Douglas Bearcat engine

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Tiger Tim

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Speaking of Franklin: before they made aero engines, they made automotive aircooled engines. L engines, at that. Perhaps that was the source?
Not on the Bearcat as far as I can tell but that thing TFF posted looks like the cylinders may be automotive Franklin.
 

TFF

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It’s hard to see but the aircooled Ford B has cylinders that almost mimic what an aircooled OX5 cylinder would look like. They may be bespoke parts. External rockers but different pushrods, but a similar cross flow. They don’t match anything I have found, but are more like WW1 like than 30s. Long stroke driven, but maybe surplus parts availability. Still the Depression.
 

Tiger Tim

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It’s hard to see but the aircooled Ford B has cylinders that almost mimic what an aircooled OX5 cylinder would look like.
Those radial cooling fins on the heads really scream late teens/early twenties, don’t they?

I was in one of the hangars today eyeing up some cross flow Franklin aircraft cylinders and thinking there might be something to them. I realize now that while I intended to walk a couple over and hold them up to a Model A block in the opposite corner I must have become distracted by some other task.
 
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Bill-Higdon

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Those radial cooling fins on the heads really scream late teens/early twenties, don’t they?

I was in one of the hangars today eyeing up some cross flow Franklin aircraft cylinders and thinking there might be something to them. I realize now that while I intended to walk a couple over and hold them up to a Model A block in the opposite corner I must have become distracted by some other task.
Squirrel
 

MACOWA

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Yup. So much knowledge and skill lost when the smaller factories were put out of business by the large-scale operations. And then we shipped those operations overseas.

It's disheartening to search for the sorts of things I used to buy 30 and 40 years ago, to build, rebuild or repair some stuff. Last year I tried to buy some C93200 (SAE 660) bronze bar to make some new bearings for the bottom end of an old outboard motor I was restoring. No machine shop or supplier had the stuff in the city. I'd have had to buy 12 feet of it from a major warehouse a long way off and pay a gazillion dollars for it. For a $100 outboard? Cheaper to buy a new outboard, nearly. I ended up machining those bearings from some Delrin scraps I had here, and it has worked well.

Nobody, it seems, builds or fixes anything anymore. They just buy new stuff and throw the old stuff away. A walk through a Radio Shack is depressing.
Delrin bearings ? What a concept ! I was thinking of having my remaining stock of bronze appraised. And then there are the four old outboards behind the shop that are just too cool to throw away.
 

challenger_II

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Delrin is some interesting bearing material. A close friend runs a machine shop. Most of his work is oilfield-related. Had a customer that very frequently bought big-end bearings for Gasso triplex pumps, machined from bronze. One day, my friend got a wild hair, and made two sets from delrin. The pump shop operator was very leery of "them plastic bearings". So, after a bit of discussion (and a LOT of arguing!), my friend gave the two sets to the pump shop operator, who donated them to a customer to test. 6 months later, the pump shop operator asked for 6 sets of delrin bearings. 6 months later, the PSO asked for 100 sets.
After 5 years of selling delrin bearings, my friend's orders for bearings dropped off to nothing. Seems that most every Gasso pump the Pump Shop Operator was servicing had the delrin bearings, and they were holding up much better than the original bronze bearing, and the demand collapsed.
 

Tiger Tim

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I had this sent to me today by a friend and chased the source of the screenshot to a Facebook group. This is so far the best picture I’ve seen of the Bearcat and shows that it had a cast nose case with I assume a fourth main bearing holding a crank extension.
E571FC8D-83D0-4CC6-A237-8DDF7ABA361F.jpeg

I see too that the cylinder heads are paired together, sort of like a VW, while the cylinders appear separate. It also looks like there are cast(?) engine mount brackets bolted to the sides of the case, which seem kind of freaky.
 

ToddK

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Yup. So much knowledge and skill lost when the smaller factories were put out of business by the large-scale operations. And then we shipped those operations overseas.

It's disheartening to search for the sorts of things I used to buy 30 and 40 years ago, to build, rebuild or repair some stuff. Last year I tried to buy some C93200 (SAE 660) bronze bar to make some new bearings for the bottom end of an old outboard motor I was restoring. No machine shop or supplier had the stuff in the city. I'd have had to buy 12 feet of it from a major warehouse a long way off and pay a gazillion dollars for it. For a $100 outboard? Cheaper to buy a new outboard, nearly. I ended up machining those bearings from some Delrin scraps I had here, and it has worked well.

Nobody, it seems, builds or fixes anything anymore. They just buy new stuff and throw the old stuff away. A walk through a Radio Shack is depressing.

Its true. The fist Aeronica 2 cylinder engines were made locally, and the entire design to prototype was just a few months and it flew fine. All designed on paper. Look how long it took to get the O-100 going even with CAD and advanced machining. Somethings have been lost.

There is still a bit of that going on. Right now on the FB Neil Hintz has been posting a bit while building another of his 80hp Autoflight 700 2 stoke engines. He casts all the parts himself. Its beefy.
 

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Tiger Tim

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Its true. The fist Aeronica 2 cylinder engines were made locally, and the entire design to prototype was just a few months and it flew fine. All designed on paper. Look how long it took to get the O-100 going even with CAD and advanced machining.
I think a major difference is the O-100 was meant to be good from the start where Aeronca et al would get it good enough then finish developing it once customer engines showed weakness. That little Aeronca twin did go through quite a number of changes in production.
 

Dan Thomas

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That little Aeronca twin did go through quite a number of changes in production.
From Wiki:

Originally fitted with a single ignition system, this was uprated to dual ignition when changes in FAA regulations made this mandatory in 1939. By that time, however, both the engine and the aircraft that it powered were facing obsolescence. Altogether, some 1,800 examples were built. Following an incident in October 2015 where the propeller detached from an Aeronca C3 in 2015, the Light Aircraft Association has issued an advisory that all aircraft fitted with these engines have the crankshaft attachment inspected prior to flying again. This issue has been recognised since 1939.
Aeronca E-113 - Wikipedia
I don't imagine it had much of a TBO, either. Its predecessor, the E-107, had a 400-hour TBO.
 

ToddK

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I think a major difference is the O-100 was meant to be good from the start where Aeronca et al would get it good enough then finish developing it once customer engines showed weakness. That little Aeronca twin did go through quite a number of changes in production.

The Aeronca was also supposed to be good to go from the start. Sure it got some upgrades along the way, but as a whole it was a massive success of an engine designed by a guy on paper by hand in a pretty short amount of time. A mandatory crankshaft inspection after 82 years of flying speaks to that.

Today you would see multiple cad revisions, years of time pass, changes in vendors, testing, and so on. Its no wonder its all so expensive, and most projects never see the light of day.

I see this in wood working. Engineer types today who get into woodworking obsesses over the nth degree and precision, but then take forever to build anything. When I gave up on that, and learned the old ways of thinking and building, my productivity went through the roof. I focus on what and how things fit together, ordering my work in a logical way that minimizes measuring, cutting, end errors. I can knock most projects out in a weekend. Did 3 desks with 3 drawers each all in a single (very sweaty) weekend a few years back. Finishing ended up taking longer then building.

Sometimes perfection is the enemy of good enough.
 
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Tiger Tim

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Can’t argue with that logic and I’m also very much a ‘cut to fit where practical’ kind of guy myself.

I know the A40 was hardly ready when it went into production and a number of early customers had to solve problems themselves and report back to Continental on what worked. Luckily most of their problems were heat rejection IIRC and could be addressed with more fins, deeper fins, and thermally conductive gaskets. Who’d have thought a change in head gasket material would prevent magneto failures?

Anyways, back to the Bearcat. What do you forensic mechanics see in that latest pic?
 

TFF

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I think a lot of people don’t know what perfection is so they turn to measurements. They can put a finger on numbers. There are so many things that are perfect that just happen to be technically not perfect.

I know how one wants their engine to stay together at 10,000ft so a lot of aviation engines are never worn down. Split a case and all the guts get changed today. 80s and before, it just got fixed. One rod, one lifter, one set of piston rings. We have become use to a behavior that insurance is a catch all. It’s raised the cost of doing business. We have become scared and business has become scared.

A-40 is just past dawn of aviation. It’s there, with the like, shutting down the last of the OX-5s. People were accepting of difficulties. Today we expect no issues; we have no time for issues.

O-100 needed to be 100% outsource ready hence the details. Until something is clone worthy, it can’t be cheap foreign made. Made in the US, it has to be made with a machine.
 

Dan Thomas

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Anyways, back to the Bearcat. What do you forensic mechanics see in that latest pic?
Those two-cylinder heads bother me. The VW did too. The head gets hotter than anything else, so it expands more, gets longer. That forces the tops of the cylinders apart. That stresses the hardware, especially the cylinder base fasteners. The cast iron case of the Model A will expand very little compared to the aluminum head.

Steel and cast iron expand at almost exactly half the rate of aluminum for a given temperature rise. It's called the coefficient of linear thermal expansion.


Aircraft engines have separate heads. Eliminates that stress. The aluminum aircraft engine crankcase expands more than a cast iron case, and for that reason we see multiple pieces of overlapping cooling baffling on TC'd engines. The rear baffle will be two pieces, or have a Z-bend in it to take up some movement. Some mechanics see the fretting occurring in the overlap between the side baffles, so they rivet them together, and the engine promptly rips them apart. See the overlap between the rocker covers? That's engineered.
1657581295587.png


Look at the skinny propshaft on that Bearcat. The Aeronca engine had a similarly spindly shaft, hence the tendency to break. Current engines have much larger shafts, and not just because of higher power. Metal props put a lot of gyroscopic precession loads on it.
 
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