Only the Tech Savvy Apply

[Bill S.]

OK --- A bit of background for this one --- A 1966 with a L-79 was rebuilt by a reputable engine builder??? New pistons, rings, camshaft, etc was installed as well as a Mallory breaker less ignition module to eliminate the Ignition Points. We noticed the No. 1 spark plug wire location in the distributor cap of a correct car and compared it to this rebuilt motor. This rebuild has its No. 1 spark plug wire in the wrong location in the distributor cap. The engine starts and runs GREAT. The firing order is correct as well as the timing --- the only problem is the location of the plug wires in the cap. In theory, all the plug wires should be moved "TWO spark plug wire positions clockwise". I have a link below showing the correct location for No. 1 CYL.---- and this mystery motors current location. (the photo is from a correct L-79)

How can this motor run so well when the No. 1 cylinder location is two steps from where it should be?
Thanks
Bill Schroeder NCRS#32822

[Clem Z.]

Re: Only the Tech Savvy Apply

# 1 plug wire can be in any of the 8 holes in the distributor cap as long as you set the distributor in the engine with the rotor pointing to #1 cyl. and the firing order is correct. all you have to do is place the engine with #1 cly on compression and move all the wires in the cap to the proper location and reinstall the distributor with the rotor pointing to the new # 1 location

[James F.]

Re: Only the Tech Savvy Apply

Bill,
Unbolt the distributor hold down. Remove the distributor cap, lay aside. Mark on the side of the distributor body (chalk) where you want # ! plug to be located. Lift the distributor an inch or so, enough that you can rotate the rotor to point in the directon you wwish. Lower the distributor back into position. The rotor will rotate slightly as you lower the distributor. You may have to adjust for this rotation by lifting it again and rotating it a little further in original direction. This is a Kentuckey windage type of deal! Probably it won't drop entirely into the manifold surface. Rotate the cap plug wires to the new termainals (correction new location). Disconnect the coil wire so the car will not start. "Hit" the starter quickly, the rotor should rotate. do this several times and the bottom of the distributor will find the slot in the oil pump and the distributor will "drop" home. Lock it in place, not real tigh. You'll need to retime the engine. I'm sure I've forgotten some step. Listen to others as well. Reaards,

[William C.]

Re: Only the Tech Savvy Apply

Clem is correct, the only significance of the "Correct" orientation is that the factory ignition (spark plug)wires were tailored to length to reach those spots. An original set or sparkplug wires will not fit with all the proper routing and the starting point in the incorrect location. Most aftermarket and replacement sets have more "slack" in the lengths.

[Lonnie Johnson]

Re: Only the Tech Savvy Apply

Well shoot! Just when I thought I had the "dimple in the gear" thing figured out, this mess shows up. If the plug wires can be at any location as long as the firing order is correct, the engine is timed right, and runs great, how does the dimple location matter if the engine can be timed right? I agree the dimple should point toward the rotor tip, but I guess the old skull has just gotten too thick to comprehend.

[Clem Z.]

we can get into timing off of # 6 *NM*

[Duke W.]

Re: Only the Tech Savvy Apply

Do the instructions for installing the Mallory ignition module say anything about reindexing the wires, rotor tip, or drive gear?

Duke

[Patrick H.]

Arrrrgh! Don't Say It! *NM*

[Terry Leeker]

Re: Cautionary tale

As we know, the ignition wire position in the Dist. cap only needs to be in the correct order to do their thing. If you are making up your own wire set, the existing wire set can be configured for a couple of possible cylinder locations, you want to match the factory location of number 1 wire location in the cap so that the wires lay as designed. This will minimize "cross fire - induced voltage surge in an adjacent wire that is not suposed to be energizing a spark plug). This really isn't an issue with the new silicone wire insulation these days but if you using vintage or repo wire sets it is.

[William V.]

Re: we can get into timing off of any cylender

Lets confuse the issue some more. ADD timing marks every 90 deg to the balancer and time off any cylender.

[Chas Kingston]

Re: we can get into timing off of any cylender

That's what I did. But, primarily for setting the lifters.

Geezer

[Wayne K.]

Re: Only the Tech Savvy Apply

Lonnie,

Getting the dimple right is to eliminate having a clearance issue with the vac can when setting the timing. I've been to school on that one myself.

[Joe L.]

Re: Only the Tech Savvy Apply

Bill-----

As others have advised, the #1 position can be set on any of the 8 cap positions as long as "other adjustments" are made. On a Corvette, though, the position to which the #1 plug wire is set has other significance and importance. That's because the "other adjustments" that I referred to above as necessary when the #1 position is changed cause the relocation of the position of the vacuum advance control AND the tach drive fitting. Any change from the original distributor position will usually result in the vacuum control interfering with the ignition shielding, shielding supports, and/or coil. It will also result in the alignment of the tach drive fitting being in such a position that excessive curvature to the tach drive cable will result, if the cable will attach, at all.

So, with a Corvette application, there is much more "criticality" to the distributor position than on most other Chevrolets. The position which you have marked as "correct" for the #1 plug wire is, indeed, "officially" correct for the 1966 L-79 application. However, one may find it necessary to change the relative positions of the plug wires by 1 position, counterclockwise. In this position, the #1 plug wire will be located on the "other tower above the window". Sometimes this is necessary to get BOTH the distributor vacuum control AND the tach drive fitting in "acceptable" positions. In your case, the #1 plug wire has been moved TWO positions, counterclockwise. I've never seen a need for this much change to accomodate the above-referenced other considerations. But, it's possible, I suppose.

[Eugene B.]

Re: Only the Tech Savvy Apply

Bill,
I've looked at this thread a couple of times and although all the information is technically correct, there is a simplier way to understand this whole issue.

By defination, the tower for the number 1 cylinder (first cylinder on the drivers side) is the tower that is at the left-hand edge of the distributor cap window. You will see this diagram in the 1963 Shop Manual on page 6Y-28.

Just get the number 1 cylinder up on the COMPRESSION STROKE and drop the distributor in so that the rotor points to the number 1 tower. Route spark plug wires per figure 52 (Page 6Y-28) and your ready to start engine and fine tune dwell and timing.

Hope that I've done a good job of explaining this.

Good luck,
Gene

[Terry M.]

Re: Only the Tech Savvy Apply (OT) *TL*

Gene et al,
Your definition of the number one position applies to C2 Corvettes, which is what the question that started this discussion is about. I must point out, without attempting to draw the discussion off topic, that is not the position for C3 Corvettes. I know you were not addressing the newer cars, but folks with a wide variety of interests read these posts.