I hadn't thought about posting on this topic, but, it is a good opportunity to reach both current users, and potential users of these ignition conversion, the small=body HEI, MSD Trigger Only and EFI-HEI. Call it a "SERVICE BULLETIN".
With any conversion done to a General Motors 'window" type point distributor, to any of the three conversions listed above, only one potential adverse condition can be inadvertently created. This applies to all brands of GM point distributors that use a distributor cap that has a window for point adjustment. It applies to rotor/rotor retainer screws to magnetic pickup clearances/interferences (strikes).
Condition: When converted, the distance between the top of the magnetic pickup and the square locating tab on the underside of the rotor, and the two rotor hold down screws is critical. If the screws, and/or the square locating tab are left stock length, there is an almost certain situation that the ends of the screws/locating tab WILL hit the top of the magnetic pickup, and damage it beyond function, causing ignition failure.
Alterations to replacement rotors and hold down screws:
Rotor: a simple cut of the excess square locating tab material to the same distance the round tab is, will shorten the square tab so it does not protrude past the bottom of the rotor mounting plate, giving adequate rotor to pickup clearance, and no interference failures. Simply stated, cut/shorten the square tab to the same height as the round tab on the underside of the rotor.
Rotor hold down screws: During the conversion process, the two stock length rotor hold down screws that hold the rotor to the rotor holding plate, are shortened to a thread length of 1/2 inch, and made to NOT protrude past the bottom of the rotor mounting plate, which stops the screw threads from hitting the magnetic pickup. Simply stated, stock screws are too long, their threads will hit the top of the magnetic pickup, and they need to be shortened to work. When done, the ends of the screw threads shold be at the same level as the bottom of the rotor mounting plate.
Suggestion on rotor hold down screws, use the ones in the old distributor rotor now, for the new rotor, so shortening will not be needed. Simply stated, if you can feel the ends of the screws, and/or the square locating tab protruding past the bottom of the rotor mounting plate, they are too long, and need to be shortened. Some very few rotors come with a short square, and round locating tab, but most rotors have a short round tab, longer square tab. ALL ROTOR SCREWS THAT COME WITH REPLACEMENT ROTORS ARE TOO LONG FOR THIS APPLICATION, AND NEED TO BE SHORTENED.
Please read your installation instructions, first page, first section, this issue is outlined with text and a drawing on what is what. If in doubt, shorten the square tab, use the screws AND washers from the old rotor, check for anything protruding below the bottom of the rotor mounting plate, alter as needed.
PLEASE NOTE, SHORTENING THE ROTOR HOLD DOWN SCREWS TO THE LENGTH NEEDED DOES NOT WEAKEN THE ROTOR TO ROTOR MOUNTING PLATE HOLDING STRENGTH.
Anyone that wishes to have me send them the first page of the installation instructions pages, to view those instructions for rotor to pickup clearances, please send me an email and I will be happy to send you the page, just ask for the rotor to pickup clearance page. Email to use: [email protected]
This is the ONLY potentially adverse issue with the conversions to the G.M. window distributors, but, if instructions are followed, no problems should occur. If you have a service facility that works on your vehicle, especially tune ups, it would be good to include the page when the car is taken into the shop for ignition system work/tune-ups.
In the decades of these conversions, there have only been 3 pickup strikes that I am aware of, one came from an owner whom altered is distributor per other's recommendations, insisted he knew what he was doing, just after throwing the instructions away, and created his own issues. Two more happened when cars went into shops and service techs failed to read the instructions.
Please, lets agree to call this a SERVICE BULLETIN, nothing else.