Above: right side view
Below: left side view
ENGINE NO. FIVE DATA
Type: Inline twin DOHC
Displacement: .889 cu in/cyl x 2 +
1.78 cu in
Compression Ratio: 6.84:1
Ignition: initially coil/spark plug; later glow plug
Fuel: 15% nitromethane/methanol mix
Max. RPM: 12,500
Est: Horsepower: 2.2
Background -- I've long been
interested in the overhead cam engines used by Harry Miller
back in the early racecars starting around 1915. These engines
became winners for many years at many tracks, including Indianapolis.
After Miller went broke, Fred Offenhauser, Miller's
shop superintendent, bought the business and was very successful
for many years. These "Offy" engines were comparatively simple
but very rugged. Development continued until the
last successful Offy fours could put out 1200 H.P. from approx.
221 cu. in.
Construction -- Building an
Offy-style engine intrigued me, but I didn’t
want to have to make four cylinders and the associated parts.
The engine I finally designed was two cylinders with head attached
to the cylinder by six bolts.
The crankcase was hogged out of solid stock but the engine
mounts were attached by welding. At the time I built this
engine I was still using spark plugs. Later on I eliminated
them and used glow plugs on the engine. Timing
belt drive plus one 2/1 gear off the crankshaft actuates
bucket-type overhead cams. A pair of model engine carburetors
were used, but have been difficult to adjust.
Another feature of this engine was taken from
the Triumph motorcycle engines. This was a three-piece, single
throw crankshaft with a center, internal flywheel.
Operation -- This engine
ran okay initially but later it was found almost
impossible to hold this crankshaft in alignment. Finally, I
broke down and built a solid, one-piece crank shaft. Although
very difficult to make, this has worked well. Later runs were
made with glow plugs and were quite sucessful. It would turn
up over 11,000 R.P.M. with almost instant acceleration.
At this writing, the engine is being hopped
up; the original carburetors are being replaced with
ones of my own design which have worked nicely on other engines.
Detail of camshaft drivetrain.
ENGINE DETAIL PAGE LINKS
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