Old Cars Weekly News \& Marketplace - Auto Restoration Guide: Advice and How-to Projects for Your Collector Car

manual. Figure 5 offers a good illustration of setting the points on a
WWII GMC CCKW. The process is simple: one turns the engine —
preferably by hand — until a distributor cam lobe comes around and
opens the breaker point contacts. After making sure that the contacts are
fully open — the breaker point rubbing block is on the highest point of
the cam lobe — loosen the breaker mounting screws, insert the correct
size feeler gauge between the point contacts, and adjust the points so
that a slight drag is felt when the feeler gauge is moved between the
contacts. Then the mounting screw is retightened.
How slight is “slight is something that can only be learned from
experience. A good rule of thumb is that when the point contacts are
properly set, there should be only a bit of resistance when slipping the
correct size feeler gauge back between the contacts. If the feeler has to
be levered between the contacts, or obviously forces them open wider,
then the points were set too close. If the correct size feeler gauge slips
between the contacts with no resistance at all, the points have been set
too wide. Of course, new points must always be set when installed.
While, again, the process is simple to describe, it is often difficult
because many distributors, especially waterproof types on military
vehicles, are not located in easy-to-reach places. Sometimes it’s easier to
remove the distributor from the engine to install new parts or reset the
points.
The rubbing block rubs against the distributor cam and thus wears
away, but this wear can be lessened by keeping the cam clean and
smooth. If the cam isn’t rusty or corroded, just wipe it clean all around
with a rag, and then apply a bit of distributor cam grease, which may be
found at most auto supply stores. A little goes a long way, so just apply a
light coating all around the cam. Too much lube or any oil inside the
distributor will be thrown off as the cam spins at high RPM and may
collect on the point contacts and burn. It’s important to use distributor
cam lubricant rather than any old grease, because ordinary grease may
produce a vapor when the distributor heats up, and this vapor may
collect on the point contacts and burn.
On older vehicles that sit a lot or have been in storage, the cam may
be rusty. If so, it will wear the rubbing block very quickly. A rusty cam
should be polished with fine crocus cloth. Be sure to get all the dust and
grit out of the distributor after the cam has been cleaned.