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By riverrock
#1586296
Lycoming https://www.lycoming.com/sites/default/ ... rcraft.pdf

Service Letter No. L180B wrote:Pulling engines through by hand when the aircraft is not run or flown for a week or so is not recommended. Pulling the engine through by hand prior to start or to minimize rust and corrosion does more harm than good. The cylinder walls, piston, rings, cam and cam follower only receive splash and vapor lubrication. When the prop is pulled through by hand, the rings wipe oil from cylinder walls. The cam load created by the valve train wipes oil off the cam and followers. After two or three times of pulling the engine through by hand without engine starts, the cylinders, cam and followers are left without a proper oil film.
Starting engines without proper lubrication can cause scuffing and scoring of parts resulting in excessive wear.
(my bold)

I suspect the difference is speed - a starter is much faster than slowing pulling a prop through, so can still do the splash lubrication.
Last edited by riverrock on Thu Jan 25, 2018 5:27 pm, edited 1 time in total.
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By Lockhaven
#1586297
Service Letter No. L180B wrote:
Pulling engines through by hand when the aircraft is not run or flown for a week or so is not recommended. Pulling the engine through by hand prior to start or to minimize rust and corrosion does more harm than good. The cylinder walls, piston, rings, cam and cam follower only receive splash and vapor lubrication. When the prop is pulled through by hand, the rings wipe oil from cylinder walls. The cam load created by the valve train wipes oil off the cam and followers. After two or three times of pulling the engine through by hand without engine starts, the cylinders, cam and followers are left without a proper oil film.
Starting engines without proper lubrication can cause scuffing and scoring of parts resulting in excessive wear.


The key to it is don't pull the engine through if you are then not going to start the engine and operate it normally.

It cannot be any different to just starting the engine without first pulling it through except the starter is turning it over and scrapping oil off the cylinders.

Or another way of looking at it, what if you don't have an electric starter then you are always pulling through to prime prior to a hand swing start.
By cockney steve
#1593323
That's all quite logical, but, in my opinion, an Engineering fudge.

If the magneto is turning fast enough to disconnect the impulse-action, It should be giving adequate output (a decent spark) anyway..

The spring always unwinds at the same rate, the variation in timing under impulse can only be due to the number of crankshaft-degrees of rotation travelled between the impulse release and the spring fully unwinding. Stopping the Mag. rotation, winding the spring and then giving the Mag, a smart rotational "flick" Is the basis of the operation. The whole issue is a lot more complex than a simple overview would have you believe.
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By Paul_Sengupta
#1593380
As I understood the above, the spring is changed so that the ignition timing *with* the impulse mag is changed. There's no suggestion of the starter being so fast that it disables the impulse coupling.
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By Sooty25
#1593398
pulling an engine through by hand doesn't spin the oil pump fast enough to create any flow or pressure, made worse with cold oil.

Invariably, hand started engines need to be pulled through in order to prime the cylinders ready for the starting swing. A no win situation.

On our hand started engine, we have a pre-lube, oil priming quick connection, to which we connect a garden weedkiller pump bottle full of aeroshell before the first start of each day. On colder days this is stood in a bucket of hot water to make the oil flow easier. A quarter to Half a litre of oil is pumped directly into the engine on the pressure side of the oil pump. This gives us oil where we need it when pulling through and instantaneous oil pressure when she starts. Being an inverted inline engine, there will invariably be oil sitting on the crank side of the rings anyway, unlike your flat fours.

Most big industrial engines in ships, trains, generators etc have electric pre-lube pumps doing exactly the same to prevent start up wear.
By cockney steve
#1593431
IIRC, it's the position of the static catch that determines the Impulse-timing.
The centrifugal pawl engages, the mag stops turning, the engine continues turning ,the spring winds up , the release, on the engine-part, comes round and trips the pawl off the static catch.
The really important thing is to time the Mag "break" (where the rotating poles break the magnetic flux) at the correct relationship with the points- break......this is far more important than the actual size of the points-gap. (though altering the points-gap also alters the spark-timing in relation to the engine crankshaft.

set the points and flux-break , then time to crank.
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By Sooty25
#1593476
soon be time aviation adopted that new fangled electronic ignition stuff, I bet its more reliable! :thumleft:
By cockney steve
#1593524
The beauty of the magneto, is this archaic device is a completely self-contained ignition-system.

The electronic system needs a generator, a battery, a magic box, a crank-position sensor and an ignition-coil

lots of potential failure-points in the wiring between the parts.
The magic box rarely gives any indication that the magic is about to run out....It just stops working. Very occasionally, the smoke will escape,- it's obviously the stuff that makes the magic work, without it, you have a dead box. You have to feed it with electrickery, I f that runs out, the box will hibernate until it gets the proper supply. Coil or sensor problems invariably cause a fit of sulks. the box will send erratic, or bad sparks. the engine will cough and splutter and try to spit them out. Usually, it has a "go-slow" protest, then goes on strike.

The magneto works, it has one wire, other than the plug-leads If that wire breaks, or the switch on the end goes faulty, it will ignore your desires and carry on working. The engine, however, needs fuel..starve it and it will stop. The magneto, however, will be eager to please and will give a friendly "belt" to the incautious.

Yer pays yer money , yer takes yer choice.

Here endeth today's lesson. :lol:
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By Sooty25
#1593645
so thats why the hard shoulders are full of broken down cars!

the automotive industry moved away from unreliable points, condensers and rotor arms for a reason, its archaic and high maintenance. Guess what is in a magneto!

You can still have dual redundant systems, just build a small alternator into a magneto size housing for your second power source.
By cockney steve
#1593773
Automotive industry moved from coil/dizzy for cost, plus ,of course, they could charge a premium price for the electronic ignition.
Distributor needed a drive -gear, vacuum advance and sometimes a retard capsule, centrifugal advance, with individual springs for each variant , a precision-ground points-cam......... Magic box = pickup coil, hall-effect rotor , a couple of standard chips, a few components and a program to flash the chips.
IIRC, the Rotax engines use(d) Ducati electronic Ignition....As can be expected of Italian electrics, they live down to their reputation and replacements are scandalously expensive....so much so, that somebody in Holland, is rebuilding these "sealed units" for about £100 a pop.
Overall, yes, electronic ignition is very reliable, but needs to be priced cheap enough that holding a spare is a viable strategy.

Alternators were a similar marketing con. greater output, smaller, lighter, no external electro-mechanical regulator, no mass of wiring between reg and dynamo, charge more for far less ! but, again, a superior solution to power-generation.