Enlightening webinar on compression testing

Timbeck2

Timbeck2

Final Approach
Joined
Nov 4, 2015
Messages
9,176
Location
Vail, Arizona
Display Name
Display name:
Timbeck2
I don't know if this has been posted before but for those aircraft owners who may be hung up on the compression readings of your cylinders at your annual, it explains a lot about compression testing and other things about engine health.

Bottom line up front - your compressions could be in the 50s and still have a healthy engine

 
Where you work as DOD Tim? I was on google earth looking at the boneyard. Those AF or DOD controllers at DM?
 
Timbeck2 said:
Bottom line up front - your compressions could be in the 50s and still have a healthy engine
Click to expand...
Don't believe TCM's tripe,, for the little engines 0-200 / 0-300 when those cylinders leak, they need to be repaired " NOW"
 
I think zero pounds of compression may indicate a problem. At least my A&P thought so a week or so ago. Piston scuffing also is thought to be a problem I guess - who knew? Anyway, nothing 4 new cylinders and pistons won't fix
 
Your engine may have a cylinder with low compression that means it is sick, but it may run well, but it is still sick.
It won't fix its self.
 
mscard88 said:
Where you work as DOD Tim? I was on google earth looking at the boneyard. Those AF or DOD controllers at DM?
Click to expand...

Four of us are DoD which are all retired chief controllers, the rest are all military.
 
Timbeck2 said:
You didn't watch the webinar then did you Tom? ;)
Click to expand...
I have,, it's just understanding dynamic compression vs the static compression. If it leaks, it leaks.. no magic there. will it run leaking, yes, is it going to get better all by its self? no.
 
Judging from that answer and question, I don't think you've actually seen that webinar.
 
This is all you need:

6595923.jpg


Or maybe this one:

1417553693.png



When I was young, there were a number of such products available that would "rebuild" your engine as you drove. Of course, they did little or no good and could even make things a lot worse. Truth-in-advertising laws, plus the advent of way too many hungry lawyers, got rid of this sort of nonsense.

Low compression can be cause by several things, but the usual suspects are worn or sticking rings or leaking valves--usually the exhaust. A leaking exhaust valve is only going to get worse, since it is leaking superheated gases that erode the valve and seat. Let it go far enough and you could be faced with a new valve instead of a valve grind. Or the valve head gets hot enough to come off and the piston pounds itself and everything else to bits and you get partial or complete engine failure. Leaking rings let more carbon, corrosive compounds and water vapor past them into the crankcase, where they do nasty things to nice, shiny precision parts.

Nothing like fixing stuff properly.
 
Dan Thomas said:
This is all you need:

6595923.jpg

When I was young, there were a number of such products available that would "rebuild" your engine as you drove. Of course, they did little or no good and could even make things a lot worse...

...Nothing like fixing stuff properly.
Click to expand...

Today we have CamGuard. :stirpot: :eek:

Okay, fights on! :incazzato:
Let the hate mail begin :D
:popcorn:
 
(Is Rislone still around?)

OK - Hate mail dept - John Thorpe (now dead) said to remove only the lower plugs before doing a compression test. If you remove the upper plugs, debris from the plug threads can fall onto an open valve seat. A few hours (minutes?) of engine operation will pound out the debris.

My experience with an O-320 E2D bore this out several times with a second successful compression test a few hours later.
 
Timbeck2 said:
I don't know if this has been posted before but for those aircraft owners who may be hung up on the compression readings of your cylinders at your annual, it explains a lot about compression testing and other things about engine health.

Bottom line up front - your compressions could be in the 50s and still have a healthy engine

Click to expand...

Okay, I watched the whole video. An hour long, but Youtube allows playing at double speed so it didn't take that long. I learned a few things. And then, at the end, Youtube showed a panel of teasers to click ... including Bryan, along with the Beverly Hillbillies.

screen-shot-2017-01-31-at-12-08-02-am-small-png.51073
 

Attachments

  • Screen Shot 2017-01-31 at 12.08.02 AM-small.png
    Screen Shot 2017-01-31 at 12.08.02 AM-small.png
    679.6 KB · Views: 72
Funny, the webinar for those who didn't watch it, was hosted by a mechanic who works at the plant where they overhaul engines. He mentioned that a lot of mechanics with say you need to fix a low compression cylinder NOW, costing the owner a lot of money. He goes on to display a chart on a test engine that at 270 hours had 56 psi of compression and over 400 hours was at 76 psi on the same cylinder. Then he displayed the exhaust valves depicting what is normal vs what is not. He also explains why the "standard" psi limit is 60 and that while the test is measured at 80 psi, the actual pressure in a running engine is closer to 1000 psi.

I'm not discouraging anything or badmouthing mechanics. I'm only sharing this because a lot of people tend to put a lot of stock in the compression readings on engines. My mechanic agrees with the webinar and explained these things to me when one of my readings was 68 and I voiced my concern that my engine was about to implode.
 
Yes, the webinar speaker recommends borescope images as much better than compression tests, for determining the health of a cylinder. He added that owners can do borescopes themselves. The compression test tells you little more than whether a cylinder prefers to leak at the valve or ring, if it leaks at 80 psi, and anyway if it does leak in the 80 psi test, that doesn't mean it will leak at 1000 psi when running.
 
NoHeat said:
Yes, the webinar speaker recommends borescope images as much better than compression tests, for determining the health of a cylinder. He added that owners can do borescopes themselves. The compression test tells you little more than whether a cylinder prefers to leak at the valve or ring, if it leaks at 80 psi, and anyway if it does leak in the 80 psi test, that doesn't mean it will leak at 1000 psi when running.
Click to expand...
When you understand dynamic compression you'll understand why that is. When you understand that compression checks are a trend to develop the pattern of wear, you will also know why troubleshooting is completed a certain way to determine which cylinders should be pulled and which should be allowed to continued in service.
There are a multitude of Service notes from both major manufacturers on this subject.
You must also know there is no magic that will replace worn metal.
 
NoHeat said:
Yes, the webinar speaker recommends borescope images as much better than compression tests, for determining the health of a cylinder. He added that owners can do borescopes themselves. The compression test tells you little more than whether a cylinder prefers to leak at the valve or ring, if it leaks at 80 psi, and anyway if it does leak in the 80 psi test, that doesn't mean it will leak at 1000 psi when running.
Click to expand...

Continental specifies using a differntial compression tester and calibrated test orifice. Immediately before the test, you connect the test orifice to the tester and set the input gauge to 80 psi; the output gauge will read a lot lower, and that number will be the minimum reading permissible for their engines on that day at that temperature and humidity and barometric pressure, all of which have a small effect on the readings. I typically see 46 PSI on the output when I do that, which means that Continental would be happy with 50 psi. But if that 50 was due to a leaking exhaust valve, I'd be concerned.

50 in a Lycoming would be a bad deal. They typically score in the 70s.
 
You must log in or register to reply here.
Back
Top