---------------------------------------------------------- Engines-List Digest Archive --- Total Messages Posted Wed 01/17/07: 3 ---------------------------------------------------------- Today's Message Index: ---------------------- 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 _____________________________________ Time: 02:20:57 PM PST US From: "Larry L. Tompkins, P.E." 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 2 _____________________________________ Time: 03:01:42 PM PST US From: "Archie" Subject: Re: Engines-List: 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 _____________________________________ Time: 03:14:53 PM PST US From: "n801bh@netzero.com" Subject: Re: Engines-List: 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." 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 ======================== ======================== ======================== ======================== ======================== ================ Roller lifters in an engine that turns 2700 rpms will last longer then your plane will...


Ben Haas
N801BH
www.haaspo werair.com

-- "Larry L. Tompkins, P.E."  <tompkinsl@integra.net> wrote:
You have made a correct observation abo ut 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-o ff runs and climb-outs will seem weaker.  Top speed would be down s lightly.
 
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).
 
This is probably more information than you wanted, but I hope it helps.
 
Larry
 
 


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