Exhaust Manifold drain

During winterization I noticed that one of my manifold drains has badly rusted threads.

The PO had put a bushing and a petcock on, but I prefer to remove the plug (bushing) and get some of the rusty bits out. So here I am, spring is here and I would like to fix this mess.

The bushing is brass and not hard enough to cut the rust, and now the 1st few threads of the bushing are flattening out.

I was thinking about chasing the threads on the manifold, but don't want to spend an arm and a leg on a single use tool like a 3/4" pipe thread chaser. Any ideas?

Clark,
You don't need a fancy or even new tap. You are just cleaning up existing threads and not really cutting new ones. I've had great results shopping ebay. I just got a 1&1/2" pipe tap for $6.00 and it was new!

The inexpensive pipe thread tap did the trick. I slowly did both sides and then bought a couple $2.00, 3/4" pipe plugs from Home Depot and they threaded right in. No more petcock for me.   
3/4" pipe plug at Home Depot

Having the right tool always make work easy.

Should I consider some type of pipe dope on the threads? Something to slow down or eliminate the corrosion?

desertskier wrote: Your link goes to a 1/2-14 tap. Isn't it a 3/4-14 for a 3/4 NPT plug?

It's a 3/4-14 just like you said

not sure how I got the link screwed up, but yes NPT 3/4" with 14 TPI. I'll see if I can fix the link.

Link is FIXED.

Clark,
Glad to hear you got the tap and chassed the threads fixing your problem but am disappointed you got rid of the stop cocks. You probably had the cheap radiator drain cocks that don't allow you to probe for sediment so it builds up at the manifold low point. I have these on all my boats, have recommended them to members who have installed them and are very happy.



They have a removable stem and are available up to 3/8" pipe size so there's plenty of room to get the crud out of the cooling passages. No threads to worry about anymore and no tools needed.

As great as they are, they seem irrelevant on the topic of 3/4" exh manifold drains... since 3/8" is the largest offered?

Soitenly!

Mine had nice 3/4 to 3/8 brass bushings then the petcock as pictured above, so I think they were decent quality.

But I found that even if I un thread the petcock the water flow was very slow, so I removed the big bushing and found a large amount of rusty crud. The bushing kinda acted as a dam so the material built up. That being said, I figured, $2.70 for a 3/4" pipe plug was worth it.

If anyone wants 2 3/8" petcocks, you pay the shipping and I'll send them to ya. The 3/4 bushings will be included, but the threads are boogered up a bit. I'll add a picture here if anyone wants them.

I wondered if the brass-to-steel petcock set up did that dis-similar metals thing and increased the corrosion at the opening. Anyway, I might add some steam rated pipe dope and go to the lake!

TRBenj wrote: 8122pbrainard wrote: TRBenj wrote: As great as they are, they seem irrelevant on the topic of 3/4" exh manifold drains... since 3/8" is the largest offered? I guess you have never heard of a 3/8 x 3/4 pipe bushing! Apparently you've never seen the size of the scale that can come out of a cast iron manifold! Sometimes you need all of that 3/4" hole to probe effectively. 3/8" ain't gonna cut it. Might not even fit with the 3" Ford or BBC risers anyways... space is tight. Sounds back yard hack to me!

Gotta say I agree with Tim 100% on this. Maybe if you live in a different rust free world necking it down with a bushing and using a petcock would work otherwise it's just plain "not to smart" Like you said Tim, plenty of scale to get out of there.

Edit   after seeing Alan's post above mine, good analogy to the corn flakes Alan

SNobsessed wrote: I just tighten the pipe plugs slightly past finger tight. They don't leak & come loose easily in the fall.

Me Too

8122pbrainard wrote: Clark, Glad to hear you got the tap and chassed the threads fixing your problem but am disappointed you got rid of the stop cocks. You probably had the cheap radiator drain cocks that don't allow you to probe for sediment so it builds up at the manifold low point. I have these on all my boats, have recommended them to members who have installed them and are very happy. They have a removable stem and are available up to 3/8" pipe size so there's plenty of room to get the crud out of the cooling passages. No threads to worry about anymore and no tools needed.

Thanks Pete. Damn it, I forgot about the j-tubes and only ordered 4 for the blocks. Oh well, another 8 bucks shipping. I have to agree that these baby's aren't going to pass many cornflakes. I think I'll stick to plugs in the exhaust.