Backward Running Engine

Cherokee w/Lycoming 0360-A4A

Normal flight in all respects. When shutting down, pulled throttle to idle
and mix to idle cut-off. Engine took just a little longer than normal to
run down. Just as it should have stopped, it caught and actually ran
backward for a couple of turns before stopping.

Any ideas as to why?

Thanks

Mike

mbremer216 wrote:

Any ideas as to why?

One of the mags may have slipped time or been set incorrectly.

George Patterson
Give a person a fish and you feed him for a day; teach a person to
use the Internet and he won't bother you for weeks.

I had this happen too a couple of months ago on my IO360. - just
happened once, everything's been normal since.

mbremer216 wrote:
: Cherokee w/Lycoming 0360-A4A

: Normal flight in all respects. When shutting down, pulled throttle to idle
: and mix to idle cut-off. Engine took just a little longer than normal to
: run down. Just as it should have stopped, it caught and actually ran
: backward for a couple of turns before stopping.

: Any ideas as to why?

Completely WAG, but extra-rich idle mixture pooling in exhaust system, gets
sucked in on the final "bounce" and either preignites from hot heads and/or mags
firing at normal 25 "BTDC" (now ATDC).

Like I said, completely WAG.... getting fuel into the thing running backwards
is the tough part to explain.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

On Mon, 29 Aug 2005 06:56:01 -0500, "mbremer216"
wrote:

Cherokee w/Lycoming 0360-A4A

Normal flight in all respects. When shutting down, pulled throttle to idle
and mix to idle cut-off. Engine took just a little longer than normal to
run down. Just as it should have stopped, it caught and actually ran
backward for a couple of turns before stopping.

Any ideas as to why?

Quite common with engines that have timing well in advance of TDC.
Usually caused by plugs that are fouled with carbon, which stays hot
and causes detonation under compression. Called "dieseling."

You can lessen the chances of it happening by revving the engine up
just before you cut the fuel mixture. Running backwards isn't good
for the engine -- and it can play hell with vacuum pumps, as the vanes
are designed to turn in one direction only. Same problem in cars and
outboard engines with water pumps.


Thanks

Mike