An experimental, gearless, horizontal 4-stroke

[geoff_p]

For a couple of years, on and off, I've been playing/struggling/getting-frustrated with this engine.  It's gone through many-and-varied attempts to make it a 'runner'. (01_overall_view.jpg)  It's 25mm bore x 30mm stroke, with a 28mm O-ring cut-down to 25mm, a very experimental carbon big-end (made from electric-motor brushes) and ball-race main bearings. 

It's near-enough all castings - even the crankshaft at one time - cast in my back-yard, and I'll bore you with that in another thread, another time. (02_failed_casting.jpg)

Since I don't have a 'proper' milling-machine (see later), I couldn't attempt to cut timing gears.  I came across this idea on You Tube and made my own version (03_close-up01.jpg)

I used "Sprocketeer" to make G-code for two sprockets: one at 13-tooth, to form the outer, stationary ring, and one at 12-tooth with every-other tooth omitted, which appears as the inner 6-tooth 'gear'.

A brass eccentric on the crankshaft 'wobbles' the 6-tooth around so every 2nd revolution of the crank, another tooth lines-up with (say) the exhaust-plunger.  By a bit of sneaky, the in-between-revolution operates the ignition-cam - hence the odd angles between the two brass plungers.

When I can get the blighter to run, I'll try to beg/steal/borrow a movie-camera, but meantime this sequence of pictures must suffice.

BTW, when it does fire, the 'kick' is enough to shear M3 cap-head screws between the flywheel and the crankshaft.  But I can't/haven't yet got it to fire regularly!

Geoff,
Thailand

My 'mill' is a CNC-ed X-Y table (with built-in vice) and much backlash - see the varying shapes of the 'teeth' in the pictures.

[Roger B]

That's an interesting concept  . I have seen several versions of this idea in books on old engine designs when they were trying to avoid the "half time" shaft.

Good luck with getting it (her?) running. It can be very frustrating but feels good when you finally get there 

[geoff_p]

Blooming 'eck!  It runs (sort-of) but not for long-enough to rush out and buy a movie camera.

I had to make another crankshaft because the screws 'securing' the flywheels were just shearing-off.  They were let in to fairly deep indents in the shaft so before shearing, they chewed-up the shaft, which made removal of the flywheels Very difficult.

The new crankshaft has steel 'ends' - the bits that go through the bearings and out to the flywheels - but retains my experimental cast-aluminium crank-webs+big-end .  I'll take some photos at the next strip-down/rebuild.  Outboard of the bearings I milled 3mm keyways ready for the next spot of madness.

Of course I can't get keyway broaches over here so it might be a long time before I save enough to get from UK or Canada - forget duMONT (USA) at their prices!

Meantime I drilled along the keyway to form a half-hole in the flywheels, gingerly tapped M3, and put a cap-head screw in to form a primitive key.

A few pops and bangs later it seemed to me I was getting more like 'explosions' rather than combustion and advancing or retarding the ignition was having little effect.  Could it be compression?

Playing with a spreadsheet suggested I was getting almost exactly 6:1, less than most of you talk about.  I could remove metal from the head to increase the ratio but what about lowering the ratio instead?

I made a spacer 5mm thick with recesses for 'O'-rings each side, which Lowers the compression to about 4:1 and Eureka! the beast popped-and-farted for much longer than ever before - about TWO-seconds!

Interestingly, though the valves seat directly into the aluminium of the head, they seem to be sealing better now than when first made.  Perhaps not for long ....

For now she'll start-and-run very easily.  All I have to do is prolong the run a bit more.

Oh, and fix the timing-eccentric, which keeps slipping.  I've put some Loctite in it for now and will try again tomorrow.

Then, maybe, I'll try to get a camera.

Geoff
Thailand
 P.S.  This my 'electric start'.  These polyurethane belts get a good grip as they warm-up.  And the motor gets really HOT after a short while.

[Roger B]

Good stuff!    The move to continuous pops and bangs is always good. Is your electric starter an 'outrunner' model aircraft motor?

[geoff_p]

Well spotted Roger, it is indeed an 'outrunner', of completely unknown brand.

It has a matching, unknown driver, a Turnigy 'servo tester' as a speed controller and a 12V lead-acid battery.

Geoff

[cfellows]

So, I guess that outrunner motor has quite a bit of torque?

Chuck

[geoff_p]

Surprisingly, Yes.

I'm old-fashioned and don't (didn't) believe in these new-fangled motors-without-brushes, so I was amazed that it can spin my engine, not merely turn-it-over.

Perhaps I'll try a Spragg-type clutch and make a proper electric-starter for my "Ultimate Weapon Mk X1V"

Geoff

[geoff_p]

Well, I did say it's experimental, so I can't blame anyone but me.

The original crankshaft was machined from an aluminium casting, but the main shafts were too soft and grubscrews just chewed grooves in it when the crank turned and the flywheels were "slow to follow."  So I replaced the main-shafts with steel, loctited and cross-pinned into the remains of the cast-aluminium gubbins.

Sorry, that's a poor description!  Pictures to follow will show it more clearly.

Anyways, when the blighter began to make "pops and bangs" (it actually ran for about 20 seconds at one try  ) it stressed this assembly both in torsion and in flexing, with this result, which I thought was just bent:

[geoff_p]

The main-shafts were also twisted (that torsion element) See next pic.

OK, perhaps I need a less-unconventional crankshaft.  So I very carefully turned a bit of steel to 6mm shafts (had to fit the existing ball-races) and 8mm where it would go through the webs.

3mm keyways were machined at both ends, right up to the bearings.

[geoff_p]

I might as well try to improve the flywheels while I'm at it, so a trip to a local machine shop got me two "rims", about 88mm O/D and 65mm I/D by 20mm wide.

These could fit on the lathe only by wedging the motor away a tad, and then the rim was just one paper-thickness clear.

Lots of "chatter" later, the outside was sort-of-smooth, and the bore opened to 72mm.  The original aluminium flywheels were turned to just fit inside, with the help of a hammer!

The end-results each weigh 350 g whereas the original (ali) ones were just 50 g.

[geoff_p]

Meanwhile, back in the jungle ...

The only "stuff" to hand for crank-webs was my precious lump of 1"sq. brass bar.  I drilled (and pseudo-reamed) right through for the main shaft and the new, all-singing, all-dancing STEEL big-end pin.  Then sawed the piece in two and cleaned up. 

Another trip, this time to York Air Conditioning, got me some Flux and a piece of "Silver brazing" rod (marked "Harris USA") with which I assembled the bits.  The (kitchen) gas cooker provided background heat and a hand-held, canister-type gas torch got the lumps to suitably hot.  I let it all cool down naturally.

On close inspection, there were a couple of places on one web where the solder (braze?) hadn't fully penetrated, so I cooked it all again and concentrated heat-and-solder on those places.  Let it cool a little then plunged the whole crankshaft into my "pickling bath" - a basin of water+lemon-juice.  (This had zero effect on the flux but dire consequences - see later.)

[geoff_p]

Those crank-webs are downright UGLY but hey, they should be strong in both torsion and flexing.  Quoth he!

With growing impatience, I re-assembled the engine, connected the fuel tube (vapour carb.), and electrics.

And she fired first turn!  Then clattered loudly.

One side of the main-shaft had twisted, not just a little but near-enough 180 degrees.

Observation: this side of the crankshaft had been allowed to cool naturally, so softening the steel, while the other side had been plunged into the pickle-bath, chilling it.  Perhaps?

Mai pen rai - Thai for never mind - let's tighten the flywheel and try again.  After a few short "pops and bags" she ran, like Billy-O, shaking all the junk off my desk (where else do you run an engine but on the computer desk?) for some minutes.  Speed control ranged from Fast to Faster.  Eventually I pulled the fuel-pipe off to stop her.

One happy fool in Aranya!

All I need now is to build (yet) another crankshaft, Oh, and to buy some broaches for keyways in the flywheels - for those of you that noticed the partial screw threads in the current shaft.  Oh, and work out how to throttle the blighter.

[Roger B]

Good stuff    I think that your crankshaft may be a little bit too small. My 25mm bore engine has a 12mm diameter crankshaft and big end.

[geoff_p]

Well, I did say the engine is experimental: it sort of evolved from some steam-engines, which were quite happy with the cast-ali, 6mm crankshaft.  That was before I joined this forum and found much more sensible 'designs'.

Thanks Roger, you are absolutely right so I'm presently making an 8mm shaft - the biggest 'bit of bar' I happen to have - and right at the limit of bearings, which-just-might-work in the original casting.  I have Loctited the lumps together (as well as cross-pins) and will give it plenty of time to cure (patience not being on my attributes-list) before doing any more to it.

The flywheel-bosses have been bored to suit, brass (Thai response: "Bronze?  Isn't that the same as copper ton deng /red metal ") bushes/bearings made, and the eccentric has been bored.  All I need now ...

Hopefully I will have some keyway broaches winging their way here "shortly" - I want to give the new shaft every chance of success.

I just never thought this engine would run, let alone have any power;  learning to the contrary is great fun.

Geoff

[geoff_p]

P.S.  Fired with the prospects of success, today I lashed out a whole 5quid on a USB Web Cam so as to provide you lot with some laughs.

Well it seemed like a good (read Cheap) idea but how do you use it to record a movie? 

It's fine on Skype, and shows a moving-image in Windows but I can only see how to save a single frame e.g.  picture001.jpg

Help, please.

Geoff