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

BruceMe · #1 09-20-2016, 05:34 AM

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.

pierre smith · #2 09-20-2016, 05:58 AM

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,

Planecrazy232 · #3 09-20-2016, 06:02 AM

Maybe we're putting the engines in upside down???

aturner · #4 09-20-2016, 06:57 AM

Don't know the answer, but the O-145, Lycoming's first boxer, had the cam down low:

https://en.m.wikipedia.org/wiki/Lyco...g_O-145_B2.jpg

rv7boy · #5 09-20-2016, 07:07 AM

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

6 Gun · #6 09-20-2016, 07:08 AM

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

BillL · #7 09-20-2016, 08:20 AM

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 . . . "

az_gila · #8 09-20-2016, 10:59 AM

Quote:

Originally Posted by Planecrazy232

Maybe we're putting the engines in upside down???

If you storing it as a core for a long time, then upside down is best with the case full of oil.

rv7boy · #9 09-20-2016, 11:49 AM

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?

Mel · #10 09-20-2016, 11:57 AM

Quote:

Originally Posted by rv7boy

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.