pressurizing the intake pipes

[Bruce Tuncks]

I was really impressed with how Horsham Aviation are putting pressure onto the induction pipes of a Lycoming engine and then testing for leaks with soapy water. They found that 3 out of 4 induction pipes had a leak on an engine I know.

 

Has anybody an idea about how you would use this method on a Jabiru engine?

 

You would have to block off the carby area somehow... could you do this by blocking the carby at the carby inlet?

 

This would apply the pressure to the carby and via the plenum to all the other induction pipes.

 

Maybe this is ok, does anybody know more?

 

 

[facthunter]

Soapy water is commonly used to test for gas leaks. You don't need to apply much pressure. To test the inlet system turn the motor slowly backwards with the throttle left at idle position. There's no vac pump to worry about. You will slightly purge the oil system but cranking it on the starter will fix that, or apply compressed air to air intake with throttle open and don't turn it at all. Nev

 

 

[onetrack]

Spraying a small squirt of Ether (starter fluid) around the intake manifold joins while the engine is running with high manifold vacuum (as at idle), is one way of picking up intake manifold leaks. The engine RPM increases when it sucks in the Ether.

 

However, you need to do this in a well-ventilated area, and you need to ensure that there's no ignition sources nearby.

 

 

[Old Koreelah]

Spraying a small squirt of Ether (starter fluid) around the intake manifold joins while the engine is running with high manifold vacuum (as at idle), is one way of picking up intake manifold leaks. The engine RPM increases when it sucks in the Ether.However, you need to do this in a well-ventilated area, and you need to ensure that there's no ignition sources nearby.

I prefer Nev's method, Onetrack. No spinning prop to worry about.

Last year a LAME replaced one of my intake tube seals, which was leaking badly. Been running evenly since.

 

 

[Bruce Tuncks]

I dunno how come I never heard about this before. I like how quick the ether trick would be but I agree about the prop being a hazard.

 

If you make up a plug to fit the carby intake, then apply pressure with compressed air, this means that you are applying pressure to the carby ( are there bleed-holes to leak or could you do any damage to the bing diaphragm?) then all the intake pipes are pressurized and all the intake valves must be closed ?

 

 

[facthunter]

Some air can go right through a motor when the valves are both off the seats in any particular cylinder. This won't stop the principle working. You only need a small pressure to get a leak indication with soapy water. (a few PSI) The dashpot diaphragm works from differential pressure. It won't move much if at all. Nev

 

 

[Old Koreelah]

Probably easier to remove the carbie and plug off the intake duct. Lots of people have jerried-up a leak-down tester by drilling out an old spark plug. Similar technique, but turning prop to open intake valves.

 

(Edit: Nev's post appeared while I was typing this; I'd defer to his experience.)

 

 

[facthunter]

IF you have one rocker cover off you can rotate the engine to have that inlet valve open and apply the pressure to a fitting in one of the spark plug holes. It's overkill as only a small pressure is advised but no problem if you do it that way. You could blow up a party ballon and use that as an air source for the manifold test.

 

Soapy water is used to check head joint leaks and also cracks if in a pressurised area. When you do your leakdown test, spray some around the exterior head area. (Usual care with prop restraint). Nev

 

 

[Bruce Tuncks]

Thanks Nev, yes I have a spark-plug leak-down tester and use it all the time. So if the cylinder with the compressed air (injected at a spark-plug fitting) has the intake valve open and the exhaust valve closed then air will go to the intake manifold via the open inlet valve.

 

And with the throttle at idle, the carby should be mainly shut down , although idle setting still has the butterfly valve open a bit.

 

If the other cylinders have their inlet valves closed ( which I think must be the case ) , this setup should give at least a few psi to all the inlet pipes, with the main leakage being through the carby.

 

If this carby leakage is too much, then a plug of some sort at the carby entrance should raise the pressure in the inlet manifold. It is much easier to remove the hose from the air filter box to the carby and block this off than it is to remove the carby itself and block the inlet plenum entrance .

 

Have I got this right? If so, I will give it a go soon.

 

 

[facthunter]

The most I'd do is wind the Carb. idle stop back a set distance to close it, (say 2 turns) and later return it to where it was exactly. Bubbles is all you need as an indication . A few psi is plenty to get the result. Wash the soap off with water afterwards to prevent staining. Nev

 

 

[bexrbetter]

Are you going to use the bathtub or a kids blowup swimming pool for this test?

 

 

 

[spacesailor]

They did that on the " de Havilland Comet"

 

Put it in a large bath to test the decompression effects.

 

Then scrapped it!.

 

spacesailor

 

 

 

[dholder]

I do this all the time. I fill a squirt bottle that squirts a stream, like a plastic Leak-Tek bottle, with denatured alcohol. With the engine running at idle, squirt each intake connection. The engine rpm will change noticeably if there is a leak. Takes only a minute to do.

 

 

[Bruce Tuncks]

What is denatured alcohol dholder?

 

Here we have methylated spirits, which is poisoned ethyl alcohol. We can also get isopropyl alcohol at great cost, I think this is cheap in the US where it is called rubbing alcohol. There is also methyl alcohol, used for model plane fuel, and as one of the poisons in methylated spirits.

 

For the purpose of squirting an engine, we have some stuff containing ether in a spray can, it is called " Start Ya Bastard"

 

 

[Old Koreelah]

...For the purpose of squirting an engine, we have some stuff containing ether in a spray can, it is called " Start Ya Bastard"

...which we should never use to start a delicate aero engine.

[Bruce Tuncks]

I didn't know that old k, not that I ever have used it for starting. I was referring to spraying it onto the induction joints to see if the engine reacted, which would be evidence of a leak at that joint.

 

 

[facthunter]

The reaction to a bit of extra combustibles is not predictable and it's not without risk. IF there's a big air leak the extra "fuel" will make it run better but normally idling mixtures are richer anyhow. That's how they are set. Don't work near a running aero engine unless you are taking effective extra precautions and MUST do it. It's ridiculously dangerous. In fact I would suggest you don't do it at all.

 

Soap solution shows even small leaks well as it foams, stays long enough to check out exactly where the leak is and another squirt will start the process off again without any risk to anything other than what water will affect and your aero engine has to cope with water from time to time. Nev

 

 

[dholder]

Methylated spirits according to wikipedia. Not dangerous at all if used with common sense. It is not so highly volatile.

 

 

[onetrack]

which we should never use to start a delicate aero engine.

Yes, overuse of ether trying to start old, tired and cranky engines, has led to more than one broken piston ring.

 

 

[onetrack]

Don't work near a running aero engine unless you are taking effective extra precautions and MUST do it. It's ridiculously dangerous. In fact I would suggest you don't do it at all.

Good advice. It was always drummed into us - and it was often written on the first page of many workshop manuals - that "the first law of safety is to never try to adjust, maintain, or repair machinery that is in motion".

 

However, once in a thousand times, there is a need to have something running to find the source of a problem - trying to find the source of a noise when running, is typical.

 

In that event, the advice of my old Sgt that always rang in our ears when we started to work on live mines or other deadly explosives, was - "Switch On, Men!!".

 

In other words, increase your alertness, be very aware of the result of simple mistakes, don't work tired, and don't become complacent.

 

 

[Old Koreelah]

Methylated spirits according to wikipedia. Not dangerous at all if used with common sense. It is not so highly volatile.

In rural Australia, where few have the patience for the Boy-Scout method of lighting a fire, metho is commonly known as "woof water".

 

 

[bexrbetter]

In rural Australia, where few have the patience for the Boy-Scout method of lighting a fire, metho is commonly known as "woof water".

in Logan City we just called it a Liqueur.

 

 

[Bruce Tuncks]

And its not denatured... you can get good and drunk on metho. The aborigines used to have a drink of metho and milk, they called it "white lady".

 

That was before they were allowed to buy booze. Yep, my memory goes back that far.

 

Methyl alcohol is always present in natural fermentation ethanol to some small extent. It is what gives the hangover headache, and moonshiners called it "wood alcohol".

 

 

[Old Koreelah]

...Methyl alcohol is always present in natural fermentation ethanol to some small extent. It is what gives the hangover headache, and moonshiners called it "wood alcohol".

Are you sure it's not the preservatives, Bruce?

I've never had a headache after drinking pure German beer- even litres of it!

 

 

[bexrbetter]

I've never had a headache after drinking pure German beer- even litres of it!

But you're meant to have days off, that's when the headaches come.