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ryan4321

Jabiru 3300 - Leak Down Test Results

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Hi Everyone,

 

I am looking to purchase a J400 and it has 480 hours and leak downs are...

 

48/80

 

55/80

 

60/80

 

62/80

 

62/80

 

68/80

 

Is this good / bad / cause for concern?

 

I spoke to the sellers LAME and he said these results can change pretty dramatically from test to test and it is nothing to worry about (with regard to some low values) he said as long as the RPM is okay (which supposedly it is). He said he has a leakdown on another plane at early 40's and then next test this cylinder was 70+ so it just depends on the ring position at the time (not 100% sure if this is exactly how he worded it.

 

He however said there is no cause for concern and although it isn't his preferred engine. There is no need to worry about it stopping.

 

Noting too sorry that the engine has had new valves, heads, camshaft and these are 200 hours old.

 

Appreciate any thoughts.

 

 

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The log books should show the figures for the cylinders for each annual or 100 hrs service. Check them out for a trend. It depends where the leak is. A good LAME will know if it is rings, inlet or outlet valve. You may consider getting an independent LAME to inspect the aircraft and to look at the log books. A lot can be gotten by what is in the log books and what is not in the log books. Buyer beware. If you don't know much about aircraft be very, very careful. I would suggest you are very much in a buyer's market especially when talking Jabiru.

 

 

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I don't know much about leak down testing (very little) but to have a cylinder go from low 40s one test to 70 plus for that same cylinder seems a bit weird to me. Maybe it's normal but I just thought that sounds like the 'tester' maybe not testing 100% correctly?

 

From what I've heard most people trust leak down testing enough that when they get a low number (not sure what individuals threshold is for that) they are very quick to investigate further before another flight.

 

 

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From my limited experience - the lower pressures could indicate that exhaust valves are starting to not seal leading to burn valve face and stem, or rings are starting to stick dropping power and burning or throwing oil out the exhaust - either is cause for further investigation before something bad happens when you don't want the engine stopping. It can very quickly go from low compressions to valve heads rolling around in the cylinder with the piston so worth taking seriously. Worth looking into for a little grief now to avoid a major problem later.

 

 

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You could track it down to rings or valves by doing a leak down test with compressed air into the spark plug hole with a proper adaptor . On top dead centre firing stroke you will hear air coming out the exhaust if it's the ex valve,out of the carbie if it's the inlet valve and out of the dipstick and breather holes if it's the rings. The one down to 48 is certainly a concern hope this helps.

 

 

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Get your own LAME to look at the aircraft and logbooks as has been advised.

 

Sadly for Jab owners this is a buyers market, good for buyers of course.

 

Personally I think Jabs would be good potential purchases at the moment. They will eventually fix this problem, or just buy one at the right price and fit a CAE engine and you are laughing.

 

 

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Guest Andys@coffs

it could be as he says a transient low, but if that's the case go with him do a circuit or 2 land and redo the leakdowns, they don't take long....if it doesn't Improve on redo then its an issue. it could be as simple as a quick head removal and a valve reseat, or it could be as a result of corrosion in the bore or rings as others have said. Either way removing the heads can give a qualified with jab motor L2 a bunch of info that can be used to determine the health of the engine.

 

Check and see how long it took to do the 200 hours after the last overhaul....if he flys less than fortnightly, then I'd suspect corrosion in the bores. They have to be flown regularly or corrosion is a fact......

 

Id also go back to before the overhaul and see which cylinders were low then...if its the same then I'd also be concerned that cooling might be an issue. Does it have EGT/CHT for all cylinders, if so what are the temps?

 

Andy

 

 

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Guest Andys@coffs

oops so it is....not many 400's on the raaus register....none the less, in your neck of the wood, I'd take Keith Rules advice on jab engines over most LAME's.....You need someone who knows what they are doing and not someone who has rarely seen one and avoids them like the plague.....

 

Andy

 

 

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As mentioned above, it is never a good idea to use the same LAME to inspect an Aeroplane that they regularly maintain .There is a conflict of interest, the LAME is never going to burn himself if he suddenly finds something wrong.

 

The LAME you use should be independant of the particular aircraft.

 

 

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a Jab with just under 500 hours with low compression? 013_thumb_down.gif.ec9b015e1f55d2c21de270e93cbe940b.gif

 

I'd look around for one that already has a fixed engine.

 

 

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a Jab with just under 500 hours with low compression? 013_thumb_down.gif.ec9b015e1f55d2c21de270e93cbe940b.gif

I'd look around for one that already has a fixed engine.

FT it had a cylinder head refurbishment only 200 hrs ago, perhaps it should have had a 'Top' overhaul.

 

 

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When I bought my plane I asked a local LAME if he would inspect the plane for me. His first comment was so long as its not one that I maintain. I thought that was the perfect answer.

 

 

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I would be concerned how much use it has had lately. More is better..You can check the bores with a boroscope for scratches and any evidence of corrosion. The LAME should know where it is leaking (refer post#6). Not just which cylinder. A proper job would have done this. Nev

 

 

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I was thinking that engine has sat for a while and the bores have rusted up and loaded the rings with rust. Either way let it be someone else's problem, there are plenty of Jabs on the market.

 

 

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It is a good price and I have been told by the LAME that previous tests were 75 on the cylinder that were showing 48. He said it is quite variable and if a leak down was done again it should be okay again. He also mentioned it was likely the rings (ie not valves or other) so it isn't as significant also.

 

I have factored in a new CAE 3300 engine also in the pricing of this one so if I get 100 - 200 hours I will be happy :)

 

 

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A L2 or LAME should be able to clear or not a low compression, just sayong it was 75 and now is 40 isnt good enough

 

Check how it was done, hot, cold where was the leak going

 

Possibly follow manual on leak testing from Jabiru. Manuals on web

 

Alternative is to discount price and swap engine out to CAE core rebuild

 

 

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All pretty ordinary figures. I do believe the jab maintenance manual puts a lower limit of 60/80. I could be wrong, just from memory. If LAME says it could be good next time then run it and do it again and see. If it is inside spec ok if not, find out why not.

 

I wouldn't be flying it! Tom

 

 

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Sounds like it is already sold to me!

 

100-200 hours can be a long time with a J-motor.

 

Having said that I just bought an airplane with a J-motor because it was priced well enough to change out the motor. But to be sure I do not intend to fly it for 100 to 200 hours before I do it. In fact tomorrow if you are down the waterfront at Wynnum I can sell you a very cheap boat anchor.

 

 

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You are being taken for a fool, as a LAME and Jabiru owner ( 2 of! one with 4cyl and one with 6cyl) if I saw numbers like that the engine would be pulled immediately. That engine needs work before it can be classified as airworthy. The LAME in question is referring to continentals which have a very broad definition on leak down tests. Jabiru's don't! If you are keen include the cost of a rebuild in the purchase price and make it a condition of sale. Experience with these engines had led me to start searching for an issue when the leakdown a hit 70/80.

 

 

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It is a good price and I have been told by the LAME that previous tests were 75 on the cylinder that were showing 48. He said it is quite variable and if a leak down was done again it should be okay again. He also mentioned it was likely the rings (ie not valves or other) so it isn't as significant also.

I have factored in a new CAE 3300 engine also in the pricing of this one so if I get 100 - 200 hours I will be happy :)

Re read post 11

 

 

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