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Compression numbers ?

31 posts in this topic

Posted

 

What TJ said.  Throttle has to be wide open.

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Posted

Depends. Are you doing a leak down test or an automotive test where you spin the engine with the starter?

For a leak down, best to be a warm engine and readings can be as low as 80/60, but 80/75 or better is very good.

For the automotive test, pull the plugs and spin the engine with the throttle wide open. You should see 120 PSI.

John M

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Posted (edited)

When you run the auto compression test...not the leak down test...make sure the throttle is wide open to get the best reading when you crank the engine. I just did one on my Jabiru and got around 160 PSI on all four. I believe I used to get 120 PSI on my 582.

 I have flown behind the Rotax 2 strokes for over 3,000 hours. This included the 447, 503 and 582. Most of it was done in ultralights and then in AvidFlyer experimental aircraft.  The avid is now powered by the Jabiru 2200.

 I have had a good reliability experience with the Rotax, but opted for the Jabiru as opposed to the Rotax 912 due to the high cost of the engine and parts plus the complexity makes the installation very cramped in my Avid Flyer. I also wanted better fuel economy and liked running at 2800 cruise as opposed to 5800. The only drawback is that I used to swing a 70" WARP but with no gearbox, I now swing a 66" Whirlwind prop. 

My climb rate with both engines is about the same for the 64 HP Rotax as opposed to the 85 HP Jabiru. I also like the sound better. Easier on the ears because most ANR headsets are designed to reduce sound in the 2000-3000 RPM range. The higher frequency of the 582 gets through.

Rotax recommends a TBO of 300 hours on the 582, but I used to get around 500 hours TBO. This is because I flew often. No winter shut down due to winter weather here in SoCal. I used 100% synthetic oil at 100:1 ratio so the oil injector was not necessary and was disabled.

I am surprised that you can get 6500 RPM on a ground static run. In my opinion, you don't have enough pitch in the prop. If you get that on the ground this means you can over rev the engine in level flight. You should get a better cruise with a bit more pitch.

A compression test is required for condition inspection. That said, my A&P never did one on my Rotax or my Jabiru, but he has since passed and the new guy wants one.

Hope this was of some help.

John M

 

 

 

Edited by skypics

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Posted

I did a leak down test on a snowmobile engine many years ago what a pain in the butt. Just stick with an simple compression tester and not one from Harbor freight.

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Posted

I prefer to use a basic compression tester on a 2 stroke because the is only two places for the air to escape, past the rings or head gasket.

On a 4 stroke a leak down test is better because it has four places for the air to leak by. Intake valve, exhaust valve, head gasket and rings.

You can open the throttle to listen for air leaking past the intake valves. Exhaust pipe for exhaust valve issue. Oil cap for a ring problem. Bubbles in the coolant for a head gasket failure.

Brooks

 

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Posted

Make sure the throttle is wide open when you do the auto type compression test.

John M

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