Broken Petcock - Block thread pattern?

[philmay75]

Hi, I have an 18.5' 89 Galaxie open bow with an OMC 4.3L V6 (432APRMED). Previous owner really neglected this thing and I was trying to remove the corroded petcocks to replace them. All the inserts came out fine, and 3 of the 4 came out of the block and exhaust manifolds fine, but managed to break the 4th one off in the block without applying much pressure.

I've tried to use the Easy outs screw and bolt extractors but it isnt breaking free. I'm considering drilling and re-tapping the block to get that brass out of there, but I am having some trouble finding the correct thread pattern for these petcocks. Part # 379957.

Two questions if I may:

1) any suggestions on my predicament, or better ways to get that brass out of there.
2) does anyone know what the thread pattern on the block-end of these drain plugs is?

Much appreciated.

 

[Howard Sterndrive]

Re: Broken Petcock - Block thread pattern?

1/4 NPT I suspect - the petcock material in there should be pretty soft - I would be trying a left hand drill bit and hope it catches and spins out as the material heats and thins as you drill it.

 

[philmay75]

Re: Broken Petcock - Block thread pattern?

1/4 NPT I suspect - the petcock material in there should be pretty soft - I would be trying a left hand drill bit and hope it catches and spins out as the material heats and thins as you drill it.

You are correct! I ran up to the orange bucket and found that the new one fits a 1/4 -18 NPT! Thanks! I'll try the LH drill bit as the 1/4 NPT tap needs a 7/16 hole anyway. But gonna have to go buy a close quarter 90 degree drill as my doghouse doesnt leave me much room to get a regular drill in there.

Thanks again!