Issue with drilling/tapping for pipe plug in 427

[fairlaniac]

I am working on putting pipe plugs in my ’66 427 cast as a side oiler but not drilled for it. I am counting five holes I need to address.

1 – oil passage on front of block above cam
2 - Oil passage opposite end (back of block) of #1 (above)
3 – hole below cam plug on back of block
4 – plug in valley behind top opening to drop distributor thru. More to follow on this hole
5 – plug in valley at the rear of the block

That is all I see for this block other than the pressure relief valve above the cam plug but that already is tapped.

I am working on hole #4 as listed above. See sketch. This hole pretty much looks like the sketch. The 15/32” hole is an estimate. A 29/64 bit will drop thru. So I assume the hole is larger but I could not find a 15/32” bit but it’s safe to say that is the size. To tap a 1/4 NPT you use a 7/16” drill bit. Obviously this hole is already over size to tap it a 1/4 NPT being at 15/32”. However I still took the tap to see how much bite I could get. It scraped in some light threads but when I put a 1/4 plug in it is very loose. Most people say a 1/4 plug fits here. Since it won’t I’m at two options unless there is another? 1) I could put another cup plug in the hole and move on or I could open the .550 counterbored hole to 37/64” and tap for a 3/8 pipe plug. Thoughts?

I have been communicating with a regular contributor to the forum but I feel as though I am monopolizing his time. I appreciate his time but I thought I'd open the conversation so I don't occupy his time too much.

Thanks,

[gdaddy01]

I can't help you , but that is some very nice drawings . If you build your engines the same way , I do not see where you would have any problems .

[Ranch]

Doug, you are facing the same deli ma I faced when it came to drill and tap or not.  The threaded plugs look like the obvious way till people realize you have a counter bore that the welch plug set in.  I thought about 3/8 NPT but figured, hey, I only have this one block.
To me there were too many problems I could foresee so I just said “the welch plugs held for all these years”, so back in they went with some permatex #2 and a couple of stakes
If you have a threaded hole under the main center galley; that’s your pressure relief valve and you can see how close those hole are, so my advice, “don’t put a NPT plug at the back of the galley”.  NPT plug just might crack the wall between the plugs.  Oh and that plug for your Relief Valve is not a NPT plug, don’t try to tap, it just wire brush it  clean.  You can buy the whole kit (plug, spring, valve) from ‘Precision Oil Pumps’.  Get the kit, better safe than sorry.
Bill

[C6AE]

I put those cup plugs in with red loctite...

[My427stang]

I tap them all to 1/4 NPT, through drill 7/16, same with distributor hole to cam. Cuts like butter...if you have a long tap, it's super easy to do the distributor hole, I don't, so I use a ratchet and 12 point socket to drive it.  I need to get one though, my way is a bit more of a PIA

Every one other than the distributor hole is a no-brainer, the distributor hole is too honestly, but best to use a shallow NPT plug as you don't have to tap as far (easier on you)

I hate those little freeze plugs, but admittedly I have never had one fail either

[fairlaniac]

I tap them all to 1/4 NPT, through drill 7/16, same with distributor hole to cam. Cuts like butter...if you have a long tap, it's super easy to do the distributor hole, I don't, so I use a ratchet and 12 point socket to drive it.  I need to get one though, my way is a bit more of a PIA

Every one other than the distributor hole is a no-brainer, the distributor hole is too honestly, but best to use a shallow NPT plug as you don't have to tap as far (easier on you)

I hate those little freeze plugs, but admittedly I have never had one fail either

The "through hole" is already bigger than 7/16". I'm doing a solid lifter 427 so no plug behind the distributor.

Thanks!

[fekbmax]

1/2" fine thread tap.
1/2" fine thread bolt. Cut off enough to make a plug. Make a nice cut in one end for a big flat head screw driver. A liberal amount of Red loc tite and your all done. Works like a charm. 

[cammerfe]

1/2" fine thread tap.
1/2" fine thread bolt. Cut off enough to make a plug. Make a nice cut in one end for a big flat head screw driver. A liberal amount of Red loc tite and your all done. Works like a charm.

+1. Make your own plug from a bolt.

KS

[67428GT500]

I have a pair of the smaller plugs for that from a kit I didn't use them from when I replaced the galley plugs. If you want them, no charge and I'll send them to you. I do also have a special tap for the front plug. If you'll promise to return the tap I'll loan it to you. It's been used one time, so it's VERY sharp and taps very easy.

                                                                                                                -Keith

[fairlaniac]

I have a pair of the smaller plugs for that from a kit I didn't use them from when I replaced the galley plugs. If you want them, no charge and I'll send them to you. I do also have a special tap for the front plug. If you'll promise to return the tap I'll loan it to you. It's been used one time, so it's VERY sharp and taps very easy.

                                                                                                                -Keith

I appreciate the offer but I used Union Butterfield taps and have plenty of them new. I also have unlimited plugs of varying sizes and thicknesses. I'm just making sure I'm not missing something here. My passage is too large a diameter for the 1/4 NPT plugs and this is apparently not the norm.

Thanks,

[Ranch]

Doug, You're not missing anything.  I was a machinist for too many years with people telling me "all you got to do is", till I start showing them the things they don't see.  You ought to try explaining to people about up dating a 62 block for a cam plate.  Anyway to tell you the truth the only hole I felt comfortable with tapping was the front of the center main because the Tangent point for the feed hole from the filter was so far into the block, as your pic shows.
Like I said those plugs do work, been working on my '406' for years.
My advice, put those drills and taps away and bag your new plugs and #2 permatex till your block is good and clean and ready to assemble.

Oh and guys its a center oiler 427 solid lifter block so there is no hole behind the distributor to tap or plug.

[fairlaniac]

Doug, You're not missing anything.  I was a machinist for too many years with people telling me "all you got to do is", till I start showing them the things they don't see.  You ought to try explaining to people about up dating a 62 block for a cam plate.  Anyway to tell you the truth the only hole I felt comfortable with tapping was the front of the center main because the Tangent point for the feed hole from the filter was so far into the block, as your pic shows.
Like I said those plugs do work, been working on my '406' for years.
My advice, put those drills and taps away and bag your new plugs and #2 permatex till your block is good and clean and ready to assemble.

Oh and guys its a center oiler 427 solid lifter block so there is no hole behind the distributor to tap or plug.

I have pondered this thought of bailing on the tapped plug. I think I'm one night's sleep away from that decision. The only thing I still must deal with is the hole I have light threads in. If I put a plug in there with the ledge compromised, will it seal properly? Hmmmm?

Thanks,

[Ranch]

The ledge at the bottom should stop the plug from shifting as you set it. 
Looking at your pic; you can see that you are already into the main center galley, so that ain't working and I'm not about to advice you to go to 3/8 npt because you could never back up to the welch cup.
Oh and the relief valve in the back.  That seems to be a size that Ford invented so don't try to tap with anything standard just clean it good with a rifle wire brush and use the kit from 'Precision Oil Pumps' and you should be ok. 
 I just rebuilt my '406' a couple of years ago so it's not like I don't understand your frustrations.

Bill

[FERoadster]

I asked a question about getting Hex head taps on Garage Journal and with about 40 responses I didn't realize there are 3 oversized and 3 undersized taps for each bolt thread size. Instead of trying to copy responses from there to here:  go to garage journal and search on "hex head tap's" my name there is Movin/on 

Richard

[BigBlueIron]

Have you tried a 3/4" taper plug or more easily said an oversized plug. Saved me on a block where I cut way to deep with a brand new tap. I was like wow this new tap cuts like butter! Aaand I was about 3 turns to deep...

[tommytt]

I am in the process of rebuilding my 427 sideoiler. 
I have done several of these engines since I am a little hard on them.  I have a 671 blown and Hilborn injected '57 Ford Ranchero drag car.
Your issue with the 1/4 NPT and or 3/8 NPT is interesting.  I do believe the 3 threaded holes, 2 in the back of the block and 1 in the front of the block, where Ford drilled the side oiler passage are not NPT (Pipe Thread).  The 2nd one in the rear is for the relief valve.  I have a bag of Ford OE plugs, maybe 25 or 30 plugs.  There are 2 types of bigger plugs (smaller NPT plugs are for the 3 side oiler holes on the drivers side of the block and numerous other locations on the block).  As far as the bigger plugs one is NPT the other appears to be a straight thread.  I believe these 3, straight threaded plugs, go in the front (1 hole) and rear (2 holes) of the block.  I also believe Ford put a 2nd, very small, allen type hole inside the big allen hole in the plug.  Maybe this was done to identify the plugs.  For sure the NPT plugs don't fit these holes.  Way to big.
Lastly I have searched all my Ford books and the internet and cannot find any info on these plugs.  You do find info on how to correctly install the relief valve but nothing on the correct plugs to use.
Tommy T

[wayne]

Go to Jim Doves web site tips on building a fe i think it may help i just did my 428 two weeks ago and could not find a longer tap.For the one behind the dist i welded a 3/8 bolt to the tap and it worked well i dont trust press in plugs but i run a 100 lb spring in the oil pump.