R

rv7plt

Member
I now have 12 hours on my ECI freedom cylinders on my IO 360 200 hp engine and decided to perform a compression check. I found that the compressions are all around 75 psi at TDC. However, if I rotate the prop forward 10-15 degrees I hear a "clunk" from inside the engine and then return the prop to TDC the compressions are all about 4 psi higher. I removed a rocker cover and felt the valves as I heard the "clunk" and could not feel any movement there. I do not hear that noise when I pull the prop though by hand with or without the plugs installed.

Thought I would see if any of you gurus have any ideas about what could be going on in my engine.

John in Florida
 
That's the rings clunking into the bottom of the ring groove. I ease forward then shove back beyond TDC to make the rings clunk on the compression side and then come forward to TDC.
 
Check warm

Remember to check the compression on a warm engine also, not cold.

rv7plt said:
I now have 12 hours on my ECI freedom cylinders on my IO 360 200 hp engine and decided to perform a compression check. I found that the compressions are all around 75 psi at TDC.
Click to expand...
 
How about counter balance weights? Doesn't explain any compression value changes, but could explain the clunk. Jim. P.S. my continental 520 clanks too.
 
Perfectly normal!

rv7plt said:
I now have 12 hours on my ECI freedom cylinders on my IO 360 200 hp engine and decided to perform a compression check. I found that the compressions are all around 75 psi at TDC. However, if I rotate the prop forward 10-15 degrees I hear a "clunk" from inside the engine and then return the prop to TDC the compressions are all about 4 psi higher. I removed a rocker cover and felt the valves as I heard the "clunk" and could not feel any movement there. I do not hear that noise when I pull the prop though by hand with or without the plugs installed.

Thought I would see if any of you gurus have any ideas about what could be going on in my engine.

John in Florida
Click to expand...

Like others have said, it's the rings.
I would describe it as more a of a "click or snap" than a "clunk"....right?
It you watch the compression gage it will jump up with the click.
The rings are just clicking into proper position.

Mark
 
I suppose it could be the rings clunking. It is definately not the impulse coupling as that is at TDC and the clunk is after tdc. I don't buy the counter weight theory since it does not clunk without the air pressure on the cylinder. I have tried it hot and cold. My concern is that at Tdc when I have ignition, I have a pressure leak for some reason and am losing power and efficency.

I have done compression checks on other engines and have never observed this phenomon. Keep the opionions coming.

John in Florida
 
Mine do it also

I have new ECI's on a 540 and it does the same thing. I do not have an impulse mag on mine due to EI.

My thought was it was the cold piston being smaller than the bore and the noise is the piston rocking in the bore and you here the piston skirt "clunk".

Mine does not do it when the engine is hot so that would lead me to think that it is not the rings but I could be wrong.

Just my thoughts.......usualy worthless:rolleyes:
 
Dude, I've been doing compression checks for a living for 30 years. Its the rings and it is normal.
 
You have the answer already sir

rv7plt said:
I suppose it could be the rings clunking. It is definately not the impulse coupling as that is at TDC and the clunk is after tdc. I don't buy the counter weight theory since it does not clunk without the air pressure on the cylinder. I have tried it hot and cold. My concern is that at Tdc when I have ignition, I have a pressure leak for some reason and am losing power and efficency.

I have done compression checks on other engines and have never observed this phenomon. Keep the opionions coming.

John in Florida
Click to expand...

John,
You've had an I.A. and two A&P's tell you it's the rings and it's ok.
Find something else to worry about:)

Mark
 
Last edited:
Bavafa said:
Why not do a differential compression check and that tells you where the leak is, if any.
Click to expand...


I'm pretty sure that's what he was doing............. ;)
Rings "Snap" or "Clunk" during differential compression checks......... As they should........ All is well.

What is NOT known is: why did the OP decide to do a compression check after 12 hours on the engine?? :confused: Were there some onerous symptoms?

Sometimes I think we have too much data these days.

Just my $0.02. (Two cents)

(BTW, isn't it time to do away with the penny? It isn't worth your time to bend over and pick up a penny. And they cost more to produce than they are worth.) OK, ........stepping down from the soapbox.....:eek:
 
rocketbob said:
Ditto... A R-1340 sounds pretty neat on compression checks. :)
Click to expand...

A Pratt-Whitney R-1340 sounds pretty neat doing anything it does! Compression check, pulling it through for start, starting it (especially), running it up, full noise for takeoff (most of which comes from the prop on a T-6), and even shutting it down.

Well, ........ one man's opinion, anyway. [And......... in no way am I prejudiced!] :rolleyes:
 
Compression checks have very little to do with power produced. Many engines produce rated power that would miserably fail a standard compression check. I would be concerned where the leak was.
 
Picture the piston/rings at TDC with air pressure on the jug. Because of the geometry, that is the point where you can move the prop blade the most with the least amount of piston movement. The rings are sealed against the cylinder wall by air pressure and don't move easily. You can move the prop tip an inch or so each way and the piston is going up and down slightly but the rings don't move until you've taken up the slack because the ring groove is quite a bit wider than the ring. On a new (clean) engine you'd better be able to make this clunk noise or there's something wrong. On an older engine the rings get thinner and the groove gets bigger (slightly) so you should still be able to make the "clunk". If you CAN'T make the noise it almost always means the rings are coked up from oil and are sticking in the grooves. The OP did a compression check because he was curious. Nothing wrong with that even though the only real data your going to get is a go/no go result. I personally wouldn't have bothered with one because I can pull one through by hand and tell you within 2 punds what the compression is. Other people with less experience may get a better handle by doing a comp check. Fine. Maybe I need to add a bunch of letters onto my signature? These conjecture postings do nothing but muddy the waters. There's some whiz-bang mo' fo's on this forum and a couple of them have posted on this thread. When they speak....listen and think. Don't just randomly hypothesize.
 
You must log in or register to reply here.