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View Full Version : Help! Can't get exhauset manifold drain plug back in


DougM
04-23-2011, 03:27 PM
So I went to get my boat ready today and I can't get the manifold drain plug threaded into the manifold on one side. It appears the threads are severely worn at the bottom of the bolt hole.

I assume I could remove the manifold and have a machine shop rethread the hole. Is there an easier fix?

If I go the machine shop route, can someone give me the steps necessary to remove and then reinstall the manifold?

The closest Mastercraft dealer is 70 miles away so I'm hoping this is something I can handle.

I have a 1996 Maristar 225 with the LT1 engine.

Thanks,

Doug
Katy, TX

Jerseydave
04-23-2011, 04:45 PM
I don't think you need a machine shop, but you may need to chase the threads with a tap.
Make sure you use the correct size, or if you're not sure how to do it try a good local marine shop or automotive shop. (Take the boat there, much easier than dealing with manifold removal)

wtrskr
04-23-2011, 04:54 PM
I can't help with the rethreading part.

In regards to removing the manifold, it is pretty easy. By the book, you should replace the gasket after you take it off, and when you put it back on, you should use a torque wrench to specifications.

When you take it off and put it back on you should have a second hand to hold the manifuld up. You will also have to remove the exhaust hose from the manifold. (When you put it back on, slide the hose back over the manifold before you put the manifold into place and bolt back on).

I'd keep the riser and manifold attached.

You can then order a new gasket from skidim.com. When you put the exhaust manifold back on, you start by fastening the middle bolts and work outward. Put some anti-seize (can get from hardware store) on the bolts so they don't get stuck if it needs to come off again in the future.

I were to guess, you could probably put it back on without a torque wrench and get away with it. Nice and snug but not too tight. But do not listen to me on that one because I'm no mechanic just had done this once before. Someone on here can provide opinions on that and also the torque specs.

Hopefully you don't have to go to the machine shop. If not, it is easy to remove and put back IMO.

thatsmrmastercraft
04-23-2011, 07:30 PM
I don't think you need a machine shop, but you may need to chase the threads with a tap.
Make sure you use the correct size, or if you're not sure how to do it try a good local marine shop or automotive shop. (Take the boat there, much easier than dealing with manifold removal)

Ditto on the tap. The threads are just gunked up. Take your plug to the hardware store and have them give you the corresponding tap. Squirt some oil on it and carefully thread it in. When you meet some obstruction, back up a quarter turn and continue. You may have to work it a few times back and forth a few times. The key is to have patience and don't force it. Use plenty of oil and some compressed air to clean it out. If you don't have a compressor, use a can of air for cleaning your computer keyboard. Good luck.

DougM
04-25-2011, 11:29 PM
Great. I'll give the tap a try.

Thanks!

thatsmrmastercraft
04-25-2011, 11:52 PM
Just remember to go slowly and take it easy.

DougM
04-26-2011, 12:13 AM
A friend recommended I put in a brass reducing bushing in after I tap the hole. Then just remove the 1/2" brass plug when winterizing. Anything wrong with that idea?

Here's a link to one I found...
(http://www.google.com/products/catalog?q=3/4+brass+bushing&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&cid=8099821060043300583&sa=X&ei=STe2TZ3JEZKWtwea_f2CAQ&ved=0CFYQ8gIwBA#)

bturner2
04-26-2011, 08:48 AM
You may want to consider PVC and getting a set up like the newer boats use (hose fittings connecting the two manifolds together). That way you'll never have to mess with the actual manifold plugs again.

JimN
04-26-2011, 10:45 AM
A friend recommended I put in a brass reducing bushing in after I tap the hole. Then just remove the 1/2" brass plug when winterizing. Anything wrong with that idea?

Here's a link to one I found...
(http://www.google.com/products/catalog?q=3/4+brass+bushing&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&cid=8099821060043300583&sa=X&ei=STe2TZ3JEZKWtwea_f2CAQ&ved=0CFYQ8gIwBA#)

You should be able to find 3/4" brass plugs easily enough. You'll need a 3/4NPT tap and a tap handle. If you know a plumber, they would have this.

Barefooter92
05-09-2011, 01:21 PM
Just removed my plastic drain plugs with heat and now the 3/4NPT will not fit. Skidim's replacements are 3/4" NPT so do they need tapped? Has anyone had luck with this?

I just installed a SCH40 plug for now to run the weekend.

JimN
05-09-2011, 01:50 PM
Just removed my plastic drain plugs with heat and now the 3/4NPT will not fit. Skidim's replacements are 3/4" NPT so do they need tapped? Has anyone had luck with this?

I just installed a SCH40 plug for now to run the weekend.

If they're too tight, I would use a thread chaser first. If that doesn't work, use a tap but go easy- the corrosion will make it easy to remove more material than needed and it may leak.