Which terminal do you have your number 1 spark plug wire at?

[Edward B.]

Guys, attached is a picture of what I'm referring to.

The number one spark plug wire on my L36 is located one terminal over from where the manual says it should be. This is causing the vacuum advance can to hit the ignition shielding. The Service manual shows the number one "should" be above the points adjusting window, but I've also seen a lot of L36's (and other big blocks) with the number one just to the (in my picture) left of that. So which is correct and where is YOUR number one spark plug wire located?

Thanks
Ed

[Chuck G.]

Re: Which terminal do you have your number 1 spark plug wire at?

You could have installed the distributor "one tooth off", or possible the distributor gear is not properly indexed to the rotor. The "bump" on the gear should align with the tip of the rotor. Could be a combination of both.

[Duke W.]

Re: Which terminal do you have your number 1 spark plug wire at?

I suspect Bubba has been working on your distributor. I'll assume your manual is correct regarding wire indexing, but if so, it's different than small blocks, which has number one on the terminal that's closest to the right side of the window opening.

I suspect the distributor gear may be installed 180 degrees from the proper indexing. On small blocks the dimple in the gear must point the same direction as the rotor tip, and I assume this also applies to big blocks.

Once you verify proper wire indexing for a big block, index the wires correctly, then set the crank balancer notch at the initial timing point BTDC #1 compression stroke. Remove the dist. and verify that the gear is properly indexed. IF not, knock the roll pin far enough out so the gear can rotate on the shaft and tap the roll pin back in. Then reinstall the distributor. You may have to tweak the oil pump drive to get the dist to fully seat, and when it does, the rotor should be pointing at the #1 wire terminal.

Rotate the dist. housing until the points just begin to open. This is called "static timing" and should get the initial timing within a degree or two of where you set the balancer notch on the timing tab, so the engine will start right up. If you use an ohmmeter it should be within half a degee. Then use a timing light to verify/set the initial timilng with the engine running.

Duke

[Wayne M.]

Re: Which terminal do you have your number 1 spark plug wire at?

There was an exception for '68 small blocks.

From Chevrolet Service News, Dec '67.

[Edward B.]

Re: Which terminal do you have your number 1 spark plug wire at?

Well, in about a half hour when I get off work, I'm goin' in! If I don't come out again, tell my kids I love them.

I'll be checking the dwell, timing, looking for vacuum leaks, etc... so I'll report what I find.

I have a feeling you're right though. I think it's off one stinkin' tooth.

Ed

[Terry M.]

Re: Which terminal do you have your number 1 spark plug wire at?

There was an exception for '68 small blocks.

From Chevrolet Service News, Dec '67.

Actually Wayne what is labeled as 1968 SB in that CSN item applies to all 1968-1972+. I am not sure if the electronic tach in the later C3s changed this orientation, but it is the location of the tachometer cable and the distributor vacuum canister that drives this. It is labeled 1968 because it appeared in a 1968 MY issue of Chevrolet Service News and of course 1969 and beyond were yet to come.

Oh, and a copy of that is in the latest 1968-69 TIM&J in part because I got tires of posting it here. Way too many people confuse the C2 & C3 orientation of the distributor and wires.

[Michael W.]

Re: Which terminal do you have your number 1 spark plug wire at?

Well, in about a half hour when I get off work, I'm goin' in! If I don't come out again, tell my kids I love them.

I'll be checking the dwell, timing, looking for vacuum leaks, etc... so I'll report what I find.

I have a feeling you're right though. I think it's off one stinkin' tooth.

Ed

Moving the distributor one stinkin' tooth probably won't fix it. The vacuum can will now hit the intake runner while trying to set timing instead of the shielding. You only need half a stinkin' tooth which can be achieved by turning the gear 180* on the shaft as suggested above.

Actually Wayne what is labeled as 1968 SB in that CSN item applies to all 1968-1972+. I am not sure if the electronic tach in the later C3s changed this orientation, but it is the location of the tachometer cable and the distributor vacuum canister that drives this.

This also applies to '73-'74 . The advent of HEI in '75 meant that everything changed, including the location of the #1 plug wire tower on the cap.

[Patrick B.]

Re: Which terminal do you have your number 1 spark plug wire at?

The 1967 AIM shows for the L-36 (and other big blocks) the no. 1 position as the place Chuck identified as No. 1 and Edward labeled as where he had seen as No. 1 for other cars. I tried to set my L-71 distributor position today according to the AIM, but it is slightly off the index marks on the original manifold and distributor that I assume were marked by the factory. The mark on the distributor gears lines up with the rotor. However, since I have a Federal Mogul cam rather than a GM cam, it may be necessary to reverse the gear to line up the rotor on No. 1 at 8* advance while keeping the distributor housing lined up with the mark on the manifold.

[Edward B.]

Re: Which terminal do you have your number 1 spark plug wire at?

Okay guys, I was able to get out of the engine compartment, but it was late last night and I was too tired to post.

Anyway, here's what I found:

1. The dimple on the gear WAS aligned with the rotor tip, so that's good.
2. My engine builder installed an aftermarket harmonic balancer, and the top dead center mark is nowhere near where it should be! With number one cylinder actually at TDC, the mark on the balancer is way over by the power steering cradle!! That's bad.
3. My REAL problem turned out to be a MASSIVE vacuum leak. When I installed the carb, I inadvertantly installed the gasket and heat shield upside down, so it wasn't covering the intake or the bottom of the carb correctly. My fault, so that's bad.
4. I didn't move the wires around (at least not yet), since I was able to get it timed correctly (4 before TDC) using a mark I made on the balancer, and the vacuum can is now in a position where it's not hitting anything. That's good.
5. Dwell is right at 30 degrees so that's good.
6. RPM at idle is right around 900, so that's pretty good, but it still fluctuates every few seconds or so. I'm not sure if that's because of the cam or I have a flaky distributor. The cam specs are:
Lift - .502/.501 and Duration 277/287 (intake/exhaust)
It's pretty mild, so I would guess it might be the distributor?
7. It's still running rich at idle (you can smell the unburned gas), but it's not as bad as it was. Before this it actually burned my eyes! I put a known good carb on it and it too ran rich, so I'm not sure what's going on. Maybe I still have a small vacuum leak.

I have a Holley 6210 Spreadbore that came off the 396 that was in my Camaro (replaced it with a 427), so I may slap that on and see how it runs just for giggles and grins. It ran great on the 396, so it should also be great on the 427.

By the way, when I had the shop rebuild the engine, I stipulated that I wanted the final compression ratio to be no more than 10:1 and preferably around 9.5:1 so I can run this cat pi$$ they call gas around here. I didn't check their work, but they assured me that they got it a little above 9.5:1.

Ed

[Mike F.]

Re: Which terminal do you have your number 1 spark plug wire at?

Shouldn't the distributor vacuum canister be pointing towards the passenger side fender, on the aft side of the orange distributor shield bracket?

[Patrick B.]

Re: Which terminal do you have your number 1 spark plug wire at?

Shouldn't the distributor vacuum canister be pointing towards the passenger side fender, on the aft side of the orange distributor shield bracket?

On a big block, a line drawn between the distributor cap hold down clamps would be perpendicular to the car's fore/aft axis with the vacuum advance pointing about 45* right of car axis. The number 1 spark tower is between the distributor cap window and the vacuum advance.

IMG_1009.jpg

[Duke W.]

Re: Which terminal do you have your number 1 spark plug wire at?

The 1967 AIM shows for the L-36 (and other big blocks) the no. 1 position as the place Chuck identified as No. 1 and Edward labeled as where he had seen as No. 1 for other cars. I tried to set my L-71 distributor position today according to the AIM, but it is slightly off the index marks on the original manifold and distributor that I assume were marked by the factory. The mark on the distributor gears lines up with the rotor. However, since I have a Federal Mogul cam rather than a GM cam, it may be necessary to reverse the gear to line up the rotor on No. 1 at 8* advance while keeping the distributor housing lined up with the mark on the manifold.

If the marks are only slightly off it's okay. Rotating the distributor gear 180 degrees will change the base clocking about 14 degrees at the same initial timing.

Also the initial L-71 timing specified in the AMA specs is five, not eight degrees. That may be why the stake marks don't align, not the camshaft. FM OE replacement camshafts are manufactured to the GM prints.

If it doesn't detonate at 8, leave it there. In fact, try 10.

Duke

[Mark E.]

Re: Which terminal do you have your number 1 spark plug wire at?

Some of the above posts aren't consistent with the 1970 AIM UPC 6-B6 (see below). For all engines (454 section shows same):
- #1 plug wire is attached to post that's mostly over the cap's window
- The distributor is clocked so the cap's hold down screws are just about in-line with the axis of the car

The means the VAC port will be to the rear of the RH cable bracket that's bolted to the intake.

Maybe this is different for other years?

1970 AIM UPC 6-B6 Spark Plug Wires Coil Shielding.jpg

[Edward B.]

Re: Which terminal do you have your number 1 spark plug wire at?

Mark, the 1968 and 1969 AIM's both show the same thing for UPC 6, sheet B6, but L36, sheet A6 is slightly different (see 1968 example attached).

By the way, just to let everyone know, I DID have another small vacuum leak (a hose had come off the carb), so once I got that back on, the right balancer installed and everything else set up correctly, the position of the number 1 spark plug is on the window, the vacuum advance canister is "pointing" just behind the bracket and the car's running perfectly!

Ed

[Patrick B.]

Re: Which terminal do you have your number 1 spark plug wire at?

The 67 AIM shows the number 1 plug wire for a 427 attached to the distributor cap at the tower between the window and the vacuum advance. So it must have changed in 68.