What is "not" parallel valve?

[BruceMe]

Ok, I really enjoy asking dumb questions... for someone who's flown probably 1800 of 2000 hours behind a Lycoming powerplant... and thinks they know engines, I can't find the answer.

What is _NOT_ a parallel valve Lycoming cylinder.. and why don't they get "sticky" valves? Is it that they valve angle better matches the rocker arm?

While I'm here... why didn't Lycoming put the cam on the bottom? Like... Continental, Franklin, Ford (Corvair)? I think it's just to lazy incentive to pilot/owners to fly more frequently to keep it lubed... our skills and the cam.

[N427EF]

What is _NOT_ a parallel valve Lycoming cylinder

An angle valve.
The angle valve cylinder provides for optimal combustion gas flow.
It is however significantly more complex and much more expensive than a simple parallel valve Lycoming.

[John RV8]

On some of the higher H.P. Lycoming engines the valve stems are "angled" (relative to each other) so they are further apart at rocker arm end than at the actual valve face. As opposed to the other engines where they are "parallel" to each other.

[BillL]

Originally Posted by BruceMe

Ok, I really enjoy asking dumb questions... for someone who's flown probably 1800 of 2000 hours behind a Lycoming powerplant... and thinks they know engines, I can't find the answer.

What is _NOT_ a parallel valve Lycoming cylinder.. and why don't they get "sticky" valves? Is it that they valve angle better matches the rocker arm?

I would think they angled the valves to get better volumetric efficiency, thus airflow and power. As mentioned, the angle allows the port geometry to flow more air. They might have better valve stem cooling that reduces the sticking. Probably luck.

While I'm here... why didn't Lycoming put the cam on the bottom? Like... Continental, Franklin, Ford (Corvair)? I think it's just to lazy incentive to pilot/owners to fly more frequently to keep it lubed... our skills and the cam.

Chevy made the Corvair. Otherwise, who knows? Why does Lycoming have to polish the connecting rods and Conti does not? Why not cross flow heads with intake on top? Designers do things differently, some end up better some don't, but everyone is stuck after it is done. Too bad Conti decided way long time ago not to pursue the experimental market.

Response in living color above.

[C-FAH Q]

Angle valve engines do get sticky valves.

[SHIPCHIEF]

Parallel valve engines have valve covers that look like square dog dishes.
Angle valve engines have flatter valve covers that are wider at the top.
I'm nobody, but I think the parallel valve heads flow without restricting the power of O-320 direct drive engines. O-360 direct drive engines with angle valve heads produce more power that parallel valve engines only at high RPM and full throttle.
Therefore, angle valve heads on a direct drive engine with a fixed pitch propeller might not have a take off or cruise power advantage over a similarly equipped parallel valve head. Fixed pitch prop take off RPM is usually 2200-2300 RPM.
If the camshaft is above the crankshaft, the push rods will be on top of the head. The intake & exhaust ports on the bottom of the engine do not have to be compromised to fit around the push rod tubes.
You could make a custom O-360 with (4 ea) TIO-540 turbo heads that have intake ports on the bottom and exhaust ports on the top. Airboaters call these "upstack" engines. That would create a nightmare of extra work and set back the first flight of an aircraft several years.
Modifying Lycoming engines for our use is common, but usually limited to compression ratio, exhaust system, ignition & intake systems.
I built a Mazda Turbo Rotary engine for my RV-8, but switched to a fairly stock O-360 Lycoming & Catto prop because I'm now more excited about flying than I am about engine development.