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Stripped drain plug help needed

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In the middle of a restoration on a 1077. The allen key of the  sundstrand drain plug was rounded out and I had no choice but to drill it out.

The 1/4" drain plug has an actual 9/16 - 18 thread. I have that tap and chased the threads out but now its still sloppy and the 1/4" plug will actually thread right into the transmission.

I have searched high and low for a oversize or double oversize drain plug but can't find one in 9/16.

I don't need to split the cases so I can't use one with the nut on the back side and would be concerned about room inside.

 

My next thought is to go to 5/8 18  and try to repair this.

 

Does anybody have a solution to this that would make my life easy?

 

Thanks,

 

ED

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The drain plug hole was tapped for 1/4 NPT (National Pipe Thread) not 9/16 -18.  NPT is tapered 9/16 -18 is straight thread

 

To seal you will need tapered threads or some sort of gasket n a very short 9/16 -18 Bolt

 

EDIT::

Drill the hole out to 9/16"  then buy or borrow a 3/8NPT pipe tap  (Cheapies are abut $10 good ones about $35) and thread it then get a 3/8" plug

 

tap.JPG

Edited by pfrederi
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The drain hole was 1/4 nptf and you put  a machine thread in it. The (N)ational (P)ipe (T)apered (F)ine has a 3/4' taper per foot for the sealing surfaces of the threads. A straight machine thread will not seal because there is clearance at the "root" of the thread, and the o.d. of the thread, on a 75% thread. 

 

 If I was doing I would put in a 3/8' nptf plug with the 3/8' recessed square then there is no hex to round out.

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Every two piece transmission I open gets a front drain hole & magnetic plug. 3/8ths NPT.  I use the square head plug and drill a 1/8" hole in it and JB well a cheapy ebay magnet in it.

20151008_175028[1].jpg

Edited by WHX14
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Nice idea...but for the lazier ones of us:)

 

 

 

plug.JPG

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If you plan to mount a tiller or blade (front or mid mount) that requires an axle bracket you will need a plug that ends up flush with the bottom of the transaxle.Hex Socket Plug,Sz 1/8 In,L 5/16 In

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Given the fact that you already retapped the hole to 9/16 - 18 I would install a 9/16 bolt with a crush washer (copper or brass). This will seal it up for you.

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A helicoil might be a option.  You can find them on eBay.  Or local parts store might have them. You are given a drill and a helicoil insert that takes you back to the original thread size.  

  

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So sounds like we have some answers to your problem Ed.......when we gonna have some  :text-coolphotos: of that 1077 .... bucket list tractor ya know!:lol:

Edited by WHX14
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I do not know if they make a helicoil for the pipe thread. I guess they do, is.   pricey at Fastenal though.

Edited by Howie

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Thank you for all the spot on advice. I went searching for a 9/16 18 x  1/2 bolt for the easy fix but that was unobtainable locally.

I was able to get my hands on a 3/8 NPT tap and stopped at the hardware store and picked up a 3/8 pipe plug.

I will definitely try to get a pipe plug with the recessed square hole but at least I have something to put in for now and get this thing ready for paint.

parts1.jpg.166bee66de7fa6969e8e97f2c61e31b2.jpgparts2.jpg.1b0f309e60461ba9b02cf6d2ba4caccd.jpg

Here are the current pictures of this machine.Trying to get everything in etching primer.

Final paint will be Candy Red urethane that I found in a old post from Rickv.

 

I will do a post in restorations when I get some paint flying... if we can get some good weather.

 

 

 

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