to my mechanical brains way of thinking changing from the friction screws to the stud/jamb nuts would naturally require running a clean up tap through them to make sure all threads weren't damaged, and the studs don't bind & run through the threads easily.

moz. geelong victoria australia.

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I COULD see where smooth running threads might be advantageous when adjustment is done with a screwdriver instead of a long handled wrench.

6 VOLTS/POS. GRD. NW INDIANA

Ford used two different thread designs for the rockers. Both are 20 tpi but the thread cut is different. The early adjusters (1954-1956) using the jam or locking nuts is a conventional 7/16 X 20 cut while the 1957 and newer rockers used a friction style of adjuster that required an interference thread design to keep the adjuster tight without the use of a jam nut. To use an early adjuster stud and jam nut combination in the later model rocker, simply re-tap the threaded hole with a conventional 7/16 X 20 tap to clear out the interference threads. It may be necessary to machine a flat on the top of the later model rocker so that the jam nut will tighten squarely on the rocker. I suspect that a TSB regarding this would have gone into more detail than to say to simply replace the adjusters from one style to another.

Lorena, Texas (South of Waco)

Good info Ted. Don't recall reading service letter in question, only it's mention. Not unexpectedly, it wasn't included in the club compilation of T-Bird related letters, as it obviously took quite some time for enough clearance adjustments to wear out the threads. Nonetheless, though I have kept up with all the available Y-Block literature & internet chat these last 15 years, surprisingly, this is the first mention of the thread incompatibility problem I have yet encountered. Strange, with the mixed grab bag of rocker ratios & adjuster types found in service over the years.

6 VOLTS/POS. GRD. NW INDIANA

I'm trying to do the opposite with my rocker arm adjusting screws.  I'm trying to switch the self-locking adjuster screws from 143.1 rockers to my new 154.1 rocker arms that have the old type screw adjusters with jam nuts.  The ball on the adjusting screws on my brand new rocker arms wore out in 100 miles because they apparently weren't hardened metal.  The self locking adjuster will go down a couple of threads in my new rocker arms and then locks up so tight that you can't turn the ratchet with a cheater bar.  I ran a 7/16 NF-20 tap through the rocker arm and it turns through with no resistance.  The 143.1 rocker arms were rebuilt and had new self locking adjusters.  Is it possible I have an oversized 7/16 - 20 self locking adjusters?        

Ford furnished .002 oversize friction adjusting screws to be used when the standard screws did not stay put.  The original standard screws had a 1/2" hex for the wrench, the oversize screws had 7/16" hex.  A bit aggravating when you find an engine with some oversize screws and some standard, causing you to keep switching wrenches as you go through the valves.  The same screws were also used in the solid lifter FE engines.

John - "The Hoosier Hurricane"

Thanks John, I suspected it had to be something like an oversized adjuster screw and mine does have the 7/16 head on the adjuster.  So I would assume that if I buy a new set of adjusters like the one's in Mac's Antique Auto Parts they should be the original standard size....I hope!

had a couple of loose selflocking, backed them off cleaned with starting fluid, aplyed some lock tight and adjusted left the engine over night.that was 3 months ago and checked the other day they have not moved.