Nash designed this 195.6 OHV engine for a world that no longer exists. Nearly all cars were manually shifted, steering was wrestled by hand, brake force provided by Grandma. Shifting wasn't cool and fun, it was a necessary chore.
To make the car eeeeeasy to drive motors were designed to lug. Transmissions had three speeds, and you could generally use just two. Smooth and easy mattered! So engines were heavy, cheap to make, and detuned into submission.
If you go by the book this old Nash power plant (sic) ran with 19 total degrees ignition lead. Cast iron and gasoline are cheap, who cares? The main side effect -- besides an utter lack of power -- is the goal: it will never ever ping. You can pull away from a stop sign, 5mph, in top gear and just press the go pedal. It goes, OK not quickly, but with no complaints.
Hmm but the year is momentarily 2008 and we have other concerns. 75mph traffic on the Los Angeles 405. Five-buck gasoline. Timing matters.
Alas there is no NASH section at Summit Racing. There's just this one dumb distributor what fits inna hole. Stock, it provides 11 degrees total centrifugal advance, and 11 more vaccuum advance. By road testing my '63 American I determined that the little motor is happy with a lot more advance. I decided to ruin the distributor to get that.Electronic ignition
The first order of business is to pitch the points. You can't even buy good ones any more, the aftermarket parts are all crap. While the speed this engine turns (red line is 4500 rpm) isn't pushing things a Pertronix Ignitor, part #1162A, ("Delco 6 cyl with vacuum advance") and the matching epoxy coil is substantially hotter, and more reliable, spark without being wasteful (and arcover-inducing) overkill. (One annoyance with the Pertronix is that you have to file a small clearance notch in the cap to clear the two wires that now come out; if I had thought ahead I would have looked at drilling the distributor body.)
|(Vacuum advance)||11||11 - 16 (see text)|
Mechanical advance on these old Delcos is limited by a pin on the points-cam assembly that lives in a hole on the main shaft assembly. The pin is small, the hole large, so the hole limits rotation to 11 degrees. Enlarging the hole is obvious, but too much and the fly weights will hit the housing. Enlarging the hole is obvious, but total advance change is limited by the weights hitting the distributor case in the outward direction, and the weights hitting each other in the retard direction.
I drilled the hole out to 33/64s (the parts are all hardened, but I happen to have a carbide-tipped bit that size) and sparingly ground the tips of the weights such that they would fold in closer. I stuck some random soft springs from who-knows-what distributor curve kit, which got the advance to come all-in around 2000 rpm, about right for this motor.
Optimum static timing is somewhere around 10 - 16 degrees BTDC, for a total of 32 degrees. It still never pings. It could use more. I did some before and after 0 - 60mph tests which were inconclusive. Mileage has been steadily creeping up with no carb changes, so that's all good.
If you need to do this to another random distributor, watch for the weights hitting the housing; that's the advance limit. I got a few more degrees out of it by grinding the tips from the weights that allowed them to fall all the way back against the cam; stock, the weight tips touched.Vacuum advance
Hint: when you are fiddling ignition timing, drive around with the vacuum advance hose removed and plugged. Vacuum advance is for part-throttle (high vacuum) cruise only, and doesn't affect power, but wil affect drivability or pinging when it's wrong, and it complicates things. Mileage will drop but it greatly eases making adjustments -- one variable at a time!
It turns out, you can easily get 16 degrees vacuum advance by filing the limit-stop down (see below) but don't bother -- once you've upped overall advance, the engine will not tolerate a lot of part-throttle advance. Stock is fine.
Here is maximum and minimum spark advance (minus springs and retainer). Max is limited by the hole (see below) and minumum by the weights hitting each other. Under the rotating assembly you can see the pin and hole that limits advance travel.
Here's the hack. It's not a big deal. A hole drilled, and weight tips ground and checked, repeated until the weights laid flat on the cam. Removed about 1/16" at the tips where indicated.
Increased vacuum advance turned out to be a bad idea; while I heard this motor ping once, with too much advance it bucks and makes weird noises... don't do that. But if you insist, the hack is easy. (I "fixed" mine by dangling a flattened piece of 1/8" brake line in the working area; ugly but reliable enough until I take the unit out for a better fix.)