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582 compression

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droadrunner(at)juno.com
Guest

Posted: Wed Jul 30, 2008 5:49 am Post subject: 582 compression

What is a satisfactory compression on a 582?

Should it be checked with the engine warm?

Should it be checked by pulling the prop through or using the starter to

actually spin the prop?

Is the compression test a good indicator of the need for an overhaul?

Thanks,

Marlin

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Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Wed Jul 30, 2008 6:28 am Post subject: 582 compression

For the reasons you mentioned, irregularities in speed of turning over the

prop (crank) and weird things that happen to the seal the rings make to the

cylinder read differently with heat.  I recommend using a differential

pressure meter.  Feed it with 80 psi of air and read the differential

pressure with the piston being read at TDC.  Readings of 70 or better are

considered execlent.



Used on four stroke engines the Differential meter will also detect and help

diagnose bad valves as well as bad rings or cylinders.  Two strokes

obviously don't have the valve trains so the only thing left is the ring

seals.



Noel



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Noel Loveys
Kitfox III-A
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rparigor(at)suffolk.lib.n
Guest

Posted: Wed Jul 30, 2008 7:30 am Post subject: 582 compression

Hi Noel



"I recommend using a differential

 	  Quote: 	
		   pressure meter.  Feed it with 80 psi of air and read the differential

 pressure with the piston being read at TDC.  Readings of 70 or better are

 considered execlent."


	


Just a quick note on differential meters, I know on the 914 Rotax

specifies how large the supply orifice needs to be on the differential

meter.



Lets go extremes for a minute, take a differential meter designed for a

diesel with a 3 foot diameter piston and take a compression test on a

Model Cox .010cu" with the piston not even in place, you will probably

show pretty good compression.



If you use a differential meter for a Lyc or a Cont with too large of a

supply orifice on a 914 the reading can show 80 over 80 even with a

problem.



On the other hand if you use too small of a supply orifice for Lyc or

Cont, can show low even without a problem.



Ron Parigoris

ptag.dev(at)tiscali.co.uk
Guest

Posted: Wed Jul 30, 2008 8:56 am Post subject: 582 compression

Noel/all

If you use a differential compression meter then please ensure someone

holds the propeller tight on Top dead centre before you feed the

compressed air to the cylinder ....otherwise you could get a severe

crack on the head.

Better be safe. If you are using this kit on a four stroke engine then

get a medical stethoscope, fit a length of small diameter  pipe to it to

listen up the carb, up the exhaust pipe and lastly down the oil filler

on a wet sump engine (this will identify where the gas is escaping and

so highlight the likely fault. On the Rotax with the dry sump there's no

where to listen for the rings passing gas, but if it's not loosing gas

from carb or exhaust then piston rings are all that's left to leak !

Regards

Bob Harrison



--

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Thu Jul 31, 2008 3:18 am Post subject: 582 compression

Differential compression test is the better way to go and should be

done with the engine warm. After all, you fly the airplane when the

engine is warm, no? The numbers you get will frequently be lower when

done cold. The numbers you get on one day can be a little different

from what you get on another day due to rings walking a bit during

engine operation, but not dramatically so.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Thu Jul 31, 2008 7:29 pm Post subject: 582 compression

Good point!  But even with a slightly oversize orifice you will be able to

tell if your compression is good or not so good.  One thing I didn't mention

is it is recommended to be a two or more man job.  The cylinder under test

has to be held at TDC while the reading is being made.  It is surprising

exactly how quickly a prop will get away from you if you aren't careful

holding at TDC.  The better the compression, the bigger the bore, the more

careful you will want to be.  I was surprised to find a differential meter

set at a local auto supply shop the other day.



Noel



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Kitfox III-A
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Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Thu Jul 31, 2008 7:32 pm Post subject: 582 compression

More great points!  When I made the original post I really expected to get a

little flamed for suggesting the differential Pressure gauge.  You guys are

really on the ball!



Noel



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Kitfox III-A
Aerocet 1100 Floats

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Fri Aug 01, 2008 11:14 am Post subject: Re: 582 compression

Hi Guys,



Everybody has certainly good advice. There are two test. One is the static test, where you turn the engine over and just read its top pressure. 

I am not sure what the 582 static pressure is supposed to be. The static pressures on the 912 typically run between 140-175psi depending on which engine you have and if it is fairly new or has a lot of time on it. The other test is the differential test. You need a differential tester with a master orifice size of .040. You indeed do find the top dead center of each piston you test. You can put your finger over the hole and you should at some point during the prop rotation feel the pressure coming out. When it starts to suck on your finger then you are a little too far. TDC is where the pressure and the sucking stop. You can use a piece of plastic to insert in the spark plug hole to check TDC also. For the 912uls your compressor side of the gage should be 87 psi and if you are right at TDC the guy holding the prop won't have much work to do, but heaven forbid you are too far either way. The pressure will want to rip the prop out of his hands. The lowest number you want to see on this test is 65psi. You don't want to see a 25% drop.  Then some maintenance needs to be done. If you are a little too far either way on TDC you may hear some air out of the exhaust or the carbs. If you are right on TDC you should be able to take the oil cap off and slightly hear some air escaping. This is normal. Some air, I didn't say all the air. I just did two annuals and pressure test. One 912uls had 100 hrs. the other had 200 hrs. The readings were 86/84psi. They had a leak down of only 2 psi. This is very good.

The 582 has steel cylinder inserts and aluminum pistons. These metals heat up at different rates. Run a 582 from a cold start in the morning and don't warm it up you could end up with a cold seizer. This engine needs to be warmed up before running it hard. The 912 is a totally different metallurgy.

Before you do either test you have to have an engine at or about it's operating temps for good accurate readings.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
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Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Sat Aug 02, 2008 4:51 am Post subject: 582 compression

I haven't done a differential test on a 4 stroke Rotax engine yet... but..

on the lycomings sometimes you will have to jiggle the prop a bit to get the

valves to seat. (that's what the boss said)  That is when the prop can

really get away from you!  My idea is if the valve train is clean you won't

need to jiggle.  I can see where if you are running a geared nose the torque

produced will be multiplied and the accuracy of the TDC will be very narrow.



Noel



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Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

occom

Joined: 26 Aug 2006
Posts: 404

Posted: Sat Aug 02, 2008 7:18 am Post subject: 582 compression

I'm sure others are more knowledgable in this procedure than I, but I have 

been dealing with two stokes for many years and would like to throw a very 

large caution out there. If you happen to apply 70 or 80 PSI to a two stroke 

engine, and for any reason the crankcase seals either by lower the piston 

for a 503 or if the rotary valve covers the port in the 582, then I would 

very much expect to blow the seals on the crankshaft. The seals cannot be 

replaced on the inner sides of the crank without dissassembly and 

reassembled cranks are not supposed to be used on aircraft according to 

Rotax. Just a thought.



Do not archive

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Sat Aug 02, 2008 10:42 am Post subject: 582 compression

That's just another couple of reasons to keep the cylinder under test at

TDC.  If there is a leak through the rings any pressure will be released

through the base into the exhaust port.



Noel



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