The infamous geared Continental six

[seattle smitty]

Everybody who has had a ride in a 172 is familiar with the small Continental flat-six. I think it started at 145hp, was used by the old Aeronca Sedan, the Cessna 170 and 170B, and the 172, and it seems like they were getting 160hp out of it by the end of the run. Later engines had a beefed-up crankcase in answer to a cracking problem with early versions, IIRC. Anyway, a smooth, reliable engine, though probably heavier than a similarly-powerful Lyc four (0-320?).

But Continental also came up with a geared version of this engine, and it got a bad reputation. I knew a guy who died trying to cross Puget Sound in a C-175, the plane which featured the geared engine. Is there an old A&P here with personal expertise in that engine? What was the problem with it? Was it the gearbox? Did Continental try to fix it? One mechanic who had only a passing acquaintance with the engine told me he thought the problem was mostly operator error, by which I think he meant that pilots tended to get the motor lugged down rather than letting it rev.

Last I looked (quite a while ago, I admit) C-175s were pretty cheap, at least by our inflated standards. On paper a 175 converted to taildragger configuration and powered by 160 geared horsepower and a big, slow-turning prop, would make a pretty neat bush-plane . . . but only if the engine's problem is fixable.

Who knows about this? I did a small Web search once, without finding anything.

[BlackCat13]

The O-300 Continental six cylinder (opposed, 300 cubic inches) was a design used in the 40s in the Temco Swift (and others) at 125 hp, and later at 145 in the Cessna 170 and 172 series until its last year of its production in 67 in the Cessna 172. (replaced in 1968 by the 4 cylinder O-320 Lycoming at 150 hp.) It was essentially 6 cylinders of a C-90 4 cyl. engine (later called O-200). Actually the C-85, C-90, O-200, O-300, GO-300 used the same cylinders and pistons. Good thinking, huh?

The geared GO-300, rated at 175 hp, was installed in the Cessna 175, an airplane that looked similar to the 172 but had some structural differences. It was sort of a mid-way sized airplane between the 172 and the 182 from 58-61, even though the wing area is identical on all three models. If you look at the firewall/cowling junction, you will see the 172 is straight, and the 175 has a step.

The GO-300 had the prop elevated a few inches higher than the crankshaft because there is a spur-gear reduction drive for the prop. The prop still turned the same rpm as the 172, but the engine turned faster.
This allowed for the engine to turn 3350 rpm instead of the direct drive 2750. The prop still turned to the right, but the engine crankshaft turned "backwards".

The biggest problem with the geared GO-300 was psycological. Pilots used to the 2750 red line had a hard time running the 175's engine at its rated rpms, and rather than cruising at 3000+, insisted on cruising it at 2500 like they were flying a 172. Stories abound about overheating, etc.
The only problem I actually know of is spur gear/gearbox wear, generally the shaft bearings which use engine oil as lube. Oil is better now.

I had a nice 59 model 175 back in 70, and another about 76. I liked them.
172s and 175s are better airplanes with the Lycoming O-360 180 hp conversion with a constant speed propeller (more $$ maintenance) but truely shine with the 220 hp Franklin conversion (like the military T-42 and L-19). But that is an ancient engine designed in the 30s also. I have seen one with a O-470 230 hp and constant speed prop conversion, which should make it like an early 182.

These Continental engines are almost indestructable. Not efficient by any stretch of the imagination, but will run forever. I have seen them with .020 piston slop and using 1 qt of oil per hour and they keep on running and running. I have seen them with 2800 hours since overhaul and still squeeking by with 60/80 compression= 25%leakdown which is acceptable.

I never had a 175 long, profit $$ and such, but I had a 145 hp with 2300 hours since overhaul that I ran 70 wt Texaco oil in it, and it would give me 1 qt in 4 hours, and burn 8.8 gph and indicate 126 mph. That is real good in any book with that many hours.
I have a million stories to tell about hot rodding airplanes....LOL, but can't do it now. Suffice to say I had a Cessna 140A (single strut) that would cruise almost at red line on the airspeed indicator.

Ah to be young and rich again..... well young anyway.
Thanks for the memories.

[seattle smitty]

Thanks, BC; I'd like to hear some of your million stories. Hot-rodding any engine is what we're here for!

Was the geared engine cammed differently than the direct-drive version? Did it use a bigger (pitch or diameter) prop? Was there an improvement in short-field performance? Would there be such an improvement if an aero-engine hot-rodder like you were to cam the engine to make power at the same revs as the direct-drive engine, but turning a big prop?

What do you think of my idea of finding a 175 today, altering the engine and prop as above, and converting to taildragger configuration? Wouldn't that make a pretty good, cheap bush plane? Those bigger engines are in demand and not cheap, as far as I know (which isn't very far, as you have seen).

[BlackCat13]

Originally Posted by seattle smitty

Thanks, BC; I'd like to hear some of your million stories. Hot-rodding any engine is what we're here for!

Was the geared engine cammed differently than the direct-drive version? Did it use a bigger (pitch or diameter) prop? Was there an improvement in short-field performance? Would there be such an improvement if an aero-engine hot-rodder like you were to cam the engine to make power at the same revs as the direct-drive engine, but turning a big prop?

What do you think of my idea of finding a 175 today, altering the engine and prop as above, and converting to taildragger configuration? Wouldn't that make a pretty good, cheap bush plane? Those bigger engines are in demand and not cheap, as far as I know (which isn't very far, as you have seen).

wow, someday.

I think the GO-300 had the same cam profile as the non geared, but I wouldn't bet my life on it. Of course the engine crankshaft rotated backwards because the prop was spur geared to turn correctly.
The prop pitch was about 4" more with the same diameter I think. I'm thinking back 35 years here....lol. Blade width and airfoil.... that is "disk loading" is an important factor. (look that up)

(OK, I'll give out one hot rod secret. Take an engine like a C85 on a Cessna or Luscombe, etc. Put a Cessna 150 prop on that engine and it feels like you pick up 20 hp, because you do. The disk loading is so improved that the airplane takes off quicker, climbs 200 fpm more, and cruises better. All without exceeding the specified engine rpm limits for the airplanes.)

Think prop tip speed. should not exceed the speed of sound due to loss of efficiency.
Ever heard a Beech 18 with its Pratt and Whitney R 985s during takeoff? Most of the noise is sonic booms off the prop tips. Some of the Cessna 185s that have 2800+ rpm limits get sonic booms too. Remember when the Cessnas started coming out of the factory with constant speed props and 2450 red lines? = noise abatement.

The 175 had a little better load capacity than the 172, and usually was a better performer at equal loads due to the hp increase. (The fuselages are real close to the same, but different) Externally the wings are the same.

Aero engines are making their max torque at their max rpm... usually around 2750. Full throttle with that load. (Try that with a car engine on the dyno.) Spin them higher and they make more. Cam technology back then was pretty lame, but so is the engine design.
The biggest thing that those engine needed was a good scavenged exhaust, which has been available the last decade or so, well at least for the 4 cyl Lycoming 172, at about $2800 for headers.
I got the hot rod ideas from the guys who had the mini race planes with C85s C90s, and O-200s and turned them 3500 rpm.

I think the taildragger idea is great. I am a taildragger pilot from waaaaaaaay back. LOL. The square tail 175 is pretty. Slant tail on the fastback 60-61 fuselage looks wrong.

As far as the engines. An O-360 Lycoming with a constant speed prop would be much better. (headers are suppose to give it 30 more hp) The CSP makes a tremendous difference too, as you can run red line rpm at most any airspeed.
I wouldn't be suprised if there is an STC out there to put the Cessna 180 engine, Cont. O-470/ 230 hp on the 175. That would be a cheap way of having a 180.

Better yet, a Cessna 182 would put you ahead of the game with the O-470 from the factory. Fun is fun, but it is hard to make a case for having or building a souped up 175 engine.
History shows the 175 died a natural death because the 145hp /172 and 230hp/182 were more popular and the 175 hp/175 which was fllling a non existent "niche" and was unnecessary airplane.

Bush plane is an interesting term. 99% of "bush plane" is the NUT BEHIND THE WHEEL. Flying on the edge is an adrenalin rush, and just plain fun. But sooner or later most everybody gets overconfident and flys into a sxxt storm and bends something. You see it most often with the pilot who sneaks weather so much and so often he thinks he is invincable...... then he gets bit in the ass and gets dead. You must learn to say "NO, I don't have to go there".

I flew bush. I've done stuff that cannot be done....... 99% of bush flying is the nut behind the wheel.

I started my flying career on my 10th birthday, and always "learned from the mistakes of others, because you won't live long enough to make them all yourself"

I also remember WELL... "There are old pilots and bold pilots, but no old-bold pilots".

I might have thousands of hours of "over cautious" but, at least I am here to tell about it.
JMO.

[seattle smitty]

Great info, BC,

Certainly first-rate skills are more important than first-rate equipment in bush-flying, but when an old but low-time guy with third-rate skills finds himself blowing an approach to a canyon airstrip, surely horsepower, a light load, and a high-lift wing are what he badly needs. I have an even older pal who regales me with his stories of flying near the edge of disaster in the Idaho Primitive Area with an 85hp Luscombe. But if I tried that, I'd want something that would climb like a rocket, and crank around in a tight enough circle as to not leave skid-marks on the canyon walls or (anywhere else), not for the purpose of becoming a bold pilot, but to save myself from misjudgments.

Of course a C-175 isn't a Fiesler Storch, even with a 220 Franklin, droopy tips, and VGs atop the wing. But it might be a good, semi-cheap TWO-place airplane for learning to land off-airport. There are lots of other choices, esp. among the homebuilts, and some of them can be trailered. But you have to work full-time for two or more years to build your own, so I have to save that for the future.

Speaking of Franklin engines, the U.S. importer (Franklins are now made in Poland) was and maybe still is Pat Goodman in Winchester, VA. I think his company was/is called Atlas Motors. Goodman was racing mechanic with an auto machine shop when he became a national news item in 1979 with a high compression, high mpg Ford Fiesta using water injection of his own design. Some news team filmed him as he drove some distance with the Fiesta getting well over 40 mpg. Goodman later cautioned, in a magazine article in Popular Science, that when the TV crew was with him he was getting aero-towed by freeway traffic, and that helped cut his fuel burn considerably. Back to Franklins, as I recall the story, the company was founded by a man who intended to build higher quality engines than the Lycs and Continentals of the time. Did he succeed? Have you had Franklins apart, BC?