Problems with Timing

[Wayne M.]

Re: Timing Minutae

Tony, the correct/proper methods of installing/checking the distributor alignment vary somewhat by year and engine. Functionally, the limits are defined by being able to set the timing without the vacuum advance unit hitting the manifold or the shielding/brackets, AND the tach drive cable able to be attached easily and without interference with shielding, etc.

The A.I.M. usually does show what the correct angle of the distributor cap should be after installation, vis-a-vis a line normal to the engine centerline. Then, the final timing adjustment is made, per the engine spec. The '65 to '67 A.I.M.s call for different angle of distrib. cap for K66 option, and even indicates where the rotor arm should point before and after easing the unit into the engine.

I agree with Chuck Gongolff that if it wasn't for the above interference concerns, the distrib could point in any direction, as long as the plug wires were rotated to different holes in the cap, respecting the firing order, so timing could be established at #1 cylinder.

I seem to remember a GM tech service bulletin reprint (in the Restorer ?) that radically changed the distrib orientation in a 1968(?) smallblock to correct an interference problem.

I'm surprised this thread didn't delve into the subject of the proper alignment of the distributor driven gear (that meshes with the camshaft), when (re)installing on the distributor shaft --- dimple on gear in line with rotor arm, otherwise you'd be "out" half a tooth, which would shift the adjustment arc mid-point.

[Wayne M.]

Re: Timing Minutae

Tony, the correct/proper methods of installing/checking the distributor alignment vary somewhat by year and engine. Functionally, the limits are defined by being able to set the timing without the vacuum advance unit hitting the manifold or the shielding/brackets, AND the tach drive cable able to be attached easily and without interference with shielding, etc.

The A.I.M. usually does show what the correct angle of the distributor cap should be after installation, vis-a-vis a line normal to the engine centerline. Then, the final timing adjustment is made, per the engine spec. The '65 to '67 A.I.M.s call for different angle of distrib. cap for K66 option, and even indicates where the rotor arm should point before and after easing the unit into the engine.

I agree with Chuck Gongolff that if it wasn't for the above interference concerns, the distrib could point in any direction, as long as the plug wires were rotated to different holes in the cap, respecting the firing order, so timing could be established at #1 cylinder.

I seem to remember a GM tech service bulletin reprint (in the Restorer ?) that radically changed the distrib orientation in a 1968(?) smallblock to correct an interference problem.

I'm surprised this thread didn't delve into the subject of the proper alignment of the distributor driven gear (that meshes with the camshaft), when (re)installing on the distributor shaft --- dimple on gear in line with rotor arm, otherwise you'd be "out" half a tooth, which would shift the adjustment arc mid-point.

[Jack H.]

Re: Check/Installation of Distributor?

The high points got addressed. Distributor has arc limits imposed by externals (radio RF shielding, vac advance hose, Etc.). Distributor also has 'correct' assy techniques covered by shop manual for early cars and CSM/COM (chassis service manual/chassis overhaul manual) that define how to install drive gear onto distributor shaft.

Over the course of time/prior owners/prior mechanics, it's possible for a number of items in the world of timing (includes timing gears on crank and cam) to be out of spec/convention. The net effect can be engines that run properly when a timing gun shows them to be grossly out of spec based on the balancer's alignment mark/scale under a timing light.

I think it's beyond the scope here to define a diagnostic algorithm for all that might be wrong and how to correct. Pointing in appropriate direction(s) was my intent.

[Jack H.]

Re: Check/Installation of Distributor?

The high points got addressed. Distributor has arc limits imposed by externals (radio RF shielding, vac advance hose, Etc.). Distributor also has 'correct' assy techniques covered by shop manual for early cars and CSM/COM (chassis service manual/chassis overhaul manual) that define how to install drive gear onto distributor shaft.

Over the course of time/prior owners/prior mechanics, it's possible for a number of items in the world of timing (includes timing gears on crank and cam) to be out of spec/convention. The net effect can be engines that run properly when a timing gun shows them to be grossly out of spec based on the balancer's alignment mark/scale under a timing light.

I think it's beyond the scope here to define a diagnostic algorithm for all that might be wrong and how to correct. Pointing in appropriate direction(s) was my intent.

[Gary Schisler]

Re: Problems with Timing

If the timing chain is installed with reference to TDC of the #1 cylinder, tune-up information assumes #1 cylinder was referenced for dist. installation, and all references to installation, repair, or timing of the engine reference the #1 cylinder, why would you want to try anything other than the "proper" installation of your distributor? I just refenced my 66 Service Manual, Chilton's Corvette repair manual, and "How to Rebuild Your Small Block Chevy". All contain specific procedures for removal, installation, and determination of TDC for distributor installation. The latter book, by the way, has a fool proof method (I have used it for 4 0r 5 dist. installations) of distributor installation for all distributors, including the HEI of the mid-70's Corvettes. Although I haven't been tuning Chevy SB's for longer than 6 years, I do feel that if you do it the factory way, you can't go wrong. The designed and built the car, they should know how to tue it.

[Gary Schisler]

Re: Problems with Timing

If the timing chain is installed with reference to TDC of the #1 cylinder, tune-up information assumes #1 cylinder was referenced for dist. installation, and all references to installation, repair, or timing of the engine reference the #1 cylinder, why would you want to try anything other than the "proper" installation of your distributor? I just refenced my 66 Service Manual, Chilton's Corvette repair manual, and "How to Rebuild Your Small Block Chevy". All contain specific procedures for removal, installation, and determination of TDC for distributor installation. The latter book, by the way, has a fool proof method (I have used it for 4 0r 5 dist. installations) of distributor installation for all distributors, including the HEI of the mid-70's Corvettes. Although I haven't been tuning Chevy SB's for longer than 6 years, I do feel that if you do it the factory way, you can't go wrong. The designed and built the car, they should know how to tue it.

[Chuck G.]

Re: Problems with Timing

Hi Gary; I'm certainly not advocating installing the distributor incorrectly. As a matter of fact, with the tach drive, vacuum cannister, ignition shielding brackets, etc, there's only really one "area of orientation" that you can install the distributor body. What I am saying, to the owner who sets his timing correctly with a timing light, and later finds out that his distributor rotor and cap are not 100% factory correct in their orientation, is that you can time your car off of any position that one decides is the #1 cylinder. If you look at Street Rods and any other small or big block Chevy applications, you'll see the #1 plug wire coming from any one of the 8 positions in the cap.

If that owner sets his timing at 4 degrees BTDC with an incorrect rotor position and a corresponding incorrect #1 plug wire position, and then later corrects the rotor postion and puts the #1 spark plug wire in the correct place in the cap, and then re-times his car, it's still the same 4 degrees BTDC off of any wire that goes to #1 cylinder. I'm not a very good "wordsmith", and didn't want you to think I was advocating an incorrect installation per the manual. Chuck

[Chuck G.]

Re: Problems with Timing

Hi Gary; I'm certainly not advocating installing the distributor incorrectly. As a matter of fact, with the tach drive, vacuum cannister, ignition shielding brackets, etc, there's only really one "area of orientation" that you can install the distributor body. What I am saying, to the owner who sets his timing correctly with a timing light, and later finds out that his distributor rotor and cap are not 100% factory correct in their orientation, is that you can time your car off of any position that one decides is the #1 cylinder. If you look at Street Rods and any other small or big block Chevy applications, you'll see the #1 plug wire coming from any one of the 8 positions in the cap.

If that owner sets his timing at 4 degrees BTDC with an incorrect rotor position and a corresponding incorrect #1 plug wire position, and then later corrects the rotor postion and puts the #1 spark plug wire in the correct place in the cap, and then re-times his car, it's still the same 4 degrees BTDC off of any wire that goes to #1 cylinder. I'm not a very good "wordsmith", and didn't want you to think I was advocating an incorrect installation per the manual. Chuck