X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Thu, 26 Jan 2012 08:42:23 -0500 Message-ID: X-Original-Return-Path: Received: from mail-lpp01m010-f52.google.com ([209.85.215.52] verified) by logan.com (CommuniGate Pro SMTP 5.4.3) with ESMTPS id 5365210 for lml@lancaironline.net; Thu, 26 Jan 2012 07:04:28 -0500 Received-SPF: pass receiver=logan.com; client-ip=209.85.215.52; envelope-from=indigoaviation@gmail.com Received: by lagy4 with SMTP id y4so232326lag.25 for ; Thu, 26 Jan 2012 04:03:52 -0800 (PST) MIME-Version: 1.0 Received: by 10.112.48.9 with SMTP id h9mr478519lbn.20.1327579431934; Thu, 26 Jan 2012 04:03:51 -0800 (PST) Received: by 10.112.61.40 with HTTP; Thu, 26 Jan 2012 04:03:51 -0800 (PST) In-Reply-To: References: X-Original-Date: Thu, 26 Jan 2012 07:03:51 -0500 X-Original-Message-ID: Subject: Re: [LML] Lycoming exhaust valve questions From: swaid rahn X-Original-To: Lancair Mailing List Content-Type: multipart/alternative; boundary=bcaec554ddec739ba804b76d2c82 --bcaec554ddec739ba804b76d2c82 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable 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 wro= te: > 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?*= * > ** > > **=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?**** > > ** ** > > I really want to nip this in the bud and not end up with a burned exhaust > valve, requiring pulling a jug.**** > > ** ** > > Appreciate your thoughts and responses.**** > > ** ** > > Cheers!**** > > ** ** > > Dan Olsen**** > --=20 Swaid L. Rahn Indigo Aviation, Inc. 940 Mock Road Springfield, Ga. 31329 Cell 912.655.0966 --bcaec554ddec739ba804b76d2c82 Content-Type: text/html; charset=windows-1252 Content-Transfer-Encoding: quoted-printable
Hi Dan,
=A0My opinion will differ from most here. It is base= d on 28 years as a professional aircraft mechanic and a cylinder overhaul s= hop owner for 17 years. Lycoming says that NO static leakage is allowed dur= ing a compression test and I agree. What will happen is that if your ex. va= lve continues to leak past it's seat it will errode a gas path in the s= eat and valve face. This will cause a "hot spot" in that area tha= t can eventually lead to=A0 valve face breakage which might do major damage= to one or more cyl. I say more than one because I have personally seen a p= iece of ex. valve leave it's cyl. through it's intake port and ente= r the next cyl. beside it and lodge itself into the face of that piston whi= le 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 guide= s much=A0quicker, there is not as much metal contact for cooling and the ps= i of force on the wear surfaces increases (same force less wear surface).
=A0Remember one compression test is only a snapshot of what is happeni= ng in your engine. You need more than one and other information to develope= a trend on what your engine is really=A0doing.
=A0I would go fly= your airplane at high power settings for one hour and come back and take a= nother compression test. Then=A0you might=A0try some of the tricks mentione= d 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..
=A0I have repaired/overhauled over a 1000 Continental and Lycoming cyl= inders and it does not take very long to R&R a cyl.
Swaid Rah= n
A&P,I.A.,ATP
LIVP-T(Walter)
LIVP-T(Garr= ett under construction)


=A0
On Tue, Jan 24, 2012 at 11= :06 AM, Dan & Kari Olsen <olsen25@comcast.net> wrote:

LML Gang,

=A0

=

Doing the annual on my 320 this week.=A0 Compression= check shows 77-78 on cylinders 1, 2, 4.=A0 #3 is 75 and I hear pretty good= leakage through the exhaust, indicating a leaking exhaust valve.=A0 I=92ve= had no indication of sticking valves or morning sickness.=A0 I pulled the = rocker cover and there is no abnormality there.=A0 This engine is typically= run lean of peak at power settings of 55-65% power.=A0 Oil changes every 2= 5-35hrs.=A0 Engine has 623hrs since new.

=A0

My quest= ion to those of you who are much more experienced with the Lycoming 4-cylin= der engines, is what should be my next course of action?

<= p> =B7=A0=A0=A0=A0=A0=A0=A0=A0 Do the valve lappin= g procedure per the Lyc service instruction?

=B7=A0=A0=A0=A0=A0=A0=A0=A0 Start using TCP = and re-check in a few hours?

=B7=A0=A0=A0=A0=A0=A0=A0=A0 Go run the engin= e hard and re-check the compression?

=B7=A0=A0=A0=A0=A0=A0=A0=A0 Something else?<= u>

=A0

I really want to nip this in th= e bud and not end up with a burned exhaust valve, requiring pulling a jug.<= u>

=A0

Appreciate your thoughts and responses.

=A0

Cheers!

=A0

Dan Olsen




--
S= waid L. Rahn
Indigo Aviation, Inc.
940 Mock Road
Springfield, Ga. = 31329
Cell 912.655.0966


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