Total Spark Advance:UPDATE

[Joe C.]

To those who showed an interest in the thread below, here is what I found this morning:

First, I disconnected/plugged the vac advance, tied the dist weights in place, and measured the initial timing at 18*. I pulled #1 plug, and verified TDC was dead nuts on the balancer mark........OK, part of the problem was "my bad", I don't know how the initial got to 18*, but I reset it to 10*, and reset the dwell angle to 30*.

Next, I verified that the 236 vac can IS, indeed providing 17* advance, as it should, at 800 degree idle (9.5 in-hg).

Finally, the suspected culprit showed up. The combination autocam/weights/springs are delivering a staggering 33* of additional advance, all-in @ 1800RPM. This adds up to the whopping 68 degrees of spark advance at cruising (non transient) speed, which I reported on Tuesday!!

So, now I'm at 10* plus 17* plus 33* = 60........much more tolerable than 68*. Next on the list is to get the centrifugal to where it should be (24* @ 2300), or thereabouts.

Moral of the story: Never trust reproduction distributor parts. Always verify your distributor timing map with a timing light, degree tape, a tach-and-dwell meter, and a vac gauge.

More to follow.

Joe

[Michael H.]

Re: Total Spark Advance:UPDATE

Ok, thought so. Between now and the time that you repair the distributor cent adv., I would probably set the initial timing at around 4*-6*, which would put you in the ball park for 38* total. (Initial plus mechanical) Your current 10* plus 33* is still way too much.

Amazing that all that pinging wasn't causing some serious damage to the internal workins below.

Some owner before you must have used the old rule of... if a little is good, and more is better... then too much must be just right.

[Verne Frantz]

Re: Total Spark Advance:UPDATE

Joe,
I noticed that you said you reset your initial timing then reset the dwell. You need to do that in the opposite order. Set the dwell first because changing the dwell will change the timing.

Verne

[Joe C.]

Re: Total Spark Advance:UPDATE

Michael,

Just modified the flyweights to provide 27* centrifugal @ 1600. Yes, that's a little bit more than factory recommendation of 24* @ 2350. Just road tested the car, and she seems to like it. The fact of the matter, is that she had way too much total advance before, and now that I took out 14*, it breaks down as follows:

Initial: 10*
Vacuum: 17* @ idle- 10 in-hg @800 (can rated @4 in-hg)
Centrifugal: 27* @ 1600

Maximum(@ steady-state cruise): 54* BTDC

Truth be told, even if there is "ping", then I cannot hear it, anyway, because of the exhaust, and my marginal hearing. The only way to know, for sure, is to put analyzer on and load engine. Hopefully, it was pinging before, and is not now, which means that she's running a bit stronger than before I checked the advance map.

Joe

[Joe L.]

Re: Total Spark Advance:UPDATE

Joe-----

Well, you're going about correction using the "in situ" method. This can create a lot of wasted effort, trial and error, and hassle, though. If it were me, I'd use the "in vitro" method. That is, I'd send the distributor out to someone that could set it up to spec on a distributor machine. Then, you know it's where it should be to start with. From there you could experiment with initial advance settings to "fine tune" everything to actual engine operating parameters (fuel, altitude, ambient temp, etc.).

[Joe C.]

Re: Total Spark Advance:UPDATE

Joe,

Total advance was unacceptable the way that it was with the artermarket autocam/weights/springs in it, and I had been driving the car that way for quite a while until checking with the degree tape, Tuesday.

There will be no trial-and-error, because I've got it where I want it right now, first trial. Initial is at original recommendation (10*), vacuum can is working as original (17* total vac advance, at idle). I've got the centrifugal set a bit more aggressively than original spec ( 27* 1700, as opposed to recommended 24* @ 2350), and matching original would be a simple matter of using heavier springs, and further modifying the flyweights.

The engine is not exactly the same as stock (heads have been ported/polished/cc'd, head gaskets are different thickness, heads have been surfaced), and today's gasoline is not the same as yesterday's. Therefore, the original recommended spec is a good starting point, but the usefulness of tweaking those settings, other than eliminating audible pinging, would be wasted effort without instrumentation to measure affect on power output.

Joe

[Michael H.]

Re: Total Spark Advance:UPDATE

Joe,

I think your centrifugal specs will be ok if you still have your valves set at the specs that the Duke recommended. (around .024?) At those "tighter than specs" settings, the slight increase in duration will kill off more of the low RPM actual compression pressure. If you do go back to the original .030-.030" lash, I would probably take out more of that early advance. The total should be ok but it should come in a little later, especially with todays fuel.

Several weeks ago,I remember you mentioning a weird rattling sound when you were driving your car. I wondered if this was the pinging that was sure to result with the timing numbers that you had at that time?