Lycoming Oil Pan

[plongson]

Here's a technical question...What is behind the design of the oil pan on a o-320 oil pan. The carburetor attaches to the bottom and the intake runners flow through the sump of the pan.

I've worked on hotrods, boats, motorcycles etc. and I'm not familiar with this design. Gott'a be a good reason...I've got a million guesses but no solid answer...

 

[kyleb]

Heats the intake and carb to reduce/ eliminate carb icing. Also helps cool the oil.

In the downside, it heats the induction air and reduces power.

 

[plongson]

That makes sense...I like the icing theory/idea.
Thanks!

 

[Salty]

Icing happens before the oil pan, so I never understood that theory.

 

[Mxfarm]

Engine cooling is what I’ve been told - I’d think there would have to be performance costs.

 

[Bell206]

I've got a million guesses but no solid answer...

I've heard a 1M answers to the same with the other reasons more to physical fit by reducing the total engine height to fit in the cowling, etc., etc.

 

[plongson]

I also wondered/considered compactness of design...with the added benefit of essentially heating the carb assembly via conduction...I guess it works just fine. I'm always curious about what goes on in the minds of designers.

 

[Dana]

Icing happens before the oil pan, so I never understood that theory.

If it heats the carburetor via direct conduction, even if the incoming air is cooled to the freezing point, it may be less likely to adhere to the interior of the venturi, instead passing harmlessly through.

It must work because Lycomings aren't nearly as susceptible to icing as Continentals are.

 

[Dan Thomas]

I also wondered/considered compactness of design...with the added benefit of essentially heating the carb assembly via conduction...I guess it works just fine. I'm always curious about what goes on in the minds of designers.

Yes, it's conduction that reduces the ice risk, but icing is still possible on nice summer days with a carbed Lycoming. There are too many myths about that. The amount of air passing through that carb is large, and it's being cooled by pressure drop and by fuel evaporation, and conduction will only reduce, not eliminate, icing.

And the cooling of the air as it passes through the carb results in fuel droplets reaching the cylinder in many engines. Heating it with the oil can actually improve power by evaporating those droplets and exposing every fuel molecule to oxygen.

Ever look at the induction system on an O-470 or 520? Induction tubing right under the hot heads and cylinders, being heated by the cooling airflow off those hot components.

 

[plongson]

Think about this...here in 2022 we consider ourselves "SO" advanced and "MODERN", but those old timers really had an amazing handle of this stuff. Think of the engineers, designers and...(HOLY CRAP!!) the test pilots that took those things up and risked their lives to prove some new theory.

Uhhh, I'm sure I would not be up to THAT task. Those aviators deserve our gratitude!

 

[Capt. Geoffrey Thorpe]

In the automotive world, it was reasonably common to have an exhaust crossover or water passage directly under the carburetor to improve fuel vaporization and cylinder to cylinder air fuel distribution.

 

[Dan Thomas]

In the automotive world, it was reasonably common to have an exhaust crossover or water passage directly under the carburetor to improve fuel vaporization and cylinder to cylinder air fuel distribution.

Yup. V-8s had that channel. Once the engine started to burn oil, that channel would coke up and get plugged. The cooling of the exhaust flow through the channel did that. Engine performance would suffer. In sixes, they bolted the intake manifold to the exhaust manifold right under the carb. The airflow out of the carb hit that hot spot.



They didn't have to build it that way, but they did. Made the engine run better and more economically.

 

[asicer]

In sixes, they bolted the intake manifold to the exhaust manifold right under the carb. The airflow out of the carb hit that hot spot.

They didn't have to build it that way, but they did. Made the engine run better and more economically.

That arrangement pretty much rules out a cross-flow cylinder. And is a hemi head even possible with all the ports on one side?

 

[Dan Thomas]

That arrangement pretty much rules out a cross-flow cylinder. And is a hemi head even possible with all the ports on one side?

What does it matter if all auto engines are now injected?

 

[asicer]

What does it matter if all auto engines are now injected?

Apparently it mattered back in the 60's when Lotus Twin-Cam came out and the Ford Kent switched to crossflow, both of those engines being carburetted.

 

[Dan Thomas]

Apparently it mattered back in the 60's when Lotus Twin-Cam came out and the Ford Kent switched to crossflow, both of those engines being carburetted.

Yeah, but most inline six-cylinder engines weren't performance engines. They were dirt-simple, sturdy beasts meant to produce reliable, low-RPM power. I owned two Ford 300s, one in an '82 F150 and the other I put into my 1951 International L110 restoration. They were sometimes known as the "Sufferin' Six." They'd take a lot of abuse. https://jalopnik.com/heres-why-the-ford-300-inline-six-is-one-of-the-greates-1795351528

 

[pfarber]

That arrangement pretty much rules out a cross-flow cylinder. And is a hemi head even possible with all the ports on one side?

Inline engines are not the same a v banked engines.

Inlines are good for certain things, V banked engines are good for another.

An inline 6 is probably the most reliable high torque car motor you can ask for.

 

[asicer]

Inline engines are not the same a v banked engines.

Inlines are good for certain things, V banked engines are good for another.

An inline 6 is probably the most reliable high torque car motor you can ask for.

In American engines, perhaps. The Toyota 3M engine and BMW M30 engine are a couple of counterexamples.

 

[Timbeck2]

Looking at the fit and finish of the cast aluminum sump in the OP's picture, it's no small wonder why they always leak.

 

[Dan Thomas]

Looking at the fit and finish of the cast aluminum sump in the OP's picture, it's no small wonder why they always leak.

Strange. I never had leaking problems with the many Lycs we ran in the flight school airplanes. Not even at TBO. Most leaks were at the rocker box oil drain tube-to-case connections. Those short rubber hoses with the little screw clamps on them. Some other leaks were at the rocker box cover gaskets, and always had to do with the cork gaskets the engines came from Lycoming with. I usually changed them out for the red silicone gaskets even before the engine was first started. Much easier to get the cork gaskets off then instead of 200 hours later when they've been baked on. And one popular leak spot as at the base of the dipstick tube, where it screws into the case. It's lockwired, but you have the guys that always use a pipe wrench to tighten the dipstick, as if the oil will escape if you don't really wind down on it, and when the next guy goes to check the oil, all that friction loosens the tube and stretches the lockwire, and now we have a leak. So I used to take it off, clean all the oil off everything, put some Hi-Tack on a new gasket and reassemble it and let the Hi-Tack set. Lockwire, too. And train everyone, students and instructors, showing them that you only need to squish the dipstick O-ring a little bit and it will stay put.

I wish Lycoming would redesign that thing to use a bayonet-style closure. Stuff it in, turn it an eighth of a turn. Like a fuel cap. Can't overtighten it. Even the little Continentals from the 1940s had it better than that.

 

[plongson]

The dipstick...the Archer 180 I train in gets the oil checked a frigg'n dozen times a day. There are times it's screwed I so tight I gott'a take my Leatherman out for leverage. Most people just don't know the difference between tight and TOO TIGHT.

 

[Dan Thomas]

The dipstick...the Archer 180 I train in gets the oil checked a frigg'n dozen times a day. There are times it's screwed I so tight I gott'a take my Leatherman out for leverage. Most people just don't know the difference between tight and TOO TIGHT.

Yup. They screw it in while it has oil on the o-ring, often while the engine is still hot. Leave thing sit and cool down, and the oil squeezes out of the o-ring's interfaces and things get stiff, and a cold o-ring gets harder and more stubborn too.