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View Full Version : Urgent Q - Cross Threaded block drain plug


Archimedes
10-09-2009, 04:26 PM
Well I finally got everything done on the winterization today and have all the hoses and plugs pulled, and I get to the very last one (starboard side block) and it appears the shop that did my last winterization may have cross threaded the plug. I will not turn and it appears that it might be slighly off angle, leading me to believe it may be cross threaded.

Should I just leave it in and not drain that side of the block (no freeze here) or force it out and deal with a repair on the hole? I'm assuming it would need to be tapped and rethreaded.

88 PS190
10-09-2009, 04:46 PM
Is it threaded all the way in or does it appear to be mostly out? I'd say chances are there are more threads in there, so I would probably remove and run a tap through to clean up the threads.

Archimedes
10-09-2009, 04:52 PM
It's not all the way in; there are a few threads showing. It will not budge. The other side was tight, but came out with a little effort. I'm concerned about giving it too much on this side and not sure if I'd be better off just leaving it in.

88 PS190
10-09-2009, 04:55 PM
I suppose it depends what sort of tools you have access to and your comfort level. Your block is steel on that correct?

Thrall
10-09-2009, 06:00 PM
Is the plug brass? If so, the block is cast iron. Block wins! You're ok.
If it's a steel plug, like the temp sender, 50/50 chance which one is messed up.
It's a 1/4 or 3/8 NPT thread, if the block is messed up, you can probably chase the threads with the proper size tap and replace whatever plug is messed up..
If it's not going to freeze, why are you bothering to winterize?
Option 2, run coolant thru the engine and leave it in (if it were to freeze). If it was me, I'd fix it and get it over with.
The 2 plugs on the bottom of the engine are the most important to get out and drain for freeze protection, as they let out all the water that is in the block and heads (the most expensive parts!).

Thrall
10-09-2009, 06:02 PM
[QUOTE=Archimedes;638485] and I get to the very last one (starboard side block) and it appears the shop that did my last winterization may have cross threaded the plug. QUOTE]

Yet another reason to do your own work. Most people couldn't give a cr@p about your stuff.

Archimedes
10-09-2009, 06:04 PM
Is the plug brass? If so, the block is cast iron. Block wins! You're ok.
If it's a steel plug, like the temp sender, 50/50 chance which one is messed up.
It's a 1/4 or 3/8 NPT thread, if the block is messed up, you can probably chase the threads with the proper size tap and replace whatever plug is messed up..
If it's not going to freeze, why are you bothering to winterize?
Option 2, run coolant thru the engine and leave it in (if it were to freeze). If it was me, I'd fix it and get it over with.
The 2 plugs on the bottom of the engine are the most important to get out and drain for freeze protection, as they let out all the water that is in the block and heads (the most expensive parts!).

I was thinking the same thing, that the brass plug couldn't damage the block and I should just force it out. I'm only draining the block because I've been told it's good to get the water out for rust reasons. The boat is stored in a heated warehouse.

JimN
10-09-2009, 06:12 PM
I suppose it depends what sort of tools you have access to and your comfort level. Your block is steel on that correct?

Motor blocks are cast iron.

88 PS190
10-09-2009, 06:38 PM
Motor blocks are cast iron.

Granted, unless its aluminum. I don't keep up on newer boats.

Chicago190
10-09-2009, 07:58 PM
The drain plug threads on one of my manifolds was destroyed by corrosion and cross threading. I was able to re-tap it this spring without having to drill it out, but I was doing it on a relatively cheap exhaust manifold and not the block. If the block is cast iron, there is a chance if you remove the plug you will be able to clean the threads up with a tap if they aren't THAT damaged, but obviously you won't know until you take the plug out.

Archimedes
10-09-2009, 09:39 PM
I forced it out with some serious elbow grease. The threads on the brass plug were crushed up high, but fine down low and the block appears to be fine. Looks like I'll be buying a couple new plugs.

JimN
10-09-2009, 11:10 PM
I forced it out with some serious elbow grease. The threads on the brass plug were crushed up high, but fine down low and the block appears to be fine. Looks like I'll be buying a couple new plugs.

You're going to put some anti-seize compound on the plugs this time, aren't you?

Archimedes
10-10-2009, 01:11 AM
You're going to put some anti-seize compound on the plugs this time, aren't you?

Will do. Whoever pulled them last time appears to have put some grease on them, though it could have been anti-seize. Looked a little darker than the anti-seize i use on my motos.

Chief
10-10-2009, 05:18 AM
True True..............

"Yet another reason to do your own work. Most people couldn't give a cr@p about your stuff.[/quote]"

TMCNo1
10-10-2009, 07:32 AM
If you do tap the treads to clean them up and the plug seems to be a bit sloppy in the hole, a few rounds of teflon pipe tape will tighten it up and assure a good seal.

JimN
10-10-2009, 10:47 AM
The bung for a petcock is tapered- just use a tapered plug and it won't matter. The next best way is to drill it out one size larger, tap it and use the proper plug. That way, it has fresh thread and won't leak at all.

TX.X-30 fan
10-10-2009, 10:52 AM
If you do tap the treads to clean them up and the plug seems to be a bit sloppy in the hole, a few rounds of teflon pipe tape will tighten it up and assure a good seal.

The bung for a petcock is tapered- just use a tapered plug and it won't matter. The next best way is to drill it out one size larger, tap it and use the proper plug. That way, it has fresh thread and won't leak at all.



Wow this place is getting seedy. :D

Miss Rita
10-10-2009, 11:15 AM
If the drain in the block/manifold is REALLY screwed up, you can drill it out bigger, then use a brass bushing that stays in permanently, and then use a brass plug in the bushing.

JimN
10-10-2009, 11:47 AM
If the drain in the block/manifold is REALLY screwed up, you can drill it out bigger, then use a brass bushing that stays in permanently, and then use a brass plug in the bushing.

I'm not sure I'd use a bushing unless it was going to be permanent. Plugs come in all sizes and IMO, the hole is too small as it is, considering the water quality in some places.

TMCNo1
10-10-2009, 03:12 PM
Wow this place is getting seedy. :D


Then I guess you've never seen Marge Simpson nakit?:rolleyes::D Now she's seedy!