Today's Message Index:
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1. 02:20 PM - Re: Lycoming Camshaft Question (Larry L. Tompkins, P.E.)
2. 03:01 PM - Re: Lycoming Camshaft Question (Archie)
3. 03:14 PM - Re: Lycoming Camshaft Question (n801bh@netzero.com)
Message 1
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| Subject: | Re: Lycoming Camshaft Question |
You have made a correct observation about which cam lobes are likely to
exhibit wear signs first.
A good sign that the cam lobes are worn is good compression but low
power. All other things being equal, your engine won't be able to make
the WOT static RPM that it could just after the engine was broken in and
developing full power and your take-off runs and climb-outs will seem
weaker. Top speed would be down slightly.
It will be interesting to see if roller tappets offer a durability
improvement for cam lobe wear. The great difficulty is that most of us
can't fly our aircraft frequently enough. If the engine operated every
day like a car there wouldn't be any internal corrosion issues. Perhaps
someone more familiar with with cam lobe surface corrosion, roller face
corrosion and internal needle bearing corrosion can comment. Race car
engines have used "roller cams" for almost three decades, but it took
nearly two decades before that to get all of the reliability problems
worked out. If the roller tappet hops and brinnells a needle bearing in
the roller, life is drastically reduced. Racing camshaft folks solved
this by reprofiling cam lobes and the addition of a "rev kit," which
are springs over the tappets themselves to keep the tappet riding on the
lobe. I don't see how that device could be incorporated in a Lycoming.
I have a hard time convincing myself that there is enought test &
development done on new designs, which is understandable since
production volumes are so low (compared to the auto industry, for
example).
This is probably more information than you wanted, but I hope it helps.
Larry
Message 2
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| Subject: | Re: Lycoming Camshaft Question |
Good answer, Larry
You covered the basics well.
Since the aircraft engine runs at an essentially steady RPM, lifter
bounce can be eliminated by adding a few more pounds of spring pressure.
The additional pressure is insignificant when using a roller, and a rev
kit would be unnecessary in this case..
Most aircraft reciprocating engines have less than 100 lbs on the seat,
whereas our racing engines run anywhere from 270 to 410, and have open
pressures around 1000 lbs.
Unfortunately, as I understand it, the factory rollers are not
rebuildable, and must be replaced, unlike the racing counterpart.
Archie
----- Original Message -----
From: Larry L. Tompkins, P.E.
To: engines-list@matronics.com
Sent: Wednesday, January 17, 2007 5:15 PM
Subject: Re: Engines-List: Lycoming Camshaft Question
You have made a correct observation about which cam lobes are likely
to exhibit wear signs first.
A good sign that the cam lobes are worn is good compression but low
power. All other things being equal, your engine won't be able to make
the WOT static RPM that it could just after the engine was broken in and
developing full power and your take-off runs and climb-outs will seem
weaker. Top speed would be down slightly.
It will be interesting to see if roller tappets offer a durability
improvement for cam lobe wear. The great difficulty is that most of us
can't fly our aircraft frequently enough. If the engine operated every
day like a car there wouldn't be any internal corrosion issues. Perhaps
someone more familiar with with cam lobe surface corrosion, roller face
corrosion and internal needle bearing corrosion can comment. Race car
engines have used "roller cams" for almost three decades, but it took
nearly two decades before that to get all of the reliability problems
worked out. If the roller tappet hops and brinnells a needle bearing in
the roller, life is drastically reduced. Racing camshaft folks solved
this by reprofiling cam lobes and the addition of a "rev kit," which
are springs over the tappets themselves to keep the tappet riding on the
lobe. I don't see how that device could be incorporated in a Lycoming.
I have a hard time convincing myself that there is enought test &
development done on new designs, which is understandable since
production volumes are so low (compared to the auto industry, for
example).
This is probably more information than you wanted, but I hope it
helps.
Larry
Message 3
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| Subject: | Re: Lycoming Camshaft Question |
Roller lifters in an engine that turns 2700 rpms will last longer then y
our plane will...
Ben Haas
N801BH
www.haaspowerair.com
-- "Larry L. Tompkins, P.E." <tompkinsl@integra.net> wrote:
You have made a correct observation about which cam lobes are likely to
exhibit wear signs first. A good sign that the cam lobes are worn is goo
d compression but low power. All other things being equal, your engine
won't be able to make the WOT static RPM that it could just after the en
gine was broken in and developing full power and your take-off runs and
climb-outs will seem weaker. Top speed would be down slightly. It will
be interesting to see if roller tappets offer a durability improvement f
or cam lobe wear. The great difficulty is that most of us can't fly our
aircraft frequently enough. If the engine operated every day like a ca
r there wouldn't be any internal corrosion issues. Perhaps someone more
familiar with with cam lobe surface corrosion, roller face corrosion an
d internal needle bearing corrosion can comment. Race car engines have
used "roller cams" for almost three decades, but it took nearly two deca
des before that to get all of the reliability problems worked out. If t
he roller tappet hops and brinnells a needle bearing in the roller, life
is drastically reduced. Racing camshaft folks solved this by reprofili
ng cam lobes and the addition of a "rev kit," which are springs over th
e tappets themselves to keep the tappet riding on the lobe. I don't see
how that device could be incorporated in a Lycoming. I have a hard tim
e convincing myself that there is enought test & development done on new
designs, which is understandable since production volumes are so low (c
ompared to the auto industry, for example). This is probably more inform
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<html>Roller lifters in an engine that turns 2700 rpms will last longer
then your plane will...<BR><BR><BR>Ben Haas<BR>N801BH<BR>www.haaspo
werair.com<BR><BR>-- "Larry L. Tompkins, P.E."
<tompkinsl@integra.net> wrote:<BR>
<DIV><FONT face=Arial size=2>You have made a correct observation abo
ut which cam lobes are likely to exhibit wear signs first.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>A good sign that the cam lobes are worn
is good compression but low power. All other things being equal,
your engine won't be able to make the WOT static RPM that it could just
after the engine was broken in and developing full power and your take-o
ff runs and climb-outs will seem weaker. Top speed would be down s
lightly.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>It will be interesting to see if roller
tappets offer a durability improvement for cam lobe wear. The gre
at difficulty is that most of us can't fly our aircraft frequently enoug
h. If the engine operated every day like a car there wouldn't be a
ny internal corrosion issues. Perhaps someone more familiar with w
ith cam lobe surface corrosion, roller face corrosion and internal needl
e bearing corrosion can comment. Race car engines have used "rolle
r cams" for almost three decades, but it took nearly two decades before
that to get all of the reliability problems worked out. If the rol
ler tappet hops and brinnells a needle bearing in the roller, life is dr
astically reduced. Racing camshaft folks solved this by reprofilin
g cam lobes and the addition of a "rev kit," which are springs ove
r the tappets themselves to keep the tappet riding on the lobe. I
don't see how that device could be incorporated in a Lycoming. I h
ave a hard time convincing myself that there is enought test & devel
opment done on new designs, which is understandable since productio
n volumes are so low (compared to the auto industry, for example).</FONT
></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>This is probably more information than
you wanted, but I hope it helps.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Larry</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV><PRE><B><FONT face=
"courier new,courier" color=#000000 size=2>
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