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Pulling the prop through

Henny

Henny

FRIEND
Ely, MN
How many times do you guys pull the prop through on a 160 HP O320 before the first start of the day? I've heard everything from "None" to "A dozen". Does it change with temperature or how long it has been since the last flight? Searched the previous threads but didn't find anything. Thanks.
 
None... Ever.. Unless the battery is dead. Then I pull it through as hard as I can and get out of the way real quick..
 
I like to give my O 470 a couple shots of prime and pull it through about three or four blades. Sometimes it'll start on the first blade with the starter. I try to check the mags after every flight to make sure they're grounded.
 
There's a school of thought that says pulling it through simply scrapes off the coating of oil on things and increases wear. I never thought anything of it prior to reading that. My 320 starts fine without pulling it through, but I've never started it without preheating below freezing.
 
As Josh noted, this is a hangover from the radial engine times. In a radial engine, you have cylinders that are inverted, and thus the possibility that some oil MAY leak down around the rings, etc, and pool in the cylinder head. Punch the starter in this case, and you'll experience a hydraulic lock, or just a "hydraulic", and more than likely something REALLY important in the engine. So, with radials, particularly ones that have sat for a while (or any eastern bloc built radials, like the Vendenyev engines) it's always good to pull them through several blades to verify that there's not a hydraulic lock. If there is, turning it through by hand won't harm anything, and you can then pull the plugs on that cylinder and clean it out.

On a horizontally opposed engine, all turning the prop through prior to start does is, as mentioned, scrape the oil coating off all the moving parts just prior to start, so that friction is increased right after start. Better to leave those fine oil coatings alone, and just start the engine. Check Lycoming's recommendations on this.

MTV
 
Interesting how pulling through a flat motor scrapes the oil off but doesn't a round one. BTW, I've helped pull a 1340 P&W on a Thrush through quite a few times.
 
P & W R 2000-4's on C-54's had a clutch in the Starter.

Uncle Sam said don't pull by hand.


Zantop operated C-46's with R-2800's.

After an engine change a "Burp Run" was required.

All plugs below 3 & 9 o'clock were removed & the engine started.

If you looked carefully you could ALMOST see the aircraft through the smoke!
 
Most say do not move a prop, but I grew up with a J-3. Next year it will have been fifty years of hand starts.

If you do not pull a radial through, you may wind up with a bent main rod - hydraulic lock on start-up is engine disaster.

But here is another way of looking at it - I catch weak cylinders immediately. I monitor them, and like as not, they stop being weak after a week or so (sorry). Folks who consider it dangerous find out about weak cylinders at annual time, and often pull a jug because the rings line up, or a piece of dirt gets under a valve.

Whatever you do, expect it to start, and take precautions.
 
On round engines, bent connecting rods are worse than scraped cylinders. I've seen the evidence;)

No hydros!
 
180Marty said:
I'm still laughing.
Click to expand...


Good answer...

OTOH, I'd say one needs to find out exactly what their engine likes. On mine, O290D with MA4SPA carb and no starter, this is my routine.

I do NOT prime, that DOES remove oil from cylinder.

Mixture rich.
Pump throttle ONE time and leave cracked.
Mags OFF
Pull through TWO blades, NO MORE/NO LESS
Mags ON
Will start first blade 9 out of 10 times..

It will NOT start until 3rd blade anyway if mags are initially hot......

I suspect most engines are NOT going to start the first blade anyway so it does not matter if you pull it through or not, the oil will be wiped off either by the starter or by hand..

take your choice.

YMMV

Find out what your engine likes

Jack

PS. If I had a starter, I'd pump throttle once and make it hot....

Whatever, at least once a week I do pull it through by hand to keep track of possible low cylinder, but only if I'm going to then start and fly.

Bottom line, EVERY "cold" start causes wear
 
See above.

Why not use primer?

I've found the above routine to work best for me hand propping usually by myself. One pump and cracked throttle and it will start and idle..

Again, why not prime?

I found it too problematic. One full shot "might" work ok but may flood the engine if it doesn't "catch" and idle, especially in summer. To keep running the throttle needed to be cracked too much for what I considered "safe" when hand propping by myself. I do tie the tail and chock. After a nice idle is established I untie and replace regular chocks with 1X2 chock. I then climb aboard and can taxi over the small chocks with 15-1800 rpm.

Like I said, works for me, YMMV

Jack
 
Last edited:
If I expect the starter will be challenged I pull it through to help loosen it up. It helps, too. But the times my starter will be challenged are in the cold or when the starting system is sick. In both cases I avoid throttle more than usual and use primer. I've demonstrated how an induction fire can't be vacuumed into the engine when the battery isn't capable of spinning it. Once was enough. Knowing my engine includes awareness of the fire risk from choosing throttle over primer.

SB
 
Here's my logic. The primer fitting is pointing straight down and the intake valve is horizontal. I doubt if any fuel gets squirted into the combustion chamber past a valve that may be open. Don't you think most of the fuel is running down into the intake runners so by the time I walk up front and pull it through a few blades only vapor is really going into the combustion chamber?
 
180Marty said:
Here's my logic. The primer fitting is pointing straight down and the intake valve is horizontal. I doubt if any fuel gets squirted into the combustion chamber past a valve that may be open. Don't you think most of the fuel is running down into the intake runners so by the time I walk up front and pull it through a few blades only vapor is really going into the combustion chamber?
Click to expand...

Good point.

I 2nd thought I don't think primer and/or pulling it through has any effect what so ever on engine wear, as long as it gets started. unless maybe it's over primed and it's turned over for 5 min on dry cylinders until the battery is dead and then left for a couple weeks.....

The only reason to NOT pull it through is not to do so if you are not going to start it. In that case you have scraped the oil off the cylinder and you may cause corosion?

Otherwise, do what works for you/your engine to get it started.

As to induction fires. Just does not seem to be an issue with my O290. I do keep a CO2 bottle handy. In the flying club, induction fires were a problem back in the C150 days, BIG problem a couple times but in my present case kick back and or induction fires have not surfaced.

Jack
 
Gravity SUCKS.

Every time I examine an engine that has not flown for some time I check the UPPER surface of

the installed cylinder barrel for rust.

Gravity & Time has often removed the protective coating of oil & the result is PITTING.

It's possible the severity may also vary with the type of oil used.

In the past; some ofthe Engine Shops would void the warranty if Multi-grade was used.

When starting one of these "Rip Van Winkle" engines I believe it prudent to remove the LOWER plugs

& squirt oil on the UPPER surface prior to start.
 
180Marty said:
Here's my logic. The primer fitting is pointing straight down and the intake valve is horizontal. I doubt if any fuel gets squirted into the combustion chamber past a valve that may be open. Don't you think most of the fuel is running down into the intake runners so by the time I walk up front and pull it through a few blades only vapor is really going into the combustion chamber?
Click to expand...

I know what happens to fuel when you pump the throttle on an aircraft updraft carb. A stream of fuel is shot a couple of inches to where it hits a horizontal surface about where the induction tubes take their first 90* turn. That raw fuel splashes and much of it drops straight down to pool in the airbox and drip into the cowl. While there's no dispute the induction tubes now are filled with vapor it's also true the airbox is wet with raw fuel and the cowl comprtment is filled with vapor. I don't assume to know your experiences but I know mine. Each and every induction fire I've ever had resulted from having jockeyed the throttle followed by slow cranking or my release of the starter allowing cranking to stop. In all cases but one I had sufficient battery to crank the engine to snuff the fire.

I've never had an induction fire in an injected engine or when I've used the primer on a carb'd engine. I'd be lying if I said I didn't occasionally use the throttle to start an engine. But I'll qualify that I always begin the start sequence by engaging the starter to get a draft going before I advance the throttle. A guy I know taught me that trick and its worked well to date. When I've been forced to hand prop I use the primer not only because it's consistent with what I just described but also because it emulates what the best Cub pilot I know does to start his no-electrics Cub.

SB
 
I agree with StewartB. Never pump the throttle unless the engine is turning over and thus creating a vacuum to suck the fuel into the manifold. Otherwise all you are doing is creating a pool or raw fuel in the airbox. I doubt pulling it through has any adverse effect, just make REALLY sure the mags are off.

In fact by turning it over then pumping the throttle you do not need a primer.

Bill
 
Just to make sure, I don't touch the throttle other than to maybe crack it open from full closed. I leave the primer plunger half ways out since I think some fuel can get sucked through the primer lines to help richen up the cold start mixture once the engine starts. After it is running, then I will adjust the throttle and close the primer.
 
Make sure you get the right training, then pull it through enough times to get every piston over TDC at least once.

The starter might be stuck engaged from a previous aborted start - weeks ago. If you hit the start button, what are the odds it will disengage after the engine starts? More important, by pulling it through, you'll know if you have a stuck valve, or ice in the jugs, or whatnot. It's a lot cheaper to fix before the piston rams into whatever shouldn't be in its way. Or how about a seized generator bearing, loose prop, loose ice in the spinner, etc.?

And why would you scrape off any more oil off the jug walls by pulling it through by hand than turning it over with the starter? Can the oil tell the difference between elbow grease and 12 volts?

Way back when, pulling the engine through (or checking the compressor fan or rotor for free rotation) was part of preflight. If you didn't do it on a ride, you just might fail right there and then. I understand it's no longer required in some jurisdictions (presumably, because it adds training cost), but that doesn't mean you should forget about it if you don't fly radials. Airmanship doesn't get obsolete no matter how hard pencil-pushers and profit-hungry operators try to label it stone age. My 2c.
 
Ok, I'm not too old to relearn. My pump throttle once routine was used and worked well because I didn't have a primer installed on the biplane. Not to mention my flying usually stopped as the days got colder. I've now removed the engine from the EAA bipe(and sold the bipe less FWF this past Thurs). The engine/FWF is now installed in my new Spezio Tu-holer which is now finished and should get inspected and get AWC next week. I do have a primer installed, but no starter as yet, and do intend to find a new routine using primer.

Thanks,

Jack
 
I am in the same school as Aviator, I don't pull the prop thru to prime but to check for abnormal noises and as a poor man's compression check. Does is "scrape the oil off"? I don't know, but when I don't do it I feel as though I left something undone. Jim
 
I seriously doubt that pulling the prop through a blade or two prior to start is going to cause MUCH damage. Most of the concern with this process is with regards to those folks who have an airplane in STORAGE for long periods, and think they're doing that engine a favor by pulling it through a few times by hand each week or so. THAT will cause corrosion issues.

That said, pulling the prop through by hand just to check compressions? If you really think your engine is going to suffer major problems such that you need to do that, you might be a little paranoid.

Then again, as one of my bosses once told me: "You know, you're a little paranoid. Then again, just because you're paranoid doesn't mean they're not out to get you". :???:

MTV
 
I usually agree with MTV, but here I disagree. Monitoring your cylinder health daily will tell you a whole lot more about the health of your engine than a once in a year compression check done by the most recent new hire at your local shop. Cylinders do get weak, and then come right back to normal. On the other hand, I have picked up cracked cylinder heads in the middle of the annual year - they might not have been caught until a big chunk came out in flight?
 
mvivion said:
...you might be a little paranoid.
Click to expand...

Key to survival on the line:

1. When your eyes pop open in the morning, your first thought should reveal your natural skepticism.

2. By the time you sip your morning coffee, you should to be awake enough to be suspicious of everybody and everything.

3. And by the time you show up for your preflight briefing, you should be exhibiting the symptoms of clinical paranoia.

4. Never assume anything; always make sure!

My $0.02.
 
FWIW I think i'm typical of most owners here in that I'm the sole operator of my airplanes. My next flight's engine performance is best indicated by my last flight's engine performance. I have no reason to believe my engine has been compromised during the inactivity in between. That being the case i assume things are good. In the event I am suspicious of a problem I'll call somebody with better qualifications than me to substantiate its worthy of continued operation. Even if just to validate what I already think.

SB
 
Well, I don't know where you guys are getting your engines done, but I've flown quite a few hours, and except when I was flying airplanes with round motors, I've never pulled an engine through prior to flight. Seems to have worked so far.

I have three engine "failures" to date: A throttle cable came unhitched from the firewall in a C 185, resulting in a landing on a lake and a looooonnggg taxi to a cabin. An induction air filter jammed mid swing in a Beaver induction....same result. A crankshaft failed in a C-185. I don't think pulling the prop through in any of those cases would have made any difference in the outcome. I've also had a few cylinders changed at 100 hour/annual inspection times.....again, no harm no foul.

On the other hand, I had an O-320 that was a total POS, passed multiple compression tests, and the only clue was that it ran hot. It had all sorts of problems once we pulled it apart, with only a few hundred hours since an "overhaul".

Again, pulling it through prior to flight wouldn't have made any difference. It had compression.

So, if your engines are THAT suspect, I'd find a different engine rebuilder/supplier if I were you.

Just a thought.

MTV
 
Sorry guys but this is getting about as anal as checking the brake fluid level in the master cylinders even thought the brakes workEd last night, as checking the torque on the prop making sure the prop safety wire has not broke and the prop might come off, as checking the tire pressure is within +\- 5 psi, as checking to making sure grease is actually in the wheel bearings jeese for bid the wheels lock up upon landing or no brakes work because we were too lazy to get the 3/4 inch wrench to check the brake fluid even though the brakes worked fine yesterday and nobody else flew the plane or that we were too lazy to jack up and pull the main wheels to check for grease in the bearings each and every flight because we were paranoid that the last flights landing used up the last dobber of grease in the bearing which might cause the plane to nose over...LOL!!!!!!!! BTW When was the last time you checked your CARS oil level?
 
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