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Dear Mr. Lycoming, why is the cam so high up in the engine?!

BruceMe

Well Known Member
What is the trade-off? Why did Lycoming put the cam on top and every other flat engine manufacturer (Continental, Franklin, Jabiru, VW & GM/Corvair) put it on the bottom where it stays nice and happy bathed in oil when we neglect them?

This seems like a pretty big flaw. I've always wondered this.
 
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Nope

They're not 'bathed' in oil. The oil level is way below the cams on Continentals...they're all splash oiled, except for the bearings which are pressure lubed.

Best,
 
Maybe Mahlon will give his valued opinion.
P.S. Mahlon Russell, where are you?
 
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cam

Just overhauld a Perkins diesel that was 32 years old and all its life has been in a boat on the ocean in a damp hole in the bottom and not a spec of rust on the cam.Maybe the Lycoming cam is made from wrong type of metal also the valve train in the Perkins is set up with more pressure than Lyco turns same RPM @ 2700 and no cam spauling.Go figure.
Bob
 
Musings

An engine design is a tangled mass of tradeoffs and contractions. Very few are a clean sheet design, and even they have compromises for fitting manufacturing machinery on hand and other influences for commonalities of volume production for lowest cost.

A loop flow combustion chamber (both intake and exhaust on the same side) means pushrods are better located on the opposite side. Aero engine designs always want to have holes in the bottom to prevent a cylinder from completely filling with liquids, oil or fuel.

So - there is no magic reason for the cam to be located high as far as I have ever been able to determine. Lubrication is not an issue either way. Lycoming has done other odd things design wise, I honestly think that if it were not for a better parent company, they would not have ended up the prime supplier of engines today.

If our engines had positive crankcase ventilation the cams would probably not have corrosion problems. PCV is very problematic for the operational profile and its failure modes, so there are some other strong reasons it is not incorporated. It is not water that is the real issue, it is sulfur in the fuel. Sulfur has been removed from nearly all world fuels worldwide as it interferes with catalytic reactions and would make sulfates . . . . . . not good. Regardless, we have methods of preventing corrosion.

Litigation and certification is tangled in there too as they drive some very odd decisions and are in many ways an impediment to improvements. " Mr Lycoming, I see you improved your connecting rod. That means the previous design was inferior and you were hiding it. Ladies and gents of the jury . . . "
 
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In addition to the location of the camshaft, which is the original topic, I am also intrigued by the decision to support the camshaft in a journal machined in the casting(s). When I saw my O-320 apart during an overhaul a few years ago, I was surprised at this. Is this common practice for all aircraft engines?
 
In addition to the location of the camshaft, which is the original topic, I am also intrigued by the decision to support the camshaft in a journal machined in the casting(s). When I saw my O-320 apart during an overhaul a few years ago, I was surprised at this. Is this common practice for all aircraft engines?

If you are referring to the fact that the cam does not ride in bearings, since all loads on the cam are from the lifters and their force is from opposing directions, there are practically no loads on the bearing surfaces. Therefore bearings are not needed.
 
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If you are referring to the fact that the cam does not ride in bearings, since all loads on the cam are from the lifters and their force is from opposing directions, there is no load on the bearing surfaces. Therefore bearings are not needed.

OK, thanks, Mel, that's exactly what I was asking, but the second question is about whether that is common practice in all aircraft engines...or just Lycomings.
 
OK, thanks, Mel, that's exactly what I was asking, but the second question is about whether that is common practice in all aircraft engines...or just Lycomings.

Most all horizontally opposed engines use this practice.
 
Most all horizontally opposed engines use this practice.

It's interesting that the lowly VW bug engine has a below crank camshaft but does use separate camshaft bearings...:)

Yes, I know Mel was talking about aircraft engines...
 
If you are referring to the fact that the cam does not ride in bearings, since all loads on the cam are from the lifters and their force is from opposing directions, there is no load on the bearing surfaces. Therefore bearings are not needed.

Mel - it is not April 1st.
 
Maybe Mahlon will give his valued opinion.
P.S. Mahlon Russell, where are you?
I stop by once in a while and due post on occasion. Honestly have no ides why Lycoming wanted to do it that way. Likely just a design choice with no real reason behind it other than frontal area or length of the engine.
Good Luck,
Mahlon
 
I stop by once in a while and due post on occasion. Honestly have no ides why Lycoming wanted to do it that way. Likely just a design choice with no real reason behind it other than frontal area or length of the engine.
Good Luck,
Mahlon

OK...thanks for stopping by...hope life is treating you well. Stop in again anytime.
 
Occam's razor answer: Because they can sell more cams that way. LOL

Real answer: someone determined that through 1000 compromises that putting it there was the best overall layout for their engine. Besides, these engines are meant to be flown and if flown the cam life is good, so no reason not to do it this way.

BTW, we just spent a bunch of aircraft monetary units on a Continental here that had, gasp, internal corrosion. Guess what.... it sat around too much!!!

Fly regularly, fly often, use CamGuard, and worry about other things!!


(We have no affiliation with CamGuard, but we do have affiliation with all of the engine makers above! And Titan too!)
 
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The Lycoming TIO-541A1A has the camshaft beneath the crankshaft.
This is a top intake, bottom exhaust, 310 HP engine, later variants are 380 HP. The TGIO-541 is 450 HP and would scoot a Sport Class aircraft along rather well?
Rare & expensive?
 
Who is Lycoming, anyway?

"Dear Mr. Lycoming, why is the cam so high up in the engine?!"

I know the engine manufacturer took the name from the Pennsylvania county where it is located, but where did the county take it's name?

A brief internet search came up with this:

On April13, 1795, an act was passed erecting Lycoming
County from a portion of Northumberland. This
county, apparently, took its name from Lycoming Creek
which means "sandy stream" in the Indian tongue.

So, apparently there is no Mister Lycoming. But if there was, then he came from the 18th century, long before the invention of the airplane. So you're going to have to blame someone else for your cam placement.

That's your trivia for the day. Carry on...
 
"Dear Mr. Lycoming, why is the cam so high up in the engine?!"

I know the engine manufacturer took the name from the Pennsylvania county where it is located, but where did the county take it's name?

A brief internet search came up with this:

On April13, 1795, an act was passed erecting Lycoming
County from a portion of Northumberland. This
county, apparently, took its name from Lycoming Creek
which means "sandy stream" in the Indian tongue.

So, apparently there is no Mister Lycoming. But if there was, then he came from the 18th century, long before the invention of the airplane. So you're going to have to blame someone else for your cam placement.

That's your trivia for the day. Carry on...

And when you go up there and talk to the long-time residents (and denizens of the engine plant), the pronounce it "Licumming", which supposedly closer to the indigenous pronunciation. We've all been saying it wrong......:rolleyes:
 
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