# LONGBOY'S "SQUARE FOUR" MODEL GAS ENGINE.



## Longboy (Mar 5, 2021)

A rare configuration in I/C engines is the square four. From the motorcycling world in the form from the British Ariel S/F classic for three decades.......






.....to Suzuki in their GP500 racing campaign years in the '70s thru 1990. 





Can I do this configuration as my usual industrial utility builds?  





Longboy's S/F build log starting next week!


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## Longboy (Mar 10, 2021)

This S/F is a pair of inline twins with a common output shaft right down their center.





One inch bore with liners and O-ring head gaskets.





A relief is milled in at the lower inside corners of the blocks to receive quarter inch aluminum plate verticals to accommodate the crank shaft throws.


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## Longboy (Mar 11, 2021)

The S/F will be using the geared crank webs. 





This is my third engine build with this method having opened up some unique design elements transferring the reciprocal to rotary motion. The webs need steel halves to balance out the piston/ rod assembly.





The webs are made by the pair.





The vertical frame members with their bearing carriers to engine blocks.


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## Longboy (Mar 13, 2021)

The webs are finished with a 5/16 in. stub shaft. A brass tube spacer on the web side of bearing spaces out to clear the screw heads. On the bearing flange side an aluminum spacer, tapered to ride the inner bearing race. The machine screws will be replaced for the spacer and the bearing carriers with socket heads to get the right angle allen wrench up there as there is no room for a screw driver.





 The extended stub will have the drive gear, both cylinder banks, meshing with the driven flywheel shaft.


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## Longboy (Mar 16, 2021)

Round stock for the cylinder heads on these rectangular bocks.





Combustion chambers are bored to 3/8 in. depth. With the pistons rising to 1/4 in. below the block deck that gives easy turnover compression to hand start with 3 -4 in. diameter flywheels. The larger diameter cut in the bottom of cyl. head is the seat for the cyl. liner.





Heads need a butt fit to each other over the cylinder liners. 





Plain top surface with some broad horizontal finning. Cooling will be subsidized with some fin overlays to the upper block surfaces.


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## Longboy (Mar 19, 2021)

The lower end of SQUARE FOUR. Looks like the start of a donkey or ore cart. Bearing end plates set the spacing between the vertical plates.





Trying out a set of 1Mod 20T helical cut bevel gears over straight cut bevels used on the SIDE SHAFTER engine. Checking the three gear fit before bearing carrier install in the end plates. I like them and not sure if better here than using the straight cut versions.





The flywheel end will have a pair of R1810RR shaft bearings with the nose end having one bearing. Between the gear and inside bearing goes another brass tube spacer to set the gear lash without any thrust movement of shaft.


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## Longboy (Mar 21, 2021)

On the nose end plate backside go the ign. points.





A slot milled into the end of the vertical plate for the insulated connection to coil.





Lead for the condenser and a quick connect spade goes under the screw nut for the 6 volts.


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## Vietti (Mar 21, 2021)

Great work.  I really like your points set up.  What is the original use so I can get a set to experiment with?

Thanks, John


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## Longboy (Mar 21, 2021)

Vietti said:


> Great work.  I really like your points set up.  What is the original use so I can get a set to experiment with?
> 
> Thanks, John


Tecumseh points and condenser. Oregon branded on Ebay seems to have best prices.
.....Dave


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## Vietti (Mar 21, 2021)

Dave,

Thanks!  I'll get some.

John


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## Patrick (Mar 22, 2021)

incredible work.


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## Longboy (Mar 23, 2021)

The cyl. head overhangs the outboard side of the block. 





On the low side of block a shallow cut mill run up its length for the lifter bar.





Installed, the pushrod will pass through the head to the exhaust valve only rocker arm on top.





Completed Lifter bar with camshaft attached


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## Longboy (Mar 26, 2021)

The cam drive......belt or geared?





Drive cogs are seven inches apart. Gonna need a belt longer than my shoe laces and three idlers in this scale. Going to do gear drive in seven gears from the cam sprocket for a more compact arrangement. 

Transfer shafts off the sprocket shaft through vertical plates to the cams. All shafts here brass bushed. All gears  .5 Mod/ 24T






Shaft support bushing bolted under heads intersecting the cam drive with the final gear pair. 









And the shaft disappears to the back of engine to drive another item!


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## Longboy (Mar 28, 2021)

Tail end of this shaft drives the distributer. Using a 3/4in.  inner dia. PVC end cap with #8 brass screws for the wire leads. Extended length brass bushing pressed into aluminum body for the dist. shaft to rotate in.





Easy placement upon a pair of 1/4in. rounds on the shaft end plate, the body sits high on the engine.





Will not need too much flywheel back set from it's bearing carrier to clear the distributor gear set.


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## Longboy (Apr 1, 2021)

Using collet locker to join flywheel to their shafts pretty exclusively over the years. A three bolt retainer squares up the flywheel to its shaft for a true run. I use Delrin collets slit on one side spaced out with a brass or aluminum tube over shaft to a length that extends the collet past the shaft end about an eighth to 3/16th inch. 
To free the flywheel from its shaft for service you need a release mechanism. Unlikely one could tap at the flywheel with a mallet to drive the flywheel back off the collet and not damage the engine.





A couple of 8-32 machine screws are threaded into the end plates at a spacing equal to the through holes around the flywheel. Flat washers on the screws push the flywheel off the collet that bottoms upon the brass spacer behind then.


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## Longboy (Apr 2, 2021)

Sometimes the price of parts one uses building models hits me the wrong way. Gives you a chance to find substitutes for these particular items..........




............or an opportunity to make your own!

The top of the electrode diameter on a CM-6 sparkplug.




I take a 3/8in brass round for the wire terminals. Offset in the lathe chuck for a thin/ thick side and tap drill for an 8-32 set screw. Finish drilling with an "A" or  15/64 in. drill to the depth of the top of electrode to where it meets the ceramic, around .230 in. Tap the 8-32 threads to the end of the length of terminal then.  




The thick side at the threaded top side of terminal is cross drilled the diameter of the wire insulation. Tucked into the hole and the set screw locks in the stripped end copper wire.




Finished length of these terminals is under 5/8th inch and do not overwhelm the small size of these plugs. I think when I do these again, I will thru drill and tap the 8-32's and start the set screw from the top side!


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## Steamchick (Apr 3, 2021)

I love your enterprise and workmanship. For the plug caps: Give them an insulating cover by moulding hot-melt adhesive (Mind you don't burn yourself - it is HOT!). That will also support the wire from fatigue failure... (Things will vibrate!).
I trust the insulation is proper High Voltage to cope with ignition voltages? - It looks like regular domestic to me - when I was testing this years ago in the factory the 240 V wires failed between 2000V and 2500V - that was the spec. Ignition is typically a lot more than that!
Take your plug gap (as the spec from ignition coil supplier) in inch thousands: I was taught 10 thou relates to 1kV of spark voltage from the coil. A 15 thou gap at ~10:1 compression needs 1.5kV from the coil, a 25 thou gap needs 2500V. Enough to fail the domestic wire insulation. (Have I got that right - or wrong by a factor of 10? - Brain fade it was so long ago...).
K2


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## Peter Twissell (Apr 3, 2021)

Wire insulation will only fail if there is a current leak path.
I've seen old aircraft engines with no insulation on the HT leads, they are just supported away from the metal parts so there is no current leak path.
Provided your HT leads don't touch any metal parts of your engine, you can get away with domestic mains cable - just don't grab hold of it while it's running!


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## Steamchick (Apr 3, 2021)

Correct. But I don't have visibility of how much air clearance you have. The factory test was with outer immersed in water. The insulation punctures with the high voltage. Usually models have much less clearance than full size, because of the scale. Dry air has good insulation resistance, wet air not so much.
I had an electrifying experience on a Matchless motorcycle with magneto, at speed on the motorway, in the wet (back in winter 1973). As I accelerated the wind drag moved the HT cable close enough the cylinder head metal to cause a flash-over and mis-fire. As I tried to figure out what was causing the mis-fire over a certain speed - it wasn't engine revs, as I tried full revs in a lower gear to check  - I moved my leg and got full sparks up it!  Only for a second or so while the mis-fire slowed the bike or I moved my leg. It was sufficiently distracting I didn't want to try it again. There was a puncture mark from the arcing where the insulation had been blown towards the engine and eroded slightly, not worn completely through. I dried it with the heat of the engine, and back then, electrical tape was bitumen impregnated fabric, so a good wrapping was water-tight and adequate insulation, so I could use some string from the frame tube to hold the HT cable away from blowing onto the engine, and carry-on home.
But I am sure you won't  have that sort of electrifying fun!
K2


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## stanstocker (Apr 3, 2021)

I'm no doubt being dumb, but what holds the brass piece to the spark plug itself?  I understand the wire gets clamped by the set screw, but not what keeps the brass fitting from vibrating off the plug.
Thanks,
Stan


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## Longboy (Apr 3, 2021)

stanstocker said:


> I'm no doubt being dumb, but what holds the brass piece to the spark plug itself?
> Thanks,
> Stan


You are right Stan, could be an issue. I did have a couple dancing around on the sparkplug while running. A solution was to give the electrode at the insulator a drop of Super Glue  or epoxy to dry ......then seat the terminal upon.. That film was enough to give the base a wedge upon the terminal to hold it in place. A superior mechanical method is to drill the terminal below the wire for a  eighth inch long 4-40 set screw to seat in the waistline of the CM-6 electrode. Then you can position on the sparkplug the terminal regardless of any flex or twist upon it by the wire insulation.
....Dave.


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## Longboy (Apr 3, 2021)

Steamchick said:


> I love your enterprise and workmanship. For the plug caps: Give them an insulating cover by moulding hot-melt adhesive (Mind you don't burn yourself - it is HOT!). That will also support the wire from fatigue failure... (Things will vibrate!).
> I trust the insulation is proper High Voltage to cope with ignition voltages? - It looks like regular domestic to me .................
> K2


Thanks Steamchick. I am not having negative issues with hardware store AWG 14-16 for high tension leads to the sparkplugs. Holds up well with the high volts and low amps. Either AA batteries or my 2Amp power supply run the ignition.


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## Vietti (Apr 3, 2021)

I simply turned down the terminal of the plug and threaded it to some rational size, then used a knurled nut like some old engines.  Plug wire has an eyelet.  Looks good on some engines.

For spark plug leads I've used test wire meant for VOMs etc.  Find it on google or ebay.  Its real flexible,  finely stranded and well insulated.  I used to think spark plug wire needed to be large gauge to carry the high voltage and I then wound some coils and realized the secondary windings, supplying the plug voltage, are only a few thousands in diameter. High voltage really low amperage.


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## Longboy (Apr 4, 2021)

Vietti said:


> I simply turned down the terminal of the plug and threaded it to some rational size, then used a knurled nut like some old engines.  Plug wire has an eyelet.  Looks good on some engines.



I like that idea too Vietti! Converting a spade clip electrode to a threaded one with an eyelet and nut.


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## Steamchick (Apr 4, 2021)

Working on HT cables back in the 1980s when I worked in Design in Automobile manufacturing...
You don't need copper conductors for HT cables.
There were 3 types. All were designed to dramatically reduce the radio broadcast (noise) from the HT cables - that act like antennae for the radio noise discharged when the voltage rises or falls rapidly. This electrical phenomenon is often missed by mechanical engineers, who mechanically connect the terminals with wire.
The 3 common types:

Copper wires - but with suppressors ( typically 10Kohm resistors) fitted at the ends, e.g. in the plug caps and/or spark plugs.
Resistor leads which had a carbon "string" for the conductor, typically somewhere around 10Kohms per lead (on the car engine).
Inductive leads, which had an inductive "string" (maye 1 ~2mm diameter) wrapped with a coil of very fine copper wire (very Fine like a human hair). 
Now on a model - like this square 4 - instead of having between 1 and 2 feet per lead acting as an antenna, x 4 antennae, there are leads of only a few inches, and the voltages are lower. So the broadcast energy (Radio noise) of an unsuppressed electrical system will not be anywhere near so big as a 1950s 4 cylinder car that probably had unsuppressed HT leads/system.
I know in the early 1970s, when my suppressed plug-cap failed on my 2-stroke single motorcycle, I fitted an unsuppressed plug cap, and my father could hear me coming from about a 1/4 mile away from the noise on his radio! He could identify the gear changes by the frequency change. Today we use FM and digital radio that is immune from this (I think?) and all cars are well suppressed. (By law...).
So my message: You can use the least amount of copper you have in the wire without affecting the spark, but do need good insulation - I recommend more than "domestic wires" because it can puncture as it is not designed for the HT voltages being applied, if it touches the metal of the engine. You'll probably "get away with it" at 1/4" to 1/2" air clearance. - But do you have this at the end of the wire/head of the plug? - Hence I suggest covering with an insulating material - like the polythene or other polymer in hot melt adhesive. Apply a blob, then when it is just about cool enough to touch, squeeze it to a desired shape over the metal cap. If you have problems running the engine, crank it in PITCH DARKNESS and look for discharge (corona) from the wires and plug caps at this zone... the likely failure. One fix may be as simple as domed tops to the brass caps. (It reduces the electric field strength locally compared to sharp corners).
Remember, making something that works is a mix of "good design and manufacture" and "getting away with something that isn't right". We ALL do it ALL the time, so not a sin, and we only advise to try and help. And a caveat: "Help" is only useful when you need it.
Have a nice day with an excellent project!
Thanks for sharing your knowledge and designs.
K2


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## Steamchick (Apr 5, 2021)

Sorry all, I'm getting too [email protected]@&y clever with my quotes! - I'll go and give myself a talking to...
K2


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## Longboy (Apr 5, 2021)

Atmospheric intake valves seem to be winning in my designs. Even more so integrating into SQUARE FOUR being to the inboard of the cylinder heads. Space being at a premium here for another cam drive.









Pair of aluminum flat stock pieces (previous model shown) sandwich the valve guides sealed by O-rings between as well as the mounting to the heads with a brass tubing between these valve blocks and head.





Long machine screws adjacent to the ports hold the blocks to the heads. With the intake plumbing in place, there is no room for a screw driver or Allen key. To get a grip on the screws, I straight knurl across 5/16th threaded rod. Drill and tap 6-32. Cut to a short length and thread up to the head of the machine screws with epoxy to lock them on. Now I can tighten down with my index fingers! I use the same finger nuts setting rocker arm clearance too.
I'm going to need some short 90 deg. elbows right out from the carburetor port side from here. I can make them.....or see what my friendly ACE hardware store has to use.........


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## Longboy (Apr 8, 2021)

From RAINBIRD Irrigation Systems, I find some 90 deg elbows that fit in nice to the valve blocks the inch and three-eights distance between them. They are the right kind of rigid plastic for use here.





Just cut off the barb and press fit into the port up to their flange. Aim them to the front of engine.





Cut up some pieces of vinyl tubing to bring up to the intake manifold.  Vinyl pretty heat sensitive so most likely substitute silicon tubing for the job.


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## Longboy (Apr 10, 2021)

Intake manifold here of black plasticky stuff is drilled for the plenum.





Bolts onto the lower valve block pieces with a couple of spacers. An O.S. carb will feed the engine.


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## Longboy (Apr 12, 2021)

Natural metal or black satin, I like contrast with dark deep color. 





For radiators, the upper part of engine blocks get the fin cladding bolted on each side.


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## CFLBob (Apr 13, 2021)

I stumbled onto this build on Sunday, and it's rather interesting.  Is this your design?  Designing it as you build it or designing each section?  Or are you building to plans?  

I find your use of what appears to be plastics, 3D printed plastics(?) and metal together interesting, too, as a guy with a new printer.  The hose barbs look to be injection molded while the plenum looks like it's printed.

I'd be interested in anything you'd say about the design; sizes, bore and stroke, that sort of stuff.  They look to be about 1" pistons, sleeved cylinders, CM-6 spark plugs...


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## Longboy (Apr 13, 2021)

Thanks CFLBob.  The S/F engine is my free standing, open crank design of a rare configuration. I do not make plans or prints and no CAD but have an idea of "what goes where" integrating the individual parts as the build progresses. My purchased items include the timing set, ignition, gears, piston rings, cylinder liner stock, spark plugs, dist caps and carbs.
The intake manifold is Delrin cut to form. In the build log you see the 90deg fittings are a hardware store item. B&S is 1 inch.  Finishing up the build log this week followed by SQUARE FOUR's presentation. You can find build logs here on HMEM and can Google, "longboy engine" to view engines that are just a little bit different than what most hobbyists make being self conceived efforts. In S/F and previous models built, you see heat sink materials for cooling and remote valve blocks for intake and exhaust.....little ideas that work!


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## Longboy (Apr 14, 2021)

Square four engines being a pair of 180 deg. crank twins, its cylinders in unison rise and fall diagonally. 





The firing order is 1-2-3-4. Though I built the engine numbering the cylinders starting with the front left, the distributor with its gear drive rotates counter clockwise. The #1 cyl. is now the front right. This allowed for a symmetrical layout of the spark plug wiring from the cap.


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## Longboy (Apr 16, 2021)

A 72T belt takes care of the cam drive. With sprockets instead of gears for the cams, that belt would have had  around 400T.





More cylinders need more fuel capacity and up front I was able to have twin on board vertical fuel tanks totaling about 2 OZ.  SQUARE FOUR idles along for over 20 minutes per fueling.





Copper tanks and mufflers, the red metal along with white and yellow metal.....my kind of jewelry!

Longboy's SQUARE FOUR concluding this weekend!


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## Longboy (Apr 18, 2021)

Thanks for joining me in an introduction to my new engine,  Longboy's  "SQUARE FOUR"  Model Gas Engine!





Only found in the motorcycling world per my research, the Square Four found its way as a production motorcycle (Ariel), a racing motorcycle (Suzuki) and a production proposal motorcycle (Kawasaki). Now in a Google search on the web......as an obscure model engine, as are its full sized examples.





SQUARE FOUR was started second week of November.





Completed first week of March.





Very smooth performer.





20 minute run time per tank full.





Geared twin cams.





And geared crankshaft to central flywheel.





....See it run!   Thanks,  Dave.

www.youtube.com/watch?v=lpLHSQOZKtI&t


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