|
-
POSTING RULES

-
Donate yearly (please).
-
Advertise in here!
-
Today's Posts
|
Insert Pics
|

08-06-2017, 03:43 PM
|
|
|
|
Join Date: Jan 2005
Location: San Antonio, TX
Posts: 1,024
|
|
You could also verify that the plug for the primer inlet is still there. I have seen that missing before.
Also, check for cracks between the spark plug holes and verify the injector is tight.
You didn't say what engine, but some Titan cylinders require regular inspection to verify that the head isn't loosening. Just sayin'
__________________
Steve Formhals
A&P, Tech Counselor & Flight Advisor
RV3B
RV8
|

08-06-2017, 03:53 PM
|
|
|
|
Join Date: Dec 2007
Location: Fredericksburg, TX
Posts: 662
|
|
It sounds to me like you have a leak in either an exhaust valve or intake valve on #1 and the #3 cylinder exhaust or intake valve is open so you are hearing the air leaking out of the #1 valve, through the intake or exhaust manifold and out the open valve in the #3 cylinder.
__________________
Jim Averett
RV-8
TS36 - Silver Wings
Fredericksburg, TX
|

08-06-2017, 09:13 PM
|
|
|
|
Join Date: Apr 2016
Location: Bucking ham, Virginia
Posts: 208
|
|
In the first post you said you can hear air @ the spark plug, remove that plug feel the seat with your finger dose it feel good and smooth or snaggey/ruff .A louse pug can erode the seat also if plug seized to the helicore insert it could have backed out a bit. Temporarily for compression check only replace copper washer with an O-ring with a good slavering of fuel lube for a good seal and do the differential pessure test again.
__________________
Maule MXT-7(daily flyer)
Lancer 235(partner)
Raidial RV-8R Ephanage Done, Wings Done, Fuselage on it's tall Grove gear & engine hung
|

08-07-2017, 12:17 AM
|
|
|
|
Join Date: Aug 2009
Location: Redding,Ca
Posts: 633
|
|
You might want to bleed the hydraulic assemblies and check the valve lash on those cylinders. It's possible they were not set correctly and with normal wear the lash is gone and the valves are not seating fully.
If I'm not mistaken, this is suppose to be done after the first 200-300 hrs anyway.
Tim Andres
|

08-07-2017, 06:34 AM
|
 |
|
|
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 2,596
|
|
Thanks
I appreciate the thoughtful responses.
I too assumed the intake valve on #1 was the culprit (not fully seating). Reading reports of this happening on Lycoming engines however all had the same pre-conditions - the engine ran very rough. This engine runs smooth as glass and considering the EGTs and CHTs are tracking with the other cylinders, we conclude #1 is making power.
I do know that Continental did a test on what happens when piston rings are filed short such that the compression check is 0/80. The engine still produced full power.
The airplane owner (a Lancair 360) has sent all the data to the engine shop that built this engine for their recommendation. I suspect we'll be pulling that jug just to make sure.
Carl
|

08-07-2017, 07:05 AM
|
|
|
|
Join Date: Apr 2016
Location: Bucking ham, Virginia
Posts: 208
|
|
I know of 2 lanceairs from Dogwood. One's a world record setter, the other is an AME for NASA is it one of these gentlemen?
__________________
Maule MXT-7(daily flyer)
Lancer 235(partner)
Raidial RV-8R Ephanage Done, Wings Done, Fuselage on it's tall Grove gear & engine hung
|

08-07-2017, 07:16 AM
|
 |
|
|
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 2,596
|
|
Quote:
Originally Posted by VA Maule
I know of 2 lanceairs from Dogwood. One's a world record setter, the other is an AME for NASA is it one of these gentlemen?
|
Yep - the Lancair 360 guy.
Carl
|

08-07-2017, 08:30 AM
|
|
|
|
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,297
|
|
Quote:
Originally Posted by Carl Froehlich
I appreciate the thoughtful responses.
I too assumed the intake valve on #1 was the culprit (not fully seating). Reading reports of this happening on Lycoming engines however all had the same pre-conditions - the engine ran very rough. This engine runs smooth as glass and considering the EGTs and CHTs are tracking with the other cylinders, we conclude #1 is making power.
I do know that Continental did a test on what happens when piston rings are filed short such that the compression check is 0/80. The engine still produced full power.
The airplane owner (a Lancair 360) has sent all the data to the engine shop that built this engine for their recommendation. I suspect we'll be pulling that jug just to make sure.
Carl
|
You are correct. Leak down testing is not a good test for gauging performance issues. In the automotive world the go to test is a dynamic compression test, measuring the actual compression, in PSI, produced by the cylinder while spinning. Leak down tests are a secondary test to help pinpoint specific problems and provide a general guide to cyl wall / ring interface condition. As you have seen, a cylinder with poor leak down results can still produce solid dynamic compression when the source of the leak is ring/wall. This is because of the static environment. Once the piston is moving, the leakage is reduced and also less relevant.
The fact that you were making good power on the cylinder was the reason I suspected stuck rings. They typically still produce enough power to be unnoticeable.
Larry
__________________
N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
Last edited by lr172 : 08-07-2017 at 08:38 AM.
|

08-07-2017, 09:50 AM
|
|
|
|
Join Date: Sep 2007
Location: Central IL
Posts: 5,516
|
|
Quote:
Originally Posted by lr172
You are correct. Leak down testing is not a good test for gauging performance issues. In the automotive world the go to test is a dynamic compression test, measuring the actual compression, in PSI, produced by the cylinder while spinning. Leak down tests are a secondary test to help pinpoint specific problems and provide a general guide to cyl wall / ring interface condition. As you have seen, a cylinder with poor leak down results can still produce solid dynamic compression when the source of the leak is ring/wall. This is because of the static environment. Once the piston is moving, the leakage is reduced and also less relevant.
The fact that you were making good power on the cylinder was the reason I suspected stuck rings. They typically still produce enough power to be unnoticeable.
Larry
|
The compression test (rotating) is a less repeatable and less sensitive test than a leak down test. I always counted the compression strokes to compare cylinders.
If it was a stuck ring (certainly one of a general list of possibilities), the "leak" would not blow air out another open spark plug.
Let's be careful about supporting idea that a bad leak down test is not relevant even if a compression test is good. While one might fly home, a small leak certainly may not affect idle or power - yet, but - it should be heeded as something to investigate. "Investigate" means it can produce false results, but that needs to be verified. In this case, it could be a piece of carbon under the intake valve or a tight valve at the limit of the lash adjuster. A list of things could cause a tight valve.
Good thing to get the engine builder involved at relatively low hours.
__________________
Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
|

08-08-2017, 02:22 PM
|
|
|
|
Join Date: Oct 2012
Location: Scottsdale, AZ
Posts: 150
|
|
Quote:
Originally Posted by dtw_rv6
Mike Busch claims that compression readings have no correlation at all to an engines ability to make full rates power. It only tells you if the engine will consume oil.
Continental says to borescope the cylinders to determine their condition. If that is okay then fly for (??) hours and then redo the compression test.
Don
|
See https://www.aopa.org/news-and-media/...ance-borescope
A compression test measures static compression. You slowly bring up the pressure and hold it, but that's not what happens when your engine is running. During the compression stroke the piston is moving very rapidly and while I'm sure the underlying physics are more complicated, there essentially isn't time for enough air to leak. 5/80 is pretty low and if you can't bump it higher by pushing on the prop then you might have a more serious leak (like the loose plug that someone mentioned), but if the borescope looks good and the engine runs fine then you are probably just going to go through a lot of oil. There might another problem that someone more knowledgeable can point to, but a compression test is not a reliable or repeatable test and shouldn't be used as the basis for airworthiness.
|
Posting Rules
|
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts
HTML code is Off
|
|
|
All times are GMT -6. The time now is 04:27 AM.
|