Stripped Drain Plug

[Michael O.]

I notice there is a lot of postings on the above subject but I don't see the answer to this question.

I have a '64 coupe with an FI engine that has a slow leak from the drain plug. The plug in the car is already an oversized plug with a smaller drain plug on the inside of the self tapping plug. Obviously, the intent is to use the smaller plug to drain the oil once you tap the new one in. My question is, how many times can you tap a new, larger, drain plug in before you run into problems? I'm not sure if the existing, oversized, plug is the first one used or one on a list of many.

Of course, the ideal option is to remove the pan and make the necessary corrections at the local machine shop. How time consuming is it to remove the pan? Is it necessary to disconnect the engine mounts and jack the engine up a little, or can I just loosen the pan and have enough clearance to get it out?

One last question. Does anyone have any experience with one of those rubber universal drain plugs? Not the road I want to take but I only put 500 miles a year on this car so I'm not changing the oil on a monthly basis. I'd rather use one of them as opposed to jumping to a larger self tapping plug and getting to a point of no return.

Thanks in advance for any guidance that can be provided.
Mike

[Rich W.]

Re: Stripped Drain Plug

Hey Mike..I have used all the methods you talked about..the oversized plug in the pan now works pretty good as long as it stays tight..the pan removal works great as all you need is a new nut welded on the inside of the pan..it doesn't have to be done by a machinist..a good welding shop should be able to do it in a few minutes...can't say how to remove it on your car though ..haven't done it so I wont say..the rubber plugs are throw away type..they usually dry out over a short period of time and can't be used twice..but they do seal up good..

[Harry S.]

Re: Stripped Drain Plug

Mike, I believe there is a nut plate welded on the inside of the oil pan. Later oil pans had a hardened nut welded on the inside. The nut plate ( a piece of steel about 2.5 inches by 1.5 inches was threaded in the center to accept the drain plug). The metal of the nut plate was softer than the plug, thus they stripped easily.

The best fix is to pull the pan, grind the old nut plate out and reinstall/spot weld a new nut plate or nut. The nut plate is still available from GM.

I repaired my 63 pan last summer this way.

The nut plate part number is 3723008 and it was $5.00. I bought a spare.

Good Luck

[Timothy B.]

Re: Stripped Drain Plug

Michael,

In this link post #15 shows the oil pan off my 67, the drain plug was a oversize plug. I used a 1/2" helicore, bought the kit with the drill bit, tap for the insert and installion tool. It's best to remove the pan for the job but I don't see why it can't be done with the pan in place. After draining the oil you may be able to look in the hole to see if you have the nut plate of the larger bolt like shown in my pics.

I never had to drill the hole because of the oversize plug that was installed, just used the tap (tapped straight) and then inserted the helicore. Works great, I feel confident the insert will stay seated and will never walk out.

https://www.forums.ncrs.org/showthread.php?t=82068

[Stuart F.]

Re: Stripped Drain Plug

I've had what I believe is an oversize plug for many years. So many, in fact, I can't recall when and under what circumstances I changed it. The plug has a number of cross cuts such that it will drain like a flower pattern when it is just partially backed out. The real seal is the nylon washer it uses. I have had no leaks from it ever that I can recall. My pan was dropped in the early 90's to remove some dents and change out the timing chain and sprockets as a matter of maintenance. I had the choice to repair the drain tap then, but decided not to as the way it is works so well, i.e. "if it ain't broke, don't fix it" kind of logic from my pre NCRS days.

Stu Fox