X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sun, 29 Jan 2012 17:16:11 -0500 Message-ID: X-Original-Return-Path: Received: from elasmtp-spurfowl.atl.sa.earthlink.net ([209.86.89.66] verified) by logan.com (CommuniGate Pro SMTP 5.4.3) with ESMTP id 5367425 for lml@lancaironline.net; Fri, 27 Jan 2012 15:59:04 -0500 Received-SPF: none receiver=logan.com; client-ip=209.86.89.66; envelope-from=colyncase@earthlink.net DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=dk20050327; d=earthlink.net; b=AA5/ciszU3nxJ/FjXVqD9PHl4irebGfY1E8zHAT0Ck2PjMMv88IKRW39e1UKXH8D; h=Received:From:Mime-Version:Content-Type:Subject:Date:In-Reply-To:To:References:Message-Id:X-Mailer:X-ELNK-Trace:X-Originating-IP; Received: from [72.73.82.72] (helo=[192.168.1.24]) by elasmtp-spurfowl.atl.sa.earthlink.net with esmtpa (Exim 4.67) (envelope-from ) id 1RqssG-0004pC-6F for lml@lancaironline.net; Fri, 27 Jan 2012 15:58:20 -0500 From: Colyn Case Mime-Version: 1.0 (Apple Message framework v1084) Content-Type: multipart/alternative; boundary=Apple-Mail-159--649134674 Subject: Re: [LML] Re: Lycoming exhaust valve questions X-Original-Date: Fri, 27 Jan 2012 15:58:19 -0500 In-Reply-To: X-Original-To: "lml@lancaironline.net List" References: X-Original-Message-Id: <629663B8-7ED7-4EEF-89ED-D2BD215F168D@earthlink.net> X-Mailer: Apple Mail (2.1084) X-ELNK-Trace: 63d5d3452847f8b1d6dd28457998182d7e972de0d01da940708c1a36268b4816bad649b093a86d3a350badd9bab72f9c350badd9bab72f9c350badd9bab72f9c X-Originating-IP: 72.73.82.72 --Apple-Mail-159--649134674 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=windows-1252 I think Swain's main point is you don't want to let the exhaust valve go = if it's starting to get a hot spot. Leaks are associated with bad seal = at the valve. maybe worry more about the bore scope than the = compression reading? re: the change interval, you might find this article informative: = http://www.avweb.com/news/savvyaviator/savvy_aviator_52_thinking_about_oil= _changes_196730-1.html On Jan 27, 2012, at 11:06 AM, Gary Casey wrote: Okay, I'll take the dare from Swain and post what might be the more = "normal" reply :-). I think he is being a little of a perfectionist. I = don't have his credentials, but from what I have seen, a compression = leakage of 74 to 76 is the most common. A compression number up to 78 = suggests that the engine is pumping excess oil past the rings and the = oil is sealing that leak path. So I would worry more about the ones = that measure 78 than I would about the one that is at 75. Assuming you = check the compression every 100 hours or so, I would wait until you have = more than 2 compression tests with ever-dropping values before I would = even start to worry. That will take another 200 hours of operation. I = wouldn't worry until the compression dropped below 70. And like Dan = said, it is always a good idea to warm the engine and then do the = compression test as soon as possible afterward. I've gone as far as to = warm the engine with the cowl off so I could do it faster, but to just = idle on the ground is not a good thing just before a compression test. = If I were really into the diagnostics I would warm the engine (cowl off) = at the normal runup rpm and then run it at full power for maybe 15 = seconds, pulling the mixture while at full power to get a "clean" = shut-off. Then you'll get as good a test as possible. And why do you change oil every 25-35 hours? With a modern engine and = modern oil, I don't see any reason to change oil that often. I would = run it at least 50 hours and try to change it before 75. If the engine = is run often, even 100 hours isn't out of line. What does the oil look = like at the oil change? Can you see the dipstick through the oil? If = so, it probably doesn't need to be changed yet. Gary Previously, from Swain:=20 Hi Dan, My opinion will differ from most here. It is based on 28 years as a = professional aircraft mechanic and a cylinder overhaul shop owner for 17 = years. Lycoming says that NO static leakage is allowed during a = compression test and I agree. What will happen is that if your ex. valve = continues to leak past it's seat it will errode a gas path in the seat = and valve face. This will cause a "hot spot" in that area that can = eventually lead to valve face breakage which might do major damage to = one or more cyl. I say more than one because I have personally seen a = piece of ex. valve leave it's cyl. through it's intake port and enter = the next cyl. beside it and lodge itself into the face of that piston = while bending the other cyl. intake valve. (BTW I keep that piece of = valve in my desk drawer as a reminder of what can happen). The only way = a valve can cool itself is through the time it sits on it's valve seat = to transfer heat from the valve to the head and also through the valve = stem. That's why when guides get worn and seats leak you wear out valve = stems and guides much quicker, there is not as much metal contact for = cooling and the psi of force on the wear surfaces increases (same force = less wear surface). Remember one compression test is only a snapshot of what is happening = in your engine. You need more than one and other information to develope = a trend on what your engine is really doing. I would go fly your airplane at high power settings for one hour and = come back and take another compression test. Then you might try some of = the tricks mentioned here ( I have never had much luck with short cuts). = If it was my airplane I would pull the cyl. and fix the problem and not = screw around with wobble test, staking the valve, or trying to lap a = valve without pulling the cyl. A gasket set is less than $20 bucks and = you don't have to replace the rings if there are serviceable and you = don't hone the cyl.. I have repaired/overhauled over a 1000 Continental and Lycoming = cylinders and it does not take very long to R&R a cyl. Swaid Rahn A&P,I.A.,ATP LIVP-T(Walter) LIVP-T(Garrett under construction) =20 On Tue, Jan 24, 2012 at 11:06 AM, Dan & Kari Olsen = wrote: LML Gang, =20 Doing the annual on my 320 this week. Compression check shows 77-78 on = cylinders 1, 2, 4. #3 is 75 and I hear pretty good leakage through the = exhaust, indicating a leaking exhaust valve. I=92ve had no indication = of sticking valves or morning sickness. I pulled the rocker cover and = there is no abnormality there. This engine is typically run lean of = peak at power settings of 55-65% power. Oil changes every 25-35hrs. = Engine has 623hrs since new. =20 My question to those of you who are much more experienced with the = Lycoming 4-cylinder engines, is what should be my next course of action? =B7 Do the valve lapping procedure per the Lyc service = instruction? =B7 Start using TCP and re-check in a few hours? =B7 Go run the engine hard and re-check the compression? =B7 Something else? =20 I really want to nip this in the bud and not end up with a burned = exhaust valve, requiring pulling a jug. =20 Appreciate your thoughts and responses. =20 Cheers! =20 Dan Olsen --Apple-Mail-159--649134674 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=windows-1252 I = think Swain's main point is you don't want to let the exhaust valve go = if it's starting to get a hot spot.   Leaks are associated with bad = seal at the valve.   maybe worry more about the bore scope than the = compression reading?

re: the change interval, you = might find this article informative:  http://www.avweb.com/news/savvyaviator/sav= vy_aviator_52_thinking_about_oil_changes_196730-1.html

<= /div>

On Jan 27, 2012, at 11:06 AM, Gary Casey = wrote:

Okay, I'll take = the dare from Swain and post what might be the more "normal" reply :-). =  I think he is being a little of a perfectionist.  I don't = have his credentials, but from what I have seen, a compression leakage = of 74 to 76 is the most common.  A compression number up to 78 = suggests that the engine is pumping excess oil past the rings and the = oil is sealing that leak path.  So I would worry more about the = ones that measure 78 than I would about the one that is at 75. =  Assuming you check the compression every 100 hours or so, I would = wait until you have more than 2 compression tests with ever-dropping = values before I would even start to worry.  That will take another 200 hours of operation.  I wouldn't worry until the = compression dropped below 70.  And like Dan said, it is always a = good idea to warm the engine and then do the compression test as soon as = possible afterward.  I've gone as far as to warm the engine with = the cowl off so I could do it faster, but to just idle on the ground is = not a good thing just before a compression test.  If I were really = into the diagnostics I would warm the engine (cowl off) at the normal = runup rpm and then run it at full power for maybe 15 seconds, pulling = the mixture while at full power to get a "clean" shut-off.  Then = you'll get as good a test as possible.

And why = do you change oil every 25-35 hours?  With a modern engine and = modern oil, I don't see any reason to change oil that often.  I = would run it at least 50 hours and try to change it before 75.  If = the engine is run often, even 100 hours isn't out of line.  What does the oil look like at the oil change?  Can = you see the dipstick through the oil?  If so, it probably doesn't = need to be changed = yet.
Gary

Previously, from = Swain: 
Hi Dan,
 My opinion will differ from most = here. It is based on 28 years as a professional aircraft mechanic and a = cylinder overhaul shop owner for 17 years. Lycoming says that NO static = leakage is allowed during a compression test and I agree. What will = happen is that if your ex. valve continues to leak past it's seat it = will errode a gas path in the seat and valve face. This will cause a = "hot spot" in that area that can eventually lead to  valve face = breakage which might do major damage to one or more cyl. I say more than = one because I have personally seen a piece of ex. valve leave it's cyl. through it's intake port and enter = the next cyl. beside it and lodge itself into the face of that piston = while bending the other cyl. intake valve. (BTW I keep that piece of = valve in my desk drawer as a reminder of what can happen). The only way = a valve can cool itself is through the time it sits on it's valve seat = to transfer heat from the valve to the head and also through the valve = stem. That's why when guides get worn and seats leak you wear out valve = stems and guides much quicker, there is not as much metal contact = for cooling and the psi of force on the wear surfaces increases (same = force less wear surface).
 Remember one compression test = is only a snapshot of what is happening in your engine. You need more = than one and other information to develope a trend on what your engine = is really doing.
 I would go fly your airplane at = high power settings for one hour and come back and take another compression test. Then you might try some of = the tricks mentioned here ( I have never had much luck with short cuts). = If it was my airplane I would pull the cyl. and fix the problem and not = screw around with wobble test, staking the valve, or trying to lap a = valve without pulling the cyl. A gasket set is less than $20 bucks and = you don't have to replace the rings if there are serviceable and you = don't hone the cyl..
 I have repaired/overhauled over a = 1000 Continental and Lycoming cylinders and it does not take very long = to R&R a cyl.
Swaid = Rahn
A&P,I.A.,ATP
LIVP-T(Walter)
LIVP-T(= Garrett under construction)


 
On Tue, Jan 24, 2012 at 11:06 AM, Dan = & Kari Olsen <
LML = Gang,
 
Doing the = annual on my 320 this week.  Compression check shows 77-78 on = cylinders 1, 2, 4.  #3 is 75 and I hear pretty good leakage through = the exhaust, indicating a leaking exhaust valve.  I=92ve had no = indication of sticking valves or morning sickness.  I pulled the = rocker cover and there is no abnormality there.  This engine is = typically run lean of peak at power settings of 55-65% power.  Oil = changes every 25-35hrs.  Engine has 623hrs since = new.
 
My question to those of you who are much = more experienced with the Lycoming 4-cylinder engines, is what should be = my next course of action?
 
I really want to nip this in the bud and = not end up with a burned exhaust valve, requiring pulling a = jug.
 
Cheers!
 
Dan = Olsen

= --Apple-Mail-159--649134674--