Hi all,

I'm building a Stinson 108 up here in Canuckistan. It's in the Canadian version of the experimental category. I'm planning to put it on floats and do the full chord droop tip conversion among other mods. I have purchased a low time O-540-B4B5 for it which is now being cleaned up.

My topic regards the weight of the beast. I'm trying to keep weight down for obvious reasons and when I was researching which engine to buy, the accepted wisdom was that the Conti O-470 is a good one but a lot heavier than the O-540. Some people claim up to 75 lbs heavier than the O-540.

Compression ratio is 7.2:1. At only 360 pounds, this engine is about 75 pounds lighter than the Continental O-470.

The O-470-R http://oceanair.ca/wp-content/uploads/2015/01/O470R_engine_specs.pdf specs state:

The O-470-R weighs in at a dry weight of 379.66 lbs. without accessories. The
weight of the engine with installed accessories is approximately 425 lbs.

But when I looked up the numbers for the O-540-B4B5 there are two numbers scattered across the intertubes in forums, sometimes both weights appear in the same post. lbs, dry weight: 395 and 366.

I think I found where the two numbers come from:

The 395 lbs dry number comes from the Lyc. operating manual (approved by the FAA): 4th Edition Part No. 60297-10.

The 366 lbs dry number comes from the FAA's TYPE CERTIFICATE DATA SHEET NO. E-295

If the former is right then there isn't nearly the weight savings that many claim. If the latter is right, then great. I have a much lighter engine. So which is it? Are they just the "with and without accessories" weights? Is the FAA right or is the FAA correct?

There is a hint that it might be the accessories because in the type sheet it states:

NOTE 11. Starters, generators, and alternators approved for use on these engines are listed in the latest revision of AVCO Lycoming Service Instruction No. 1154.

I'm so curious now, I may buy a scale just to weigh mine.

Are you planning amature build, under the 51% rule or OM

If you have a trucking center there, they may have a pallet scale. They may let you weigh it for evaluation purposes. Tell them your thinking of shipping it, so you need the weight for a quote.

There are so many configuration options mount deviations, baffle installations and so on. The only weight to use is one that your engine gives you from being on a scale. There is lots of useful information that comes off these forums, but something like that I would not trust the answer.

Personally, I like working on Lycoming engines better. The ones I have had seemed to need less work period. Then again I am not the engine goto guy for pistons. Got a turbine question, then I'm your guy.

I’ve got a O-540-B2B5 in the hangar in a crate. I’ll put it on the scales in the next couple days and let you know what it weighs.

I’ve been meaning to weigh it for a while as I had the same questions regarding the different numbers I’ve see for the engine weight.

Marshall

Mapleflt wrote:Are you planning amature build, under the 51% rule or OM

It's already under the 51% rule. I'd like it to conform to the US rules too in case I ever sell it but not sure it will pass if they require the 51% paperwork to be re-done. I have the Canadian paperwork but the US checklist seems much tougher to pass. Could just be a rubber stamp if the Canadian paperwork is good but you never know with pencil pushers.

I’ve got a O-540-B2B5 in the hangar in a crate. I’ll put it on the scales in the next couple days and let you know what it weighs.

That would be interesting. Is it a fresh one?

Got a turbine question, then I'm your guy.

Cool. How fast does the flame front travel on average?

There are so many configuration options mount deviations, baffle installations and so on. The only weight to use is one that your engine gives you from being on a scale.

That's true, once you add your accessories, but it's good to know the base weight, then you can enjoy the sport of optimizing. How else will you be able to humble brag about how light your install is?

I looked into this quite deeply a few years back when deciding on an engine for my Bearhawk. After pouring over TCDS, overhaul manuals, etc I made calls to Lycoming and Continental. Continental includes everything but oil on their TCDS weights. Lycoming includes everything but oil, starter and alternator. I checked around and determined adding 30lbs to the Lycoming TCDS numbers was appropriate when comparing to Continental TCDS numbers. Also, if looking at parallel valve O540s (which most people are when looking at the lighter weight 540s) but plan to use angle valve cylinders you need to add 30 more pounds. The Lycoming rep told me each angle valve cylinder is 5lbs heavier than a parallel valve cylinder.

What I found, based purley on the TCDS numbers, is that the O470 weighs 24lbs more that the light parallel valve O540. Add angle valve cylinders and it is a wash.

My vote...IO470 with GTSIO520 cylinders That's the engine I should have put on my Bearhawk.

whee wrote:My vote...IO470 with GTSIO520 cylinders That's the engine I should have put on my Bearhawk.

I don’t think I’ve ever heard of that combo - what’s special about it?

whee wrote:Also, if looking at parallel valve O540s (which most people are when looking at the lighter weight 540s) but plan to use angle valve cylinders you need to add 30 more pounds. The Lycoming rep told me each angle valve cylinder is 5lbs heavier than a parallel valve cylinder.

Wouldn't an angle valve -540 develop considerably more horsepower than a -470? Not exactly apples with apples?

For 250-260hp you are looking at an average of 428 lbs of -470 across the 25 or so models they offer. An angle valve -540 would develop more than 260hp

CamTom12 wrote:

whee wrote:My vote...IO470 with GTSIO520 cylinders That's the engine I should have put on my Bearhawk.

I don’t think I’ve ever heard of that combo - what’s special about it?

There is no approval or anything for that combo. It's a harebrained idea I thought I came up with a couple years ago. Some airboat guys use it though. The things I like about it: O470 mount is available for the Bearhawk (and the Stinson), 470s are a dime a dozen, cross flow cylinders which puts the induction on top of the engine, puts out around 310hp without having to increase rpm.

Battson wrote:

whee wrote:Also, if looking at parallel valve O540s (which most people are when looking at the lighter weight 540s) but plan to use angle valve cylinders you need to add 30 more pounds. The Lycoming rep told me each angle valve cylinder is 5lbs heavier than a parallel valve cylinder.

Wouldn't an angle valve -540 develop considerably more horsepower than a -470? Not exactly apples with apples?

For 250-260hp you are looking at an average of 428 lbs of -470 across the 25 or so models they offer. An angle valve -540 would develop more than 260hp

I don't know. Weight was the primary consideration for me so I can't call out models and horsepower. Since weight differences are mostly a factor of accessories I didn't pay too close attention to the horsepower ratings. Also, I don't know how much horsepower is gained from angle valve cylinders. Bob told me his low compression angle valve O540 is 260hp.

Progress on weighing my O-540 B4B5

What I got was based on a pretty bare engine. All it had on it was the mags, plug wire harnesses, vac pump, oil filter adapter and prop governor. Of the baffles, only the under cylinder and rearmost baffles were on. Intake tubes (5lbs) fuel pump (?lbs) and carb (6lbs) were off. So, I think, if you did the exchange weight with the mags and prop governor, you would be right around the bare weight. Scale was checked by weighing a known amount of water. 1 litre = 1 kg. It was right on the money.

Dry weight equipped as above on a non calibrated scale: 369.2 lbs.

That seems to back up my contention that the 366 lb number in the type cert is a bare engine.

Now, How does that compare to the O-470? Anyone care to weigh a bare one up... for science?

Just for my own entertainment, I put most of the other bits and accessories in a box and weighed them separately. Sky-Tec 149-12HT High torque starter (8.2 lbs) , light weight 40A Denso alternator (6lbs), carb (6lbs), intake tubes (5lbs), spark plugs, engine to top cowl baffles, brackets, belt and flywheel (7lbs). That came out to 41 lbs. So far that makes 410.2 lbs

What I don't have yet are the rest of the baffles, the exhaust system, the air filter box, the oil cooler, and the oil filter, some bracketry, oil hoses etc. Custom lightweight exhaust systems are around 12 lbs so that does not add much. I'm not sure which accessories are included in quoted in engine weights but that's what I have so far. I'm going to look around for some more weight savings such as drilling out my flywheel.

Texas Skyways O-520 weighs 413# or 431# don’t recall exactly. Built using O470R with IO520 cylinders. I’m recalling 280 hp.

For my Bearhawk I’ve built a permold 7th stud heavy case IO520 using the IO520-D induction/injection system, 1200 series Bendix mags, full size alternator and starter and large oil cooler behind cylinder #6, Bonanza exhaust manifolds...weighs 461# less oil and upper engine baffles.



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I thought the O-540, 235 HP model, was a good engine on most Pawnees I flew. Could haul 20 more gallons with 250 HP, but worked you more. High time and tired, they would run 245 redline all during the hot months with only one oil cooler. Little Continentals on my people airplanes had to be rested at 220 redline.

contactflying wrote:I thought the O-540, 235 HP model, was a good engine on most Pawnees I flew. Could haul 20 more gallons with 250 HP, but worked you more. High time and tired, they would run 245 redline all during the hot months with only one oil cooler. Little Continentals on my people airplanes had to be rested at 220 redline.

You get to go to 240F (instead of 225F) on the little O-300 when you run 100W oil.

Weight be damned. I'd never use a Continental if there was a Lycoming that would work. My O-470 and TSIO-520's insatiable appetites for cylinders nearly drove me from aviation.

contactflying wrote:I thought the O-540, 235 HP model, was a good engine on most Pawnees I flew. Could haul 20 more gallons with 250 HP, but worked you more.

Yeah. The guy I bought my project from is an AME and he thought the 0-540 was the most reliable choice for a bush plane (that you could run on mogas).

Of course, I'm interested in the higher hp model so while I was looking into the weight issue, I poured over the parts manual and from what I could tell, the only substantive differences between the 235 hp 2575 rpm B4B5 and the 260 hp 2700 rpm E4B5 are the installation of a hydraulic pump (reflected in the higher weight) in the E4B5, and the pistons. All of the critical engine components and specs are exactly the same. Even the rings. All of the the hp seems to from the compression and rpm difference. Crankcase, crankshaft, counterweights, cam etc. The only differences I could find were down to accessory provisions like governor studs, starter rings, etc. Can anyone more expert that I corroborate that?

Needless to say, I'm on the lookout for a set of pistons so If I ever have to take off the jugs, I can give myself an easy 25 hp boost. Not to mention a nice boost in fuel efficiency. (12.5% on paper at best economy.)