aircraft engine details?

[gestalt1]

Hi all, I was just watching How Its Made and they showed the assembly of a Lycombing air cooled flat six. i know porsche engines have been used for aircraft, i did not realize there were other alternative engines similar to the porsche six that were so similar. the interesting things were that the crank was polished with a friction type pad were the rod bearing would be and a jack handle (it looked like a large connecting rod) used to polish the crank. they also used a silk string around the perimeter os the case mating edge to act as a seal. the really odd thing is they had a spark plug in the head but also one in the cylinder under the piston pointing to the bottom of the piston - what is that for? i'm just curious about these things and would like to know more - possibly details that could be used for our engines.

[DohertyCM]

Wish I could have seen that show...
I am around aircraft engines all the time, and i have never seen what you are describing..usually its just two plugs per cylinder like a porsche twin plug set up. Are you sure you saw it correctly?

[HawgRyder]

The polishing of the crank journals is an old way of "micro-polishing" usually with #600 or finer grit cloth.
The idea of the shoelace is to get all the way around the journal at the same time rather than part way and risk forming flats on the surface.
The second "plug" you saw is probably an oil spray injector for cooling the underside of the piston.
We call them piston squirters.
The silk thread was to help seal a less then perfect surface at the mating line.
And yes, very similar to our flat 6's.
Lycoming once made a series called the Tiara....a flat 6 with the cam shaft above the crank line (pushrod style) with the end of the cam driving the propeller....it did not need a reduction gear assembly, and so reduced the weight.
Bob

[cgarr]

Are you talking about the alum oil return line from the rockers?? Next week I might put up the Assembly of our Continental C-85 in OT

[Steve@Rennsport]

Sure looks like an IO-360 of some kind,...

[OldTee]

Intake tubes too small. More like a 0320 or new 0240. The vac pump drive is in the wrong place for a 0360 if my fading memory serves. But it has a pad for hyd prop control.

[gestalt1]

i think your right about the second plug - it must be an oil squirter. the show sometimes is a little in-accurite about the details. the engine did have the single over crank cam with pushrods. i also wonder why porsche chose to sandwich the cylinders between the head and case with the long studs instead of bolting the cylinder to the case directly.

[HawgRyder]

As per Harley Davidson with the Knuckle, Panhead, and Shovelhead....the cylinders are bolted to the case...the heads bolted to the top of the cylinders.
If Porsche were to do that...the cam chains would go through a elongation sequence with each heat/cool cycle.
As the cylinders heat up...they get taller (longer) and the cam chains would have to take up the slack.
I know we have chain tensioners, but I'm not sure they have enough take up to do the job in their current configuration.
Also...the exhaust....the return tubes...and averthing else that goes from the crankcase to the heads would need to be re-engineered.
Bob

[Steve@Rennsport]

Bob,....

Aircraft engine heads are screwed, not bolted, to the cylinders and they, in turn, are bolted to the case.

[OldTee]

The head and cylinder are one unit on aircraft engines. What would be a head is screwed on my the manufacturer and are not maintained in the field. Then the cylinders are bolted to the case to studs that go from one side to the other. The valves are operated from the cams thru push-rods and hydraulic lifters. Since the engines operate at below 3000 rpm it all works well and is very stout. An aircraft engine will go for between 2000 and 2500 hours between overhauls which equates to about 250,000 miles (@125 mph) and 300,000 miles.

[HawgRyder]

Steve....no argument in the attachment of the heads to cylinders...I have seen very old radial engines in both screw-in and one piece style (very old LeRohne I think).
Also reminds me of the old Offy engines...block and head all in one...no head gasket.
The point I was trying to make was the thermal expansion problems with maintaining valve settings or chain tension in such an engine.
And yes...I do know about the TBOH factor of aircraft engines ( flew for several years).
Bob

[blue72s]

Originally Posted by Steve@Rennsport

Aircraft engine heads are screwed, not bolted, to the cylinders and they, in turn, are bolted to the case.

Wow. Learn something new everyday. Does that solve the argument between dilavar and steel studs and if so, can't this be done to Porsche engines?

[cgarr]

The barrels are steel and the heads are alum so they are actually screwed on, pretty neet the way they do it, I dont know if it would hold up to high compression but it works good for our aircraft, I am finishing up the top overhaul on our O-200 this week, hopefully be in back in the air this weekend.

[Steve@Rennsport]

Originally Posted by blue72s

Wow. Learn something new everyday. Does that solve the argument between dilavar and steel studs and if so, can't this be done to Porsche engines?

Not really,...aircraft engines generally use 6 to 8 studs & nuts to fasten each cylinder to the case,.....

Such arrangements would require a totally redesigned case and thats not likely to happen.

[engguy]

All aircraft engines have 2 separate ignition systems, spark plugs included. Its a redundant saftey feature.
And there are some aircraft engines that have way more than just 6 or 8 studs and nuts holding the cylinder assemblies to the case.
And yes the heads can be removed and installed on new cylinders. On some makes the cooling fins on the cylinders are removeable as well.
And unlike doing a project like this for your car, there are strict guidelines that must be followed when overhauling one of these engines. If it causes an accident the mechanic could end up in prison if he didn't follow the rules.

[blue72s]

Originally Posted by cgarr

The barrels are steel

Like Porsche Biral cylinders?

[cgarr]

Originally Posted by blue72s

Like Porsche Biral cylinders?

All steel, not a liner.

[blue72s]

Originally Posted by cgarr

All steel

Cooling fins too?

[cgarr]

Originally Posted by blue72s

Cooling fins too?

Yes: Here is a good picture of how they are made:

[engguy]

Originally Posted by cgarr

All steel, not a liner.

All depends on the model and make of engine. No liners per say, steel barrel/cylinder with a flange on one end, cooling fins slipped on and head screwed on.
And yeah the pictured integral fin design for some.