The ¼” hexagon aftermarket oil drive shafts are indeed more prone to breakage at the ends but that’s to be expected with the design where it steps down at the ends whereas the stock ¼” shafts are known for their ability to twist like a pretzel before snapping.  But the shafts never break because of a defective or weakened shaft but generally because of the oil pump locking up.  As a rule, the aftermarket shafts are strong enough that snapping the roll pin in the distributor gear can take place before a shaft failure which is a good safety fuse versus a shaft that simply twists until it breaks and the engine keeps running.

The original thought process on the heavier shafts was to reduce the harmonics being transmitted to the distributor thereby reducing spark scatter at the higher rpms.  This was very important with point distributors and although not as big a player with the more modern electronic distributors, is still worth considering in this regard.

Lorena, Texas (South of Waco)

how much free play would you imagine the shaft having between the oilpump & dizzy in looking in the hex in  my dizzy shaft the wear pattern  in the hex indicated less than 1/4" of shaft in the dizzy.

moz. geelong victoria australia.

graduate 1980, bus, truck, car, hot rod, boat, submarine, hovercraft, hydrafoil, firetruck, mobile home, jet, helicopter, cruise ship, motorcycle, bicycle, santa's sleigh, clock, alloy bullbar, alloy fuel tank, lens, dr who's tardis, matter - anti matter warp drive buffer & y-block lover

Moz.  There’s no imagining to this as checking oil pump shaft free play is a prerequisite while prepping for engine assembly.  I prefer a minimum of 0.075” freeplay and really don’t have a maximum value as long as there is what would be deemed adquate penetration at both ends of the shaft.  The key here is for some endplay to be present and not having a shaft that is sandwiched tightly or with zero freeplay between the oil pump and distributor which promotes both premature oil pump and distributor gear wear.  A ¼” of penetration at the distributor end on a Y should be adequate but this has to be with a given amount of freeplay being present.

Lorena, Texas (South of Waco)

you gave me the answer i was looking for in the dizzy shaft i have half of that in up & down movement which in the case of my worn hex shaft  could in theory  when the dizzy shaft moves to its upper limit of movement the most worn part of the hex slips in the dizzy this being on the last 1/8" on the very end of the shaft i have also noticed in the 3 times it's happened that it is always on first start up early in the morning when the oil is at its coldest & heaviest.

one other thing i noticed was my shaft has 2 different ends one flat one conical  the marks from the spring/lock washer is at the conical end no marks to suggest it has been on the flat end yet the conical end was in the dizzy its possible the engine was assembled this way ive removed the shaft twice & put it back the same position it came out this time ive turned it over so the flat end is in the dizzy shaft & i seem to have slightly more shaft in the dizzy.

moz. geelong victoria australia.

graduate 1980, bus, truck, car, hot rod, boat, submarine, hovercraft, hydrafoil, firetruck, mobile home, jet, helicopter, cruise ship, motorcycle, bicycle, santa's sleigh, clock, alloy bullbar, alloy fuel tank, lens, dr who's tardis, matter - anti matter warp drive buffer & y-block lover