On Sat, Jun 11, 2011 at 2:48 PM, <jtw...@aol.com> wrote:
Really weird ignition firing sequence: front two cylinders fired
simultaneously, then aft two cylinders fired simultaneously - - I have
never read or heard an explanation for this oddity,
There is a really simple explanation for the firing sequence. In a
2-stroke engine, the fuel-air-oil mixture goes into the crankcase to
lubricate the bearings, and is then compressed slightly by the
downstroke of the piston(s) before entering the combustion chamber(s)
when a port opens up near the bottom of the stroke. The MAC engine has
two separate crankcase cavities; one for the front two and one for the
rear two cylinders.
A "normal" boxer engine sequence wouldn't pressurize the crankcase.
> How many readers would be interested in a revival of a ('modernized')
> up-dated Mac 72-type engine???
I would. I have three of these engines, two are brand new and still in
the original shipping cases. The third had a prop strike after about
an hour.
