Sometimes I despair of some contributors to this Forum. Guys, if you don't know
, Look It Up
. Certainly do not post such complete and unmitigated drivel.
You have not done any "damage" to your engine case threads - just at 1/4" major diameter, Cycle and BSF are exactly the same 26 tpi pitch. The only - tiny!
- difference is each Cycle thread has a 60-degree included angle while BSF is 55 degrees.
In a brand-new, perfect thread cut with brand-new, perfect tools, you might've removed a microscopic sliver of metal from the bottom of each thread trough. In this real world, even if the threads started out brand-new perfect, they're now 48 years old, aluminium alloy is relatively soft so it wears faster than steel anyway, not to mention those threads have been subjected to 48 years of owners and mechanics (not to mention 'mekaniks') with vastly-different levels of ability and mechanical sympathy.
When I put the timing cover onto the crankcase and tighten down the screws, they tighten fully and hold tightly without any wobbling and the cover is secure.
You've done exactly what I did to my basket-case T100 engine case threads over a decade ago (although I knew I was using a Cycle tap), I secured it with Cycle-thread stainless Allen screws ('cos 1/4"BSF stainless Allen screws don't exist) and I haven't had any problems whatsoever.
One caveat: after forty-eight years, to paraphrase George Orwell, not all screw threads will be equal; I haven't found any need to use "thread locker", or any other gunge; in actual use
, you might
find one or more threads on your
engine need help with gunge or, as Rod's suggested, a helicoil, but that'll be as a result of wear and/or lack of mechanical sympathy, not the use of a 1/4"Cycle tap in a 1/4"BSF thread.
One other tip, if buying new screws. Meriden never threaded blind holes to the bottom; using a hand-tap, you almost-certainly have; if you check, you will find that many of the holes will now accept the next-longer screw without bottoming in the hole; a longer screw will have more thread to secure it, and it'll use the newly-cut thread.