| Non-GMC engine question [message #88987] |
Thu, 17 June 2010 11:54  |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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Last night on the way home I noticed one of my airplane cylinders was running 1642 degrees EGT. It got my attention to say the least as I was about 1 hour from home well after dark which limits your landing options in case of an emergency.
I have never seen an EGT over 1520 or so. Adding carb heat decreased the reading by about 75 degrees but that was still higher than I have ever seen before. The interesting thing is the CHT was the same on that cylinder as all of the rest which was around 340 degrees. Oil temperature was also in the green.
I was running full rich at about 3500 feet with an OAT of 72 degrees. This is a carburetored non-turbocharged 87 octane O-320 engine.
I have always thought from past leaning experiences that 1500 degrees or slightly higher was the theoretical limit on 100% non-turbo gasoline powered engines.
I'm thinking and hoping that this is simply a bad probe.
Note: I also intend to run a differential compression test on the cylinder in question in the next couple of days.
Is there anyone out there that has any knowledge on this subject?
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Non-GMC engine question [message #89032 is a reply to message #88989] |
Thu, 17 June 2010 16:18  |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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I have limited experience with aircraft engines, but extensive experience
with air cooled normally aspirated racing go cart engines and your egt seems
too high for the conditions you describe. I would substitute a known good
reading thermocouple for your suspect one and verify if it is the probe or
the cylinder. Just my personal experience.
Jim Hupy
Salem, Or
1978 Royale 403
On Thu, Jun 17, 2010 at 10:08 AM, Gary Worobec <gtw5@earthlink.net> wrote:
> Ken ,
> Would you define the phrase "limits your landing options" to be similar to
> the situation of the pilot that landed the jet in the Hudson. :)
>
> Thanks
>
> Gary and Joanne Worobec
> 1973 GMC Glacier
> Anza, CA
>
>
>
> Original Message -----
> From: "Ken Burton" <n9cv@comcast.net>
> To: <gmclist@temp.gmcnet.org>
> Sent: Thursday, June 17, 2010 9:54 AM
> Subject: [GMCnet] Non-GMC engine question
>
>
> >
> >
> > Last night on the way home I noticed one of my airplane cylinders was
> > running 1642 degrees EGT. It got my attention to say the least as I was
> > about 1 hour from home well after dark which limits your landing options
> > in case of an emergency.
> >
> > I have never seen an EGT over 1520 or so. Adding carb heat decreased
> the
> > reading by about 75 degrees but that was still higher than I have ever
> > seen before. The interesting thing is the CHT was the same on that
> > cylinder as all of the rest which was around 340 degrees. Oil
> temperature
> > was also in the green.
> >
> > I was running full rich at about 3500 feet with an OAT of 72 degrees.
> > This is a carburetored non-turbocharged 87 octane O-320 engine.
> >
> > I have always thought from past leaning experiences that 1500 degrees or
> > slightly higher was the theoretical limit on 100% non-turbo gasoline
> > powered engines.
> >
> > I'm thinking and hoping that this is simply a bad probe.
> > Note: I also intend to run a differential compression test on the
> cylinder
> > in question in the next couple of days.
> >
> > Is there anyone out there that has any knowledge on this subject?
> > --
> > Ken Burton - N9KB
> > 76 Palm Beach
> > Hebron, Indiana
> > _______________________________________________
> > GMCnet mailing list
> > List Information and Subscription Options:
> > http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: [GMCnet] Non-GMC engine question [message #89036 is a reply to message #89032] |
Thu, 17 June 2010 16:39 |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
Karma: 0
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Senior Member |
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Arn't most EGTs thermocouples?
If so I'm wondering how a bad thermocouple could show higher voltage...
Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
ask me about MicroLevel
Cell, 763-732-3419
My427v8@hotmail.com
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| Re: Non-GMC engine question [message #89078 is a reply to message #89053] |
Fri, 18 June 2010 02:07 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| mcolie wrote on Thu, 17 June 2010 20:19 |
| Ken Burton wrote on Thu, 17 June 2010 12:54 |
Last night on the way home I noticed one of my airplane cylinders was running 1642 degrees EGT. It got my attention to say the least as I was about 1 hour from home well after dark which limits your landing options in case of an emergency.
I have never seen an EGT over 1520 or so. Adding carb heat decreased the reading by about 75 degrees but that was still higher than I have ever seen before. The interesting thing is the CHT was the same on that cylinder as all of the rest which was around 340 degrees. Oil temperature was also in the green.
I was running full rich at about 3500 feet with an OAT of 72 degrees. This is a carburetored non-turbocharged 87 octane O-320 engine.
I have always thought from past leaning experiences that 1500 degrees or slightly higher was the theoretical limit on 100% non-turbo gasoline powered engines.
I'm thinking and hoping that this is simply a bad probe.
Note: I also intend to run a differential compression test on the cylinder in question in the next couple of days.
Is there anyone out there that has any knowledge on this subject?
|
Ken,
Let's start with the bad side. . .
In my decades of lab work, T/couples failed reading low or open. (our systems could detect open)
Let's hope for the good side...
You were at cruise - probably 20-24" map????
If you have developed and intake runner leak, that cylinder would go lean. The lean mixture will burn more slowly - hence high EGT. CHT might go up a little, but that is more dependent of BMEP.
Let's hope it is one of those gaskets where the intake goes into the head.
Matt
|
Matt Here is my point. On an airplane we have control of the mixture and we lean out the engine when flying over 5000 feet. We lean the mixture until we see peak EGT. If we continue lean the engine past peak EGT very much the engine starts to miss due to an over lean condition. We richen (if that is a word) the mixture so the EGT on the highest cylinder goes down by 50 degrees. (some people go 75 degrees) I have never seen a peak EGT higher than 1520. The reading of 1642 really confuses me. The probes are indeed a thermocouple. I thought thermocouples fail by reading low and not high. This is why I am questioning what I think I know about this whole thing.
Some aircraft have only one EGT probe and some like mine have probes on all cylinders. My past experience has been the peak EGT reading never exceeds 1520 degrees and usually it is around 1500 so I can not understand a reading of 1642 degrees with no change in CHT or engine running smoothness. I would buy your idea of an intake leak on one cylinder if the EGT reading peaked around 1500 and or the engine ran roughly.
I'll still check for an intake leak on that cylinder.
Please tell me more.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Non-GMC engine question [message #89082 is a reply to message #88989] |
Fri, 18 June 2010 05:47 |
Steven Ferguson
Messages: 3447
Registered: May 2006
Karma: 0
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Senior Member |
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That means that Ken has to stay very close to the edges of the air Gary.
On Thu, Jun 17, 2010 at 10:08 AM, Gary Worobec <gtw5@earthlink.net> wrote:
> Ken ,
> Would you define the phrase "limits your landing options" to be similar to
> the situation of the pilot that landed the jet in the Hudson. :)
>
> Thanks
>
> Gary and Joanne Worobec
> 1973 GMC Glacier
> Anza, CA
>
>
>
> Original Message -----
> From: "Ken Burton" <n9cv@comcast.net>
> To: <gmclist@temp.gmcnet.org>
> Sent: Thursday, June 17, 2010 9:54 AM
> Subject: [GMCnet] Non-GMC engine question
>
>
>>
>>
>> Last night on the way home I noticed one of my airplane cylinders was
>> running 1642 degrees EGT. It got my attention to say the least as I was
>> about 1 hour from home well after dark which limits your landing options
>> in case of an emergency.
>>
>> I have never seen an EGT over 1520 or so. Adding carb heat decreased the
>> reading by about 75 degrees but that was still higher than I have ever
>> seen before. The interesting thing is the CHT was the same on that
>> cylinder as all of the rest which was around 340 degrees. Oil temperature
>> was also in the green.
>>
>> I was running full rich at about 3500 feet with an OAT of 72 degrees.
>> This is a carburetored non-turbocharged 87 octane O-320 engine.
>>
>> I have always thought from past leaning experiences that 1500 degrees or
>> slightly higher was the theoretical limit on 100% non-turbo gasoline
>> powered engines.
>>
>> I'm thinking and hoping that this is simply a bad probe.
>> Note: I also intend to run a differential compression test on the cylinder
>> in question in the next couple of days.
>>
>> Is there anyone out there that has any knowledge on this subject?
>> --
>> Ken Burton - N9KB
>> 76 Palm Beach
>> Hebron, Indiana
>> _______________________________________________
>> GMCnet mailing list
>> List Information and Subscription Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Steve Ferguson
'76 EII
Sierra Vista, AZ
Urethane bushing source
www.bdub.net/ferguson/
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| Re: Non-GMC engine question [message #89095 is a reply to message #89078] |
Fri, 18 June 2010 07:55 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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to others:
The post is getting long, if interested, back up and read the prior.
To Ken:
Everything you think you understand, I completely agree with - Except the miss issue.
I suspect you are lean on that cylinder because the only other answer that could make any sense would be vastly retarded timing on that one cylinder, and we know that cannot happen.
Even with the mixture to one cylinder was significantly lean, that cylinder may still not misfire. (Aircraft ignition is pretty robust that way.) It may not even lose a whole lot of BMEP (that would require more MAP to make engine speed for your normal IAS), but it would slow the flame speed in that cylinder enough that the fire was still burning when the exhaust valve opened. (This is also real hard on exhaust valves.)
Even if you had the fuel rate instrument on many IO-320s, you might not have been able to detect the change.
If you were experiencing a notable loss of power and a severe missfire, I would suspect that an exhaust valve was a problem as that will also cause an individual high EGT. There are not many other common mode failures that will get you there.
Good Luck and please let me know what you find.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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