tapping and plugging oil galley holes

[wrench87]

has any one ever replaced the push in plugs to a 1/4 pipe plug? just looking for some tips. it says to use a 7/16 drill bit and then to use a pipe reamer, but i have read if you use a pipe reamer you need to use a 27-64 drill bit.
my holes were 7/16 from the factory i tapped one at the back of the block in the lifter galley that is straight up and down, but the plug does not go all the way in should it be flush? any tips would be appreciated. steve

[Woodz428]

I always tap and thread the ones I do, probably not neccesary, but part of the process anyway. I will have to look at the tap I have for the hole. I know I had to get another one that is longer for the one behind the dist hole. Only tip I can give is to make sure that the plug doesn't obstruct the oil passage. Also since it is a pipe thread, it's tapered. If you want the plug down further, you tap the hole deeper, but remember what I said regarding blocking the oil passage. There are also different depth plugs. Since it is tapered, as long as it's seated well it shouldn't leak, if the protrusion interferes with something you have the 2 above options.

[c6ae]

There are many types of threaded pipe plugs.
The “correct” plug for that application is a PTF-SAE Short. (The “PT” stands for pipe thread “F” stands for fuel and the ”SAE short” insures a flush mounting)
These have a different taper (7/8 inch/foot as opposed to std pipe at ¾”)
and a different thread profile to positively seal without sealant. (An interference fit at the tip of the threads)
The thread profile is referred to as “dryseal pipe thread” this is special for fuel and oil.
They are designed to install flush or almost flush in a standard NPT pipe threaded bore and they will also work in NPSI (national pipe thread straight internal) threads
You should have the plugs on hand before you tap the holes to insure that you get a correct fit.

To make a long story short, Fastenal stocks them; you only need to specify
¼ pipe plugs - 7/8 taper - socket head. (They will get confused with any more detail than that!)


http://www.fastenal.com

[wrench87]

the kit i received from percission oil pumps appears to have straight plugs, i did not know until now that there is a npt tap and a nps tap. i bought the npt tap should i get different plugs or just get a nps tap. the instructions dont specify it just said 1/4 pipe tap? will both type plugs seal ok?

[c6ae]

I suspect that you have NPT or NPTF plugs (“F” - is for fuel, and uses a slightly different thread form, you probably cannot discern this by eye). The straight thread plugs are unusual. Doug at precision Pumps knows his stuff, and I would call him and confirm the correct tap.
If I had to guess, I would say use an NPT tap and fit each plug to the tapped hole for the desired depth.
A word of caution here – A tapered plug can exert a huge amount of force on the OD of the tapped hole and I have seen more than one casting split by an over-exuberant mechanic, often at great expense to repair or replace.

Often in production machine work an internal straight thread is used with a tapered dryseal plug because it is problematic to control the exact depth of an internal tapered cut thread. Just a few thousandths in dia will vary the depth of the fit by a relatively huge amount. Anyone that has machined mating precision tapered fits will confirm this.

To further complicate matters an internal straight thread tap can be one of several types… see below
(This more info than you need! – LOL)

NPSC – general purpose (pipe couplings)
NPSF – Dryseal American Standard Fuel Straight Internal
NPSI - Dryseal American Intermediate Straight
NPSM – American Standard Straight Pipe threads for free- fitting mechanical joints
(For example, hydraulic fittings often use this thread form; these may use a gasket seal)

There are probably more than twenty various pipe thread forms that you can find today - including British and Metric. With many products coming from overseas this is often an obstacle for the mechanic that deals with Hydraulic systems.

[wrench87]

i emailed doug. he confirmed that they are tapered plugs so i guess it is hard to tell unless you have them side by side. i only did one hole i will let the machinest do the rest. the block needs to be machined yet just trying to get the rest of my parts i need a cam and pushrods and the cylinder heads.