oil gallery plugs,68 390

[djburton]

The block has 4 expansion-core plugs at the back but the plug kit I have has screw in pipe plugs for these so I guess I will be using them. The question(s)...It looks like I need to use a 7/16 drill in the holes for the pipe tap. How deep do I need to drill or do I need to drill at all? The block has a dribble valve behind the cam gear that I would like to knock out for cleaning that passage.I'm worried that I will damage the valve or not get it back in right.Is this thing necessary?   Thanks!

[blykins]

You'll just have to pay attention on which passage you're drilling.  Some passages intersect other passages and you just don't want to drill/tap so deep that you end up blocking another passage with the plug.  Just be cautious and take your time and you'll get it.   Just in case you're not familiar, pipe plugs are tapered and you need to drill deep enough so that you get adequate depth on the plug as well.  The pipe plug behind the distributor needs to be deep enough that it doesn't hang your distributor up on installation.  If the plug is below the surface of the distributor bore, you will be ok, but just test fit your distributor before going further.  You will probably need to run a little ball hone through the lifter bore to clean up where the tap will come through.  Otherwise it will leave a little burr there.

I never use the dribble plugs.  They're not necessary. 

[C6AE]

Typically the tapped hole will be a straight pipe thread, with the plug being a National Pipe Taper Fuel (NPTF), also called Dryseal
These are not " water pipe" threads.

edit to add: a 3/8" dia plug has an area of .11 sg. in. Implying that if you had 100 psi oil pressure there will be 11 pounds of force trying to " push out" a drive in cup type welch plug. I have never seen one come out in well over 50 years of dealing with FE's
Edit: a google search  will find the differences in these "plugs" Different tapers (7/8" vs  3/4" per foot),  SAE short, extra short," flush seal and etc.
Look here for a brief introduction. (As a machinist/repairman I have been plagued with these differences for years!)
https://www.seawaybolt.com/faqs

[djburton]

Pipe threads are confusing at best. Looking at the plugs I have,I would say they are the water pipe variety.To simplify things,I'm going to stick with the welsh plugs as the motor is basically stock with a standard oil pump.I made a nice little tool to tap them in so it should be easy enough.Of course,I'll be 4 short on the welsh plugs so I'll have to buy another plug kit. Always something...

https://www.buyfittingsonline.com/pages/npt-vs-nps-vs-nptf-thread-connections-the-difference.html

[Ranch]

You’re smart staying with welsh plugs.  Your block is counter bored for them and if you were to try to tap for threaded plugs your threads would start at the bottom of the counter bore and like Brent sez, you’ll wind up to deep and block intersecting galley.  I smeared a little permatex #2 on the OD of the plugs then put a couple of stake punches at the top, never have a problem and I’m cold starting with 80# oil pressure at Idle.  If you are doing this yourself ‘Yes’ knock out all the plugs and run a rifle brush thru the passageways washing with soapy hot water, if not your Machinist should do it as standard procedure.
Don’t forget the plug behind the distributor ....JMO

[My427stang]

I really like converting to NPT, don't let the NPS/NPTF discussion distract you.  They are simply 1/4 inch pipe thread.  We use allen head style for clearance and looks but you could use a hardware store water fitting or any NPT fitting on the engine, water of oil. 

I don't believe the shoulder for the plug affects the threads as the hole is 7/16 up to the shoulder I believe, you are adding depth not starting deep, if that makes sense.  I would however, if you are unfamiliar with tapping cast iron, or have a cheap and short tap, bring it to a machine shop.  They can do it quickly and cheaply and it's done

I have never had a press in plug fail, but I sure like them better when I can feel that I tightened an NPT plug

[frnkeore]

My rule of thumb, for these plugs, when looking at local, hardware sources, is if the Allen type, socketed plug is white and soft, it will be a NPT thread and most, if not all socket head plugs, that are black oxide and hardened, will be NPTF.

The NPTF are much better plugs to use for this type of use.

[turbohunter]

I just ordered them from Doug at POP.

[C6AE]

A light quick summary of the difference between "water pipe" threads and NPTF can be read here.

https://www.natool.com/national-pipe-taper-vs-national-pipe-taper-fuel/

(the tooling is different)

[wayne]

Screw are a part of any rebuild for me i have seen one come out in a 289.