I stripped the threads on a drain plug

[AlanM]

I have stripped the threads on the rear axle housing transmission drain plug and hole on my ZD326. I can see in the hole that there appear to be good threads beyond the stripped portion in the hole. My plan is to install a longer bolt in place of the stripped plug, but the bolt I tried to install will not screw beyond the damaged portion of the hole. The bolt I am trying to install has 12mm x 1.25 threads. I am not positive that they are the correct threads. Before I try to clear the threads with a tap, I need to confirm what the existing threads are.
Can anyone tell me what those threads are?
Also, does anyone have a different suggestion for repair? I have heard of expansion plugs that can be installed in place of damaged drain plugs, but do not know what might be available.

 

[dirtydeed]

Can you look up the bolts on a parts diagram? Many times the provide the size in the description.

Or take the bolt to a hardware store to verify the correct size and get a tap.

 

[AlanM]

I did take it to the local hardware store, but it is hard to compare stripped threads with good ones, especially when there is a 12mm x 1.25 and a 12mm x 1.5 to choose from. My best guess was the 12mm x 1.25, but that would not screw into the hole.
I also called Kubota customer Service and they said they do not provide technical service but they would try to get an answer to my question. Problem is they said it might take up to a week to get an answer.
Do you know where to find parts breakdown diagrams?

 

[Tughill Tom]

look at http://www.stanleyengineeredfastening.com/brands/heli-coil/screw-thread-inserts
it will get you all fixed up!

 

[rjcorazza]

The parts list at Messicks does not give the bolt specs. Why not remove the opposite side drain to match up the thread?


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[AlanM]

You asked a good question and I don't have a good answer other than I was gun shy after the experience with the stripped plug - I didn't want to disturb the other one that I had already installed. Also, I didn't realize it would be so hard to identify the thread size because of the close options and I thought it could be found in available manuals on line. I'll remove the other one if all else fails. In the meantime I will look at the site suggested by Tughill Tom.
The other option is a call or a 50 mile trip to my closest Kubota dealer on Monday.
Thank you everyone for your help.

 

[North Idaho Wolfman]

The parts list on:
http://apps.kubotausa.com/illustrated-parts/
has the threads listed.
It's not a bolt thread because it uses a sealing washer.
It looks to be BSPP 1/8 thread.

 

[Russell King]

Try to get all thread pitch bolts and see if any fit. The threads may be damaged and not let any bolt start.

I think there may be three pitches in that size and Kubota seems to like fine more than coarse thread pitch.

Edit since NIW POSTED

Ignore the previous suggestions

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[AlanM]

NIW - Thank you for the great link to the parts breakdown. I think I found the flange bolt and the seal washer, but I can not find the thread size. Can you tell me how to find that? Thanks again.

 

[Dave_eng]

NIW - Thank you for the great link to the parts breakdown. I think I found the flange bolt and the seal washer, but I can not find the thread size. Can you tell me how to find that? Thanks again.

Could you post some photos of the hole and the removed plug.

Here is a description of what BSPP stands for.
The thread will not be the same as a normal or metric bolt.
It is possible some hydraulic fittings would use that thread.

BSPP Connections

BSPP (British Standard Parallel Pipe) is most popular in the UK, Europe, Asia, Australia, New Zealand and South Africa. It is a parallel thread fitting that uses a bonded seal ring to do the sealing. This bonded ring seal is sandwiched in-between a shoulder on the male fitting and the face of the female fitting and is squeezed in place. No thread sealant is needed to form a seal. Ralston Instruments has male BSPP adapters , female BSPP adapters,.....

I have had success in making a thread chaser from a new fitting when a tap was hard or impossible to come by.

Since you believe you have found the correct plug, buy it.

If you can find a fitting which screws easily into the good drain plug hole then you can turn it into a thread chaser by cutting two slots across the fitting like a cross each cut 90 degrees from the other. Use a thin cutting disk on an angle grinder.

Remove any roughness caused by the cutting of the slots with a wire wheel otherwise you will damage the thread further.

There are many threads whose pitch and thread angles are close but not the same. If the new hydraulic fitting does not screw into the good drain plug easily and by hand before cutting the slots, you do not have the correct thread.

If it is the correct thread, then carefully screw the modified fitting into the damaged thread hole. Don't just continue to screw it in but frequently back it out to cut off and then remove any material the slots have removed.

It is not the ideal technique but when desperate to get a Machine back to work it can do the task if done with great care.

Dave

 

[AlanM]

Dave - Thank you for your suggestions.
Pictures of the hole are in my first post.
When I said I found the flange bolt and seal washer, I meant I found them in the parts diagrams at the site provided by NIW, but I could not find the thread information that he said was listed. I don't know how he found the BSPP info.
The threads are stripped nearly clean in the outer portion of the hole where the bolt was engaged, but beyond that there are good threads remaining.
If I can get a positive ID on the threads, I can buy a tap to chase what is remaining and then install a seal washer and bolt longer than the original to reach the good threads.

 

[bearbait]

I haven't used the loctite repair but looks simple enough. I have used the helicoils and they do work great, good luck with your repair


https://www.youtube.com/watch?v=zUI6GMkTOjU

https://www.youtube.com/watch?v=DaGLq70BTw8

 

[Yooper]

Dave - Thank you for your suggestions.
Pictures of the hole are in my first post.
When I said I found the flange bolt and seal washer, I meant I found them in the parts diagrams at the site provided by NIW, but I could not find the thread information that he said was listed. I don't know how he found the BSPP info.
The threads are stripped nearly clean in the outer portion of the hole where the bolt was engaged, but beyond that there are good threads remaining.
If I can get a positive ID on the threads, I can buy a tap to chase what is remaining and then install a seal washer and bolt longer than the original to reach the good threads.

Since you're going to buy a tap anyway, I would suggest taking the time to drill and tap to a new size rather than having a drain plug held in by just a few threads. A little vibration and the plug comes out...gets real ugly real fast. My suggestion is to tap it to an NPT (national pipe taper) thread. Taps are available at any hardware store and they are not expensive. Plugs to fit are available there also with different types of removal such as square head, allen, hex head, etc. If the existing hole is approx. 5/16", an 1/8" npt tap may be able to give you the threading without drilling. The next size up would be 1/4" npt, which requires a 7/16" drill. Since this is a taper thread sealing system, there is a little forgiveness built in. Main thing is to not over tighten and the use of some thread sealer is highly recommended. Good luck!
http://www.engineershandbook.com/Tables/npttap.htm

 

[Charlie5320]

Since you're going to buy a tap anyway, I would suggest taking the time to drill and tap to a new size rather than having a drain plug held in by just a few threads. A little vibration and the plug comes out...gets real ugly real fast. My suggestion is to tap it to an NPT (national pipe taper) thread. Taps are available at any hardware store and they are not expensive. Plugs to fit are available there also with different types of removal such as square head, allen, hex head, etc. If the existing hole is approx. 5/16", an 1/8" npt tap may be able to give you the threading without drilling. The next size up would be 1/4" npt, which requires a 7/16" drill. Since this is a taper thread sealing system, there is a little forgiveness built in. Main thing is to not over tighten and the use of some thread sealer is highly recommended. Good luck!
http://www.engineershandbook.com/Tables/npttap.htm

I agree. You don't have enough threads to get a leak proof fix. You also don't have enough threads to use the loctite fix. Helicoil is the proper way to fix this. You can choose what thread you want to use with a helicoil. If you just bore it over size and rethread the hole use a oil pan kit for an automobile. Most of those kits use a seal under the head. You could also use a npt tap, then screw in a street 90, then use a pipe plug. Then you wouldn't be trying to seal that aluminum up. If it were mine, I'd go with the helicoil and bolt with a gasket.

 

[Mainah]

Dave - Thank you for your suggestions.
Pictures of the hole are in my first post.
When I said I found the flange bolt and seal washer, I meant I found them in the parts diagrams at the site provided by NIW, but I could not find the thread information that he said was listed. I don't know how he found the BSPP info.
The threads are stripped nearly clean in the outer portion of the hole where the bolt was engaged, but beyond that there are good threads remaining.
If I can get a positive ID on the threads, I can buy a tap to chase what is remaining and then install a seal washer and bolt longer than the original to reach the good threads.

If you have a good NAPA store nearby take the old plug with you, explain the issue, and they’ll fix you right up. Probably not on Sunday though

 

[Ortimber]

Since you're going to buy a tap anyway, I would suggest taking the time to drill and tap to a new size rather than having a drain plug held in by just a few threads. A little vibration and the plug comes out...gets real ugly real fast. My suggestion is to tap it to an NPT (national pipe taper) thread. Taps are available at any hardware store and they are not expensive. Plugs to fit are available there also with different types of removal such as square head, allen, hex head, etc. If the existing hole is approx. 5/16", an 1/8" npt tap may be able to give you the threading without drilling. The next size up would be 1/4" npt, which requires a 7/16" drill. Since this is a taper thread sealing system, there is a little forgiveness built in. Main thing is to not over tighten and the use of some thread sealer is highly recommended. Good luck!

http://www.engineershandbook.com/Tables/npttap.htm

This is a very good suggestion. [emoji106]

 

[Dave_eng]

The suggest BSPP thread is a Whitworth thread with a 55 degree pitch angle which is why finding a bolt is a challenge.

In the days when I rode a 1950's era BSA motorcycle, Whitworth bolts and nuts were common on these machines. My Nuffield 465 used Whitworth as well. A big mistake was to find a SAE fine thread American bolt and think it was the same as Whitworth because the bolt would start threading into the hole.

The thread pitch was different from the Whitworth 55 degree and if you continued to screw in the bolt, soon it was jammed and ripping out threads.

There are many people around restoring old British motorcycles and cars. Ask around. They all have a bucket with miscellaneous Whitworth bolts.

This is a link to a supplier of parts for old British motorcycles.
https://www.classicbritishspares.com/

Dave

 

[North Idaho Wolfman]

Alan,
I'm sorry I gave you wrong info, that is not the right size for that plug, I crossed up two parts.

I would do as Yooper said and replace the plug with a NPT plug, it would be the safest and quickest fix.

 

[Tughill Tom]

The suggest BSPP thread is a Whitworth thread with a 55 degree pitch angle which is why finding a bolt is a challenge.

In the days when I rode a 1950's era BSA motorcycle, Whitworth bolts and nuts were common on these machines. My Nuffield 465 used Whitworth as well. A big mistake was to find a SAE fine thread American bolt and think it was the same as Whitworth because the bolt would start threading into the hole.

The thread pitch was different from the Whitworth 55 degree and if you continued to screw in the bolt, soon it was jammed and ripping out threads.

There are many people around restoring old British motorcycles and cars. Ask around. They all have a bucket with miscellaneous Whitworth bolts.

This is a link to a supplier of parts for old British motorcycles.
https://www.classicbritishspares.com/

Dave

Where's that Nutffied????

 

[AlanM]

Thanks again for all the replies and suggestions.
I have attached a couple pictures of the plug as requested. The threaded portion of the bolt beyond the washer is only about 3/8".
From what I'm hearing from you, finding out what the original threads were won't lead to the best solution because of the minimal good threads left in the hole.
Drilling the hole larger seems to be the best option. Since a helicoil requires drilling and tapping, it seems to me the best option is to drill and tap for a new bolt or fitting.
I like the idea of the NPT option, but right now the hole is larger than 7/16". It measures about .455 - .461" now where the threads are gone so I would have to go to a 3/8" NPT which requires a 37/64" hole (.578125"), not much larger than what I have.
Keeping chips out of the transmission will be a challenge, but I can flush it with hydraulic fluid before I seal it up. I might consider putting a piece of cloth in the hole prior to drilling. With a hole this large, I should be able to fish it out after the tapping.
Thanks again.