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Engine Leak Tester


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not actually much to them, two gauges and an orifice, obviously need good quality gauges.

 

Most important is the fittings and setup suits the engine otherwise youll have to change all that.

 

Jabiru are an "odd" size by GA standards

 

 

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The object of a leak down test is to determine how well pressure is held within the combustion chamber of a cylinder. This is done by introducing air at a known pressure to the cylinder via the spark plug hole, and observing the ability of the sealing elements (rings and valves) to hold that pressure. Therefore a leak down tool has two gauges. One to measure the introduced pressure, and one to measure the pressure within the cylinder.

 

The two readings are compared and reported in the order- Cylinder Pressure, Introduced Pressure eg 72/80. The results may also be reported as a percentage (Cylinder Pressure divided by Introduced Pressure x 100 [72/80 x 100 = 92%]). It must be noted that these results are dimensionless ratios, and are compared to a manufacturer's published minimum requirement for the engine. If the result falls below the minimum requirement, then further inspection and repair is required.

 

Since the result is merely a comparison of the readings of two gauges, then, as long as the gauges are of similar accuracy, then the quality of the gauges is not of great concern. In purchasing a tester, I would look at whether the kit contained adapters for 14mm and 18mm spark plug holes, and how the valve controlling the introduced pressure. For a Jabiru engine, you should supply 80 psi, so you also need a compressor that will produce and hold that pressure. AND - CAUTION . Doing this job is dangerous. You need someone to hold the prop against the introduced pressure. If you don't you could get a nasty whack.

 

I had a look on Ebay and I think that this one: http://www.ebay.com.au/itm/0-100PSI-Leak-Down-Engine-Cylinder-Leakage-Gauge-Tester-Testing-Auto-Tool-Kit-/161617083624 would suit your needs. I assume that you are an owner, wanting to be able to check things before you head off to an maintenance shop.

 

The one I looked at had a nice carry box, which is important in protecting the tool and for keeping all the bits and pieces together.

 

Old Man Emu

 

 

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I bought similar, however, got rid of flexible hoses, new push on couplers to suit every thing else I had, and ended up getting rid of % gauge for two psi versions.

 

think regulator died so it was replaced too. Also fitted small valve on incoming air so I could control when it was on or off AFTER i had hold of the prop.

 

BUT for $40 theres not much other better way to buy adapters and orifice block even if thats all you keep and use over time. So its a good recommendation.

 

Now it fits rigid to engine in use, adapter has male coupler, disconnect gauges and hose to move to next cyl. , gauges face you when holding prop, open small ball valve slowly to test, quickly turn off if theres any problems.

 

 

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there are many available where the 2nd gauge shows percentage on the scale...for the ones I have seen they only work when the source pressure is 100psi. Both gauges are the same psi rating so as long as you can extrapolate you'll be Ok. On mine I used a permanent texta to mark the glass with psi markings after the hose to the plug adapter was crimped off and I adjusted the regulator to give various psi down to 10psi.

 

Andy

 

P.S there are different sized restriction orifice sizes (no im not talking about plug size...different thing), obviously if it was designed for thumping great monsters then the orifice and the compressor need to be bigger....to be IAW your manual you need to be very sure that the size is the same as the manufacturer specifies

 

 

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  • 2 weeks later...

I bought the same off eBay. Wasn't useable in stock format. Took a lot of modification ( like fitting .040 " orifice and different guage. Better off buying one from an aviation supplier, about $120 or so

 

Tom

 

 

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Your time has to be worth something. Get the right thing from the start, if it's available. Most aircraft engines have 18 mm plugs. ( The GA stuff Generally cars are 14 mm and some bike engines and Jabiru are smaller)..Nev

 

 

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I bought one of the eBay types a while back, my advice - don't bother as it is unusable

Hi Tony, did you get another one? If yes, what and where?

Cheers Peter

 

 

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Hello Peter... flown that Onex yet?

 

Not yet, intend to borrow one for the next compression check.

 

Thought about making one out of the bits, I can reuse the plug adapters and hose.

 

 

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Guest Maj Millard

The suggested orifice in the leak down tested by the engine manufacturer is important if you want readings to be useful and accurate. Buying the tester that has the on/ off tap on the air supply to the cylinder is useful and makes the whole proceedure quicker and safer. Spend the extra money. Leakdowns are best done with two persons involved...one operating the tester...one holding the prop.

 

In the states (GA) minimum cylinder pressure allowed is 50/80 PSI....here in Oz the powers decided our air is different to the rest of the world, and set the lower acceptable limit to 60/80 PSI.....strangely they are exactly the same engines worldwide so once again us thinking we know more than the engine manufacturers.

 

Doing leakdown checks on a cold engine is pointless....most engine manufacturers recommend these checks be performed with the engine at normal operating temps. This is to ensure the thermal expansions of up to around eight different metals within the engine. ( Pistons, rings, cyl heads, cylinders, valves, valve seats, valve guides, case) to ensure correct and proper sealing of all these items. You also want that film of oil on the cylinder walls to properly seal the rings. You are after all checking that all these components are leak free and holding required compression in a normal operating scenero.

 

 

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If it's been sitting for a while most engines are going to give a poor reading (or two) If you know what you are looking for, pulling the prop through will give you an idea how you are going, but if it feels reasonable go for a good fly before doing the test where you record the figures. If it's an impulse magneto equipped engine, be careful and on those engines I would take steps to make sure the magneto cannot possibly fire. That requires more than just turning the switches off. Nev

 

 

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If it's been sitting for a while most engines are going to give a poor reading (or two) If you know what you are looking for, pulling the prop through will give you an idea how you are going, but if it feels reasonable go for a good fly before doing the test where you record the figures. If it's an impulse magneto equipped engine, be careful and on those engines I would take steps to make sure the magneto cannot possibly fire. That requires more than just turning the switches off. Nev

Standard minimum safety precautions are to turn off fuel, mixture to idle cutoff, throttle to idle.mags off

 

 

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This is the latest guidance from CASA regarding engine leak testing.https://www.casa.gov.au/sites/g/files/net351/f/AWB 85-019.pdf

So on Page 3..sect 3 sect 1 and 2..it clearly indicates engine should not only be warm, but at full operating temps plus a film of fresh lubricating oil should be present on the bores. Pretty much what I was taught under the FAA system of training, and also aligns with AC43.13 recommendations.

A lot of mechanics will drop the oil the first thing the aircraft comes in the hangar, after the required engine run.

 

I don't,.....I jump straight onto the compression checks while everything is hot and I drop the oil after that is done. Keeping the hot oil in the engine helps keep the engine warm also for longer. This is handy particularly if you have a 'soft' cylinder and need to retest, as is sometimes the case on certain engines.

 

Compression testing of 912s ( although a requirement) needs to be done as part of normal servicing however, in my opinion is usually a waste of time as I've yet to find a cylinder below normal specs ...unless of course that engine is very high time.

 

 

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The 912 holds compression well. Perhaps running with avgas may cause a loss sometimes with exhaust valve leakage, which usually rectifies itself if returned to mogas. Might not happen every time. Nev

 

 

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That AWB from CASA was a waste of space. Anyone who thatw as directed to already has all that knowledge. But I suppose the staff of CASA have to find something to do.

 

 

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  • 1 month later...

There was a great article from Mike Busch about the leak-down test being not nearly as good as a camera inspection of the valves. You could google it up I reckon.

 

Jab7252, if you have not got one yet, you are welcome to borrow mine.

 

I still think that it is a useful thing to do, and it will help you calibrate your pull-through check. You do the pull-through and note down what you think the compressions are, but of course you don't have the cylinder numbers at this stage.

 

 

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The only real inspection of a valve that is worthwhile is to remove it clean it thoroughly and inspect it. If it has been over heated it may show fine cracks on the stem near the hot end of the valve. It could also be warped and have pitting on the seat. If I was running a Jabiru I would replace the exhaust valves anytime I thought they might be suss and in any case at around 400 hours. It's cheap insurance.(Relatively) Nev

 

 

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