Interested in 320 Rebuild Information

[Fly Guy]

I'm new to experimental aircraft and am surprised by a number of
things. The first was a peek inside a Lycoming IO-360. I've spent
most of my life around things mechanical...from building cars and
racing motorcycles so my first look inside a Lycoming was a surprise.

Given the size of the reciprocating components, it'd appear that the
engine beats itself to death before it wears anything out. The size
of the connecting rod pins, push rods, and valve spring pressures, on
the surface, seem to be way out of scale for a 180 HP engine.

Thin walled wrist pins that withstand 7000 HP in Funny Cars and push
rods that weigh in grams, not pounds that withstand 700 HP and 8000
RPM are common place, even in "hot" street machines. I guess what I'm
most curious about is why this technology, common place for 20 years,
is not included in certificated engines?

I was also stymied by some odd looking (excuse me for using the wrong
terminology) floating counter weights on the crankshaft. I'd expected
to see a solid, balanced crank. Can anyone help me understand the
advantage to have floating weights?

Why do you suppose they made the cylinder and head a single piece?
There are some pretty reliable, high horse power, high cylinder
pressure motorcycle engines that use a separate head and cylinder. If
the single piece was better, I'd expect factory race teams to follow
suit.

Any help would be appreciated.

[Bill Daniels]

"Fly Guy" > wrote in message
...
> I'm new to experimental aircraft and am surprised by a number of
> things. The first was a peek inside a Lycoming IO-360. I've spent
> most of my life around things mechanical...from building cars and
> racing motorcycles so my first look inside a Lycoming was a surprise.
>
> Given the size of the reciprocating components, it'd appear that the
> engine beats itself to death before it wears anything out. The size
> of the connecting rod pins, push rods, and valve spring pressures, on
> the surface, seem to be way out of scale for a 180 HP engine.
>
> Thin walled wrist pins that withstand 7000 HP in Funny Cars and push
> rods that weigh in grams, not pounds that withstand 700 HP and 8000
> RPM are common place, even in "hot" street machines. I guess what I'm
> most curious about is why this technology, common place for 20 years,
> is not included in certificated engines?
>
> I was also stymied by some odd looking (excuse me for using the wrong
> terminology) floating counter weights on the crankshaft. I'd expected
> to see a solid, balanced crank. Can anyone help me understand the
> advantage to have floating weights?
>
> Why do you suppose they made the cylinder and head a single piece?
> There are some pretty reliable, high horse power, high cylinder
> pressure motorcycle engines that use a separate head and cylinder. If
> the single piece was better, I'd expect factory race teams to follow
> suit.
>
> Any help would be appreciated.
>
>
There are some really knowledgeable engine people on this newsgroup who will
probably give you better answers than I can, but I'll give it a try.

Direct drive aircraft engines produce their power at very low RPMs compared
to the automotive engines you mentioned because a propeller needs to turn at
the lowest possible RPM for aerodynamic efficiency. That means that for a
given HP the torque must be far higher at that lower RPM. (You remember
that old hotrod formula HP= RPM x Torque divided by 5252?)

Higher torque means that the stressed parts need to be much more robust -
thus the beefy crank and rods in the Lycoming. Direct drive aircraft
engines are more like low RPM tractor engines than high revving race car
engines.
Keep in mind that all that torque is from only four cylinders.

As for the floating counterweights, a seemingly rigid crankshaft/propeller
system responds in strange ways to two massive power pulses each
revolution - it wants to wiggle around. The crank twists and the prop bends
with each whack. The dynamic counterweights help smooth that out a bit.

These low RPM, high power engines work with a lot of gas pressure above the
piston which is why the heads are integral with the cylinders. Back when
this design was adopted, head gaskets did tend to leak frequently.

A guy like you will probably want to know, "why direct drive?" Well,
they're cheaper to make that way. If you use a gear reduction system
(called a Propeller Speed Reduction Unit by this crowd) , the engine gets
heavier and more complicated. PRSU's tend to work better with a larger
number of cylinders - you can feed them smoother power that way. A lot of
people think that aircraft engine design should follow the race car example
with high revving 8 cylinder engines geared down to slow props. I tend to
agree.

There may be a better way and that is a diesel engine. Diesels produce lots
of torque at low RPM's and they use a lot less fuel doing it. There's no
worry about detonation either. I like that idea too.

Bill Daniels