How
to set the Timing on a Cushman Cast Iron Engine with a degree wheel.
By Jason Glass
www.fastcushman.com
After securing a degree wheel on the clutch side of the
engine (locked in place with a nut on each side of the degree wheel or with tape
or Velcro to the clutch) you can began to set the timing.
- Fabricate
a pointer out of a piece of wire similar to a coat hanger that can be bolted
securely to the transmission brace mounting hole on the rear of the engine
block. Before bolting to the block make the other end into a point. Bend the
pointer around in a L shape so that the pointed end is just at the edge of
the degree wheel.
- With
the head off of the engine and a using a dial indicator, locate Top Dead
Center (TDC) of the piston. (This needs to be on the compression stroke both
valves will be closed) Mark the degree wheel were the pointer is located,
this mark will be your 0 (zero) degree mark.
- With
the TDC located and marked on the degree wheel as 0 (zero), turn the engine
back (against normal rotation) until the pointer has counted out 18. This
will be 18 degrees Before Top Dead Center (BTCD) Mark this point on the
degree wheel as 18 degrees.
- Now
with the TDC located and marked, and the engine turned backwards 18 degrees,
go over to the points side of the engine to set the timing. (It is
recommended to use a Continuity tester to determine the exact time that the
points break open and discharge the fire to the plug…human eye is not as
accurate, also make sure the points gap is correct.)
- With
NOTHING connected to the points (no condenser or any wires) connect the
Continuity tester to the points where the condenser wire would normally be.
Rotate the engine back (against the normal rotation) 20-30 degrees. This
will put the piston in the hole as if it has started the fire stroke and is
on the way to the top. The continuity light should be lit at this point. Now
slowly rotate the engine Forward (as if the engine is running-normal
rotation) Watch the continuity light and stop the rotation at the point that
the light goes out. This is when the points break and at this point the
spark plug would fire. Look at the degree wheel and see where the pointer is
located. You want the pointer to be pointing at the 18 degree mark you made
earlier when the points open-thus you create the spark from the spark plug
at 18 degrees BTDC.
- If
the continuity light has gone off and the pointer is not at 18 degrees you
will need to loosen the magneto plate just enough to allow you to rotate the
plate in the direction needed to obtain a spark (or at this point the light
on the tester to go out) at the 18 degree mark. NOTE: In many instances you
may be required to drill the Magneto plate mounting holes with the next size
larger drill to allow the magneto plate to move enough to get the spark at
the recommended 18 degrees. A Stock factory specification was at 17 degrees.
With a Mikuni Stage I, or other performance modifications it is recommended
to have a little advance on the timing so we recommend 18 degrees. Often the
timing was just guessed at the factory, this made some scooters run better
than others as the timing was more accurate on some than on others.
- Once
the magneto plate has been adjusted, re-tighten the two magneto plate bolts
and re-check the position on the degree wheel when the test light goes off.
Many times the adjustment changes when the bolts are tightened down and the
timing is changed. Also, at this point be sure to re-check the gap of the
points with a feeler gauge set at .020. Check and re-check after all
adjustments have been made to ensure that the test light goes off at 18
degrees.
Tools required: A degree wheel 7” to 9” works
fine, Pointer-can be fabricated from a metal coat hanger, a continuity tester
(battery powered pen light type) and a feeler gauge.
Click
here for a free printable 7" degree wheel
