From: hotrod@dixie.com (The Hotrod List)
Subject: Engines of Yore #3
Date: Sat, 09 Jan 93 05:23:38 GMT
Organization: Dixie Communications Public Access.  The Mouth of the South.
To: hotrod@dixie.com
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Posted-Date: Saturday, Jan 09 00:23:21
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                         Engines of Yore:  Part 3.
               Scott 596cc Twin.      created 26 April 1992
             by Dave Williams   dave.williams@chaos.lrk.ar.us

 The 596cc Scott twin is famous in engineering literature, where it is
used as an example of how not to design engines.  Despite their several
outright bizarre characteristics the engines were reliable enough for
their time.

 The Scott was a two stroke.  A BIG two stroke, 30 degree forward
inclined, water cooled twin.  With only those specifications, any
modern designer could design an engine that would dislocate your arms
when you whacked the throttle open.  The Scott unfortunately isn't
that sort of engine.

 The crankcase was a hefty one piece aluminum casting, evidently
designed to have its primary machining done on a lathe.  The intake
ports are cast into the crankcase, siamesed together to a single
carburetor flange in the center.

 The crankshaft was built up inside the crankcase; it was not
removable as an assembly.  An enormous flywheel in typical British
fashion, with two tapered crankwheels fitted into bosses on the side
of the flywheel, joined by a long bolt.  Take a penny and stick a
thumbtack on each side, with the heads out.  The penny is the flywheel
and the heads are the crankwheels.  Visualize a sprocket on each side
of the flywheel for primary drive takeoff, and a ball bearing next to
each crankwheel, or thumbtack head.  Imagine a little stub on the
crankwheel for the connecting rod.  That's it.  Only two closely spaced
main bearings, and the rods flail around unsupported.  Now add the
piece de resistance - it's a 180 degree twin, not the more common
360 degree type.  When one piston is up, the other is down, creating
a rocking couple across the narrowly spaced main bearings.  The Scott
was seriously weird.

 The outboard side of the rod journal was attached to a sheetmetal disc.
At first sight you might think they were rotary valves.  Nope, they were
there to drive the magnetos, one at each end of the crankshaft.  The
sheetmetal disc had a little shaft and shaft carrier plate, which also
mounted the magneto.  All assembled it looked sort of like a
conventional crank, only it was sheetmetal.

 All bearings are rollers or balls, and they are pressure fed through
the drilled crankshaft by dual oil pumps.  Pressure feed is unusual for
rolling element bearings.  No mention was made of premixing oil and
gasoline; apparently once the oil passed the bearings it mixed with
the induction charge and was burned.  Yamaha made a major production
of their "Yamalube" system in the early 1970s, but Yamaha was doing
much the same thing.

 The cylinder block is spigoted into the crankcase and is held on by
four bolts, two on each side of the crankcase.  They feed up from the
crankcase to the cylinder block at the approximate place the outboard
cheeks of a conventional crank would occupy.  The cylinder block
contained the exhaust ports.  The aluminum cylinder head was held down
by sixteen studs (vs 4 bolts for the entire assembly).  Combustion
chambers were hemispherical with centrally positioned plugs.

 No water pump was used.  The Scott depended on thermosyphon; ie
natural convection with hot water rising to the radiator (which was
presumably mounted higher than the engine) and cool water coming back
into the bottom of the block.

 The pistons were alumimum, with three rings and floating pins retained
by thrust buttons.  The long skirts had no windows.  The domes were
steep; the exploded view drawings indicate the internal airflow might
have been very similar to the Schneurle Loop popularized many years
after the Scott's original design.

-30-
                                                                                                       

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Posted by: emory!chaos.lrk.ar.us!dave.williams (Dave Williams)
Newsgroups: alt.hotrod,wiz.hotrod