Distributor Locking Screw, HELP!

[MurphyJ]

I replaced the head on my engine and after the distributor was placed down in position I attempted to install the distributor locking screw and find that the screw will not turn or screw all the way in to reach the distributor base. The screw appears to be tapered and the hole in the head's threads appear to be tapered as well. I'm stumped to say the least. Have other Model A owners experienced the same problem ? Any tips, suggestions, comments will be of great help. I thank you.

[alexiskai]

The distributor hold-down screw is 3/8"-24 (UNF). Shouldn't be tapered.

[Dick M]

Are you referring to the distributor cam lock down screw or the one the goes into the side of the head to lock and ground the distributor?

It sounds like you are referring to the latter. If so, you should also have a jamb nut on the screw. Be sure it is backed off enough so that the screw can be turned in far enough to make contact with the distributor. You can then tighten up the jamb nut once you have made contact with the distributor.

If you are referring to the cam lock down screw, it has a washer under the screw that keeps the cam locked down...

[lrf]

And don't over tighten the screw that pushes against the distributor, it can crack the base of the distributor, the jam-nut will hold the screw in place. LRF

[700rpm]

Originally Posted by lrf

And don't over tighten the screw that pushes against the distributor, it can crack the base of the distributor, the jam-nut will hold the screw in place. LRF

This is a very important piece of info.

[jack wingard]

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It don't use a regular 3/8-24 screw. Look what the vendors sell and see if yours is the same

[Bob Bidonde]

According to the Ford Parts Price List, the special headless lock screw that secures the distributor is an A-20928-S8 which is 3/8-24 x 11/16 and zinc plated. The lock nut is A-21750-S8 hex with a 3/8-24 thread. This info appears in the Price Lists of January, 1928 and July, 1931 so the screw & nut are the same for 1928 through 1931.

[Fullraceflathead]

The only tapered thread on the model A. engine is the 1 just above the oil pump which is an external plug.

[talwrench]

Are you sure the distributor is full seated in the head?

[Benson]

Not on engine BUT the Carb GAV housing A-9528 is tapered pipe thread also.

1/8-27 NPT

[jg61hawk]

It sounds like the above responses have helped you...Here's a tip that may or may not apply...I was at a national meet a car came to the repair tent with the threaded hole stripped in the head so the distributor was loose and no way to tighten it in place. The owner was very upset thinking the entire head would need to be replaced. One of the guys at the tent simply suggested tac welding a jam nut onto the head and that would basically become the new threaded hole. Great idea.

[Bruce of MN]

Originally Posted by jg61hawk

It sounds like the above responses have helped you...Here's a tip that may or may not apply...I was at a national meet a car came to the repair tent with the threaded hole stripped in the head so the distributor was loose and no way to tighten it in place. The owner was very upset thinking the entire head would need to be replaced. One of the guys at the tent simply suggested tac welding a jam nut onto the head and that would basically become the new threaded hole. Great idea.

I’m no welder, so a steel nut to cast iron seems exotic. One of these requires .5” of metal, is there enough? https://www.mcmaster.com/94165A255/

[nkaminar]

Special welding rods are made for welding cast iron.

If the treads in the head are buggered up, pull the distributor and place a rag down the hole and re tap the threads. Vacuum out all the chips before removing the rag. Then buy a new screw and nut.

[TerryO]

Originally Posted by nkaminar

Special welding rods are made for welding cast iron.

If the treads in the head are buggered up, pull the distributor and place a rag down the hole and re tap the threads. Vacuum out all the chips before removing the rag. Then buy a new screw and nut.

Also putting a magnet in the hole helps...


TOB

[JayJay]

Considering the risk of chips getting into the valve galley, i personally would pull the head, drill out the hole, and then either install a heli-coil (or variant, I generally use TimeSert) or thread oversize. If you do the latter you will need to face the new stud with the little teat on the end to fit into the groove on the distributor.