Re: All Very Good Information
Your example will theoetically work, but it's a moot point since swapping wires one position over and rotating the distibutor base 45 degrees to realign the new terminal indexing to the rotor tip will cause vacuum can interference on most Midyear engines. I believe that later Shark engines have the #1 wire indexed on a different cap terminal with the distributor base suitably rotated due to changes in the ignition shielding design.
In my posts I have tried to address the practical problems associated with the inability to achieve proper timing before the vacuum can interferes with other components.
The inability to achieve proper initial timing before the vacuum can interferes with something usually starts with installing the drive gear 180 out. This is the issue in the original post on this thread that I was trying to address. The "fix" is to move the wires over one postion and reinstall the distributor a tooth off.
The drive gear has 13 teeth - 27.6 degree spacing. The eight cap terminals and cam lobe have eight positions - 45 degree spacing. With the coil wire indexed in the correct position on the cap, the gear on properly, and the distributor corrected installed on the engine, the rotor tip and cap terminals will be very closely aligned. If you swap the wire one position over, move the distributor one tooth, and rotate it to achieve correct #1 timing you have about 20 degrees of misalignment between the rotor and cap terminal. If the gear is 180 out the misalignment is halved.
Will it work? Yes, but marginally.
Since the single point ignition is marginal on energy to begin with, you can't afford to lose energy by forcing the spark to jump a big gap between the rotor and cap termimal. The greater the misalignment, the greater the frequency of intermittent misfires. This is what happens when the gear is installed backwards and someone tries to "fix" the inability to achieve initial timing by moving the wires one position over and installing the distributor a tooth off.
You can determine the misalignment for any combination and some may be less than the example above.
So, I return to and reiterate my basic premise that there is only ONE CORRECT WAY to assemble and install the distributor and index the plug wires on a Midyear small block engine, and if you deviate from this you're likely to have problems. This is the way I choose to do it, and I highly recommend the same to others.
It's unfortunate that GM never mentioned in thier service publications - at least the ones I have - anything about proper indexing of the drive gear relative to the rotor tip. Since most guys never knew this, and many still do not know about it, there's about a 50/50 chance of getting it wrong, and then most resort to the jury rig of moving the distributor wires one position and reintalling the distributor a tooth off. It allows them to achieve the initial timing before the vacuum can interferes, but they have a weak spark and the engine runs poorly.
This is why I harp about the distributor drive gear indexing and proper indexing of the plug wires. Indexing the drive gear properly is something we have to learn by experience. Once you know this and index the wires according to the applicable year service publication, you will be able to time the car and have maximum spark energy at the plug.
Duke
Your example will theoetically work, but it's a moot point since swapping wires one position over and rotating the distibutor base 45 degrees to realign the new terminal indexing to the rotor tip will cause vacuum can interference on most Midyear engines. I believe that later Shark engines have the #1 wire indexed on a different cap terminal with the distributor base suitably rotated due to changes in the ignition shielding design.
In my posts I have tried to address the practical problems associated with the inability to achieve proper timing before the vacuum can interferes with other components.
The inability to achieve proper initial timing before the vacuum can interferes with something usually starts with installing the drive gear 180 out. This is the issue in the original post on this thread that I was trying to address. The "fix" is to move the wires over one postion and reinstall the distributor a tooth off.
The drive gear has 13 teeth - 27.6 degree spacing. The eight cap terminals and cam lobe have eight positions - 45 degree spacing. With the coil wire indexed in the correct position on the cap, the gear on properly, and the distributor corrected installed on the engine, the rotor tip and cap terminals will be very closely aligned. If you swap the wire one position over, move the distributor one tooth, and rotate it to achieve correct #1 timing you have about 20 degrees of misalignment between the rotor and cap terminal. If the gear is 180 out the misalignment is halved.
Will it work? Yes, but marginally.
Since the single point ignition is marginal on energy to begin with, you can't afford to lose energy by forcing the spark to jump a big gap between the rotor and cap termimal. The greater the misalignment, the greater the frequency of intermittent misfires. This is what happens when the gear is installed backwards and someone tries to "fix" the inability to achieve initial timing by moving the wires one position over and installing the distributor a tooth off.
You can determine the misalignment for any combination and some may be less than the example above.
So, I return to and reiterate my basic premise that there is only ONE CORRECT WAY to assemble and install the distributor and index the plug wires on a Midyear small block engine, and if you deviate from this you're likely to have problems. This is the way I choose to do it, and I highly recommend the same to others.
It's unfortunate that GM never mentioned in thier service publications - at least the ones I have - anything about proper indexing of the drive gear relative to the rotor tip. Since most guys never knew this, and many still do not know about it, there's about a 50/50 chance of getting it wrong, and then most resort to the jury rig of moving the distributor wires one position and reintalling the distributor a tooth off. It allows them to achieve the initial timing before the vacuum can interferes, but they have a weak spark and the engine runs poorly.
This is why I harp about the distributor drive gear indexing and proper indexing of the plug wires. Indexing the drive gear properly is something we have to learn by experience. Once you know this and index the wires according to the applicable year service publication, you will be able to time the car and have maximum spark energy at the plug.
Duke
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