Big block distributor orientation

[Roger G.]

Can someone tell me how the distributor was installed from the factory on a 70 LS5? Was the vacuum bulb pointing to the side of the car or was it pointing toward the #4 cylinder? Which tower was #1? The one to the right of the door on the distributor cap or to the left? I see a service bulletin for the 68 small block where the orientation was changed, vacuum bulb facing the side of the car. The service note stated it was for the small block.

[Bill C.]

Re: Big block distributor orientation

i am pretty sure the nipple pointed towards #8 cylinder.
I know for 100% certainty it was that way for late 70, and all 71-72

early 70 got the same shielding setup as the 69's did. and I think it pointed to #8 also, or maybe somewhere between #6 and #8
it would depend on where the vacuum advance canister cut-out is in the shielding.


Bill

[Joe L.]

Re: Big block distributor orientation

Can someone tell me how the distributor was installed from the factory on a 70 LS5? Was the vacuum bulb pointing to the side of the car or was it pointing toward the #4 cylinder? Which tower was #1? The one to the right of the door on the distributor cap or to the left? I see a service bulletin for the 68 small block where the orientation was changed, vacuum bulb facing the side of the car. The service note stated it was for the small block.

Roger-------


Like this:



corvettedistributor 001.jpg

[Wayne M.]

Re: Big block distributor orientation

And here's another that I think is small blocks. Says that 427's are definitely not affected.

I wonder if this continued beyond the 68 MY ?

[Duke W.]

Re: Big block distributor orientation

It appears that the '68-up small block dist. orientation is the same as all big blocks. Is that correct?

Is the dimple on the gear still installed pointing the same direction as the rotor tip?

Duke

[Michael W.]

Re: Big block distributor orientation

Yes and yes. The change on the SB engines was to lessen the strain on the tach cable. The revised position was retained to the end of 1974 production.

[Mark E.]

Re: Big block distributor orientation

It's not with me right now, but the '70 AIM has a diagram for our LS5 that's similar to what Joe shared above. However, unlike Joe's diagram, I think it designates the tower to the left of the points window as #1 (I could be wrong so check). With that said, other than being "correct", it really isn't important which tower begins the firing order.

The orientation of the distributor housing relative to the engine is important to avoid bends in the tach cable. That's achieved with the VAC pointing almost directly to the right side of the engine as specified in the diagram. When installed properly, the vacuum tip will be behind the bracket for the shielding.

Duke- I'm curious why you ask if the tach gear dimple should be aligned with the rotor tip. Have you heard of exceptions?

[Duke W.]

Re: Big block distributor orientation

With that said, other than being "correct", it really isn't important which tower begins the firing order.

Duke- I'm curious why you ask if the tach gear dimple should be aligned with the rotor tip. Have you heard of exceptions?

That may be true for most installations, but on a C2 small block if the dimple isn't pointed the same direction as the rotor tip, you can't get the initial timing to spec on most engine configurations without the VAC interfering with either the coil bracket or the inlet manifold.

There have been reports that sometimes the dimple has to be rotated 180 degrees, opposite of the OE configuration, to get the initial timing in range. It appears this is an issue with some aftermarket camshafts.

Also, I recall at least one report where someone with a 283/245 engine installed a single point distributor in place of the dual point to get vacuum advance and reported that the dimple had to be rotated to get the initial timing in range, and that's probably why that engine had the dual point rather than a single point like the base single four-barrel 283s that had the same long block.

Duke

[Patrick B.]

Re: Big block distributor orientation

It appears that the '68-up small block dist. orientation is the same as all big blocks. Is that correct?

Is the dimple on the gear still installed pointing the same direction as the rotor tip?

Duke

Apparently, big blocks changed too. The 67 AIM shows the #1 plug wire between the distributor window and the vacuum advance
with the distibutor oriented like the pre-68 SB picture for the L-36. The LS-5 section of 70 manual has the #1 plug behind the window with an orientation like the 68 SB picture.