Atomic 4 points gap - which is correct?
Bob B.
I am a little confused. After launching my boat yesterday I replaced the points on my
1979 Atomic 4 engine (Delco distributer) and set the gap at .018 - .020 as specified in
my service & repair manual (from Seacraft publications). However, other sources that
I have found on say that the proper gap setting is .018-.020 for Prestolite (older)
distributers, and .025 for Delco (newer) distributers.
This to me (a neophite mechanic) is a very significant difference. Can anyone shed some
light on this discrepancey, especially since, all across northern America this month,
hundreds of people are probably setting their new Atomic 4 points?
Does it really make that much difference? What would be the symptoms of an incorrect
setting of +/- .05-.07?
AHAngelini
Points wear closed and dwell increases with wear!
Rod McInnis
Bob B. wrote:
>
> I am a little confused. After launching my boat yesterday I replaced the points on my
> 1979 Atomic 4 engine (Delco distributer) and set the gap at .018 - .020 as specified in
> my service & repair manual (from Seacraft publications). However, other sources that
> I have found on say that the proper gap setting is .018-.020 for Prestolite (older)
> distributers, and .025 for Delco (newer) distributers.
>
> setting of +/- .05-.07?
The bottom line is that it doesn't make much difference, *at the time
you adjust the points*. The requirements are that the points have to be
closed for a long enough period of time to allow the current to build up
in the coil, and then open far enought to prevent the spark from jumping
the points.
If the points are set too far open, then they won't close at all and
the engine simply won't run. Closeing them down just a little would
allow the points to close while the flat of the cam passed by, but
wouldn't leave them closed for very long. Idle would probably be OK,
but you might incur a miss as the RPM increased (and current buildup
time was reduced).
With too little gap, the spark will want to jump the points, which
would cause very erratic behavior. Opening them up just a little bit
more would provide good performace to begin with, but it would quickly
deteriorate over time. With use,the cam lobes will wear the follower,
causing the gap to decrease. In addition, arcing at the points can
build up a "tit" on one surface, which would also result in an
insufficent gap.
The "proper" point gap is a trade off between dwell time (coil current
buildup time) and wear tolerance. In general, a four cylinder engine
has so much excess dwell time that anywhere in the middle is OK. For an
eight cylinder, on the other hand, striking that balance is a bit more
difficult.
The optimum setting will also depend on the build of the distributor.
If the cam lobes are taller, then it will open the points farther, and
the gap setting will want to move out as well.
One *really* important thing to remember is the changing the point gap
will also change the timing. So after you set the points, check the
timing.
Rod McInnis
CptnRn
I have also been told by a pretty reliable source in the AOL Atomic 4
message boards that the gap should be .025 for Delco distributers. I
find it curious that my Owner's manual (1975 Pearson 28, w original A4)
lists the gap setting at .018 - .020 . Which I had been using. I guess
I'll try the .025 setting and see if it seems to make a difference.
CptnRn
I've recently been advised of another contridiction regarding the timing:
the Owner's manual recommends rough setting of the timing with the timing
mark, and final adjustments to the timing while the engine is running
under load, by ear. I've been told that this is not a good practice with
todays gasolines, and a timing light should be used instead, or you could
damage the engine.
Any opinions on this?
CptnRn