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View Full Version : What do I need to know about threads on PCM exhaust drain plug?


strad
10-22-2012, 05:23 PM
Made the huge mistake of just checking to see if it would move easily prior to winterizing probably next month. Of course the drain plug broke in half and left half of itself in the bore. And it started leaking to boot! I hardly even put any torque on it to do that either! I've mostly solved that problem (it was corroded badly enough to make getting the pieces out pretty easy), but I'm wondering what I need to know about the threads on it to get another one, preferably local and before this weekend. I'm sure skidim could get me one but not by Friday. boat service place here can't reference it by PCM part #.

Amazingly enough the threads on the manifold side are nice and shiny. It is a 351 PCM from 1984 btw. The plug is 1" in diameter, but I don't know anything else at this point. So is it 1" NPT or something else? I want to use the boat this weekend, not just look at it lol.

TRBenj
10-22-2012, 06:19 PM
I'm sure skidim could get me one
Yup, and they even have a website!

3/4" NPT (http://www.skidim.com/prodinfo.asp?number=RS3533)

east tx skier
10-22-2012, 06:20 PM
1/4" NPT on the block.
3/4" NPT on the Riser.

strad
10-22-2012, 07:01 PM
Yeah I stupidly thought that 3/4 = 3/4. That's why I was lost. Would not have guessed that 3/4 NPT is actually 1"!

I don't think this boat has ever been winterized. It's from the SF Bay area and has always lived in a garage. I think it probably gets a bit colder here in LV at 2000 ft asl, so like it or not I'm going to have to take my chances with the other plugs sooner or later. It's stored in a garage but still. . .

Miss Rita
10-22-2012, 08:23 PM
buy some nice new shiny brass plugs in the sizes listed, use Anti-Sieze or teflon tape on the threads, and you're good to go.

strad
10-22-2012, 09:59 PM
Hey how many block plugs are there supposed to be? I see two -- one aft on port side, one forward on starboard side, and one place above the starter that is threaded but does not have a plug in it (opposite side of the block from the location that has a drain plug in it). It doesn't leak so I don't know what's supposed to be there. edit: I found a PCM manual. It appears that one forward on starboard side and one aft on port side is correct.

Got a temporary solution in place on the manifold btw -- will work until I get the proper plugs from skidim. I also hit the other riser plug with penetrating oil. Not sure if I'm going to touch it yet but a little penetrating oil can't hurt.

waterlogged882
10-22-2012, 10:33 PM
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east tx skier
10-23-2012, 12:32 AM
J-tube plug is 1/4" as well.

The clearance on those riser plugs is pretty tight. I recommend a very large box wrench.

TRBenj
10-23-2012, 10:37 AM
Riser plugs? You mean manifold plugs? There shouldnt be a plug on the risers. Brass plugs that accept the 1/2" ratchet or breaker work best, IMHO. Much harder to strip.

http://www.skidim.com/images/RS3533.jpg

Mcmaster (http://www.mcmaster.com/#brass-threaded-pipe-fitting-plugs/=jufz7i) part number 4429K192, $6.83 ea (Skidim's are coated steel).

A google search for NPT (National Pipe Thread) dimensions (http://machiningproducts.com/html/NPT-Thread-Dimensions.html) shows that 3/4" NPT = 1.05" OD.

east tx skier
10-23-2012, 11:59 AM
Sorry. I needed coffee yesterday. Yes. Manifold plugs.

mikeg205
10-23-2012, 01:39 PM
And don't over torque them...just need to be snug to the point they don't leak...you can use a teflon tape - it's good to almost 500 degrees.

strad
10-23-2012, 02:27 PM
Well I've got the first problem solved thanks to Lowe's and Mead's Hardware. I'll get the correct plugs next time I order from skidim, but what I have will do for this weekend.

I'm dreading touching the other four plugs lol. I hope for the best but don't expect it! Maybe I'll get lucky -- on the outside the other plugs look less rusty than the manifold plugs.

mikeg205
10-23-2012, 02:34 PM
Well I've got the first problem solved thanks to Lowe's and Mead's Hardware. I'll get the correct plugs next time I order from skidim, but what I have will do for this weekend.

I'm dreading touching the other four plugs lol. I hope for the best but don't expect it! Maybe I'll get lucky -- on the outside the other plugs look less rusty than the manifold plugs.

Fedex - Standard - - :)

Or go to hardware store and see if you can make a plug...not high pressure... I've seen a hose connect risers via that riser/manifold plug.

Miss Rita
10-23-2012, 02:41 PM
You should have five drain plugs to remove:

1 - J-tube plug
2 - block plugs
2 - exhaust riser plugs

What is the J-tube? Curious minds want to know.

TRBenj
10-23-2012, 02:48 PM
Id still go with brass manifold plugs as opposed to the coated steel ones that SkiDIM sells.

The remaining 1/4" drain plugs should be brass already, and should come out easy. Thats the advantage of using brass... they wont sieze in there like steel will.

PCM Fords have an additional cast piece at the low point of the circ pump to 'stat housing (1-3/4") hose, which allows you to drain it by removing a plug, as opposed to pulling the hose off. Its referred to as a "J-tube".

tph
10-23-2012, 05:08 PM
What is the J-tube? Curious minds want to know.

Next to the raw water pump at the left in this picture (with brass drain valve on bottom)

waterlogged882
10-23-2012, 08:53 PM
..........

strad
10-25-2012, 06:33 PM
Well dadgummit. Back in business now, but danged if the other manifold plug didn't break off just like the first! I'm leaving the other three until next week lol.

strad
10-28-2012, 02:05 PM
Okay, the last three plugs came out as easily as pie. Look in great shape too. So now my question is, just so I understand the route water takes into the engine, when I go to start it again, the raw water pump will first fill up the engine with water, then fill up the exhaust manifolds, then I'll see water out the exhaust? In other words the water can get past the thermostat on the intake side?


I'm used to filling up car cooling systems but this is new. . .

mikeg205
10-28-2012, 02:16 PM
Yes, There's a raw water bypass to fill the engine...but it won't circulate out until the thermostat opens.

This is kind of a nice explanation.

http://www.boatinghowto.com/content/how-boat-cooling-systems-work-240/

waterlogged882
10-28-2012, 03:22 PM
..........

strad
10-29-2012, 10:37 AM
Haha thanks. I just wanna make sure I am not going to eff it up because I didn't know something I should have known!