How important is this ? I can't recall seeing one without a lot more than
the .010 (?) that I see recomended. From a performance or wear standpoint should I reduce the .050 play that I have now (GMPP crate motor dist.) ??
Yup, I know to keep the gear dimple in line with the rotor if I pull the gear to shim.

Daffy

 

Daffy,
I'd throw a shim set on there. I don't think the end play makes much difference from a performance standpoint BUT -- you need to make sure the distributor gear meshes properly with the camshaft gear.

My distributor had about .050 and it was fine but why tempt fate?

Brian

 

Don't worry about the dimple. The gear only goes back on two ways, and regardless, you can set the timing anywhere you want. I don't think shimming the gear has any appreciable affect on gear wear. But because the gears are helical, as the distributor shaft goes up and down, it must turn, which changes the timing. Distributor shaft end play is a source of "spark scatter". Shim it!

 

Daffy,

The orientation of the drive gear does actually affect your ability to set the timing correctly. If you had a cast iron manifold with the smaller runners, you would be able to compensate for any misalignment.

BUT - since you probably have the 3844461 hig rise (365 HP), there is little room for timing adjustments as the distributor is rotated between the coil bracket and the intake runner. You will have all kinds of issues while setting your timing if you don't put the align the dimple with the rotor tip. Again, if you have the distributor off, why mess around?


I just converted my motor to full-out 365 specs and the distributor is now a whole lot more crowded due to the intake - I can hardly get a wrench in there to tighten the distributor.

Brian

 

Tight end play is critical to avoiding ignition breakup on the old single point systems on high revving SHP engines. The GM spec is two to seven thou and they used to sell six and 30 thou shims to achieve this value.

Sloppy end play can cause both point bounce and spark scatter. HEI systems don't have point bounce, but you can still get spark scatter with sloppy end play.

On C2 327s you can't achieve the initial timing spec unless the drive gear is installed with the dimple pointing in the same direction as the rotor tip due to limited angular travel before the vacuum can hits the coil bracket or inlet manifold. The drive gear has 13 teeth, so if the drive gear is on "backwards" the clock position of the distributor changes by about 14 degrees.

Duke

 

Thanks for the good info. I'll be shimming it.

Daffy

 

where can i read exact info on this??? haven't done,,,,Yet prob. will
need to soon Thanks

 

The end play spec for the single point dist. in is the '63 Corvette shop manual. I know of no GM service publication that discusses proper indexing of the dist. drive gear, but trust me, you better have the dimple pointing the same direction as the rotor tip if you want to achieve the correct initial timing before the vacuum can interferes with the manifold or coil bracket.

It's one of those "system knowledge" things. Trust me - been there done that - 35 years ago.

Duke

 

I don't buy it. This is the first legitiment reason for the dimble idea I've heard and I can't accept there's not enough adjustment left. I crunched the numbers using: 360*/13 teeth = 27.7*/tooth and since theres an odd number of teeth yes I can see that roll pin be will be located to split 7 teeth on one side and only 6 teeth on other side. So yes that forces the gear on with 27.7*/2 = about 14* difference when swapping sides.
But I get at least 45* (really more than that) adjustment on my dist ('74). And since the wires are only 45* apart on the cap I would rotate (and have) the firing order on cap 1 location (CW or CCW) to put the mech tach drive where needed. This has never been a problem for me and have a hard time accepting other claims.

As far as end play I just used a cheap shim kit from PAW and reduced the endplay until gear turned free and smooth without friction or drag. Never bothered to measure a thing. Don't forget the gasket between dist and intake Daff. Good Luck. cardo0

 

Read my post again, dummy - C2 327s, not '74s; '74s don't rev to 6500, so end play is not as critical, and C3s SBs have different distributor clocking and wire indexing than C1 and C2.

Duke

 

I was tempted to write a similar post. I couldn't imagine the situation where the distributor couldn't be "adjusted" for the proper timing. When the tight confines of certain set ups was mentioned, I thought better of it. *I* haven't worked on ALL sbc set ups to know for sure. Maintaining the rotor to gear orientation, certainly, can do no harm.

I'll tell what doesn't work. That is installing the distributor gear, upside down. When I shimmed my distributor end play, I wasn't paying attention and did it with the gear, wrong side up. No matter how many times I adjusted the oil pump driveshaft, I just couldn't get the distributor to "drop". Finally, I pulled the distributor to see if any of my forcing had raised any burrs to prevent installation. THAT is when I noticed the flat thrust surface and no chamfer for the shaft facing down. After I reversed the gear, the distributor practically jumped into the hole. What really surprised ME, was the shim pack for proper end play changed very little. Dot be damned! Chamfered end DOWN. Hee Hee.

RACE ON!!!

 

This is nonsense. The locked down position of the distributor only determines the initial advance. Who are you kidding? Clocking? You mean phasing? Phasing is controled by the constrution of the cap/dist housing which are the same for both C2 & C3. And I just checked my Chevy interchange manual and all Gen I engines will use same dist (BTW same as BB too). Wire indexing? Sorry only one firing order for the sb Chevy. Now your inventing things to support you bad understanding. And I did read your C2 statement which is nonsense also as both C2 and C3 can use and interchange the same dist., intake, carb on same engine. If your C2 has some unique obstruction preventing the same angle of rotation then post it. But as I see it would have only less obstructions without The EGR and plumbing of a '74. Vacuum fitting? Then change it. Air cleaner housing? Then prove it or shut up.
All I can see is your lack of understanding the dist timing is getting in the way. And I'm not here to be labeled or call other people names so if you can't control yourself I'll have to report you to the Mods! cardo0

 

 

Cardo0,
I usually do not participate in internet arguments but in order to understand the validity of your posts I need to know if have you ever worked on a correctly configured 327/365. That fact that your particular set up on your '74 will work does not imply that it works in all situations - particularly on a 327/365. If you hop on over the the C2 section, you will see that this is a common problem for owner of stock configurations of higher HP motors.

everybody relax

Brian

 

Well have you ever measured the arc angle a dist turns through from stop at firewall to that accused intake runner or any other stop? You can do this with a long straight edge and protractor or just a long straight edge and some of that high school math - trigonometry. And yes on that 327/365 even thought Duff's intake is different than both the old LT1 alum and my '74 iron piece (its not the low ZZ4 intake either). And all you need is 45* to rotate to the nearest wire in the firing order and ruin the advance firing on #1 (your on #2 by then).
I say that if you can't get the intial advance you need, more the rotor over one tooth for another 28*. Yes add advance with the rotor to cap orientation and who cares where the number one wire is located as long as the firing order remains 18436572. That #1 wire can be anywhere on the cap as long as the rotor points at #1 with #1 cyl at TDC (and both vlvs shut) minus the initial advance desired. What I'm saying is this dimple idea continues to get perpetuated when there's plenty of adjustment to use with advancing the rotor a tooth (28*) or more plus relocating the firing order on the cap one location (= 45*) if nessesary and last then fine adjust with the dist housing. So really all you need is about 30* of an adjustment angle. Maybe try and draw some circles for dist and crank and label each cyl at each interval of 45* but remember that dist turns once for very 2 turns of crank.
I give up. Mark and follow your dimples all you want. Put a dimple on the dist cap if you want - maybe on that LT1 intake runner too. I'm pooped and going to bed. cardo0