3 Cyl Radial Aero Engine

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Motorman1946

Active Member
Joined
Mar 13, 2014
Messages
41
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Location
Somerset, England
In March 2014 I purchased this part built engine:
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I bought it from a friend of a model engineer who sadly had departed for the great shed in the sky and left it as is, part built - what you see is all that's been completed so far. I did ask around on several forums if anyone recognised the engine, as it came with no plans and despite all efforts of the friend none could be found. Someone did think it was similar to Gerald Smith's Osprey engine, but that was as far as it got.

Now, 5years on, I aim to start work on finishing it. Why the great delay? Well, we also have a motorhome and go off in that for up to a month at a time, plus we spend 4-6 months of the year in France, which restricts available shed time. Then another engine came up along the way, a single cylinder sleeve valve engine, which took quite some time as most bits had to be made twice and sometimes 3 times; although I'm a retired engineer it's many many years since I used a lathe and never had used a vertical milling machine before so there was a great learning curve to spend time on, and learning how to hold work was like starting almost from scratch. Plus there were some other little projects, like re-motoring both lathe and mill with VFD controlled 3 ph motors, repositioning the motor on the mill to the side from the back so I could get the mill on the bench, machining a chuck back plate which involved making a dummy nose spindle first, making a ER32 collet chuck to fit the lathe and, just finished, a lathe apron overall, remaking a shaft and bearing bush and fettling several gears in the lathe apron after a very solid crash! Plus I don't work very quickly, most times it's just the 2 speeds, dead slow and stop.

Well, the sleeve valve engine didn't run, no compression, still uncertain why, plan to remake the junk head and liner to fit better, but that's on the back shelf for now, I want to get on with the 3 cyl radial. I have called it by the name of Mystic, as it's a mystery where it came from and how it was proposed to be finished.

You can't have reached an engine build that complicated with no plans surely; but no plans could be found so the first job was to measure every component I had, draw it all out in CAD - another delay as I gradually taught myself CAD, good job I did, and loved doing, engineering drawing in my youth! - and then design, and redesign, and draw out all the bits necessary to complete the job.

So. Drawings drawn and printed, stock bought, enough to make a good start, I'm ready to go.

I have a Weiler LZ280 lathe from the late 1960's early 70's, not sure how old, originally a quality built lathe and still in reasonable condition after some TLC from me, with power feeds both longitudinal and cross, ability to cut a very wide range of metric and imperial threads, and a round column Warco 'Economy' mill/drill and a small bandsaw, worth it's weight in gold for the work it does for me, hate hacksawing. I work in both metric and imperial but think in imperial, a product of my upbringing and training, and both lathe and mill are in imperial. I can visualise thousands of an inch, it means something to me, bits of a mm mean nothing until they get translated back into thous! My shed calculator is my best friend. Not a lot of kit but enough.

I will post bits on here as I go, but don't hold your breath, as I said I'm a slow worker and exit visa's for the shed have to be earned first, but I hope to make a start later this week.

Chris
 
Interesting looking engine.
Must be a 4 stroke.
Are the ducts from crankcase to head's sides Intakes?
What is that big tube in front of the cylinders? Looks to big for one push rod and possibly too small for two.
 
Interesting looking engine.
Must be a 4 stroke.
Are the ducts from crankcase to head's sides Intakes?
What is that big tube in front of the cylinders? Looks to big for one push rod and possibly too small for two.

Agreed, 4 stroke.
Any chance that it could have atmospheric intake valves, meaning that only the exhaust valve push rods are enclosed? Problem with that suggestion is that in the era of atmospheric valves, the push rod would probably have been exposed and this looks like a more modern design. But just a thought anyway.

Very nice workmanship so far.

Dave
The Emerald Isle
 
Yes, it's a 4 stroke. The inlet is piped to the crankcase and the big tube ahead of the cylinders is the enclosure for the pushrods and cam followers. The lump of aluminium at the base of the tube is already drilled for 2 followers.

Initially it will be a glow engine I think, the carby will be attached to the back of the crankcase, so the oil mix in the glow mixture will lubricate the crankcase. The gearcase forward will be splash lubricated. I hope that will work, I've not included for an oil pump initially. Adequate lubrication is a concern, so we will see. That's if I ever get this one to run!

Chris
 
All the parts of the engine so far made are really on display in the photos in my first post. So, still to make are pistons, piston rings, gudgeon pins, rockers and their shafts, valves, springs, tappets, push rods, cam followers and the whole cam/gear drive assembly, still a fair bit.

That said, there was quite a bit of work involved in drawing out what is existing and adding each bit as designed as I went along in a general arrangement drawing, and the from there to draw out each part fully dimensioned to manufacture from. That usually resulted in minor design changes as I went along too, just to add to the task. In the end I called a stop and decided to go with what I had as I could have modded the drawing for ever!

Some, most, bits were quite easy to design, but a lot of thought and options were mulled over before I settled on a design. Other people would have probably opted for a different arrangement, but I wanted one that I thought would work and would not tax my machining skills too hard (just hard enough - I've not made cams or gears before). I settled on a cam ring, with one long exhaust and one equally long inlet cam, mounted on a cam ring carrier, rotating around the crankshaft and driven by gear secured to the crankshaft via an idler gear to an internal gear mounted on the cam ring. Enough there to manufacture to capture my interest and get the little grey cells working.

For those who don't know about cams, and I didn't, much, before I started on this, the number and direction of cams is derived from:
If X = Number of inlet or exhaust valve cam lobes
Y = Number of cylinders, and
R = Gear ratio of crankshaft to camshaft,

Then, if cam disc runs in the opposite direction to crankshaft,
X = (Y-1)/2 and R = Y-1

And, if the cam disc runs in the same direction to the crankshaft,
X = (Y+1)/2 and R = Y+1

So, for my engine with the cam rotating opposite to the crankshaft direction,

X = (3-1)/2 = 1 exhaust and inlet cam, and
R = 3-1 = 2, or camshaft = 1/2 crankshaft speed.

That sorted there were still some other issues to be resolved:
Glow or spark ignition
Cylinder breathing
Lubrication.

Decided on glow ignition, as the engine was obviously set up for breathing through the crankcase (more on this under lubrication) and there was no-where obvious set up as it stood for a distributor/hall effect sensor drive.

Cylinder breathing is still a worry. I don't like the narrow pipes and the right angle bends as existing but have not worked out if this will be a great restriction or not. Still pondering it. Will probably go with it initially and see what happens.

Lubrication I decided on being basically splash, again because of lack of an obvious take-off for a lub oil pump and possibly scavenge oil pump. The crankcase I will separate from the gearcase and have splash lub in the gearcase and the crankcase will be lubricated by the oil in the glow fuel plus a bit I will squirt in to splash about in the when the time comes.

So, that's what went on as and when I could spend the time from the time I bought the engine to the end of last year

Now to make a start.

Chris
 
First bit up is the cam support ring. This started as a piece of 2.25" dia. x 1" HE30 (6082) aluminium, or aloominum as our friends across the pond would say. Actually, I prefer aloominum, only 4 syllables instead of 5 and it rolls off the tongue easier!

This was set up in the 4 jaw to run true, the end faced off true, the location step for the cam ring was machined, the centre bored to 1/2" (in 2 steps, 15/32 then 1/2" dia drills to help ensure a close drilled to size hole) and then the recess for one of the 1/2"x3/4"x 5/32" ball bearing race.

Machined up an expanding mandrel with a 1/2" dia spigot with a tapered 8mm internal thread which was then slit with a slitting saw N to S and E to W. Mounted the cam support ring on that and turned the OD to finished diameter, and machined up the other end face to size plus about 9 thou for finishing later.

Then another mandrel was made, roughly to a design from Joe Pieczynski's You-Tube series, to hold the cam support ring by its outside diameter. If you've not watched any of his videos they're well worth watching, lots of good advice and ideas. Basically, the mandrel has (ideally) 3 slits equally spaced, with one wide one all the way through. As my mandrel was relatively thin walled I just went for the wide through slot. You put a spacer in the slot that's a slack fit, clamp down in the 3 jaw until the spacer is held tight, turn to diameter, slacken VERY slightly, just enough to remove the spacer but not too much so the registration is lost, add your part and retighten and away you go. Simples! On mine, the part not fitted exactly on OD but also located against a back face in the mandrel as well

Using this faced the end to finished dimension, I bored out the other bearing recess (the part runs on 2 small ball bearing races), then over to the mill/drill onto the rotary table to drill the outer ring of 3 mm holes at 45 deg. spacings which will allow the cam ring and internal gear to be bolted to the support ring by M3 bolts, and then the inner ring of 1/4" dia. holes which are only there to remove a smidgeon of weight.

Must get into a habit of reducing the write-up, all seems too lengthy!

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Inside that lump of HE30 there's a cam support ring lurking. The eagle-eyed amongst you will have spotted that 0.528" + 2 x 0.063" does not equal 0.7". Bum dimension on the drawing due to sloppy dimensioning. The 0.063" dimensions are actually 0.0625" but the CAD doesn't like saying so. 0.528" dimension should be 0.0575", corrected on the updated drawing!

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Making Joe's mandrel

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Mandrel in use

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On the rotary table getting drilled

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Cam Support Ring finished. Actually, again the eagle eyed will spot there is one 1/4 hole a fraction out, 2.5 degrees out to be precise, but at least it's not a critical, I can live with it. Must pay more attention to detail!
 
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It is obviously based on Gerald Smith's Osprey 3cyl, although with some changes. He also built 5 cylinder (Buzzard) and 7 cylinder (Red Kite) versions of it. The 7cyl was finished posthumously by a good friend of Gerald. His original design was very clever, using the the pushrod tubes as the inlet manifolds to transfer the air-fuel-oil mix to the inlet ports. That way the fuel mix lubricates all internal parts as it passes through the engine. The carby, magneto and distributor are all at the rear of the engine. There was a construction series in one of the magazines, EIM I think. He was an outstanding model engineer.

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On my last post "Simples! On mine, the part not fitted exactly on OD but also located against a back face in the mandrel as well' should have read "........the part not only fitted exactly on OD....... Obviously tired and missed that.

Thanks radial1951, now you have posted a picture of the 'Osprey' engine I can see the resemblance very clearly - not seen a picture of it before. On mine the air inlet is separate to the tube with the push rods in it, probably having both together would be better for lubrication reasons, but no provision had been made on the heads for a cover over the rockers which would be required.

The crankshaft is what I think is termed an overhung crankshaft, that is with a crankweb only on one side of the pin. Please correct me if I am wrong! So there is no drive to the rear of the engine for a distributor.

Chris
 
"So there is no drive to the rear of the engine for a distributor."
Not necessarily. An accessory drive mounted in the rear crankcase cover can be driven by the end of the crank pin. Saito use this method to drive the diffuser impeller in their 5cyl radial. The crank pin engages in a radial slot in the face of the "crank disc" of the accessory drive. These days much simpler and more effective to use a 3cyl electronic ignition unit rather than a distributor.
 
Agreed. For both drive and electronic ignition unit. Had thought of a drive off the crank pin - saw it used to drive an impeller on the "PIP" 3 cylinder radial, and it's used to drive a sleeve valve gear on the sleeve valve engine I built, but here the crank pin would have to be "extended", that is, drilled and tapped with an extension pin. It's an option, perfectly possible, but no-where near that far on yet!

Chris
 

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