Technical Distributor Gear Indexing

Maybe I'm the last to know this,
I was just going thru my sbc distributor collection to build a few to use. Going with points (hp) higher tension. 32oz.

Had 1 or 2 last few years that didn't seem to arc at the correct spot when static timing engine?

FYI: Fellow Jr Stock racer asked if the distributor gear was "indexed" . All the years messing with SBC's never heard of that. Shimmed distributors for clearance, most times I put gear right back on, as it was removed. Maybe lucky.. who knows.

Gear Indexing is aligning the rotor location to the cap. 13T gear. Pin can be between 2T or align with 1T.

I picked 5x random distributors.
1x wrong
3x correct(divot aligns with rotor)
1x after market gear, no markings. On line sites, note align after market gear to original location.

 

I'm going to look close at the after market distributors I have as well. Made in China might be interesting.

I've only checked caps with a fully degree balancer, only found one that was grossly off on 1 cyl in my buddies sportsman dirt car.

 

Did some digging, found some more sites noting Vac Advance is key, for clearance indexing. I've had issues where factory intakes with firewall or intake runner fouling. Going to check my 62 dual point, dual window cap distributor, it was always difficult to drop in/ locate with a GM factory high rise intake. I had gear off that one 15yr back.

 

I was not aware of this...learned something new...another good day!

 

All the years looking at distributor gears, I (missed) never paid attention to the divot.

 

Amazing, learn something every day
Thanks Doug
Dan

 

I had a '68 Corvette, and when I tried to install the ignition shielding, it would not go on unless I turned the distributor. When I did that, I could not get the timing set right. I lived without shielding for about 6 months until I found out about this. I removed the distributor, and yep, the gear was indexed incorrectly. I changed it around, and everything went back together just like it was intended.

 

Did not even think about Corvette shielding. Thx for that information. I know my dual window cap, I ended up putting the windows on back to time properly.

 

Great! Now you got me wanting to pull out at least two unit’s.

 

Put me in the “I didn’t know that” crowd.
Thanks

 

I need to pull 2x as well, I'll wait until the wife is in the house.

 

Mine are fine. See I’ve always spiked the shaft and gear on the underside because I counted the number of teeth many many moons ago. Odd number told me one way only. Never have I looked and made the connection of the dot to rotor. Always thought why the need to balance such a small gear???

 

Although the one distributor I would have bet, was never apart, was off.

I remember making gears in swing boxes on cranes, good fail safe journeyman practice.

 

I always put a mark on the shaft and gear so it went back on the same. Now that doesn't mean someone before me didn't put it on wrong.

 

This 327 hp intake always problematic with some of my distributors.

 

I figured out the divot thing many years ago...I think I wondered what it was, then noticed that it was always where the rotor was pointing.

good thing to know

 

If you take apart a distributor
you will see there quite a few timing precision in machining .
Point & none

 

Huh?

 

Yeah,WHAT?

 

I have purchased gear shim kits since the late 70s, do not remember instructions noting the alignment. But who reads instructions... might be in a drawer.

 

I better be careful, I am stealing parts from one to build another. Any characteristics on switching the point cam mech to another. Early 60s cast iron dual point, to early 60s dual point distributor. DP Shaft,Tach Gear are fine... weight pin was damaged.

 

Point Plates.... most have Patent Number. I found one Patent Pending...is that from 1955?

 

57 or 58 I think was the first year of the distributor with the weights on top, the 55-56 used a different distributor. I had a pat pend cap on a 58 Chevy I had years ago, didn't realize I should have saved the cap!

 

As a tune up guy, I always took care to mark before dis***embly if needed.
Ran into the doesn't flip offset Ford drilling deal on later stuff, but didn't add up the divot to rotor on these. Learning!

 

I'll be damned. Three quarters of a century old and still learning. I guess that remark could be taken a couple different ways. Makes a lot of sense though if you think about it.

 

Interesting. Add me to the list of “did not know this”.

 

There are Adjustable rotor ****ons for phasing.
I think most think just a distributor,
All parts from gear to Machined areas to rotor ****on , terminals in cap
Affect timing Not so much on DD

 

How bout the centrifugal advance spacer many time missing on rotor pin. I remember an article way back, where a speed shop also brazed up the advance slot and filed it to the advance desired. Dang we are getting old...

 

I did know about the advance slot. If you mess with MOPARs you’ll find that setting the total mech advance to a reasonable amount say 34 or 35 degrees your initial timing will be too low, and you’ll have to narrow the slot.
One thing for sure nobody knows it all.
I’m not sure how many Chevy distributors I’ve pulled - quite a few- but I only remember tearing one down, I must of match marked or something I sure don’t remember a divot.
Dan