Stu,
You have two pumps that were made several decades apart. The pump with
the brass rollers was a very early design. Later pumps came with a four
lobe plastic armature guide with the lobes attached together such that
is resembled a square. Later still (in 1985) they started using the 5
figure eight guides.
> My question, are rollers necessary/important? The six bolts that marry the
>whole assembly together should align the diaphragm anyway . . . Or am I just
>assuming too much?
Yes, you are assuming too much. The holes in the periphery of the
diaphragm are clearance holes for 2BA screws rather than alignment holes
and as such will not hole the diaphragm, or more important the armature
of the diaphragm assembly perfectly centered in the coil housing.
Unless the armature is perfectly aligned, it can start hitting against
the core piece in the coil. If you look at the coil core, you will see
that it projects beyond the bottom of the core and there is a
corresponding relieved area in the center of the armature on the
diaphragm. If the edge of the relieved area on the armature is
misaligned it will start hitting on the outside edge of the coil core,
with will cause the pump to become unstable and eventually quit
pumping. The armature guide pieces, whether the original brass rollers
or the newer figure eight plastic pieces, keep the diaphragm perfectly
centered until the coil housing/diaphragm assembly is attached to the
pump body are screwed together. The guide piece could be removed after
the pump is completely assembled, except they haven't figured out how to
do that once the pump is assembled
As far as the plastic covered diaphragm vs. the diaphragms without the
plastic cover - the plastic cover was an attempt to keep the fuel from
coming in contact with the diaphragm material. This was originally
necessary because the diaphragm would not withstand the newer formulated
fuels. The diaphragms on the newer diaphragms (again starting around
1985) have a different diaphragm material that is resistant to the fuels
of today. The older sandwich style diaphragms with the plastic cover
also had two layers of the elastometer material and over time the two
layers would fuse together, causing the diaphragm to become stiff to the
point that the pump wouldn't operate properly.
Another difference in the two pumps that you may not have noticed is the
diameter of the cores in the two coils. The early pump has a core that
is about 1/2" in diameter, while the later pump has a core diameter of
nearly 3/4". Looking at the armature of each diaphragm, the older one
should be flat on the top up to the edge of the relieve area that fits
over the projecting section of the core. The late diaphragm should have
a raised ring around the relieved area of the armature. The result of
this change is to produce a pump that pumps much faster than the earlier
pumps, while putting out the original low pressure pumps.
I would advise against routinely disassembling the pumps to perform
adjustments and cleaning of the points unless there are other problems
being experienced. There are just too many things that can go wrong
when reassembling the pumps, and it is not necessary. Among other
things, the procedure for adjusting the points has changed with the
advent of the newer points assembly that have adjustment tangs on them.
If you want to e-mail me at SUfuelpumps@donobi.net, I can send you a
procedure for cleaning the points that will work much better than just
dragging a piece of sand paper between them and an adjustment procedure
to use with the newer points assembly.
Finally, if you are experiencing repeated problems with you fuel pump,
it is perhaps time to contact me about restoring your pump and
converting it to solid state.
Cheers,
Dave
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