What thread size is this hole???

[Race Ready Fabrications]

I'm looking at hooking up an oil accumulator and I want to use this hole. It's smaller than 3/8" NPT and larger than 1/4" NPT. Appears to be a striaght thread and not tapered. I don't have the plug that goes in there to compare to but the plug from under the timing cover seems to fit. I need a fitting with whatever thread this is to a #10 AN female. Any help??

[Barney]

You could always tap it with a 3/8 NPT tap to simplify things when it comes to getting a fitting.

[dfree383]

I don't remember the size, but they do make AN Fittings to adapt to it.

[jbozzelle]

5/16" ???

Mine has a hex head pipe plug in it. I don't remember it being hard to source that either. And I think it is typical NPT. Factory deals had a long hex tube in there that the factory oil pressure sending unit screwed onto.

[Lem Evans]

3/8" NPT on all the ones I've had my hands on.

[Race Ready Fabrications]

This hole has no taper like a NPT thread. It's straight and a finer thread than NPT as well. This is a DOVE block, I pulled the plug out of a D1 block and it's different than this one. Pretty sure I'm just gonna tap it to 3/8" NPT. Figures....I got the bastard block!!!!

[jbozzelle]

Maybe someone tapped it to a typical bolt thread? In that case you could use an o-ring style AN fitting (ORB fitting). The threads on those are straight and seal with the o-ring.

[Race Ready Fabrications]

Maybe someone tapped it to a typical bolt thread? In that case you could use an o-ring style AN fitting (ORB fitting). The threads on those are straight and seal with the o-ring.

I tried that too..... No such luck. It's definitely a bastard. It'll be 3/8" NPT shortly after work.

[Barney]

Maybe someone tapped it to a typical bolt thread? In that case you could use an o-ring style AN fitting (ORB fitting). The threads on those are straight and seal with the o-ring.

I tried that too..... No such luck. It's definitely a bastard. It'll be 3/8" NPT shortly after work.

There ya go.... If it don't fit make it fit...

[Paul Kane]

I'm looking at hooking up an oil accumulator and I want to use this hole. It's smaller than 3/8" NPT and larger than 1/4" NPT. Appears to be a striaght thread and not tapered. I don't have the plug that goes in there to compare to but the plug from under the timing cover seems to fit. I need a fitting with whatever thread this is to a #10 AN female. Any help??

The factory thread in that location is almost always 3/8-NPT. Although extreeeeemely rare, it is possible it was tapped as a Ford J-thread (for example we have seen 3/8-NPT in the front of the passenger car lifter galleries on ultra-rare occasion) but the one you are asking about is supposed to be a 3/8-NPT female thread.

Having said that, I don't think that is the ideal place to plumb your accumulator. Why? Because whenever the accumulator is being refilled, the upstream oil is being diverted to the accumulator and away from the engine bearings before they've been adequately fed.

I think a better location is at the oil pressure port at the rear of the block after enlarging the 1/4-NPT thread to 3/8-NPT and also enlarging the block passage which leads to the rear of the passenger-side lifter gallery. That puts the accumulator on the other side of the engine bearings and at the "end of the line" which backfills the oiling system if the oil pump is not delivering oil. Also, during normal engine operation the accumulator gets refilled by the oil pump after the bearings get all the oil they need.

Paul

[Doug Rahn]

I don't have a clue as to why they chose this but here it is, 3/8-18 NPSF A variation of the Dryseal thread is the NPSF (National Pipe Straight Fuel). It is used for internal threads and a NPTF external thread can be screwed into it to provide a satisfactory mechanical connection and a hydraulic seal. The combination of a parallel and tapered thread is not regarded as ideal but is widely used.

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