2 miliohms.
So as least in my case; grounding in this manner is not an issue.
So weak spark during
cranking is some other reason; I’m wondering if it could be due to very
short dwell time from EC2 at low rpm that Steve Boese reported here some time
back. Don’t know if 3-rotor would have same effect,
but likely would. Tracy; maybe you could
comment on whether that could be a factor. Never had starting problem, just
noted spark during cranking significantly weaker than test mode – hard to
get it to jump ¼”.
Al G.
-----Original
Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of
Steve Brooks
Sent: Sunday, November 22, 2009 7:44 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Ground isn't ground
The
mystery of my intermittent spark is solved. Thank you to all of
those
who made suggestions, as it helped get to the bottom of the issue.
This
morning I decided to repeat the test I made yesterday hooking the
starter
to a separate spare battery that I had.
This
time I removed both the large cables going to the starter and
engine
block ground. That way, I didn't have to mess with a jumper
cable.
I hooked up the battery, turned the master on and engaged the
starter.
To my utter amazement the spark was intermittent again. I
thought
thgat certainly I hadn't made a mistake yesterday an imagined
that
the spark was good on a separate starting battery. After some
swearing,
I thought about yesterdays test, and the only thing different
was
the ground cable. So, I removed the ground cable from the
battery,and
hooked up a jumper cable from the negative terminal of the
battery,
and hooked it up to the reduction drive plate, as I had done
yesterday.
Cranked the starter and had good spark. Did it twice, just
to
make sure.
What
the **** !
So,
I decided to connect the jumper cable to the ground cable end,
instead
of clamping it the the reduction drive plate. Cranked the
starter,
and had intermittent spark again. Somewhat amazed, but onto
something
here.
I
measured the cable (0 gauge multi-strand silicone) with the Fluke
meter,
and it showed pretty much zero ohms. I measured from the spot on
the
front engine housing where I had the ground bolted on to the
reduction
plate, and measured about 3 tenths of an ohm.
Since
my original installation, I always had the ground cabled bolted to
the
front housing, with a bolt into one of the tapped holes where the
air
conditioner mount was. It is a pretty large bolt, and I never
suspected
that, considering all of the bolts that hold the engine
together,
and the many bolts that hold the reduction drive plate, that
there
would be any issue. Boy was I wrong.
I
reconnected the cables to the main battery, instead of the spare
battery,
and instead of bolting the negative cable back on, I used the
jumper
cable to connect to the reduction plate again. Perfect spark
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
My
current ground cable isn't long enough to reach from the battery to
the
mounting plate. I found the cable that I had left, and I have
plenty
of spare cable, but I don't have any more of the lugs for the
ends,
so I will have to order some. I am going to attach to ground
inder
one of the mounting bolts for the starter.
Regards
and thanks for the help,
Steve
Brooks
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