Stripped / Rusted drain plug hole

I need some engine expert help. I was winterizing my boat and have a problem. The aft / left side drain plug hole has rusted to the point there there are no more threads. I purchased a new drain plug and I can't get it started at all. So I am now stuck in my winterizing process since I can't pour the antifreeze in until I can put back in my drain plug.

The plugs appear to be 1/4" pipe thread. What do I do? I need to tap the block drain spot. Can I buy a tap somewhere and do this? What size? What thread? Please be specific. Do I need to take it to an engine shop?

Been there.    Just need a 1/4” NPT pipe tap.   Some hardware stores carry, maybe HD or Lowe’s. McMaster- Carr for sure.   Just don’t tap in too deep as it will make the hole bigger and tough to seal because of the taper.

Awesome. Will stop by ACE on my way home tomorrow. Thanks for the link too. 2010! That a good deep track there. :)

Hollywood wrote: Solid brass pipe plugs tend to run fatter than hollow

Agree on that. But, if the threads are not too far gone, meaning you have some decent resistance right away when you start the tap, I'd try putting in a petcock so you don't have to use the threads any more once you have it in. I've also used 3-4 wraps of teflon tape to add some sealing bulk on the new threads.

How about careful drilling to 3/8" and tapping new NPT threads? Is there enough metal to do that?

Here comes the "backyard hack" in me

I'd try the 1/4 inch pipe tap whether you think it'll work or not and see what you get for results. It'll cost you less than 10 bucks or so to try it.

If that doesn't work and you want to get antifreeze into it for the winter, I'd get an expandable rubber plug of the appropriate size and put that in.

Here's an example in the link and they do make them small enough. A good hardware store should have what you'd need.

link

As far as laying on the floor with a 1/2 inch drill with a big bit (37/64), getting a straight shot at the hole with any kind of precision and then getting the 3/8 npt tap started/ finished with any kind of leverage/force................it ain't gonna be easy.

The rubber plug would give you all winter to decide what to do if the 1/4 inch tap doesn't work.

Disclaimer..................A really accomplished, full fledged "backyard hack" might use that as a permanent solution

You could also do the drain and pour some antifreeze in and drain that out and leave it dry method for the winter.

I can see Pete clutching his chest as I type this.

Let's not forget you don't need to plug that hole for winter...

Good suggestions above. Have encountered this several times. Running the 1/4” tap deeper and then taping the heck out of the new fitting will almost always solve it. If clearance allows (fords aren’t usually problematic), the McMaster quick drains are nice and will prevent you from putting additional cycles on marginal threads.

Yes

I don’t know what everyone else does, but I usually put a small amount of grease on the threads, marine grease, bearing grease, etc. it can help to act as a rust preventative if you are going to leave your plug out.

I use Teflon tape and snug them up, not crank them down.

Riley wrote:    I once used a whittled stick to plug a hole for the winter so the engine could be pickled. It didn't become a hack job until the boat owner thought it held up so well over the winter that he could run it like that all summer.

Seachoice wood emergency plugs.

KRoundy wrote:    Going to look at McMaster quick drains right now...

The McMaster part is 4921K2. It's a 1/4 with the removable stem/T handle so you can still probe the drain with some wire checking for sediment/blockage.

Riley wrote: Hollywood wrote: Let's not forget you don't need to plug that hole for winter... No, but if you do that, pour some antifreeze through the engine to flush the water out.

I thought that when you did the " drain only method " you didn't need to add any anti freeze at all ?

8122pbrainard wrote: Faceplant wrote: Riley wrote: Hollywood wrote: Let's not forget you don't need to plug that hole for winter... No, but if you do that, pour some antifreeze through the engine to flush the water out. I thought that when you did the " drain only method " you didn't need to add any anti freeze at all ? Jeff, Correct. If you drain only, no antifreeze is needed.

I've always squirted a bit of antifreeze in each engine drain, manifold drain, raw water hose, top engine hose. Likely not needed, just an old habit. When I say squirt, I'm using a syringe so barely a few ounces total.