3.0 Liter Manifold Drain Plug

[bbook83]

1974 140 3.0 liter. The one on the bottom and on the exhaust elbow are stripped. In the past, I may have forced a straight plug into these, but I believe they are pipe threads. Researching prior posts on this I am unsure whether the existing hole is for a 1/8" NPT or 1/4" NPT. Perhaps my confusion is in people recommending drilling out the 1/8" NPT for a 1/4" NPT. Anybody know what the stock hole is?

 

[Bt Doctur]

the manifold is usually 1/8 pipe thread , its tapered so there`s no need to crank the snot out of it installing the plug..
If totally stripped out , remove the manifold, support it correctly, redrill for 1/4 pipe thread and retap, , Install reducer bushing for 1/8 pipe plug

 

[bbook83]

Thanks Doc. I'll try running a 1/8 NPT tap to clean the threads, and put in the proper plug with some plumber's tape. If it doesn't hold, I will drill and retap with 1/4 NPT.

 

[fishrdan]

1/8 NPT as BT said.

I have a 1972 140 HP and have had to run a tap through the manifold, elbow and block drain fittings several times, when the plugs get so buggered up they won't go in anymore. A little at a time, backing out the tap often, to clear out the junk it's clearing. Pop in a new plug and it's good to go

 

[bbook83]

After seeing Dan's post, I checked my tap and die set and see that I have a 1/8-27 NPT tap. Is that the right one?