Quantifying exhaust valve leaks

Let'sgoflying!

Let'sgoflying!

Touchdown! Greaser!
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Dave Taylor
When I was doing my compressions I thought I heard a difference at the exhaust on cyl#2. I didn't think it was louder, just different. (my hearing has been tested and its ok) There are always several minutes between cylinders such I find it hard to remember what the last one sounded like. Also, there is definitely 'referred' sound in the exhaust from leakage past the rings; I have heard that on every engine I've ever been around during a compression test. I posted earlier; how could I verify or quantify leakage past an exhaust valve?

I tried two methods.

A) the cell phone dB meter method. At airplane-side, I downloaded SLA lite dB meter. I stuck the phone at the exhaust stack, trying to maintain the same position for each cylinder. I also put it over the open oil filler neck. Here are the readings:
Cylinder# /Compression (hot)
dB exhaust / dB oil filler

1/75 48/73dB
2/73 66/75
3/78 50/81
4/74 60/84
5/74 45/85
6/76 45/82
ambient dB in the room was 35-43dB

The exhaust noise was highest in cyl#2 (and it had one of the lowest oil filler readings) so I tried another Rube Goldberg test.
I pressurized it from the exhaust stack while it was at tdc compression stroke, I have a way of attaching a pressure regulator to the exhaust pipe (mainly used to inspect for leaks). I set it to about 7psi and watched how much air is coming from the spark plug hole via the compression testor adapter hose. Check out the videos of cyls 2 (and 6 for comparison). There is obviously way more bubbles being produced from cyl2.

I'd still like to actually measure the amount of leakage from the exhaust valve but that will either be later, or when someone takes my idea to the next stage!

(high-time IO-520, 800+ on Superior Milleniums, no changes in compressions over several years, 1qt/30yrs (edit; hours not yrs), no problems, running strong, filter looks normal, LOP at cruise but only cruise.)

Links to YT videos of 'bubbling':
ExValveCyl2
ExValveCyl6

Ex valve scopings attached in order 123456
1Ex.jpg 2Ex1.jpg 3Ex.jpg 4Ex.jpg 5Ex.jpg

Before I work on these valves, I will be scoping them again, in the open position to get a look at the sealing surface if I can.
 

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Let'sgoflying! said:
When I was doing my compressions I thought I heard a difference at the exhaust on cyl#2. I didn't think it was louder, just different. (my hearing has been tested and its ok) There are always several minutes between cylinders such I find it hard to remember what the last one sounded like. Also, there is definitely 'referred' sound in the exhaust from leakage past the rings; I have heard that on every engine I've ever been around during a compression test. I posted earlier; how could I verify or quantify leakage past an exhaust valve?

I tried two methods.

A) the cell phone dB meter method. At airplane-side, I downloaded SLA lite dB meter. I stuck the phone at the exhaust stack, trying to maintain the same position for each cylinder. I also put it over the open oil filler neck. Here are the readings:
Cylinder# /Compression (hot)
dB exhaust / dB oil filler

1/75 48/73dB
2/73 66/75
3/78 50/81
4/74 60/84
5/74 45/85
6/76 45/82
ambient dB in the room was 35-43dB

The exhaust noise was highest in cyl#2 (and it had one of the lowest oil filler readings) so I tried another Rube Goldberg test.
I pressurized it from the exhaust stack while it was at tdc compression stroke, I have a way of attaching a pressure regulator to the exhaust pipe (mainly used to inspect for leaks). I set it to about 7psi and watched how much air is coming from the spark plug hole via the compression testor adapter hose. Check out the videos of cyls 2 (and 6 for comparison). There is obviously way more bubbles being produced from cyl2.

I'd still like to actually measure the amount of leakage from the exhaust valve but that will either be later, or when someone takes my idea to the next stage!

(high-time IO-520, 800+ on Superior Milleniums, no changes in compressions over several years, 1qt/30yrs, no problems, running strong, filter looks normal, LOP at cruise but only cruise.)

Links to YT videos of 'bubbling':
ExValveCyl2
ExValveCyl6

Ex valve scopings attached in order 123456
View attachment 57115 View attachment 57116 View attachment 57117 View attachment 57118 View attachment 57119

Before I work on these valves, I will be scoping them again, in the open position to get a look at the sealing surface if I can.
Click to expand...

This looks pretty normal.
 
In my own path of ownership I 'we been shown how big Continental engine E valve leaks are usually related to worn guides and that's usually related to poor geometry and contact between rocker and valve. Performance minded cylinder shops can correct the rocker contact and that will keep your valve guides happy and E valves sealing nicely.
 
> " . . .cylinder shops can correct the rocker contact and that will keep your valve guides happy . . ."

How do they do that? That is, how do they correct the rocker contact if the geometry is off? Serious question . . . not looking to argue about anything.
 
They square up the contact surfaces. If the rocker only contacts the forward edge of the valve that valve is trying to tilt in the guide. Eventually the guide wears as a result.
 
Valve looks normal. I see no hot marks and the pattern is concentrical. I'd scope it again in 50 hours. Do you have pics from a prior check? How does this compare? If you don't have pics, start saving & hour and time stamp so you have references. This will allow you to compare over time.
 
Stewartb said:
They square up the contact surfaces. If the rocker only contacts the forward edge of the valve that valve is trying to tilt in the guide. Eventually the guide wears as a result.
Click to expand...

That relationship is extremely important because exactly as you've said, pressure exerted that's not perfectly centered will cause guide wear . . . and it's all downhill from there. I know my guides are perfectly placed and valves perfectly concentric upon the seats because I've had my engine apart to look at these things. I KEEP everything so perfectly placed by using swivels (elephant feet) at point of contact between rocker arm and valve stem. Are these not allowed in engines used in certified aircraft? Sounds like not . . . and if not, I wonder why? A cylinder shop can adjust that relationship at one point in time, with re-adjustments as time goes by. With swivels, wear is compensated for automatically for the life of those particular valves, rocker arms and guides. I currently live in the Experimental world so I'm assuming swivel tips are not approved for use in engines in non-Experimental categories? I've witnessed the dramatic superiority provided by swivels, so I'm wondering why they aren't used more widely . . . if that is indeed the case.
 
MikeS said:
That relationship is extremely important because exactly as you've said, pressure exerted that's not perfectly centered will cause guide wear . . . and it's all downhill from there. I know my guides are perfectly placed and valves perfectly concentric upon the seats because I've had my engine apart to look at these things. I KEEP everything so perfectly placed by using swivels (elephant feet) at point of contact between rocker arm and valve stem. Are these not allowed in engines used in certified aircraft? Sounds like not . . . and if not, I wonder why? A cylinder shop can adjust that relationship at one point in time, with re-adjustments as time goes by. With swivels, wear is compensated for automatically for the life of those particular valves, rocker arms and guides. I currently live in the Experimental world so I'm assuming swivel tips are not approved for use in engines in non-Experimental categories? I've witnessed the dramatic superiority provided by swivels, so I'm wondering why they aren't used more widely . . . if that is indeed the case.
Click to expand...

Mike, can you point me at a source for swivels?

Paul
 
All good reading. I would like to start scoping my cylinders. What is a reasonably priced scope? I have been looking around and the prices are all over the board.
 
Ablescope, Bill. under 200$ ebay etc
get the one with a swiveling head and the newer ones are sealed at the tip from liquids.
 
PaulMillner said:
Mike, can you point me at a source for swivels?

Paul
Click to expand...
Sorry no . . . I was hoping to learn why swivel adjusters aren't used normally in certified aircraft application. It's possible rollers are used but I don't even know that for sure at this point. Interesting subject.
 
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