My M20 fill plug has been abused by previous owner to the point the normal plug threads all the way through without being tight enough to get a good seal, even with a ton of Teflon tape. Is there a slightly oversize plug available? Any repair short of welding and rethreading?

 

You don't suppose somebody used a Non-NPT plug do ya? One way to find out. Take the plug to the hardware store and compare.
If thats not the issue then you could use some Thread Sealant, white, comes in tooth paste tube, compatable with oils & trans fluids.
Use a thin layer on the first couple threads. Then lay it on thick on the last threads. Let it set-up overnite.

 

Sorry I wasn't clear - case has the correct threads just opened up so badly the stock plug EASILY screws all the way through. No amount of sealant is going to seal. I want to see if anyone makes an oversize tapered NPT plug for this problem. Or maybe a helicoil but I've never seen one for a NPT.

 

NPT pipe plugs come in a wide variety of sizes.
You should have little trouble moving up to the next size though you may be better off going with a NPT insert.

 

The next size up NPT jumps a 1/4"- that's a LOT of work AND trouble.

Here's a neat temporary fix- go to the autoparts store and look at the oil drain plug repair stuff-





You can use the temporary fix till you save up enough to buy the Helicoil kit- aint cheap-


Another thought was a -10AN O-ring fitting-7/8" - 14 But I don't think you'll have enough metal left....

https://www.zoro.com/zoro-select-hel...2k/i/G1550586/

https://www.threadtoolsupply.com/12-...epair-kit.html





1/2 versus 3/4 NPT

 

You might try a NPT metric plug in a slightly larger size from your stock plug. The in between size might get you a tighter fit without playing with the case.

 

did you try a NEW plug? the plug wears down more than the case thread wears bigger. and get brass so it stops wearing out the case as much. then there is this... http://www.timesert.com/html/taperpipe.html

 

You might inquire with your local machine shop? Never know what they might be able to do.

 

HeliCoil makes Helicoil pipe thread repair inserts. Just get a pipe thread HeliCoil with the tap & tools and fix it right. No problem.

Lars

 

Metric threads?

 

I don't believe there is metric pipe.

 

NPT is the US standard for tapered pipe thread
EVERYONE ELSE uses British Standard Pipe Taper = metric


He's still better off with the HeliCore route

 

I just had to NPT helicoil my water temp sender in my head. Look on ebay for a partial kit, you can save alot of money but it still may cost you $75 to $150 if you can find one. I just pieced together a 1/2"-14 NPT kit and it added up fast. Is the plug 1/4"NPT? I think it is.

If you have a plumber friend or a machine shop , find out how much it would be for them to do the work. It may cost you only $50 or $75 for the machine shop.

The helicoil insert is easy to find, the STI tap is the expensive hard to find part, the insert tool isnt bad. the insert isnt like a normal helicoil insert as it is sprung out oversize and has to be coiled to insert versus the normal old school helicoil

 

True life experience:

Keep in mind (so you do not think I am crazy) that I use many structural adhesives In the body repairs that I do due to that is what is being used and what is approved for use and often times can be stronger than welding.

I have personally seen the effect ( for what ever that is worth) of these adhesive when in tech classes we bond two pieces of steel together. And using a frame machine towers, we clamp and begin to pull at these steel plates. Depending on the gauge of steel we are using....the metal tears BEFORE the adhesive lets loose. This was to show us that using these adhesives in place of specifically placed spot welds IS NOT what you want to do due to you can total effect the crash safety of the car being repaired due to you have taken away places in the body that are design to break-away and absorb force.

SO...
One day I was working on draining the coolant out of a 1982 and was removing the knock sensor out of the engine block. It was factory installed and when I went to remove it... a good portion of the cast iron of the engine block around the hole came out with it and fell on the ground.

What I was left with was about 30% of the diameter of the threaded hole still being the thickness of this boss area that still had the pipe threads...and the rest of the cast iron was gone but I did still have a perfect complete hole showing where the block was drilled an tapped for the sensor still showing. Even though I still had a complete hole...there was not enough thickness of cast iron for me to put the sensor back in and HOPE that it would not leak...thus no way of using any heli-coil or Keensert......SO...

I contacted JB Weld and explained my situation and got some of the product and used it ...following their instructions and knowing that the product could handle the torque. When I completed the repair...the hole was PERFECT and ALL of the threads were like they were in cast iron and it has been over 6 years that the engine is still doing just fine.

SO...knowing that this is the fill plug and not the drain plug. This may be an option if using a heli-coil for pipe threads is something that is not wanting to be done and possibly take the risk of having aluminum shavings in the transmission that will not get picked up by the magnet inside of it.

DUB

 

My Vintage Hondas use the metric pipe thread........maybe one of these will work?

https://www.mcmaster.com/#pipe-plugs/=1ccfpws

Jebby

 

If you post picture of thread we might be able to help you determine if an os plug would work. Standard 1/2-14 npt threads are slightly larger than the British thread so that will not help. Dub may have given you the most cost effective answer if the threads are severely damaged.
Hope this helps,
Dave

 

It's a tapered thread. I'm sure you know that. but some of the new plugs are longer which means wider at the back end. Or possibly a 1/4 inch pipe nipple. Pick through the stuff at home depot or Lowe's. You'll find a longer wider one.

 

If it not matching numbers you could just replace the case.

 

I'm with DUB. I'd JB Weld it then cut new threads with a tap. That stuff has bailed me out a few times.

 

Easier said than done and not cost effective. The repair I suggested can all be done and not one bolt needs to be removed...other than the drain plug...obviously....so the threads of the fill plug can be cleaned really well....and the contact cleaner that may get in the transmission can drain right out and not hurt anything.

NO DRILLING OR TAPPING THREADS!

The process JB Weld told me did not even cause me to use a tap to cut new threads. The threads were already there when I pulled out the pipe thread plug.

I have used this process and I have repaired numerous threaded holes and did not need to run a tap into them.

DUB