Small Block Distributor Again

[Al C.]

In a prior thread titled "Small Block Distributor Alignment", Tom Wander told us: "I installed a vacuum advance dist on my 2x4 by rotating the drive gear 180. It works perfectly with room to time correctly. No other changes were made."
I just pulled my dual-pont and substituted a single-point distributor with vacuum advance. The crank was sitting close to TDC, about 4 deg advance; DP rotor pointing about 22 deg right; the SP rotor points at about 14 degrees right. There's only a tiny amount of distributor body swing available between hitting the coil on one side and the carb vacuum takeoff on the other, but I'm able to run the engine.
Both distributors' gear dimples point with the rotor. How could they install pointing in significantly different directions (Not multiple of 27.7 deg). It's as if the single-point gear is already reversed, but its' dimple appears correct.
... Al '58 245hp

[William C.]

Re: Small Block Distributor Again

Dimple pointing toward the rotor is the "usual" orientation to obtain satisfactory alignment. The opposite orientation is only a potential "fix" if the situation merits it for some reason.

[Al C.]

Re: Small Block Distributor Again

i jsut pulled the single point ditributor back out to reconfirm that the dimple points to the rotor; it does. But at #1 TDC, the rotor points about 14 deg right rather than 22.5 deg. In other words, this distribuIor installs as if it were Tom's (with reversed drive gear).
The total advance was going to about 40 degrees at 2500 RPM with the vacuum advance functioning.
I am about to conclude that the cam/timing gears are installed wrong (or have slipped?). Before I start taking everything apart, should I double-check anything else? I don't know what if anything to trust on this engine.
... Al '58 245hp

[William C.]

Re: Small Block Distributor Again

Try rotating the dist gear one tooth on the camgear and see if that doesn't fix your problem, before you start messing with the gear on the dist.

[Duke W.]

Re: Small Block Distributor Again

The first thing you need to do before installing the distributor is rotate the crankshaft until the balancer notch is opposite the proper initial timing value on the tab for #1, NOT TDC. Then install the distributor with the rotor about 20 degrees to the right of center. I have never tried to measure the exact angle. If you can rotate the housing so the points just begin to open then the distributor is installed correctly, and it should be within a couple of degrees of the proper initial timing.

If you can't rotate the dist housing so the points just open, then try engaging another tooth fore or aft, and if this doen't work, you can try rotating the drive gear 180 degrees and see if that works at some tooth engagement. The reason why the 283/245 did not have vacuum advance is because a normally configured vacuum advance distributor would not fit at the proper initial timing location due to lack of clearance for the vacuum can.

Total cruise timing will vary depending on the centrifugal and vacuum advance characteristics. For example, with the very aggressive timing map of the 64-65 mechanical lifter SHP/FI FI engines the total cruise timing at over 2350 revs is up to 54 degrees. This is achieved with 14 initial, all 24 degrees of centrifugal, and all 16 degrees of vacuum advance. Total idle timing will be about 32 degrees - 14 initial plus 16 vacuum, plus a couple of degrees of centrifugal since it starts at about 700, which is less than the the minimum idle speed that will yield acceptable idle quality - about 900. Total WOT timing is 14 plus 24 full centrifugal, which totals 38.

A medium performance engine will probably not tolerate such an aggressive timing map, which means you have to limit initial timing, the rate of centrifugal advance, and since your engine should pull over 16" of manifold vacuum at idle, it should have a 16" vacuum can, versus the 8" can that works best with SHP/FI engines.

I have no idea what your centrifugal and vacuum advance curves are or the initial timing value you are using, but a good starting point would be the 283/230 HP engine specs.

Duke

[Al C.]

Re: Small Block Distributor Again

Duke said: "The reason why the 283/245 did not have vacuum advance is because a normally configured vacuum advance distributor would not fit at the proper initial timing location due to lack of clearance for the vacuum can. "
That's exactly the point of my quandry. My "normally configured" 946 single-point distributor with vacuum advance (actually for a '59 Vette, but with centrifugal specs identical to my dual point 891) DOES fit the very limited space between coil and rear carb. And it SHOULDN'T, unless the distributor gear is reversed (it isn't) or unless SOMETHING ELSE is off.
I stated that I was at 4 degrees from TDC when installing – that's my static spec.
I guess the first step is the piston stop to determine if the balancer is slipped (it feels very solid).
This car has never run right since I got it, so I can't trust that the guts are correct.
... Al '58 245hp

[Al C.]

Re: Small Block Distributor Again

Bill -
The vacuum can distributor doesn't have room to fit at the nearby tooth orientations; hits the coil or the carb. If swung around behind, hits the oil gauge line and/or road draft tube (I haven't tried every potential permutation YET). I'm trying the sp distributor mainly to verify anomalies with the dp distributor.
... Al '58 245hp

[Tom Wander]

Re: Small Block Distributor Again

Al,

As I read it Duke didn't just say it wouldn't fit. He said that it wouldn't fit AT THE PROPER INTIAL TIMING. That is the problem that I had. If I had the dist. in the usual configuration the max. adj. (rotation of the dist.) would leave the timing either retarded or too far advanced depending on which tooth you dropped the dist in on. In other words, I needed a 1/2 tooth of mechanical change to get in the middle of the range and thus allow room for proper timing adjustment. Removing and rotating the dist. drive gear 180* is equivalent to a 1/2 tooth change.

Tom

[Al C.]

Re: Small Block Distributor Again

Hi Tom -
Thanks for the input. My issue is that my 946 dropped in AND timed in that very, very limited space, WITHOUT the dist gear being reversed. Does that not mean something else is off, for that to happen??
...Al '58 245hp

[Tom Wander]

Re: Small Block Distributor Again

Al,

The suggestions above by others should insure that you do not have any other problems. But I did find that with points in my dist. I had to rotate the drive gear 180*. However, using the SAME dist. with a Pertronix II installed it works with the drive gear installed in the usual position. Since dwell affects timing, I'm assuming that there is enough difference in the dwell to account for that.

Tom