Today's Message Index:
----------------------
1. 12:14 AM - Tiger Annual update. (TeamGrumman@aol.com)
2. 01:58 AM - Re: Tiger Annual update. (Philip A. C.)
3. 06:59 AM - Tiger Annual update. (Fiveonepw@aol.com)
4. 08:19 AM - Re: Tiger Annual update. (Philip A. C.)
5. 09:12 AM - Re: Tiger Annual update. (Fiveonepw@aol.com)
6. 09:58 AM - Re: Tiger Annual update. (Philip A. C.)
7. 10:18 AM - Re: Tiger Annual update. (Scott Bilinski)
8. 10:30 AM - Re: Tiger Annual update. (Fiveonepw@aol.com)
9. 10:48 AM - Re: Tiger Annual update. (TeamGrumman@aol.com)
10. 10:50 AM - Re: Tiger Annual update. (TeamGrumman@aol.com)
11. 11:16 AM - Re: Tiger Annual update. (Scott Bilinski)
12. 11:30 AM - Re: Tiger Annual update. (Archie)
13. 11:33 AM - Re: Tiger Annual update. (TeamGrumman@aol.com)
14. 11:41 AM - Re: Tiger Annual update. (TeamGrumman@aol.com)
15. 12:03 PM - Re: Tiger Annual update. (flyv35b)
16. 01:49 PM - Re: Tiger Annual update. (Fiveonepw@aol.com)
17. 06:06 PM - Re: Tiger Annual update. (TeamGrumman@aol.com)
18. 07:13 PM - Re: Tiger Annual update. (cgalley)
Message 1
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| Subject: | Tiger Annual update. |
--> Engines-List message posted by: TeamGrumman@aol.com
I mentioned a Tiger that came in for an annual.
I took the cylinders to LyCon for inspection. No serious cracks, just some
small stress cracks. That was the good news. The bad news was that the
valve guides were all blown out. To the tune of 0.020. Several exhaust valves
had sunk into the head quite a way. Ken said it looked like the engine had
been running on auto fuel. ALL of the intakes were tulipped; that is, they
had been run so hot that they were deformed. Ken said it looked like the
engine had been run real lean.
However. The owner has placed this plane on lease back and placarded the EI
CHT/EGT gauge to say " DO NOT LEAN for an EGT HIGHER THAN 1200 degrees. "
or something to that effect. When I asked him about it, he said if the EGTs
were kept the CHTs would be cool. Nice in theory.
My experience is that a rich mixture has very little effect on keeping the
CHTs down. Mixture has a big effect on EGT though.
The cylinders in question have less than 600 hours on them. And, they are
trashed. #3 was pulled at 200 hours and had the valves reground and
reinstalled. These cylinders WERE new ECI cylinders with Cermi-Nil. The cylinders
had
0.003 choke. It's supposed to be 2-3 times that. All of these cylinders
had a lot of excess flashing between the fins. The area between the valves
(under the plug) was about 70-80% blocked off by flashing. The spaces between
the fins on the head otherwise were also partially blocked with flashing.
Add to this very poor baffling and I think this engine had been run really hot
for a long time.
I suspect that even though the EGT was kept below 1200, the CHTs were high
enough to cause serious damage to the engine. I discussed with Ken the
possibility of instrumenting a head to measure the exhaust valve guide temperature.
I would be curious to see if a mixture lean enough to make the CHT go down
and the EGT to peak would make the guide temperature to go down. Maybe even
install several EGT probes in the riser and exhaust pipe to see if the high EGT
is across the length of the pipe or more localized.
Just to recap. I leaned aggressively during a takeoff from Bakersfield a
few weeks ago and brought the CHTs down from 440+ to 417. The temp difference
between the 4 CHTs was less than 2 degrees. Ken (at LyCon) could not be
pinned down as to whether the lower CHT was helping the valve guides or not.
Does anyone have an idea how to measure the temp on the face of a valve while
it's running?
Gary
Message 2
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| Subject: | Tiger Annual update. |
--> Engines-List message posted by: "Philip A. C." <philipac@suncraftgroup.com>
Gary,
There has been some pretty extensive work done on leaning procedures, by a
team that ultimately set up a series of seminars on the matter.
It is REALLY worth studying the matter, you'll find out that most of the
"correct leaning procedures" taught and applied in GA today are BS.
You want to check the following:
http://www.avweb.com/news/columns/182544-1.html
Check also all the articles on maintenance and operation on this site, they
make a good read.
Then go to:
http://www.gami.com/framestxtonly.htm
Check "Future Series", these are good articles.
It appears that the good ol' guys of the big radials times knew a lot of
stuff about engine operation, stuff that has been "lost" since.
As for exhaust valves problems in Lycomings, there are two guys who seem to
have nailed one particular underlying problem, specific to Lycoming.
Interesting stuff as well:
http://egaa.home.mindspring.com/valves.html
I did some pretty extensive research on these and other engine operation
related topics, and was astonished to see how little was really known in the
average hangar. If you want more info I can send you compilations of
articles, etc. Just drop a note in my mail.
Philip
-----Original Message-----
From: owner-engines-list-server@matronics.com
[mailto:owner-engines-list-server@matronics.com]On Behalf Of
TeamGrumman@aol.com
Subject: Engines-List: Tiger Annual update.
--> Engines-List message posted by: TeamGrumman@aol.com
I mentioned a Tiger that came in for an annual.
I took the cylinders to LyCon for inspection. No serious cracks, just some
small stress cracks. That was the good news. The bad news was that the
valve guides were all blown out. To the tune of 0.020. Several exhaust
valves
had sunk into the head quite a way. Ken said it looked like the engine had
been running on auto fuel. ALL of the intakes were tulipped; that is, they
had been run so hot that they were deformed. Ken said it looked like the
engine had been run real lean.
However. The owner has placed this plane on lease back and placarded the
EI
CHT/EGT gauge to say " DO NOT LEAN for an EGT HIGHER THAN 1200 degrees. "
or something to that effect. When I asked him about it, he said if the
EGTs
were kept the CHTs would be cool. Nice in theory.
My experience is that a rich mixture has very little effect on keeping the
CHTs down. Mixture has a big effect on EGT though.
The cylinders in question have less than 600 hours on them. And, they are
trashed. #3 was pulled at 200 hours and had the valves reground and
reinstalled. These cylinders WERE new ECI cylinders with Cermi-Nil. The
cylinders had
0.003 choke. It's supposed to be 2-3 times that. All of these cylinders
had a lot of excess flashing between the fins. The area between the valves
(under the plug) was about 70-80% blocked off by flashing. The spaces
between
the fins on the head otherwise were also partially blocked with flashing.
Add to this very poor baffling and I think this engine had been run really
hot
for a long time.
I suspect that even though the EGT was kept below 1200, the CHTs were high
enough to cause serious damage to the engine. I discussed with Ken the
possibility of instrumenting a head to measure the exhaust valve guide
temperature.
I would be curious to see if a mixture lean enough to make the CHT go down
and the EGT to peak would make the guide temperature to go down. Maybe
even
install several EGT probes in the riser and exhaust pipe to see if the high
EGT
is across the length of the pipe or more localized.
Just to recap. I leaned aggressively during a takeoff from Bakersfield a
few weeks ago and brought the CHTs down from 440+ to 417. The temp
difference
between the 4 CHTs was less than 2 degrees. Ken (at LyCon) could not be
pinned down as to whether the lower CHT was helping the valve guides or not.
Does anyone have an idea how to measure the temp on the face of a valve
while
it's running?
Gary
Message 3
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| Subject: | Tiger Annual update. |
--> Engines-List message posted by: Fiveonepw@aol.com
Re: Bill Scott/Bill Marvel examination of Lycoming oil flow design problem
After review of the entire series describing lack of oil flow to the rocker
boxes, it would appear that a flat along the side of the lifter (similar to the
brand C design) extending from the annulus all the way to the pushrod end of
the mushroom-style lifter would effectively allow oil to flow from the lifter
gallery, along the side of the lifter provided by the flat, into the pushrod
tube and therefore to the rocker box, regulated of course by the size of the
flat. This seems pretty simple and obvious. Any idea if this was ever tried or
is there a fundamental flaw in this concept?
Interesting stuff-
Mark Phillips - O-320 (E3D) powered RV-6A
Columbia, TN
Message 4
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| Subject: | Tiger Annual update. |
--> Engines-List message posted by: "Philip A. C." <philipac@suncraftgroup.com>
Seems to me that if the oil has free passage by the lifter's side, it would
see no reason why it should go and do its job of pressurizing the inside of
the lifter. Pretty lazy things, these fluids: you give them a chance to
escape the easy way, and they drop everything they are doing...
I may be mistaken, though, and I'd be interested if someone has the correct
answer.
Philip
-----Original Message-----
From: owner-engines-list-server@matronics.com
[mailto:owner-engines-list-server@matronics.com]On Behalf Of
Fiveonepw@aol.com
Subject: Engines-List: Tiger Annual update.
--> Engines-List message posted by: Fiveonepw@aol.com
Re: Bill Scott/Bill Marvel examination of Lycoming oil flow design problem
After review of the entire series describing lack of oil flow to the rocker
boxes, it would appear that a flat along the side of the lifter (similar to
the
brand C design) extending from the annulus all the way to the pushrod end of
the mushroom-style lifter would effectively allow oil to flow from the
lifter
gallery, along the side of the lifter provided by the flat, into the pushrod
tube and therefore to the rocker box, regulated of course by the size of the
flat. This seems pretty simple and obvious. Any idea if this was ever
tried or
is there a fundamental flaw in this concept?
Interesting stuff-
Mark Phillips - O-320 (E3D) powered RV-6A
Columbia, TN
Message 5
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| Subject: | Re: Tiger Annual update. |
--> Engines-List message posted by: Fiveonepw@aol.com
In a message dated 10/29/04 10:20:37 AM Central Daylight Time,
philipac@suncraftgroup.com writes:
> Seems to me that if the oil has free passage by the lifter's side, it would
> see no reason why it should go and do its job of pressurizing the inside of
> the lifter. Pretty lazy things, these fluids: you give them a chance to
> escape the easy way, and they drop everything they are doing...
>>>>>>
I don't believe the flat would have to be very large to allow a significant
inclease in volume, (compared to normal leakage around the outside of the
lifter) which is what is needed to carry away the heat. I know this would be
x8
lifters (or possibly just 4 for exhaust valve cooling) but with 40-80 psi
available, providing at least triple the "normal" leakage, I doubt much pressure
would be lost- I've no idea if the pressure relief valve is normally allowing a
fair volume of by-pass in normal operation anyway? (somebody else do the math-
VERY challenged in that department!)
Mark
Message 6
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| Subject: | Tiger Annual update. |
--> Engines-List message posted by: "Philip A. C." <philipac@suncraftgroup.com>
Mark,
I know what you mean, had thought of it, but what made me doubtful is that
the pressure drop depends on the flow you have to start whith. As I
understand it, the flow to the lifter is quite puny, and to substract any
reasonable amount from it may upset the pressure enough to create a problem
while trying to solve another.
One of the Bills told me a few weeks ago that they are experimenting with a
permanent fix, and that they are close to have it worked out. You may try to
drop them a line, I keep an eye on their site to see if they post anything
in regard.
Philip
-----Original Message-----
From: owner-engines-list-server@matronics.com
[mailto:owner-engines-list-server@matronics.com]On Behalf Of
Fiveonepw@aol.com
Subject: Re: Engines-List: Tiger Annual update.
--> Engines-List message posted by: Fiveonepw@aol.com
In a message dated 10/29/04 10:20:37 AM Central Daylight Time,
philipac@suncraftgroup.com writes:
> Seems to me that if the oil has free passage by the lifter's side, it
would
> see no reason why it should go and do its job of pressurizing the inside
of
> the lifter. Pretty lazy things, these fluids: you give them a chance to
> escape the easy way, and they drop everything they are doing...
>>>>>>
I don't believe the flat would have to be very large to allow a significant
inclease in volume, (compared to normal leakage around the outside of the
lifter) which is what is needed to carry away the heat. I know this would
be x8
lifters (or possibly just 4 for exhaust valve cooling) but with 40-80 psi
available, providing at least triple the "normal" leakage, I doubt much
pressure
would be lost- I've no idea if the pressure relief valve is normally
allowing a
fair volume of by-pass in normal operation anyway? (somebody else do the
math-
VERY challenged in that department!)
Mark
Message 7
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| Subject: | Tiger Annual update. |
--> Engines-List message posted by: Scott Bilinski <bilinski@kyocera-wireless.com>
Your keeping an eye on their site.......Which one is that?
At 05:56 PM 10/29/2004 +0100, you wrote:
>--> Engines-List message posted by: "Philip A. C."
><philipac@suncraftgroup.com>
>
>Mark,
>
>I know what you mean, had thought of it, but what made me doubtful is that
>the pressure drop depends on the flow you have to start whith. As I
>understand it, the flow to the lifter is quite puny, and to substract any
>reasonable amount from it may upset the pressure enough to create a problem
>while trying to solve another.
>
>One of the Bills told me a few weeks ago that they are experimenting with a
>permanent fix, and that they are close to have it worked out. You may try to
>drop them a line, I keep an eye on their site to see if they post anything
>in regard.
>
>Philip
>
>-----Original Message-----
>From: owner-engines-list-server@matronics.com
>[mailto:owner-engines-list-server@matronics.com]On Behalf Of
>Fiveonepw@aol.com
>To: engines-list@matronics.com
>Subject: Re: Engines-List: Tiger Annual update.
>
>
>--> Engines-List message posted by: Fiveonepw@aol.com
>
>In a message dated 10/29/04 10:20:37 AM Central Daylight Time,
>philipac@suncraftgroup.com writes:
>
> > Seems to me that if the oil has free passage by the lifter's side, it
>would
> > see no reason why it should go and do its job of pressurizing the inside
>of
> > the lifter. Pretty lazy things, these fluids: you give them a chance to
> > escape the easy way, and they drop everything they are doing...
>
> >>>>>>
>I don't believe the flat would have to be very large to allow a significant
>inclease in volume, (compared to normal leakage around the outside of the
>lifter) which is what is needed to carry away the heat. I know this would
>be x8
>lifters (or possibly just 4 for exhaust valve cooling) but with 40-80 psi
>available, providing at least triple the "normal" leakage, I doubt much
>pressure
>would be lost- I've no idea if the pressure relief valve is normally
>allowing a
>fair volume of by-pass in normal operation anyway? (somebody else do the
>math-
>VERY challenged in that department!)
>
>Mark
>
>
Scott Bilinski
Eng dept 305
Phone (858) 657-2536
Pager (858) 502-5190
Message 8
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| Subject: | Re: Tiger Annual update. |
--> Engines-List message posted by: Fiveonepw@aol.com
In a message dated 10/29/04 12:00:05 PM Central Daylight Time,
philipac@suncraftgroup.com writes:
> One of the Bills told me a few weeks ago that they are experimenting with a
> permanent fix, and that they are close to have it worked out.
>>>>>>>
Cool- will be interesting to see- I'd never really heard about the flow
"problem" until you provided the link, and it looks like they've done their
homework- Thanks!
Mark
Message 9
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| Subject: | Re: Tiger Annual update. |
--> Engines-List message posted by: TeamGrumman@aol.com
In a message dated 10/29/04 1:58:53 AM, philipac@suncraftgroup.com writes:
> http://www.avweb.com/news/columns/182544-1.html
>
Thanks for your help,
I've read most if not all of the articles available on leaning. I
understand the confusion most people have and continue to question why engine builders
recommend running the engine rich.
I was curious as to whether or not anyone had investigated the temps of the
valve guide and valve itself during leaning.
My internet connection (DSL) really sucks today so I'll have to try another
time to look at the sites you sent.
I also found articles written in the 30's and 40's regarding sodium filled
valves and all of the research that was done on air cooled engines. I agree,
most 'hangar' talk reveals a complete lack of knowledge on the subject.
Gary
Message 10
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| Subject: | Re: Tiger Annual update. |
--> Engines-List message posted by: TeamGrumman@aol.com
In a message dated 10/29/04 1:58:53 AM, philipac@suncraftgroup.com writes:
> http://egaa.home.mindspring.com/valves.html
>
Regarding the article here from Scott et al. They come to a conclusion that
is totally in disagreement with basic research done by Kettering et al.
Draw your own conclusions. I believe Kettering.
Message 11
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| Subject: | Re: Tiger Annual update. |
--> Engines-List message posted by: Scott Bilinski <bilinski@kyocera-wireless.com>
Sorry to do this again but who is Kettering?
At 01:47 PM 10/29/2004 -0400, you wrote:
>--> Engines-List message posted by: TeamGrumman@aol.com
>
>
>In a message dated 10/29/04 1:58:53 AM, philipac@suncraftgroup.com writes:
>
>
> > http://egaa.home.mindspring.com/valves.html
> >
>
>Regarding the article here from Scott et al. They come to a conclusion that
>is totally in disagreement with basic research done by Kettering et al.
>
>Draw your own conclusions. I believe Kettering.
>
>
Scott Bilinski
Eng dept 305
Phone (858) 657-2536
Pager (858) 502-5190
Message 12
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| Subject: | Re: Tiger Annual update. |
--> Engines-List message posted by: "Archie" <archie97@earthlink.net>
Without getting into a dissertation here, suffice it to say that in the
aircraft experimental/racing engines, I have installed bronze liners
in the lifter bores, and enlarged all oil passages, placing restrictors
in the areas in which I wanted reduced flow.
There are many reasons for this, and I will not go into details,
but think about it. Nuff said.
Archie Frangoudis
Archie's Racing Service
Message 13
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| Subject: | Re: Tiger Annual update. |
--> Engines-List message posted by: TeamGrumman@aol.com
Kettering and company did extensive research on fuel and oil and engines druing
the 30's and 40s. I don't have the references at hand but I do have them on
mt web site.
www.AuCountry.com
Click on TeamGrumman
Click on Technical.
Gary
Message 14
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| Subject: | Re: Tiger Annual update. |
--> Engines-List message posted by: TeamGrumman@aol.com
<<After review of the entire series describing lack of oil flow to the rocker
boxes, it would appear that a flat along the side of the lifter (similar to the
brand C design) extending from the annulus all the way to the pushrod end of
the mushroom-style lifter would effectively allow oil to flow from the lifter
gallery, along the side of the lifter provided by the flat, into the pushrod
tube and therefore to the rocker box, regulated of course by the size of the
flat. This seems pretty simple and obvious. Any idea if this was ever tried or
is there a fundamental flaw in this concept?>>
Sodium filled valves are to be run with a minimum amount of oil. Heat transfer
to the head is INCREASED with a minimum amount of oil.
Message 15
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| Subject: | Re: Tiger Annual update. |
--> Engines-List message posted by: "flyv35b" <flyv35b@ashcreekwireless.com>
Ken (at LyCon) could not be
> pinned down as to whether the lower CHT was helping the valve guides or
> not.
A 20F reduction in CHT (and possibly more) is achievable by running on the
lean side of peak vs. a richer, max power setting. But, the real question
is not that the valve guide temp will be lower (it obviously will) but will
it be significant enough to provide a real benefit? A temperature drop of
100F may be needed, or even more, to achieve any tangible benefits. Seems
to me that the only "easy" way to achieve this kind of temperature reduction
would be with oil cooling.
> Does anyone have an idea how to measure the temp on the face of a valve
> while
> it's running?
>
> Gary
In John Schwaner's Sky Ranch Engineering Manual he shows a curve of valve
temperature for the solid stem vs. the sodium valve as a function of
distance away from the valve face (up the stem) based (apparently) on Eaton
Manufacturing Co. data (the valve manufacturer). So they obviously have
measured valve temperatures and probably the guide temperatures as well.
BTW, the two curves are mislabeled; the names should be reversed. Notice
how much hotter the valve stem is in the area where the head is welded on
and at the lower portion of the guide.
Cliff A&P/IA
----- Original Message -----
From: <TeamGrumman@aol.com>
Subject: Engines-List: Tiger Annual update.
> --> Engines-List message posted by: TeamGrumman@aol.com
>
> I mentioned a Tiger that came in for an annual.
>
> I took the cylinders to LyCon for inspection. No serious cracks, just
> some
> small stress cracks. That was the good news. The bad news was that the
> valve guides were all blown out. To the tune of 0.020. Several exhaust
> valves
> had sunk into the head quite a way. Ken said it looked like the engine
> had
> been running on auto fuel. ALL of the intakes were tulipped; that is,
> they
> had been run so hot that they were deformed. Ken said it looked like the
> engine had been run real lean.
>
> However. The owner has placed this plane on lease back and placarded the
> EI
> CHT/EGT gauge to say " DO NOT LEAN for an EGT HIGHER THAN 1200 degrees.
> "
> or something to that effect. When I asked him about it, he said if the
> EGTs
> were kept the CHTs would be cool. Nice in theory.
>
> My experience is that a rich mixture has very little effect on keeping the
> CHTs down. Mixture has a big effect on EGT though.
>
> The cylinders in question have less than 600 hours on them. And, they
> are
> trashed. #3 was pulled at 200 hours and had the valves reground and
> reinstalled. These cylinders WERE new ECI cylinders with Cermi-Nil.
> The cylinders had
> 0.003 choke. It's supposed to be 2-3 times that. All of these
> cylinders
> had a lot of excess flashing between the fins. The area between the
> valves
> (under the plug) was about 70-80% blocked off by flashing. The spaces
> between
> the fins on the head otherwise were also partially blocked with flashing.
> Add to this very poor baffling and I think this engine had been run really
> hot
> for a long time.
>
> I suspect that even though the EGT was kept below 1200, the CHTs were high
> enough to cause serious damage to the engine. I discussed with Ken the
> possibility of instrumenting a head to measure the exhaust valve guide
> temperature.
> I would be curious to see if a mixture lean enough to make the CHT go down
> and the EGT to peak would make the guide temperature to go down. Maybe
> even
> install several EGT probes in the riser and exhaust pipe to see if the
> high EGT
> is across the length of the pipe or more localized.
>
> Just to recap. I leaned aggressively during a takeoff from Bakersfield a
> few weeks ago and brought the CHTs down from 440+ to 417. The temp
> difference
> between the 4 CHTs was less than 2 degrees. Ken (at LyCon) could not be
> pinned down as to whether the lower CHT was helping the valve guides or
> not.
>
> Does anyone have an idea how to measure the temp on the face of a valve
> while
> it's running?
>
> Gary
>
>
>
Message 16
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| Subject: | Re: Tiger Annual update. |
--> Engines-List message posted by: Fiveonepw@aol.com
In a message dated 10/29/04 1:41:48 PM Central Daylight Time,
TeamGrumman@aol.com writes:
> Sodium filled valves are to be run with a minimum amount of oil. Heat
> transfer to the head is INCREASED with a minimum amount of oil.
>>>>
If I understand correctly, you are saying the minimum amount of oil between
the valve stem and the guide? (oil is an insulator here? less oil, better heat
xfer?)
I thought the issue with incresing the oil flow was the amount of oil flowing
over the part of the stem exposed within the rocker box, which is largely
surrounded by air (REAL good insulator) and that by increasing the flow of oil
coming out the pushrod and tube, more oil runs over the end of the valve stem
and rocker where it is in contact with the stem, absorbing additional heat from
the stem- how would this have any effect on heat xfer from the stem to the
guide and therefore to the head?
Mark
Message 17
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| Subject: | Re: Tiger Annual update. |
--> Engines-List message posted by: TeamGrumman@aol.com
In a message dated 10/29/04 1:50:29 PM, Fiveonepw@aol.com writes:
> surrounded by air (REAL good insulator) and that by increasing the flow of
> oil
> coming out the pushrod and tube, more oil runs over the end of the valve
> stem
> and rocker where it is in contact with the stem, absorbing additional heat
> from
>
My understanding is that the excess oil will coke on the vavle stem. This
reduces the clearance and causes sticking.
Message 18
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| Subject: | Re: Tiger Annual update. |
--> Engines-List message posted by: "cgalley" <cgalley@qcbc.org>
Only on the passageway side not the Spring side of the guide. When we clean
the guide it is generally lead deposits. How can I say that? We use Hoppes'
#9 lead dissolver on guides that are still operating. This frees them up but
the only cure is to drop the valve into the cylinder, clean the guide, and
reassemble according to the SB put out by Lycoming. I have a man that can
do the entire procedure in under a half hour.
Cy Galley - Chair,
AirVenture Emergency Aircraft Repair
A Service Project of Chapter 75
EAA Safety Programs Editor - TC
EAA Sport Pilot
----- Original Message -----
From: <TeamGrumman@aol.com>
Subject: Re: Engines-List: Tiger Annual update.
> --> Engines-List message posted by: TeamGrumman@aol.com
>
>
> In a message dated 10/29/04 1:50:29 PM, Fiveonepw@aol.com writes:
>
>
> > surrounded by air (REAL good insulator) and that by increasing the flow
of
> > oil
> > coming out the pushrod and tube, more oil runs over the end of the valve
> > stem
> > and rocker where it is in contact with the stem, absorbing additional
heat
> > from
> >
>
> My understanding is that the excess oil will coke on the vavle stem.
This
> reduces the clearance and causes sticking.
>
>
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