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Oil Drain Plug Size


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#1 kopi

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Posted 01 February 2014 - 04:22 AM

Hey guys, I have a '92 cooper spi and during a (supposedly routine) oil change I realized the original drain sump plug was a normal bolt! So I ordered a minispares magnetic plug but it's too loose (just spins but doesn't tighten). On closer inspection it looks like the previous bolt was of a finer thread. Does anyone know if spi' drain plug are of a different thread size and what it would be?. Photos here comparing the two.

Thanks guys!

Attached Files


Edited by kopi, 01 February 2014 - 04:33 AM.


#2 Dan

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Posted 01 February 2014 - 07:11 AM

All sump plugs are the same, I would suggest what has happened is a previous owner has stripped the thread and tapped it to a different size as a repair. It's bad practise to do that anywhere but in this case very problematic indeed. It should be Heli-coiled back to the original thread but there may now not be enough material left for that.

#3 kopi

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Posted 01 February 2014 - 08:25 AM

That is bad news indeed. Guess i'll try to order a custom magnetic pug first? I'm not exactly sure how a heli coil would work. 

 

http://www.magneticd... to measure.htm



#4 Dan

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Posted 01 February 2014 - 08:31 AM

A Heli-coil is a thread repair. You drill out to a larger size and tap to suit a specially made fitting that has an internal thread of the original size. There are other forms of thread repair too that can deal with more extensive damage. Speak to a local engineering shop as they might have a solution. If you get a custom part made to fit this now you will be following the poor practise of the previous owner. Leaving any future owner or servicing mechanic in the same position you find yourself in now if they ever loose or damage the plug. Obviously if that's the best solution for you for whatever reason then go ahead, it's your car. Ideally though the thread would be repaired to standard size.

Edited by Dan, 01 February 2014 - 08:35 AM.


#5 dklawson

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Posted 01 February 2014 - 12:35 PM

Agreed.  Ideally you would have the HeliCoil fitted as Dan says.  I have done this for a friend a few years ago.  It can be done with the gearbox in the car but to do the job properly requires a bit of care.  For the factory plug to seal properly the repaired hole needs to be tapped perpendicular to the boss on the gearbox where the plug goes.  Therefore, if you opt for the HeliCoil fix, call around and see if you can find a Mini garage that has done the repair before.  Shops who are not familiar with Minis and have never done the repair may not do it properly.

 

If the HeliCoil repair is not practical for you for whatever reason, I suggest you measure that bolt that has been used and buy a couple of comparable ones but shorter in length.  Choose the length by measuring the depth of the tapped hole in the gearbox during your next oil change.  You may want to drill the center of the bolt to accept a cylindrical magnet to catch swarf like the factory magnetic plug.  A good (slow cure) epoxy will be fine for securing the magnet to the hole drilled in the bolt.  Make at least two of these bolts up and keep the second in the car at all times... just in case.  Finally, take your custom plug to the parts store and find nylon drain plug washers that will fit it.  The factory sealing washer will have been copper and it requires a bit of torque to seal properly.  The nylon washer will crush more and develop a seal with lower loads on the threads in the sump.  

 

Knowing that the threads in your car's sump have been damaged before you need to be vigilant about not over-tightening the sump plug.  The HeliCoil is the strongest and best solution.  A custom bolt with nylon washer is less desirable but workable solution.



#6 tiger99

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Posted 01 February 2014 - 01:58 PM

If you can't find a suitable nylon washer, try a Dowty seal, which is a metal washer with a bonded rubber insert, or a drain plug washer for some modern cars, which is vaguely similar to a Dowty seal. For example, the Ford Focus uses such a seal. Don't know if it is the right diameter, but your local Ford parts department could show you one, as they are consumables, changed at every service.

 

If all else fails (you are not at that point yet!) a machine shop can make up a top hat bush in ali, with the sealing face accurately parallel to the drilled and tapped thread, a simple lathe job, and that can be MIG or TIG welded, or possibly even epoxied, into the transmission case, but it is probably an engine out job to get a sufficiently oil-free environment for the welding or adhesive bonding. Or, a steel top hat bush could be made with a tapered thread, screwed in tightly and sealed with PTFE tape, in situ.

 

I think that there may be a way to align a heli-coil correctly, by using some kind of guide to align first the drill, and then the tap, accurately perpendicular to the sealing face, or a tool could be made which locates in the heli-coil thread and skims the sealing face perpendicular to the thread. I am surprised that no-one seems to offer a mobile service doing exactly that, as stripped drain plug holes in ali transmission cases are rather common, not just on Minis, and the tooling to do the job would not be difficult or expensive for anyone with a machine shop to make.



#7 dklawson

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Posted 01 February 2014 - 02:35 PM

Tiger, the HeliCoil kit I used was borrowed from a friend.  He had made a couple of angle-iron brackets to use as a guide to keep things square when drilling and tapping.  I made an additional part for his kit that insured the angle-iron pieces could be more accurately clamped to the subframe than simply located "by eye".  Unfortunately my friend loaned his kit to someone else who was not so careful about returning it!  I wish I had photographed the brackets during the HeliCoil installation so others could see what works.



#8 kopi

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Posted 02 February 2014 - 02:11 PM

Wow thanks guys, great information here. I couldn't really find a custom sump plug anyway (needed a M16 x 2.0, but most are M16 x 1.5 out there) so i guess its helicoils then. Where I'm from, there aren't that many mini mechanics ... actually there's only 1. And yes, that's the same guy that left the normal non-magnetized bolt in there. 

 

Tough choices ... I guess I'll have a go at it myself. Any recommendations on a good kit? i.e. taps and helicoils for the correct size, 5/8 i believe? I have a power drill so that parts sorted. 



#9 ukcooper

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Posted 02 February 2014 - 03:09 PM

Could you not use the other bolt and put a magnet on the end of it ? if it was not leaking before.

or helicoil kit http://www.minisport...ug-5-8-unc.html its 5/8 unc and make it comes with the drill bit if you buy from else's where.

or put the other bolt back and put one of these on the gearbox http://www.minispare...classic/gearboxbut clean it every 1500 miles or so.

Edited by ukcooper, 02 February 2014 - 03:14 PM.


#10 dklawson

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Posted 02 February 2014 - 04:40 PM

While you can HeliCoil this yourself, pay attention to my comments about keeping things perpendicular and use of the nylon or Dowty washers that Tiger mentioned.

 

If you do this yourself, drain all the oil out of the box by lifting the the left front wheel as high as you can, then... with the oil completely drained, lift the right wheel while working.  This will minimize the oil dripping out while you work.  Load the drill bit and tap with heavy grease when you perform the tasks.  The grease will hold most or all of the swarf as you drill and tap.  Be vigilant about picking out any metal chips that the grease does not hold.

 

You say there are no Mini mechanics near you.  You might want to start a thread specifically asking for help with the HeliCoil and list your general location.  You may find someone near you who has done this and can help... and may even have the tools.  Otherwise, using the existing bolt with either the nylon or Dowty washer may be your best solution for now.



#11 Jordie

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Posted 02 February 2014 - 05:53 PM

Green and white mini spares did mine in situ afew yrs ago. They are mini specialists nr newcastle

#12 kopi

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Posted 08 February 2014 - 11:03 AM

Thanks guys. I couldn't find a helicoil kit but a local hardware shop assued me the powercoil kit works the same. Its a 5/8 UNC thread repair kit, cheaper than a helicoil but I had to buy the 16.5mm drill bit myself. 

 

Now ... I'm really concerned about being able to line it up at a perfect 90 degrees. I've done a fair bit of wall drilling myself but with my precious mini i'm naturally more cautious. Has anyone done this without a custom jig of some sort and still made it out ok? Or some specific instructions for a simple jig? I'm using a Makita HR2020 drill if that's relevant. 



#13 dklawson

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Posted 08 February 2014 - 01:39 PM

Since I have no pictures I started a lengthy text description of what I did.  I decided it was simply too involved to follow.

 

Instead I'll ask a question.  Do you have access to a metal lathe or a friend with one?  I will wait for your reply before elaborating, but having a friend make a few simple guide blocks may be the easiest solution.



#14 mini 4o

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Posted 08 February 2014 - 02:54 PM

http://www.minispare.../plug.aspx|Back to search

hi all, not to sure about using this plug,, anyone used it ?

#15 kopi

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Posted 08 February 2014 - 03:42 PM

I do not have access to a metal lathe nor a friend with one. I plan to do this simply as is, with the car jacked up slightly and all. Would appreciate any guidance on this.




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