Does anyone know what this is?

[Allen Smithee]

[as I don't know what this is I couldn't decide where to post it - if you want to move it to another section please do so!]

A fellow RC flyer in my club handed me this today. Apparently a client of his (a retired surgeon) now sadly has Alzheimers, and his wife gave him this in case he could do anything with it:





Initial examination suggests it's a 4-stroke diesel machined from bar stock rather than castings. I haven't measured it [yet] but I'd guess at around 10cc. It seems to have a one-piece steel cylinder with alloy block and head. There is no provision for a glowplug, and the tommy-bar driven feature at the back of the head seems to open or seal a small blow-hole (perhaps like the "decompression device" found on some vintage bikes for starting?). There is a conventional airblead carb and a substantial (unfinished) pegged prop-driver/spinner nut assembly.

It seems to be almost complete, missing only pushrods, rockers, rocker mountings, tappets, throttle lever and exhaust pipe/silencer plus the completion of the propdriver/spinner-nut.

Does anyone recognise this engine? 4-stroke diesel aero engines aren't exactly common, so is it a known design or something he did himself? If it's a known design does anyone have the drawings of know where I could get them from?

I'd like to finish this engine off and get it running. All the missing bits are things which I could design and make without the original drawings because I can see what was intended, but it would be good to have the drawings if they're available...

All help appreciated

AS

[Admiral_dk]

My first thoughts where a that the bottom end looks a bit like a Saito .... but not the top end.

I'm sure it's a CI (Compression Ignition ~ diesel) engine and it is supposed to run on a mix of ether, kerosene and Castor oil - you might add an Ignition improver (1-2%). The Tommy Bar it the compression adjustment in a special configuration I'm sure Greg (Diesel Pilot) has used many times when he converted Glow Plug engines to CI.

It could be a home design, from a magazine or a bought "kit" / drawing.

[Allen Smithee]

I'm familiar with model diesel 2-strokes, but the only 4-strokes I've seen were the experimental one Laser did (which I don't think went into production) and the curious Saito one that was supplied as a partially disassembled "kit". Both of these had glowplugs for starting.

The tommy-bar doesn't set a contrapiston (there is no contrapiston) - it has a tapered nose the seems to just seal a very small blowhole in the head. The blowhole is about 0.25mm dia, which is why I think it might be a decompression device to allow the engine to be spun-up on a starter.

AS

[dieselpilot]

I don't recognize it. I would guess it was his own effort. There just isn't much out there in four stroke diesel. I'd love to see larger photos, the craftsmanship looks excellent.

Decompression device in an engine this small is unnecessary. If it is a diesel and has so much compression a starter won't turn it over, it likely has excessive compression ratio.

[Admiral_dk]

Greg I know it isn't a contra piston in a four-stroke and that it is just about the size off a normal Glowplug - but what are they called (I know you have made some) ?

Could it be that in this case it is the same but made in such a way that if you lift it almost all the way out it opens to the atmosphere so you can "Blow out" a "drowned" engine ?

[Admiral_dk]

Allan you could look here at Greg's webpage http://www.dieselrc.com/dieselrc.com/engines/ and go down to the Thunder Tiger and see the conversion done with a Tommy Bar (the OS engines above are sligthly different in style).
On this particular subpage (of all Greg's pages) all engines are converted to CI (diesel) - to give you an idea about how minor the looks change outside from the conversion.

[dieselpilot]

In a thread on RCUuniverse the "lanova cell" was described as a method to adjust compression in a converted engine. The arrangement is much like a precombustion chamber in an indirect injection diesel. The Lanova Energy Cell was a unique design for IDI where fuel was shot across the combustion chamber and into the precombustion chamber where it ignited and was pushed out to the combustion chamber.

There is a good image near the bottom of this page. https://www.dieselworldmag.com/diesel-trucks/1939-the-first-dodge-diesel/

[Allen Smithee]

I took the head off for a quick look and have established a few things:

1. The bore and stroke are 22x26.5mm, which my fag packet says is a nominal 10cc
2. The inner face if the cylinder head is completely flat with the piston sitting at 2mm below the top of the bore at TDC (so I guess the CR is 13.25:1)
3. That device is indeed a small contrapiston - looks like a hardened and ground part about 8mm dia with the lower end machined at an angle so it's parallel to the underside of the head. It has a tiny pin in the side which engages in a slot in the head (that's what I mistook for a blead hole) to keep it correctly oriented. It looks like the total range of movement of the contrapiston is a bit under 3mm upwards.

This detail doesn't photograph well with my phone, so I'll have to dig out my camera (which has a better lens for close-up work) to get some pictures for posting.

I need to find something hardenable to make the rockers from, and I need to do some measurements to work out the geometry so that I can get the curve radius for the tappet face of the rocker where it slides on the valve head. My initial thought is something like 3mm gauge plate or perhaps a bit of 8mm dia silver steel milled to 3mm thick. I guess the alternative would be to just use mild steel and get someone to case-harden (or nitride) the tappet face.

I can't see any way to get lubrication to the rocker bearings, so I feel they should have either bronze or oilite bushes - am I over-thinking this?

AS

[Jasonb]

Small ballrace in the end of the rocker arm may solve two of those problems eg hardness and radius, look at Malcom Stride's Bobcat based designs. Or silver solder a piece of silversteel onto the end of a MS rocker and quench as soon as the solder solidifies but still 500deg plus.

It all depends on how much you will run the engine, if it will just be a few odd bench runs to see if it goes then may not be worth the effort, if you intend to fly it that may be a different matter.

[Allen Smithee]

That's a good shout Jason - thanks!

I'll measure the cam lifts and get a feel for how much angular movement there will be at the rockers - if there's a lot of angular movement the ballrace option will put a side-load on the valves that could cause problems. But it looks like it would be less of a faff to make.

The head in your photo seems to have no provision for rocker lubrication - do the bronze bushes just run dry or is it a matter of an occasional squirt of oil between flights?

AS

[Jo]

I had a phone call from Pete today about this engine so I thought I would post on the thread to see if any of our new members might have any idea as to what this engine is. 

4 stroke Diesels are rather rare 

Jo

[Roger B]

Small four stroke diesels are rather difficult 

[Jo]

I'm having a senior moment  Is that: Difficult to make, design or run 

Jo

[Zephyrin]

some infos here on a similar engine, a 4 stroke model auto ignition "diesel" model engine

https://modelenginenews.org/gallery/p8.html

and another similar one, in attached picture.
in Model Engineer vol 152, p144,  (issue 3722) feb. 1982. Rex Swensen : A Compression Ignition Four Stroke Engine.

[Roger B]

I'm having a senior moment  Is that: Difficult to make, design or run 

Jo

Design  may be easy, make and run is more difficult