LONGBOY'S "SQUARE FOUR" MODEL GAS ENGINE.

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Longboy

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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!
 

Longboy

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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.
 

Longboy

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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.
 

Longboy

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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.
 

Longboy

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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

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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.
 

Longboy

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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

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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
 

Longboy

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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
 

Longboy

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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
 

Longboy

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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

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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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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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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

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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
 

Peter Twissell

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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!
 

Steamchick

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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
 

stanstocker

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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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