[Spridgets] points part one

David Riker davriker at nwi.net
Tue Mar 17 15:47:26 MST 2009


This seems to be getting filtered due to length, so here is part one:

Points are a mechanical system.  Mechanical systems usually fail slowly due
to wear.  The kinds of wear that a points system encounter are:
1.  Natural arcing occurs as the points open and close.  This "burns" the
surface of the points, interfering with the flow of electricity.  Once this
happens, the electricity looks for an easier path, causing missfire.
2.  The points block rides on the distributor lobes to open and close them.
Over time, heat, dirt and friction wear down the block, causing the gap to
change and close.  The change in gap changes the timing.  Points that don't
open as far are more likely to arc.  See #1 what happens when points arc.
When the gap wears down to zero, the car won't run.
3.  As a mechanical system, the points have a built in spring that keeps the
points block in contact with the distributor lobe.  The faster the rpm of
the engine, the more potential for the points to bounce open beyond where
they should, changing the dwell time.  Inacurate dwell time causes high rpm
missfire.
4.  As a mechanical system, that block that rides on the distributor lobes
depends on the shaft having zero wobble.  Over time, the bearings in the
distributor shaft wear (basically, the british thought we'd be throwing
these cars away after about 75,000 miles, so after that point the shaft
bearings are usually worn out).  Wobble in the shaft causes the lobes to
"appear" different height and spacing instead of uniform.  This makes the
points open irratically, scattering the dwell and timing events.  This
causes missfires.

CONTINUED IN "POINTS PART   TWO" 


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