X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Fri, 27 Jan 2012 13:40:37 -0500 Message-ID: X-Original-Return-Path: Received: from imr-da06.mx.aol.com ([205.188.169.203] verified) by logan.com (CommuniGate Pro SMTP 5.4.3) with ESMTP id 5367178 for lml@lancaironline.net; Fri, 27 Jan 2012 12:31:34 -0500 Received-SPF: pass receiver=logan.com; client-ip=205.188.169.203; envelope-from=Sky2high@aol.com Received: from mtaomg-db02.r1000.mx.aol.com (mtaomg-db02.r1000.mx.aol.com [172.29.51.200]) by imr-da06.mx.aol.com (8.14.1/8.14.1) with ESMTP id q0RHUsH3003321 for ; Fri, 27 Jan 2012 12:30:54 -0500 Received: from core-mtb005a.r1000.mail.aol.com (core-mtb005.r1000.mail.aol.com [172.29.234.209]) by mtaomg-db02.r1000.mx.aol.com (OMAG/Core Interface) with ESMTP id EE6B2E000099 for ; Fri, 27 Jan 2012 12:30:53 -0500 (EST) From: Sky2high@aol.com X-Original-Message-ID: <1d287.19272bc1.3c54394d@aol.com> X-Original-Date: Fri, 27 Jan 2012 12:30:53 -0500 (EST) Subject: Re: [LML] Re: Lycoming exhaust valve questions X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="part1_1d287.19272bc1.3c54394d_boundary" X-Mailer: AOL 9.6 sub 168 X-Originating-IP: [67.175.156.123] x-aol-global-disposition: G X-AOL-SCOLL-SCORE: 1:2:508964896:93952408 X-AOL-SCOLL-URL_COUNT: 1 x-aol-sid: 3039ac1d33c84f22df4d2a1e --part1_1d287.19272bc1.3c54394d_boundary Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en Grayhawks says high readings on a Lyc 320,360 may be OK based on the tester= =20 orifice. Here's a bit of additional info: =20 =20 FAASTeam Maintenance Safety Tip=20 November 2011 =20 Differential Compression Test (AC 43.13-1B)=20 The differential pressure tester is designed to check the compression of= =20 aircraft engines by measuring the leakage through the cylinders caused by= =20 worn or damaged components.=20 The operation of the compression tester is based on the principle that, for= =20 any given airflow through a fixed orifice, a constant pressure drop across= =20 that orifice will result. The restrictor orifice dimensions in the=20 differential pressure tester should be sized for the particular engine as = follows:=20 =20 (Although AC 43.13-1B was revised in 1998, the following information was= =20 revised in Chg. 1 in September 2001. The identification criteria was revis= ed=20 from using =E2=80=9Cengines with a certain cubic inch displacement=E2=80=9D= to cylinder=20 bore) (1) For an engine cylinder having less than a 5.00-inch bore; 0.040-inch= =20 orifice diameter;=20 .250 inch long; and a 60-degree approach angle.=20 (2) For an engine cylinder with 5.00 inch bore and over: 0.060 inch=20 orifice diameter, .250 inch long, and a 60 degree approach angle.=20 Remember, some of the smaller production engines have 5 inch or larger=20 cylinder bores (e.g. Lycoming O-320-A1A has a cylinder bore of 5.125 inche= s).=20 Therefore, an orifice of 0.060 diameter should be used to perform the=20 compression test.=20 See _AC 43.13-1B_=20 (http://rgl.faa.gov/REGULATORY_AND_GUIDANCE_LIBRARY/RGADVISORYCIRCULAR.NSF/= 0/99c827db9baac81b86256b4500596c4e/$FILE/Chapter%2008.pdf)=20 , Chapter 8, paragraph 8-14 for more information. ALSO at Sacramento Sky Ranch note that Lyc's are expected to result in =20 higher pressure readings - BUT orifice is not mentioned....... =20 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =20 In a message dated 1/27/2012 10:24:58 A.M. Central Standard Time, =20 casey.gary@yahoo.com writes: =20 Okay, I'll take the dare from Swain and post what might be the more =20 "normal" reply :-). I think he is being a little of a perfectionist. I do= n't=20 have his credentials, but from what I have seen, a compression leakage of = 74=20 to 76 is the most common. A compression number up to 78 suggests that the= =20 engine is pumping excess oil past the rings and the oil is sealing that le= ak=20 path. So I would worry more about the ones that measure 78 than I would= =20 about the one that is at 75. Assuming you check the compression every 100= =20 hours or so, I would wait until you have more than 2 compression tests wit= h=20 ever-dropping values before I would even start to worry. That will take= =20 another 200 hours of operation. I wouldn't worry until the compression=20 dropped below 70. And like Dan said, it is always a good idea to warm the= =20 engine and then do the compression test as soon as possible afterward. I'= ve=20 gone as far as to warm the engine with the cowl off so I could do it faste= r,=20 but to just idle on the ground is not a good thing just before a compressi= on=20 test. If I were really into the diagnostics I would warm the engine (cowl= =20 off) at the normal runup rpm and then run it at full power for maybe 15=20 seconds, pulling the mixture while at full power to get a "clean" shut-off= . =20 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=20 modern oil, I don't see any reason to change oil that often. I would run = it=20 at least 50 hours and try to change it before 75. If the engine is run=20 often, even 100 hours isn't out of line. What does the oil look like at t= he=20 oil change? Can you see the dipstick through the oil? If so, it probably= =20 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 =20 professional aircraft mechanic and a cylinder overhaul shop owner for 17 y= ears.=20 Lycoming says that NO static leakage is allowed during a compression test= =20 and I agree. What will happen is that if your ex. valve continues to leak = =20 past it's seat it will errode a gas path in the seat and valve face. This w= ill=20 cause a "hot spot" in that area that can eventually lead to valve face = =20 breakage which might do major damage to one or more cyl. I say more than on= e =20 because I have personally seen a piece of ex. valve leave it's cyl. through= =20 it's intake port and enter the next cyl. beside it and lodge itself into= =20 the face of that piston while bending the other cyl. intake valve. (BTW I= =20 keep that piece of valve in my desk drawer as a reminder of what can happe= n).=20 The only way a valve can cool itself is through the time it sits on it's= =20 valve seat to transfer heat from the valve to the head and also through th= e=20 valve stem. That's why when guides get worn and seats leak you wear out=20 valve stems and guides much quicker, there is not as much metal contact fo= r=20 cooling and the psi of force on the wear surfaces increases (same force le= ss=20 wear surface). Remember one compression test is only a snapshot of what is happening in= =20 your engine. You need more than one and other information to develope a=20 trend on what your engine is really doing. I would go fly your airplane at high power settings for one hour and come= =20 back and take another compression test. Then you might try some of the=20 tricks mentioned here ( I have never had much luck with short cuts). If it= was=20 my airplane I would pull the cyl. and fix the problem and not screw around= =20 with wobble test, staking the valve, or trying to lap a valve without=20 pulling the cyl. A gasket set is less than $20 bucks and you don't have to= =20 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= =20 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 <_olsen25@comcast.net_= =20 (mailto:olsen25@comcast.net) > wrote: =20 LML Gang, =20 Doing the annual on my 320 this week. Compression check shows 77-78 on=20 cylinders 1, 2, 4. #3 is 75 and I hear pretty good leakage through the=20 exhaust, indicating a leaking exhaust valve. I=E2=80=99ve had no indicati= on of sticking=20 valves or morning sickness. I pulled the rocker cover and there is no=20 abnormality there. This engine is typically run lean of peak at power=20 settings of 55-65% power. Oil changes every 25-35hrs. Engine has 623hrs = since=20 new. =20 My question to those of you who are much more experienced with the=20 Lycoming 4-cylinder engines, is what should be my next course of action? =C2=B7 Do the valve lapping procedure per the Lyc service instruc= tion? =C2=B7 Start using TCP and re-check in a few hours? =C2=B7 Go run the engine hard and re-check the compression? =C2=B7 Something else? =20 I really want to nip this in the bud and not end up with a burned exhaust= =20 valve, requiring pulling a jug. =20 Appreciate your thoughts and responses. =20 Cheers! =20 Dan Olsen --part1_1d287.19272bc1.3c54394d_boundary Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en
Grayhawks says high readings on a Lyc 320,360 may be OK based on the t= ester=20 orifice. Here's a bit of additional info:
 
 =20

FAASTeam Maintena= nce Safety=20 Tip
November 2011

Differential Compression Test (AC 43.13-1B)

The different= ial=20 pressure tester is designed to check the compression of aircraft engines by= =20 measuring the leakage through the cylinders caused by worn or damaged=20 components.

The operation of the compression tester is based on the principle that, = for=20 any given airflow through a fixed orifice, a constant pressure drop across = that=20 orifice will result. The restrictor orifice dimensions in the differential= =20 pressure tester should be sized for the particular engine as follows:=20

(Although AC 43.13-1B was revised in 1998, the following=20 information was revised in Chg. 1 in September 2001. The identification cri= teria=20 was revised from using =E2=80=9Cengines with a certain cubic inch displacem= ent=E2=80=9D to=20 cylinder bore)

(1) For an engine cylinder having les= s=20 than a 5.00-inch bore; 0.040-inch orifice diameter;
.250 inch long; and= a=20 60-degree approach angle.
(2) For an engine cylinder with 5.00 i= nch=20 bore and over: 0.060 inch orifice diameter, .250 inch long, and a 60 degree= =20 approach angle.

Remember, some of the smaller production engines ha= ve 5=20 inch or larger cylinder bores (e.g. Lycoming O-320-A1A has a cylinder bore = of=20 5.125 inches). Therefore, an orifice of 0.060 diameter should be used to pe= rform=20 the compression test.

See AC 43.13-1B, Chapter 8, paragraph 8-14 for more=20 information.

ALSO at Sacramento Sky Ranch note that Lyc's are expected to result in= =20 higher pressure readings - BUT orifice is not mentioned.......
 
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
In a message dated 1/27/2012 10:24:58 A.M. Central Standard Time,=20 casey.gary@yahoo.com writes:
=
Okay, I'll take the dare from Swain and post what might be the more= =20 "normal" reply :-).  I think he is being a little of a perfectionist= .=20  I don't have his credentials, but from what I have seen, a compress= ion=20 leakage of 74 to 76 is the most common.  A compression number up to = 78=20 suggests that the engine is pumping excess oil past the rings and the oil= is=20 sealing that leak path.  So I would worry more about the ones that= =20 measure 78 than I would about the one that is at 75.  Assuming you c= heck=20 the compression every 100 hours or so, I would wait until you have more t= han 2=20 compression tests with ever-dropping values before I would even start to= =20 worry.  That will take another 200 hours of operation.  I would= n't=20 worry until the compression dropped below 70.  And like Dan said, it= is=20 always a good idea to warm the engine and then do the compression test as= soon=20 as possible afterward.  I've gone as far as to warm the engine with = the=20 cowl off so I could do it faster, but to just idle on the ground is not a= good=20 thing just before a compression test.  If I were really into the=20 diagnostics I would warm the engine (cowl off) at the normal runup rpm an= d=20 then run it at full power for maybe 15 seconds, pulling the mixture while= at=20 full power to get a "clean" shut-off.  Then you'll get as good a tes= t as=20 possible.

And why do you change oil every 25-35 hours?  With a modern eng= ine=20 and modern oil, I don't see any reason to change oil that often.  I = would=20 run it at least 50 hours and try to change it before 75.  If the eng= ine=20 is run often, even 100 hours isn't out of line.  What does the oil l= ook=20 like at the oil change?  Can you see the dipstick through the oil?= =20  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=20 professional aircraft mechanic and a cylinder overhaul shop owner for 17= =20 years. Lycoming says that NO static leakage is allowed during a compressi= on=20 test and I agree. What will happen is that if your ex. valve continues to= leak=20 past it's seat it will errode a gas path in the seat and valve face. This= will=20 cause a "hot spot" in that area that can eventually lead to  valve f= ace=20 breakage which might do major damage to one or more cyl. I say more than = one=20 because I have personally seen a piece of ex. valve leave it's cyl. throu= gh=20 it's intake port and enter the next cyl. beside it and lodge itself into = the=20 face of that piston while bending the other cyl. intake valve. (BTW I kee= p=20 that piece of valve in my desk drawer as a reminder of what can happen). = The=20 only way a valve can cool itself is through the time it sits on it's valv= e=20 seat to transfer heat from the valve to the head and also through the val= ve=20 stem. That's why when guides get worn and seats leak you wear out valve s= tems=20 and guides much quicker, there is not as much metal contact for cool= ing=20 and the psi of force on the wear surfaces increases (same force less wear= =20 surface).
 Remember one compression test is only a snapshot of what is=20 happening in your engine. You need more than one and other information to= =20 develope a trend on what your engine is really doing.
 I would go fly your airplane at high power settings for one ho= ur=20 and come back and take another compression test. Then you might = ;try=20 some of the tricks mentioned here ( I have never had much luck with short= =20 cuts). If it was my airplane I would pull the cyl. and fix the problem an= d not=20 screw around with wobble test, staking the valve, or trying to lap a valv= e=20 without pulling the cyl. A gasket set is less than $20 bucks and you don'= t=20 have to replace the rings if there are serviceable and you don't hone the= =20 cyl..
 I have repaired/overhauled over a 1000 Continental and Lycomin= g=20 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, Da= n &=20 Kari Olsen <olsen25@comcast.net>=  wrote:
LML Gang,
 
Doing the annual on my 320 this week.&nbs= p;=20 Compression check shows 77-78 on cylinders 1, 2, 4.  #3 is 75 and = I=20 hear pretty good leakage through the exhaust, indicating a leaking exha= ust=20 valve.  I=E2=80=99ve had no indication of sticking valves or morni= ng=20 sickness.  I pulled the rocker cover and there is no abnormality= =20 there.  This engine is typically run lean of peak at power setting= s of=20 55-65% power.  Oil changes every 25-35hrs.  Engine has 623hrs= =20 since new.
 
My question to those of you who are much = more=20 experienced with the Lycoming 4-cylinder engines, is what should be my = next=20 course of action?
=C2=B7    = ;     Do=20 the valve lapping procedure per the Lyc service=20 instruction? =C2=B7    = ;     Start=20 using TCP and re-check in a few hours? =C2=B7    = ;     Go=20 run the engine hard and re-check the compression? =C2=B7    = ;     Something=20 else?   I really want to nip this in the bud and = not end=20 up with a burned exhaust valve, requiring pulling a jug.<= /DIV>   Appreciate your thoughts and=20 responses.   Cheers!<= FONT=20 color=3D#888888>   Dan=20 Olsen --part1_1d287.19272bc1.3c54394d_boundary--