I was de-winterizing the boat last night and when putting in the starter side block brass drain plug it (the plug) stripped out. It was getting late and dark so I just stopped there. I felt around as best I could and I think they might be damaged a little, but given the location it was impossible to see w/o a mirror which I didn't have along with me. The engine is a 1989 454 330hp Mark IV.

My current plan is to 1) run a tap into the block to clean up the threads, 2) go back into the block with a m-f adapter and bond that into the block, 3) add a cap to the end of that so future seasons I leave the block/adapter joint alone.

Thoughts, advice, comments?

The block threads shouldn't be damaged from the brass plug.

Altough you might wanna clean the threads with a tap before putting in a new plug.

I'm just wondering how a brass plug stripped the threads on an iron block. Are the threads missing on the plug? If so, they're probably still in the threads in the block- I'd try removing them with a pick first. A tap migh catch the wrong way and then you's have two sets of concentric threads in the block- a bigger mess.

You might want to get a closer look before you do anything.

I'm sorry, I wasn't clear. The brass plug threads are stripped. I don't know the condition of the block threads.

How about a round wire bush to clean up the threads first? Given it's location it's going to be tough to get a pick on the threads, but I'll give it a try.

ECeptor.. the iron block is pretty tough. It may have the brass threads wedged in. One thing you may try is a thread restorer. Sort of like a tap but without the sharp cutting teeth. A wire brush may just dislodge them, but as Chris said, the pic would be better.. Just have to stand on your head to see what you're doing.. Mirrors and flashlight can help also.

Good luck with it..

I think you guys are right. I should get a good light, good mirror, good pick or two and be in a very patient mood then get in there and manually clean out those threads. Then run a restorer or tap in after that to make sure everything is nice and clean.

My take away is new brass plugs every few (3?) seasons. I suspect the one that failed is the original.

As tight as it is down there, you just don't want to risk cross-threading a tap in there and turning this into an engine removal/disassembly deal. Pull the exhaust if you have to and do it right.

On block drains, I use a NPT to JIC (37 degree flare) and a cap. They're steel and tough. use a hardening sealant on the block side so it doesn't come out when you pop the cap. Order a couple extra caps for when you drop one in the bilge.

Good advice all-around - thanks guys!

A digital camera with Macro mode is good way to find out what you're dealing with. I agree that the block is probably fine. Remember that you're dealing with tapered threads - run a tap in too deep, and the plug or fitting might not ever tighten up.....

Man, I hate pipe threads.

Got the answer <--------- Right Here. Just fill the hole with JB Weld. Every Fall just drill it out with your Dewalt Cordless. Come Spring, Re-apply JB Weld.

Problem Solved