Preflight Checks for piston engines

[QJB]

Hi all,

Just wondering if anyone can give me some good preflight checks for GA piston engine aircraft. I'm flying a C172 RG Cutlass II currently, and I've been taught some basic checks by my flying school, i.e check that this hose is secure, that belt etc. Just wondering if there are any other good ones that are not generally taught. A mate of mine suggested, making sure the mags are off and giving the prop a pull through to check each cylinders compression. Any others come to mind?

Cheers J

[MarkerInbound]

So how are you measuring the compression, with a calibrated wrist? Just remember, just because the key is off DOESN"T always mean the mags are grounded.

[Tarq57]

No point in pulling the prop through to check compression. I believe that on some engines that was considered normal, but the reason was to let oil out of the combustion chambers ( Gypsys, Wrights and the like.)

Look to the POH for what to check- which covers all the normal things, or your local flying school/aero club. I reckon anything not in the manual is really the territory of a LAME to be peering into.

[DA-10mm]

if you're doing a "pull through" with the prop on your pre-flight, hopefully the guy/gal who flew the thing before you did a magneto ground wire check/test prior to his/her shut down.
if not, you could be in for a big surprise if things aren't as they should be.

[clearedtocross]

It is not a bad idea to check compression occasionally in the way described above, particularly after a longer winter pause. Sticking valves are not unusual and can be detected that way. Listen for funny noises as well as you move the prop. But you should hear the klick of the mags.

Do it in a way you do not get hurt if the engine catches or backfires. If you are not able to pull the engine through easily because the engine is stronger than you, leave it to the mechanic at the next annual.

check the condition of the exhaust / heating / carb heater / muffler assembly occasionally as leaks can be deadly due to carbon monoxide inhalation.

And keep thy airspeed up! luckily, there are no autothrottle issues in a cutlass!

[Jumbo Driver]

Originally Posted by QJB

... A mate of mine suggested, making sure the mags are off and giving the prop a pull through to check each cylinders compression ...

Originally Posted by Tarq57

No point in pulling the prop through to check compression.

Yes there is a point, I regularly pull through my engine (90hp) before start - always before the first start of the day when all is cold and quite often otherwise.

What are the advantages? First, if you do it regularly, it is possible to detect a difference in compression between pots. This is not through a "calibrated wrist" but simply because each cylinder can be compared with the previous and following cylinders. You will not find a small difference but a significant loss of compression will be obvious, whereas in flight it may not be noticeable. Second, if you have a stuck valve - or exhaust valve leak - you will hear this through the exhaust as you pull through. You also are likely to hear air moving/hissing within, if you have (say) a broken piston ring. None of these may be detectable either during run-up or static checks, or in normal flight. You will also hear the "click" of the impulse mag(s) as the engine turns.

Furthermore, if you prime before you pull through, you will be "sucking in" a fuel/air charge to each cylinder which makes the work of the starter (whether it be electric or Armstrong) easier, as the start becomes almost immediate, saving cranking the engine before start, which not only wears the starter and engage assembly but also can deplete the battery. Following this procedure, my engine will routinely fire on the first turn with switches ON. If it doesn't, that is usually indicative of another problem, like oiled plug(s).

There are plenty of advantages to a routine manual "pull through" of a small piston engine before start - don't let anyone tell you otherwise - although once you get much above 100hp, the effort required will make it progressively harder work.


JD

[snrub]

Be very wary of the prop QJB,

Its just not worth it remember to accident always happens to the other guy, and guess what you are the other guy to me!

[Tee Emm]

Yes there is a point, I regularly pull through my engine (90hp) before start - always before the first start of the day when all is cold and quite often otherwise.

What are the advantages? First, if you do it regularly, it is possible to detect a difference

All very fine if you own your own aircraft, and know each tick, click, buzz and rattle and roll intimately. But try that with a flying school aircraft and then write up the various tick,click, buzz and rattle and roll in the maintenance document - and you haven't even flown the plane yet and you can guarantee the flying school will tell you to go fly someone else's banger but not theirs.

The manufacturer's Pilot Information Manual gives you all the minimum required information to operate the aircraft safely and you will notice nowhere does it mention carefully turning the prop to check the compression in each cylinder or priming the engine before hand turning the prop to make starting easier. And never rely entirely on the advice from instructors at any flying school. They may look cool in their pilot suits with bars and wings and big watches but the majority are hardly out of flying school themselves and all they know is what their instructor told them and so on.

[captjns]

There are plenty of advantages to a routine manual "pull through" of a small piston engine before start - don't let anyone tell you otherwise - although once you get much above 100hp, the effort required will make it progressively harder work.

Nah... I perform a check on my IO-540-C4B5s every time I fly my Aztec. Been doing it since I bought my E model in June of 1976. I do it for two reasons.

Make sure there is are no unusual pressures during the pull through, and no unusual grinding from the accessary section.

[QJB]

Thanks for all of the responses, I didn't really mean to create such a controversy with the prop pulling suggestion.

The manufacturer's Pilot Information Manual gives you all the minimum required information to operate the aircraft safely

I'm sure that this is correct in some sense, but I don't think its the right attitude, I was more looking for a few tips that the old blokes you see around the place use. You know the old, "don't forget to do this sonny it may just save your life one day". I hear what everyone is saying about the prop pulling, and I don't intend to do it myself unless I've been taught the proper way.

And never rely entirely on the advice from instructors at any flying school. They may look cool in their pilot suits with bars and wings and big watches but the majority are hardly out of flying school themselves and all they know is what their instructor told them and so on.

Don't worry I realised some time ago to anything that ANYONE in aviation says with a grain of salt, and to talk up if you think they are wrong.

Many thanks again for all the replies,

J

[Tarq57]

Well, for anyone doing this, another thing to bear in mind (apart from the whole lethality issue) is don't turn it backwards.
Some vacuum pumps can have the vanes damaged if this is done.

[captjns]

Well, for anyone doing this, another thing to bear in mind (apart from the whole lethality issue) is don't turn it backwards.

Some vacuum pumps can have the vanes damaged if this is done.

Give the man a cigar. The accessory drive section and components contained there on are designed to rotate in one… and only one direction. You will not cause any harm to the alternator/generator, hydraulic pump, or oil pump… but the vacuum pump??? you can sure hurt that component.

[bfisk]

Just do what the checklist says. Cessna knows best.

[werbil]

Had a cutlass with a stuck exhaust valve found by pulling the prop through. There was no mistaking it - no resistance. Engineers flew up and the did the 'old rope trick'.

When pulling props though always ensure:
Mixture is in idle cutoff
Throttle is at low idle
Mags are off
Brakes are on, chocks are in, and preferably tied down as well.
Always, always pull in a manner and from a position that if it starts the prop isn't going to touch you.
No loose clothing (ties etc)

From memory with the 172 RG at TDC the propeller is at a very difficult position - not an aircraft that I'd be in any hurry to hand start.

One engineer I know is very definite about the direction of rotation - always backwards - as a result of having seen someone cut up by a prop.

[SNS3Guppy]

A mate of mine suggested, making sure the mags are off and giving the prop a pull through to check each cylinders compression.

What you're accomplishing by pulling the propeller through isn't checking compressions or engine function, but removing residual oil from cylinder walls, and exposing yourself to unnecessary hazard. Otherwise, you're not accomplishing anything.

Yes there is a point, I regularly pull through my engine (90hp) before start - always before the first start of the day when all is cold and quite often otherwise.

Really? There's something about the temperature of the engine which suggests it's best to do it when cold, or there's any advantage based on cylinder temperature? As stated before, what you're doing is removing residual lubricant on cylinder walls and causing wear, and nothing more. What has horsepower to do with the price of tea in china? Neither the rated horsepower (exactly how much hp is your engine producing when it's not running?) nor the displacement is relevant.

What are the advantages? First, if you do it regularly, it is possible to detect a difference in compression between pots. This is not through a "calibrated wrist" but simply because each cylinder can be compared with the previous and following cylinders. You will not find a small difference but a significant loss of compression will be obvious, whereas in flight it may not be noticeable. Second, if you have a stuck valve - or exhaust valve leak - you will hear this through the exhaust as you pull through. You also are likely to hear air moving/hissing within, if you have (say) a broken piston ring. None of these may be detectable either during run-up or static checks, or in normal flight. You will also hear the "click" of the impulse mag(s) as the engine turns.

It's possible to detect a difference in compression between cylinders? This is the speech of the layman. Most knowledgeable mechanics understand that engine compression means very little, while most laymen place some degree of stockin it it as a symbol of engine health. Test compression five times and you'll get five different values. Test it hot and cold and you'll get different values. Have two different people test it, and you'll get...everybody say it together...different values. Yet you can do it without a calibrated compression tester, simply pulling the propeller through by hand. Most remarkable.

You can tell if you have an exhaust valve leak by pulling the propeller through by hand? Really? It's time to give up being a private pilot and go become a mechanic, because you're on the edge of a miraculous breakthrough. Sort of like the guys who touch bare wires and profess to know the voltage and amperage to the tenth value.

Further, you're telling us that you can detect by hand what can't be detected during an engine run? Truly amazing, you are. Without test equipment and nothing but magic calibrated fingers, you can detect things with the engine that can't even be detected when it's running. Wow.

You really think you're going to hear a broken piston ring? You really think this will make a change in compression, most of the time? (it won't). You may even subscribe to the myth that piston rings lined up will cause a loss of compression, but the truth is that a broken piston ring, most of the time, will do little more for you than cause excess wear. This is why we use more than one ring.

As far as listening to the impulse coupling, this tells you nothing, and is more akin to examining your handgun by looking down the barrel from the muzzle end...it makes very little sense.

Furthermore, if you prime before you pull through, you will be "sucking in" a fuel/air charge to each cylinder which makes the work of the starter (whether it be electric or Armstrong) easier, as the start becomes almost immediate, saving cranking the engine before start, which not only wears the starter and engage assembly but also can deplete the battery. Following this procedure, my engine will routinely fire on the first turn with switches ON. If it doesn't, that is usually indicative of another problem, like oiled plug(s).

Ah, priming and then moving the propeller by hand...there's a wise move if ever there was one. Putting a fuel charge in the motor and then moving the propeller...places you at even greater risk, and if you do manage to actually get fuel into the cylinder and not draining back down the intake manifold, you're simply using a solvent to wash the remaining fuel off the cylinder walls and further increase wear as you pull the propeller through by hand.

Have you thought this through, at all?

As far as what to look for during the prefligt...the "checklist" is not the be-all and end-all of inspecting your engine. You should touch, tug on, feel, move, inspect, illuminate, and test everything you possibly can during a preflight, and that includes your engine. While you've got access to the engine, either bent down on the ground looking up through the underside of the cowl, or while looking in the oil filler door or dipstick door, use a flashlight and look around. Look for exhaust stains, fluid leaks, components of the engine touching one another (such as hoses touching baffling or the induction manifold) and causing wear, wires that are frayed or bare, fuel stains, loose or disconnected spark plug leads, etc. Make sure your oil filler cap is fully in place, as well as the dipstick. When you drain your fuel sump don't simply let it go on the ground. Catch it, feel it, smell it, inspect it...make sure not only that there's no water, but that it's really the proper fuel. Check the engine mounts and mount assembly for rust, pitting, straightness, and wear. Check for oil leaks, and fuel leaks. Look for shiny areas between cylinder heads indicating a crack or a lifting cylinder head. Check the front crankshaft seal for leakage, and the oil filter adapter (if applicable) for security...it's an AD requiring inspection on every flight, for some aircraft/engines). Verify that the air filter is secure, and check the rigging of the throttle, mixture, and carburetor heat from the cockpit for full travel, no binding.

Inspect the propeller for nicks, scratches, cracks, pitting. Small imperfections in the propeller leading edge or face can lead to cracking and failure; these should be "dressed out" with a file by a qualified mechanic ("engineer"). Check for security. Check the spinner for security. Always run your hands and fingers all over the propeller to feel it. Don't simply look. Check that the distance between the spinner and the engine cowling is the same above and below. You're checking for a drooping engine mount or buckled firewall (common on this airplane from landing hard on the nosewheel). Look for evidence of dirt or grease the cowling, propeller or nosegear. If you find any, determine if it's fresh or old, and if possible, the source. Engines, like airplanes, talk to you with a quiet voice, often warning you with little things of bigger things to come. Get to know the little things and address them before they become the big things.

Check the cowl itself for uniformity, security, and that all fasteners are in place, not loose, and without cracks surrounding the fastener holes or access. Look down the cowl from the front, across the clinders and try to spot tennis shoes, bird nests, or the odd grenade (things that ought not be there)...mechanic's tools, etc. Always be on the lookout for the things you don't find...continuously ask yourself "what is it that I've missed?" and then go find it.

Look on other parts of the airplane for clues as to the engine health. Look at the exhaust stack. Give it a tug, see that it doesn't move. Look at the color of the deposits in the exhaust; this tells you a lot not only about the health of the engine, but also it's care and how it's been operated. Look down the belly to see how much oil is there, and on the windshield to see about oil or other evidence of leakage.

Verify the starter drive (bendix drive) isn't engaged. Look for an alternator belt. Tug on it. Try to hand turn the spark plug lead connectors nearest the cowl entrance; ensure they're tight.

You needn't simply pull out the checklist and follow along blindly. Look at everything; it's all worthy of your attention. Extra time spent scrutinizing the airplane is for your own safety, and for your benefit. Take full advantage.

[Jumbo Driver]

SNS3Guppy, you are clearly not the expert I might once have thought you were. You are entitled to express an opinion on what I have written, of course - but why in such an aggressive and opinionated manner? I am not going to sink to your level and trade insults.

I stand by what I posted ... and yes, thank you, I have thought it through. Perhaps you should realise that yours is not the only opinion of worth on this forum.


JD

[SNS3Guppy]

Your contribution to the thread is noted, jumbo driver. Now, have you anything worthwhile to contribute?

As long as that doesn't appear to be the case, we might as well address your final salient point before you went off the reservation...

There are plenty of advantages to a routine manual "pull through" of a small piston engine before start - don't let anyone tell you otherwise - although once you get much above 100hp, the effort required will make it progressively harder work.

Now I may not be the "expert you once thought I was," but I've spent a lot of time pulling through R985's, R1340's, R2600's, R2800's, R3350's, and R4360's...each of which has just a tad more than "100 hp" (again...the engine has displacement, but produces NO horsepower when it's not running; you understand this, right?). These engines actually have a legitimate reason for pulling through in certain cases, when checking for hydraulic lock...but even in those cases, even when we were all qualified mechanics and "engineers," none of us ever was arrogant enough to assume we could tell the compression or identify internal faults by pulling an engine through.

Limit yourself to 100 hp, you say? As you wish.

I work with a couple of very experienced individuals who have both taken prop strikes to the skull. You keep on rotating that propeller with it's charge of fuel and believing what you will...because after all, you've thought it through. You've no valid reason for it, but again...as you will and as you wish. Best of luck to you and your sub-100 horsepower behemoth. I certainly hope that one day it doesn't bite you in the back.

[captjns]

Used to fly the DH-2 on floats. It has the R-985 Jr Wasp motor attached to the front. Part of our pre-flight procedure was to check for hydraulic locks with the pull of the prop.

Important checklist item for the newbies... remember to take a towel a change of clothes and shoes down to the dock. Oh yeah... remember to put your keys and wallet in a neoprene carrier and leave them on the dock before pulling the prop through. Oh yeah.... Summer time operations are preferable.

Wouldn't fly any other plane on floats in its class.

[Jumbo Driver]

Originally Posted by SNS3Guppy

Your contribution to the thread is noted, jumbo driver. Now, have you anything worthwhile to contribute?

As long as that doesn't appear to be the case, we might as well address your final salient point before you went off the reservation...

There you go again ...

May I remind you this forum is intended to be informative, to discuss facts and offer opinions. It is not the arena for unprovoked personal attacks or ridicule, as you are doing. You are both misrepresenting my views and then rubbishing the result in a highly personal and disdainful manner.

As I have said, I stand by my post and I fully accept that others may hold different views. You may indeed have some experience which is worth bringing to this forum but if you do so in a way that is sarcastic, offensive and personal, rather than informative and objective, you will neither be respected nor be furthering the aims of PPRuNe.

Have a nice day ...


JD

[stevef]

Vacuum Pumps

Sorry - it's a myth about not turning the engine backwards by hand: it doesn't harm the carbon vanes. The only way you can damage the vanes is to fit a clockwise-rotating pump onto a counter-clockwise drive (CW - CCW) or vice-versa and then run the engine. I've got a letter to this effect from the Parker-Hannefin Service Department.
Props are routinely rotated backwards during maintenance during magneto timing with no adverse effect.
The quickest way to kill a vacuum pump is to let oil/solvents get onto the vanes.