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Author Topic: Cross Threaded Oil Drain plug  (Read 729 times)
Fred Mc
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« on: November 22, 2017, 05:29:01 PM »

Changing the oil on my GMPD4106 8v71  and when I went to put the drain plug back in it won't go, like it is cross threaded. Didn't force it but it definitely won't go.  It looks like the first thread on the drain plug is damaged. What are my options.
Try a new plug first?
New drain plug and tap for the pan?
 If so anyone know the sizes. I read on the net that the threads are  1/2-14npt. Is this correct? Isn't npt pipe thread? I know its not a pipe thread.

Regards

Fred.
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chessie4905
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« Reply #1 on: November 22, 2017, 05:45:54 PM »

According to the 4108/4905 parts book, it is 1/2 inch pipe thread. There should be no washer head on the plug, so it has to be a pipe thread because, otherwise it wouldn't tighten up.
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GMC h8h 649#028 (4905)
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Fred Mc
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« Reply #2 on: November 22, 2017, 06:33:06 PM »

Here is a picture. Notice it does have a washer and doesn't look like pipe threads to me as I think pipe threads are tapered.
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luvrbus
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« Reply #3 on: November 22, 2017, 06:48:25 PM »

That is a DD plug and is pipe thread but is 18x1.5 MM pipe(new) part number is 5138456 if that helps and it does use a seal,Ebay or PC Industries has those for around 10 to 15 bucks  
« Last Edit: November 22, 2017, 06:58:09 PM by luvrbus » Logged

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Iceni John
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« Reply #4 on: November 22, 2017, 07:14:21 PM »

An option for the future is to use a Fumoto oil drain valve there, to make it easier when changing the oil or drawing samples.   I use a Fumoto T-202 in my 6V92, but I don't know which Fumoto you'd need for your engine.   The only downside is that you won't have a magnetic plug any more to trap ferrous particles, but completely eliminating any further risk of buggering up the thread again is well worth it.   And if you're wondering if the valve could get snagged on things and get broken off, on my bus the transmission's oilpan sits much lower than the engine's.

Just an idea.

John  
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Fred Mc
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« Reply #5 on: November 22, 2017, 07:16:20 PM »

Thanks John.
I have a fumoto on my Ram.

Think I will get one for the bus too.
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Fred Mc
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« Reply #6 on: November 22, 2017, 07:19:38 PM »

So if I get a new plug(Fumoto or stock) is it advised to run a tap thru the pan to clean up the threads.Would the tap be a standard 18X1.5mm pipe tap?

Thanks

Fred.
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chessie4905
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« Reply #7 on: November 23, 2017, 04:25:06 AM »

Unknown with that change from original. I know Pep Boys sell drain plugs incrementally larger with thread cutter teeth to slightly enlarge hole. Have used them in past with stripped original hole. If the threads on your current drain plug look perfect, you could get the metric tap to clean up the hole. If it is still a pipe thread, metric or us, go easy, just chase the first thread or two, don't try to bottom the tap as the taper may enlarge the hole to the point here your current plug won't hold when tightened, but tear out what's left of the marginal threads.
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eagle19952
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« Reply #8 on: November 23, 2017, 01:15:19 PM »

fumoto...on a bottom drain...nope, not me.

fumoto on a side of pan drain...maybe.

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Donald PH
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« Reply #9 on: November 23, 2017, 01:28:05 PM »

I concur with Eagle on this one. If that drain plug is on the bottom front, like my 4905, I wouldn't use one. Too easy to knock it off in right conditions. It's not like the oil needs changed that often anyway.
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« Reply #10 on: November 23, 2017, 01:57:19 PM »

  Yeeeaaa,,,but it's really sweet when you do change it. You can do it with a one gallon pail if need be and not spill a drop.>>>Dan
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Utahclaimjumper 
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Geoff
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« Reply #11 on: November 24, 2017, 09:17:48 AM »

Fred

Your oil pan should have a pipe plug.  It looks like someone changed it to a straight thread that was "clse" to the pipe thread but needs the washer to seal.  I would get a 1/2 NPT tap and see if the threads clean up and put a pipe plug in.  Don't go too deep with the tap, you'll make the hole too big a deal the pipe plug won't seal.  And yes, you can put pipe sealant or tape.
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Geoff
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Fred Mc
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« Reply #12 on: November 24, 2017, 10:38:38 AM »

Thanks Geoff. Thats what I suspected.
I have ordered a Fumoto  plug(I have one on my Ram Cummins and really like it)which is 1/2 -14 npt and will try it. If necessary will get a tap(they are expensive little devils) to clean up the threads.

Regards

Fred
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luvrbus
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« Reply #13 on: November 24, 2017, 11:49:45 AM »

I doubt it been tapped larger I have a new oil pan for a 8v71 that has a side drain with the 18x1.50 plug   
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Geoff
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« Reply #14 on: November 24, 2017, 02:39:24 PM »

I doubt it been tapped larger I have a new oil pan for a 8v71 that has a side drain with the 18x1.50 plug   

It must be very new.  DD didn't have anything metric in the days of the 4106.  Thank's for the heads up
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Geoff
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« Reply #15 on: November 24, 2017, 03:01:32 PM »

Those have been around for awhile Geoff,the DD number I gave him is for the newer style that doesn't have the magnets protruding they have a round disk magnet embedded in the plug.Lot of DD oil pans did have 1/2 or 3/4 pipe though,I don't he going to make a 14 x 1/2 inch Fumoto work those plugs are just larger than a 1/2 inch     
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