X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml Date: Wed, 20 Sep 2006 19:38:06 -0400 Message-ID: X-Original-Return-Path: Received: from [64.12.137.3] (HELO imo-m22.mail.aol.com) by logan.com (CommuniGate Pro SMTP 5.1c.4) with ESMTP id 1412299 for lml@lancaironline.net; Wed, 20 Sep 2006 18:18:12 -0400 Received-SPF: pass receiver=logan.com; client-ip=64.12.137.3; envelope-from=JIMRHER@aol.com Received: from JIMRHER@aol.com by imo-m22.mx.aol.com (mail_out_v38_r7.6.) id q.c7b.67397d (29678) for ; Wed, 20 Sep 2006 18:17:30 -0400 (EDT) From: JIMRHER@aol.com X-Original-Message-ID: X-Original-Date: Wed, 20 Sep 2006 18:17:29 EDT Subject: [LML] Backfires LOP X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1158790649" X-Mailer: 9.0 Security Edition for Windows sub 5324 X-Spam-Flag: NO -------------------------------1158790649 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en =20 Gentlemen,=20 This is my comments in answer to both Walter's and George's response to my =20 posting regarding LOP on a TSI0-550E I first want to thank both of these gentlemen for there informative =20 participation in the LML. I also want to state that these guys are by far th= e experts=20 on engines and I am merely an old ME engineer with enough knowledge to get=20 myself into trouble. I have posted my credentials at the end. =20 Walter wrote; I don't know upon what data you are relying to make that assumption, but it= =20 is incorrect. The hottest mixture for exhaust valves is found at 25dF ROP= . =20 LOP mixtures run the exhaust valve MUCH cooler than ROP mixtures. That was= =20 first proven by a NACA report in 1943, subsequently reported by Lycoming in= =20 1966 and again confirmed by GAMI's test facilities in 2004. Raw EGT value=20= has=20 essentially nothing to do with exhaust valve temperature. =20 I agree with what is said here. However, I run at least 100F ROP not 25F RO= P=20 and sometimes much more, like at full power I think I'm about 300F ROP.=20 Therefore, I believe that the ROP has excess fuel which should cool the bur= n and=20 just maybe leave MORE lead on the valve stem than while LOP. The major factor in guide wear is related to MANUFACTURING fit, and not=20 mixture management. =20 I think this comment fits my background and I can only confirm that my New =20 cylinders that were provided by TCM came from the factory out of spec. I had= =20 all the valve's removed, measured, and hand lapped into the seat to insure=20= a=20 full wide seat and correct valve to stem clearance. On two cylinders the=20 exhaust valves would not clean up to provide a uniform seat all around with= just=20 lapping and had to be reground. This is unbelievable and therefore would ha= ve=20 had a short life if put into service that way. I suspect that the original=20 cylinders that came on the new engine had this problem also. In all fairness to TCM on my original installation, which used Lancair's =20 baffling and a New Dukes fuel pump, I had very hot #2 cylinder all the time=20= and =20 was my gauge for temp management. When we removed all the cylinders this sam= e =20 cylinder was Fine=3DPerfect when three others had less then 40/80 compressio= n. =20 Does this say High CHT's doesn't matter? Also, after having a TCM rep. go over all my early problems he told me to =20 replace the Electric fuel pump. I almost thought this was a joke and a real=20= =20 diversion to their engine cooling problem. Much later I changed the fuel pum= p =20 and he was correct. ( longer story). George wrote; =20 Ah=E2=80=A6 that is the conventional theory and wisdom - - that is - - th= at HOT =20 EGTs translate into HOT exhaust valves. It just turns out that isn=E2= =80=99t true.=20 The value of the exhaust gas temperature flowing past the exhaust valve is= =20 often inversely proportional to the temperature of the exhaust valve. =20 I ************* KNOW *********** that comment appears to be completely=20 crazy and verging on the area of silly.=20 But there is good hard data on this subject going back to the 1940s=E2=80= =99 That=20 data shows that the exhaust valve temperatures follow the CHTs - - NOT the= =20 EGTs. =20 And by advancing timing, as just one example as to why this is true, one=20= =20 will LOWER THE EGTS - - but that will make the exhaust valves run very muc= h=20 hotter (along with the CHTs).=20 By retarding the timing a lot, the EGTs go VERY HOT - - but the exhaust =20 valves get very cool - - along with the CHTs.=20 In short, EGTs do not correlate with exhaust valve temperatures very well=20 at all.=20 I do understand this because the exhaust valve is on the closed seat for 3=20 or the 4 cycles, and is only heated during the one exhaust cycle. In the re= al=20 world the condition of the seat has a very large effect on the cooling=20 thermal time constant. And we can't ignore the EGT temperature effect to th= e Oil=20 film on the exposed valve stem. Please, note that on my second set of cylin= ders=20 that after 82 hrs the Stem's and Guides were wore out of spec. only on the=20 first 1/3 of the valve guide length. This says that the guide is not=20 lubricated enough and/or the stem diameter is too small in diameter, making= a smaller=20 bearing surface. This could be solved by having sodium cooled valves which=20 require a larger stem, and using better lubrication.=20 BTW, I talked to 4 different engine builders about the above and they all=20 commented "probably ALL IO and TSIO TCM engines have the same valve ware at= 82=20 hrs but don't show compression loss until 400 hrs or more" For the record m= y=20 engine was overhauled after 82 hrs because of a lifter disintegration probl= em=20 which replaced everything that sees oil.=20 >> My second set of cylinders had stem and guides wore beyond limits at 82=20 hrs and I hadn't gone LOP for the first 40 hrs and then maybe half the time= =20 for the next 42 hrs. This is the mechanical fuse, so to speak, of the =20 Continental engine, the exhaust valves. Now I run ROP and let the fuel save=20= my exhaust=20 valves and save money. I use about 4 or 5 gal. more on a 540 nm flight and=20 go faster and quicker.<<=20 I suspect your problem was the dimensional fit of the exhaust =20 valves/guides before you ever started your engine the first time. George=20 George, I hope I answered the fit issue with respect to the second set of=20 cylinders? I also did that same routine on the present set of cylinders. Al= so,=20 after this present overhaul I have done major baffling sealing similar to=20 what George has shown in the past plus more between cylinders, and this tim= e=20 around I can now keep full power on up to what ever altitude I need without= =20 CHT's going over 405F. I, however, would like to swap #6 and #2 injectors t= o get=20 a better distribution but then I should probably just fly to Ada and get it= =20 really balanced?=20 Sincerely,=20 Jim Hergert, BSME with manufacturing option, 40 yrs. in Tool design, plasti= c=20 molds, die casting, Sheetmetal mfg. with State of the art, NC machines,=20 Lasers, automation and Solid modeling CAD systems. Material's and Just In =20= Time=20 specialty. 250 employees. All in the past. So I built a plastic airplane. L4P, N6XE (An Sexy) 409 hrs. -------------------------------1158790649 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en
Gentlemen, 
This is my comments in answer to both Walter's and George's response to= my=20 posting regarding LOP on a TSI0-550E
I first want to thank both of these gentlemen for there informative=20 participation in the LML. I also want to state that these guys are by far th= e=20 experts on engines and I am merely an old ME engineer with enough knowledge=20= to=20 get myself into trouble. I have posted my credentials at the end.
 
Walter=20 wrote;
I don't=20 know upon what data you are relying to make that assumption, but it is=20 incorrect.  The hottest mixture for exhaust valves is found at 25dF=20 ROP.  LOP mixtures run the exhaust valve MUCH cooler than ROP=20 mixtures.  That was first proven by a NACA report in 1943, subsequently= =20 reported by Lycoming in 1966 and again confirmed by GAMI's test facilities i= n=20 2004.  Raw EGT value has essentially nothing to do with exhaust valve=20 temperature.
 
I agree with what is sai= d here.=20 However, I run at least 100F ROP not 25F ROP and sometimes much more, like a= t=20 full power I think I'm about 300F ROP. Therefore, I believe that the ROP has= =20 excess fuel which should cool the burn and just maybe leave MORE lead on the= =20 valve stem than while LOP.
 
The=20 major factor in guide=20= wear is=20 related to MANUFACTURING fit, and not mixture management.
 
I think this comment fits my background and I can only confirm that my=20= New=20 cylinders that were provided by TCM came from the factory out of spec. I had= all=20 the valve's removed, measured, and hand lapped into the seat to insure a ful= l=20 wide seat and correct valve to stem clearance. On two cylinders the exhaust=20 valves would not clean up to provide a uniform seat all around with just lap= ping=20 and had to be reground. This is unbelievable and therefore would have had a=20 short life if put into service that way. I suspect that the original cylinde= rs=20 that came on the new engine had this problem also.
In all fairness to TCM on my original installation, which used Lancair'= s=20 baffling and a New Dukes fuel pump, I had very hot #2 cylinder all the time=20= and=20 was my gauge for temp management. When we removed all the cylinders this sam= e=20 cylinder was Fine=3DPerfect when three others had less then 40/80 compressio= n.=20 Does this say High CHT's doesn't matter?
Also, after having a TCM rep. go over all my early problems he told me=20= to=20 replace the Electric fuel pump. I almost thought this was a joke and a real=20 diversion to their engine cooling problem. Much later I changed the fuel pum= p=20 and he was correct. ( longer story).
 
George wrote;

Ah=E2=80=A6=20 that is the conventional  theory and wisdom - -  that is - - that=20= HOT=20 EGTs  translate into  HOT exhaust valves.   It just turn= s=20 out that isn=E2=80=99t true.  The value of the exhaust gas temperature=20= flowing past=20 the exhaust valve is often inversely proportional to the temperature of the=20 exhaust valve. 

I  *************   KNOW ***********  that= =20 comment appears to be completely crazy and verging on the area of  sill= y.

But=20 there is good hard data on this subject going back to the 1940s=E2=80=99&nbs= p; =20 That data shows that  the exhaust valve temperatures follow the CHTs -=20= -=20 NOT the EGTs.  

And=20 by advancing timing,  as just one example as to why this is true, = one=20 will  LOWER THE EGTS - - but that will make the exhaust valves run very= =20 much hotter (along with the CHTs).

By=20 retarding the timing a lot,  the EGTs go VERY HOT - - but the exhaust=20 valves get very cool  - - along with the CHTs.=

In=20 short,  EGTs do not correlate with exhaust valve temperatures very well= at=20 all.

I do understand th= is because=20 the exhaust valve is on the closed seat for 3 or the 4 cycles, and is only=20 heated during the one exhaust cycle. In the real world the condition of the=20= seat=20 has a very large effect on the cooling thermal time constant. And we can't=20 ignore the EGT temperature effect to the Oil film on the exposed valve=20 stem. Please, note that on my second set of cylinders that after 82 hrs the=20 Stem's and Guides were wore out of spec. only on the first 1/3 of the valve=20 guide length. This says that the guide is not lubricated enough and/or=20= the=20 stem diameter is too small in diameter, making a smaller bearing=20 surface. This could be solved by having sodium cooled valves which requ= ire=20 a larger stem, and using better lubrication.

BTW, I talked to 4= different=20 engine builders about the above and they all commented "probably ALL IO and=20= TSIO=20 TCM engines have the same valve ware at 82 hrs but don't show compression lo= ss=20 until 400 hrs or more" For the record my engine was overhauled after 82 hrs=20 because of a lifter disintegration problem which replaced everythi= ng=20 that sees oil.

>> My second set of cylinders had stem and guides wore=20= beyond=20 limits at 82 hrs and I hadn't gone LOP for the first 40 hrs and then maybe h= alf=20 the time for the next 42 hrs. This is the mechanical fuse, so to speak, of t= he=20 Continental engine, the exhaust valves. Now I run ROP and let the fuel save=20= my=20 exhaust valves and save money. I use about 4 or 5 gal. more on a 540 nm= =20 flight and go faster and quicker.<<

I=20 suspect your problem was the  dimensional  fit of the exhaust=20 valves/guides before you ever started your engine the first time.=20 George

George, I hope I a= nswered=20 the fit issue with respect to the second set of cylinders? I also did that s= ame=20 routine on the present set of cylinders. Also, after this present overhaul I= =20 have done major baffling sealing similar to what George has shown in the=20 past plus more between cylinders, and this time around I can now keep f= ull=20 power on up to what ever altitude I need without CHT's going over 405F. I,=20 however, would like to swap #6 and #2 injectors to get a better distribution= but=20 then I should probably just fly to Ada and get it really=20 balanced?

Sincerely,<= /FONT>

Jim=20 Hergert, BSME with manufacturing option, 40 yrs. in Tool design, plastic mol= ds,=20 die casting, Sheetmetal mfg. with State of the art, NC machines, Lasers,=20 automation and Solid modeling CAD systems. Material's and Just In=20 Time specialty. 250 employees. All in the past. So I built a plastic=20 airplane.
L4P, N6XE
(An Sexy)
409=20 hrs.

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