hand-propping a 172SP

Hey guys,

I tried hand-propping a 172SP yesterday, without success. I don't have
experience of hand-propping (I was at the controls), but the guy
throwing the prop did.

I understand that it's tricky with a fuel-injected engine (which the
172SP has). Anyone have any tips on how to do it?

Tom

This may be a silly question. If you were hand proping it because the
battery was dead, was there enough battery for the fuel pump and
injectors to work?


On Mar 3, 8:53*pm, Tom wrote:
Hey guys,

I tried hand-propping a 172SP yesterday, without success. I don't have
experience of hand-propping (I was at the controls), but the guy
throwing the prop did.

I understand that it's tricky with a fuel-injected engine (which the
172SP has). Anyone have any tips on how to do it?

Tom

On Mar 3, 9:07*pm, Tina wrote:
This may be a silly question. If you were hand proping it because the
battery was dead, was there enough battery for the fuel pump and
injectors to work?

On Mar 3, 8:53*pm, Tom wrote:



Hey guys,

I tried hand-propping a 172SP yesterday, without success. I don't have
experience of hand-propping (I was at the controls), but the guy
throwing the prop did.

I understand that it's tricky with a fuel-injected engine (which the
172SP has). Anyone have any tips on how to do it?

Tom- Hide quoted text -

- Show quoted text -

Bingo! Tina, you get an A. I bet there's not enough pressure on the
injectors to spray the fuel.

Wil

On Mon, 3 Mar 2008 18:57:50 -0800 (PST), William Hung
wrote:

On Mar 3, 9:07*pm, Tina wrote:
This may be a silly question. If you were hand proping it because the
battery was dead, was there enough battery for the fuel pump and
injectors to work?

On Mar 3, 8:53*pm, Tom wrote:



Hey guys,

I tried hand-propping a 172SP yesterday, without success. I don't have
experience of hand-propping (I was at the controls), but the guy
throwing the prop did.

I understand that it's tricky with a fuel-injected engine (which the
172SP has). Anyone have any tips on how to do it?

Tom- Hide quoted text -

- Show quoted text -

Bingo! Tina, you get an A. I bet there's not enough pressure on the
injectors to spray the fuel.

The electric fuel pump is turned off before you engage the starter in
a normal start.

Still, Peter, would you not agree a dead battery would prevent a hand
propped injected engine start? You'd not be able to charge the fuel
system with the electric fuel pump, nor would the injection computer
have power to run.

If the OP was trying to hand prop an engine that just had a failed
starter motor my questions are rendered moot: he didn't tell us the
specifics, but maybe he will.






wrote:
On Mar 3, 9:07*pm, Tina wrote:
This may be a silly question. If you were hand proping it because the
battery was dead, was there enough battery for the fuel pump and
injectors to work?

On Mar 3, 8:53*pm, Tom wrote:

Hey guys,

I tried hand-propping a 172SP yesterday, without success. I don't have
experience of hand-propping (I was at the controls), but the guy
throwing the prop did.

I understand that it's tricky with a fuel-injected engine (which the
172SP has). Anyone have any tips on how to do it?

Tom- Hide quoted text -

- Show quoted text -

Bingo! Tina, you get an A. *I bet there's not enough pressure on the
injectors to spray the fuel.

The electric fuel pump is turned off before you engage the starter in
a normal start.- Hide quoted text -

- Show quoted text -

On Tue, 4 Mar 2008 07:27:21 -0800 (PST), Tina
wrote:

Still, Peter, would you not agree a dead battery would prevent a hand
propped injected engine start? You'd not be able to charge the fuel
system with the electric fuel pump, nor would the injection computer
have power to run.
If the OP was trying to hand prop an engine that just had a failed
starter motor my questions are rendered moot: he didn't tell us the
specifics, but maybe he will.






wrote:
On Mar 3, 9:07*pm, Tina wrote:
This may be a silly question. If you were hand proping it because the
battery was dead, was there enough battery for the fuel pump and
injectors to work?

On Mar 3, 8:53*pm, Tom wrote:

Hey guys,

I tried hand-propping a 172SP yesterday, without success. I don't have
experience of hand-propping (I was at the controls), but the guy
throwing the prop did.

I understand that it's tricky with a fuel-injected engine (which the
172SP has). Anyone have any tips on how to do it?

Tom- Hide quoted text -

- Show quoted text -

Bingo! Tina, you get an A. *I bet there's not enough pressure on the
injectors to spray the fuel.

The electric fuel pump is turned off before you engage the starter in
a normal start.- Hide quoted text -

- Show quoted text -


Injection computer? In a 172R/S? All there is is a completely
mechanical fuel distribution servo and a spider. As for priming the
system, wouldn't pulling through enough times make the engine driven
pump eventually suck enough gas in? I've never tried to hand prop
anything so I don't know where the process here failed.

On Mar 4, 7:55*am, Peter Clark
wrote:
On Tue, 4 Mar 2008 07:27:21 -0800 (PST), Tina
wrote:

Injection computer? *In a 172R/S? *All there is is a completely
mechanical fuel distribution servo and a spider. *As for priming the
system, wouldn't pulling through enough times make the engine driven
pump eventually suck enough gas in? *I've never tried to hand prop
anything so I don't know where the process here failed.

I"ve never flown an injected engine that would start without first
priming it with the electric pump. Perhaps if you pulled through 30-40
blades the fuel may pressurize put the goal in hand propping is to
have the engine primed and ready so it starts on the first pull.
Pulling too many times wears you out and is asking for trouble.

-Robert, CFII (Aeronca propper)

Let me provide a couple more details:

The engine was hot - had just been flown for 1 hour, and had only been
off for maybe 15 minutes. The starter was malfunctioning in some way
but the battery was good. When I tried to start it with the starter,
it made a noise as though the starter motor was spinning but the
engine didn't crank.

A couple of hours later, we tried again: I turned the key, and it
started instantly. I am aware of potential problems with hot starts
(vaporized fuel in the lines) but this was clearly a starter motor
problem.

When trying to get it going the first time, we tried a few different
variations on hand-propping it, including trying to after priming it
using the electric fuel pump, and trying without this step. Every
time, the hand-propper pulled through 2-3 blades before the 'contact'
start attempt. We tried with the mixture on idle cut-off (which is the
technique for normal starts - as soon as it kicks in, you go full
rich). We tried with full rich. We tried with 1/3 throttle. We tried
after pumping the throttle.

I didn't provide all these details before because I wanted to focus
the discussion on how to hand-prop a 172SP (or similar fuel-injected
spam can) rather than what might have been wrong with it in the first
place. I should have known that pilots would question the question
rather than answer it! Not saying that's a bad thing ;-)

Any further insights appreciated, especially with regard to the hand-
propping, or anything else I could have done differently to get it to
start without waiting 2 hours.

Thanks
Tom







---------
Still, Peter, would you not agree a dead battery would prevent a hand
propped injected engine start? You'd not be able to charge the fuel
system with the electric fuel pump, nor would the injection computer
have power to run.

If the OP was trying to hand prop an engine that just had a failed
starter motor my questions are rendered moot: he didn't tell us the
specifics, but maybe he will.

On Mar 4, 11:07*am, Tom wrote:

Still, Peter, would you not agree a dead battery would prevent a hand
propped injected engine start? You'd not be able to charge the fuel
system with the electric fuel pump, nor would the injection computer
have power to run.

It won't prevent hand propping but if there isn't enough juice to
power the alternator field you'll be flying w/o power.

-Robert

Tom wrote:
Let me provide a couple more details:

The engine was hot - had just been flown for 1 hour, and had only been
off for maybe 15 minutes. The starter was malfunctioning in some way
but the battery was good. When I tried to start it with the starter,
it made a noise as though the starter motor was spinning but the
engine didn't crank.

I'll bet that was your problem with the hand prop attempt. Hot starts on
injected engines can take quite a few cranks even with a working starter.
Doesn't the 172 hot start procedure have the mixture lean, then you move it
to rich as the engine starts to catch? It would seem to be tough to
duplicate that with the engine turning one revolution at a time.

Your starter problem sounds like a sticky bendix gear. When the bendix
shaft gets gummed up, the bendix gear won't pop out and engage the ring gear.
It just spins. As you found, it will sometimes cure itself, but a permanent
fix involves cleaning and lubing of the bendix shaft. This is a common
problem on Cherokees, whose wacky design leaves the starter exposed to the
airstream (and all of the dirt, bugs and debris).

I usually carry some silicone spray lube and a very long, skinny
screwdriver (since I fly a Cherokee). If the bendix gear strands you, you
can always try dousing the bendix shaft with lube, then poking the bendix
gear a bit with the screwdriver. That's always worked for me.

John Galban=====N4BQ (PA28-180)

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