From: Jim Weir <jim@rst-engr.com>
Newsgroups: rec.aviation.homebuilt
Subject: Re: Aircraft That Landed On The Flatbed Truck
Date: Mon, 11 Sep 2000 09:41:05 -0700

valcraig@dhc.net (Craig C.)
shared these priceless pearls of wisdom:

->Only place the crank could possibly break and have this happen is in
->the area of the journal for the last cylinder, with the break confined
->to being under one rod end. There is a billion to one chance that it
->broke in a diagonal across both rods though...

That's about as close a guess as I think necessary to declare a WINNER.  Craig
C, whoever you are, you win.

The break was just forward of the journal for the #4 cylinder, between #4 and
#3.  Here is what we believe the scenario to have been:

1.  A very close inspection of the journal and a very detailed questioning of
the previous owner of the engine revealed that there was some "work" done on the
#4 journal.  We suspect (although it would be holy hell to prove) that there was
a fault in the #4 journal that was welded up and then ground back to standard.
The #4 journal is colored differently than the other 3 journals and the main
bearing surfaces.

2.  When this weldment took place, the heat treating of the crank in this area
went to hell.  Weldments are NOT permitted on engines in "standard" certificated
service, but with a homebuilt, anything goes.  Especially if it isn't noted in
the engine log.  Over time, the crank cracked at an angle of about 30° forward
of the #4 cylinder, on the throw between #3 and #4.

3.  The pressure of the rear and center main bearings held the crank together.
However, with each succeeding piston blow, the "crack" got a little wider.
Since it was a blow and not a grind, the metal of the crank held together.  The
end of the broken pieces look like somebody took a ball peen hammer to them.
There was no grinding, especially on this softened metal, so there was no metal
to find in the oil screen.

4.  As a function of this crack getting wider, and where the crank chose to
"freeze" itself together on any given flight (advance or retard, one or the
other) the mags would go out of time.  When this first happened, it was maybe a
3-5° error and the mags were retimed.  When it got larger, then it became a
function of where the crank stopped when the mags were timed.  If it was on the
power stroke for the #4 cylinder, the mags would advance.  If on the intake
stroke, retard.  If in between, in between.

5.  When that last 40° "error" was found and the mags retimed just before the
flight, the crank had peened itself to the point where it was just barely
holding together.  That and the vibration from the busted crank had opened the
rear main clearance up to about 200 mils from the normal 20 or 30 mils.  With
the back part of the engine slopping about like this, the crank finally let go
and the mags stopped turning all at once.

Be careful, boys and girls, those iron bastards are out to kill us {;-)

Jim
Jim Weir    (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST   Pres. Cyberchapter   EAA Tech. Counselor
http://www.rst-engr.com              jim@rst-engr.com

From: Jim Weir <jim@rst-engr.com>
Newsgroups: rec.aviation.homebuilt
Subject: Re: Aircraft That Landed On The Flatbed Truck
Date: Mon, 11 Sep 2000 11:04:29 -0700

John Kunkel <JohnLKunkel@worldnet.att.net>
shared these priceless pearls of wisdom:

->
->Interesting thread, but, in the initial post you stated that the mags
->would jump time, not always the same mag. Quote "the odds were 50/50
->that it would be any one mag".

Good question, John.  What I'm guessing (and I'm not the teardown artist on this
one) is that by the time the "timing" error was noticed and got to be so great
that the rear main had slopped up to the point that the gear was missing a tooth
every now and again, purely randomly.  The aft end of this sucker was torn up so
badly in the accident that I don't think we will EVER know for sure how this
happened.

And, I should have said that the OWNER REPORTED the mag timing to be off this
way.  Since he isn't a mechanic, it could have been that both mags were off
sometimes, and sometimes just one.  Verbal memories sometimes lose their
crispness when you've just come through something that should have killed you.

Jim
Jim Weir    (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST   Pres. Cyberchapter   EAA Tech. Counselor
http://www.rst-engr.com              jim@rst-engr.com

From: valcraig@dhc.net (Craig C.)
Newsgroups: rec.aviation.homebuilt
Subject: Re: Aircraft That Landed On The Flatbed Truck
Date: Mon, 11 Sep 2000 20:11:43 GMT

Jim Weir <jim@rst-engr.com> wrote:

>valcraig@dhc.net (Craig C.)
>shared these priceless pearls of wisdom:
>
>->Only place the crank could possibly break and have this happen is in
>->the area of the journal for the last cylinder, with the break confined
>->to being under one rod end. There is a billion to one chance that it
>->broke in a diagonal across both rods though...
>
>That's about as close a guess as I think necessary to declare a WINNER.  Craig
>C, whoever you are, you win.
>

I've had this happen to me once, but it was in my truck's engine.
Pissy little 305 finally decided to break the crank off...and cleanly
at that, under a heavy acceleration load. The failure was confined to
being under the #1 rod.  Only clue that I had to the failure was a
momentary hard knock from the engine and suddenly losing all the
belts. Finally found the problem when I could reach down and wiggle
the crank pulleys and dampner assembly. Believe it or not, that motor
would fire up and run right up to the afternoon that I pulled it our
of the truck.

Final clue for me was things being loose it he back of the motor and
it being intermittant.

Craig C.