You are forgetting one really big thing--the other end of shaft drives the
oil pump which probably takes a couple of horsepower to drive if you set
your bypass for maximum pressure--that's why it breaks. Incidentally, you
shouldn't set your bypass to maximum--all you probably need is ten pounds
per thousand RPM.
The shaft breaks down inside the oil pump, as you would expect. The drive
for the oil pump has a squared off slot, which creates a stress riser across
the base of the slot. The driven side of the slot breaks off and breaks the
tang off the shaft. You can dramatically increase the part reliability by
radiusing the bottom of the slot carefully to eliminate the stress riser,
and radiusing the tang of the shaft. It might be worthwhile to eliminate the
tach drive gear, but I doubt that it's significant.
If you do something like that, be careful with what you wind up with--the
thrust on the drive gears is taken up on the base of the distributor, and
that clearance is critical. Too loose and you and partially disengage the
pump, perhaps breaking the tang in a whole new way. Too tight and you'll
turn the drive gear into a mill, shearing the drive teeth off the cam. Don't
ask why I know this.
In my opinion you have two ignition choices depending on what you do about
electricity. If you run total loss with a battery, then you need to run
battery-point-coil, because all the modern systems assume (and demand) more
than twelve volts--the alternator runs at 13 to 15 volts. With a battery
under load in a total loss system the voltage is 12.5 max, and 12 or less
under load. The MSD systems draw a fair amount of current and therefore drop
system voltage even lower. The result is unreliable electronics.
Battery-point-coil is relatively insensitive to the drop--in fact the
ballast resistor (which you MUST have) drops the voltage under load to about
seven volts. If you run BPC, you need a good distributor, which the Lucas is
not. The runout is unacceptable for precise timing for all four cylinders.
You'll need to switch to something with better bushings and design--the
Mallory is the easiest.
If you run an alternator you can afford the sloppy Lucas because you can use
a hall effect or optical ignition and the electronics will be happy. The
runout doesn't matter because the spark is triggered by rotational position
rather than the point clearance. You can easily see the runout on a Lucas
distributor with any timing light--the sparks will scatter. If you put it on
a scope and look at all four cylinders it looks really awful.
So it all comes down to alternator or no alternator. Here's the nasty
part--you need to be pretty careful about alternators. In the range of RPMs
that racing tractor motors reach, the alternator needs to put out reasonable
voltage at idle and still live at 7000 RPM. Lots of folks have had problems
with alternators--even trick little ones that should work. Either the pulley
choice runs the alternator too slow to make good running voltage a low RPM,
or the little buggers come apart. I've opted to revert to BPC with a
Mallory and no alternator.
|