Oil Drain Plug Advice

[98_Martin]

Hi all, this is my first post on here so figure I should give a bit of background before diving into my question. I'm 23 and a second year apprentice in Mechanical-Electrical Engineering but mainly specialise in machining, no CNC experience just manual machines from 70's-80's. It's a small workshop with only me and my supervisor so I end up getting experience doing a bit of everything, jack of all trades and master of some...

The question I had was regarding an oil drain I added to my Jaguar X-Type's AWD transfer box as the engineers/marketing considered this assembly sealed for life and therefore didn't design one into it. That of course isn't the case as oil doesn't last forever especially when it's only able to hold 600ml and lives beside the exhaust.

The process common among owners is to use the box's only accessible plug which sits too high to be a drain and too low to be a fill by jacking up the car in such a way as to turn it into those. One side jacked up drains most of the oil out and then jacking up the opposite side allows you to add oil back in. I personally don't really like this approach as it requires the car to be elevated 500mm from the ground to the sill and never actually drains all of the oil out, hence why I drilled a hole in mine at the lowest point. I can't take credit for this idea as an owner before me was the first to do this idea and one I followed for the future simplicity of further oil changes. What I instead would like to do is improve it and apply it to the rear differential also where the same problem occurs, only you suck the oil out through a hose into the fill plug (again considered sealed for life).

So here is how it is currently after doing the modification:



The plug is a modified engine sump plug that I turned down to 8mm and threaded with a M8x1.0 die. I figured a fine thread was more suited to a drain plug but that made the tapping of the hole in the transfer box slightly more tricky when you're working above your head lying on the ground...




As you can probably see in the first image is how vulnerable the plug currently sits under the car which is what I want to fix. It's sealed against a semi-flat surface that I filed which a rubber O-ring as a copper crush washer wouldn't have taken up the same slack that I left. Sealing compound won't currently work as I fill the box through that same hole with an adapter that I made so I can attach a hose going to an oil suction gun:




Any recommendations regarding the plug? A low-profile allen socket shoulder plug? Or a grubscrew/plug fitting with some sealant/Teflon tape?

The thread unfortunately has to ideally stay the same M8x1.0 as material wall thickness (~7mm) doesn't allow for effective sealing with a NPT/BSP taper thread.

Thanks in advance

 

[crossthread]

That plug is kind of hanging out there. I think your idea of a very low profile allen socket bolt is a good idea. Make it so that the "guts" are internal instead of external.

 

[Joe Gwinn]

The main idea of a BSP pipe thread seal is the soft copper washer crushed between steel (flange) screw and steel seat. On can make one's own non-standard version of such, using any convenient thread. Probably best to design around a common size of copper washer.

 

[Garwood]

The main idea of a BSP pipe thread seal is the soft copper washer crushed between steel (flange) screw and steel seat. On can make one's own non-standard version of such, using any convenient thread. Probably best to design around a common size of copper washer.

Where's a BSP thread used with a head/flange? A tapered pipe thread with a flange sounds like a mess. I have only ever seen straight threads used with crush washers and seals.

IMO if it doesn't leak leave it alone. Even a low profile headed drain plug will fair very poorly in 7mm wall thickness cast aluminum housing if it hits a rock.

If this were my vehicle I'd buy a spare housing. I'd TIG on some 3/4" 6061 so the bar was HORIZONTAL. Then I'd face, drill, chamfer and tap the threads HORIZONTALLY for an O-ring plug. Then I'd swap out the housing.

If the plug had to be vertical I'd make sure to recess the plug into the bung so the plug was protected from rocks and stuff. That's what the decent OEM builders do anyway.

 

[GregSY]

My first thought on seeing that drain was it hangs too low...then I read your comment stating so.


I've added tons of drains to all sorts of components that didn't come with one. I know you said you started with work someone else had done...but aside from that...it looks pretty complicated.

My go-to for transmissions and differentials - unless they hold a bunch of oil - is to drill and tap for an 1/8" NPT allen head plug. It sits almost flush, needs little wall thickness, and is easy to manage due to its small size. A hole tapped for 1/8" NPT will drain plenty fast....go have a warm beer while you let it drain and it'll be done when you get back. If the sump holds a bunch, I might go 1/4" or 3/8" NPT.


But...NPT threads seal very well, require no washer or machined surface, and last forever, assuming you are not draining the oil every weekend.

 

[boslab]

I suck oil out with a vacuum thingy, pump it, poke probe in and slurp, ok gear oil is thick but warmed it’s not so bad, I changed my van from the dipstick hole, worked fine.
Mark

 

[Joe Gwinn]

Where's a BSP thread used with a head/flange? A tapered pipe thread with a flange sounds like a mess. I have only ever seen straight threads used with crush washers and seals.

British pipe threads come in two kinds, parallel (straight) and tapered. The copper washers are used only with the parallel threaded variety.

British Standard Pipe Thread | BSP Thread Chart | Apollo International

Nor are we talking a standard pipe seal here.

 

[98_Martin]

Where's a BSP thread used with a head/flange? A tapered pipe thread with a flange sounds like a mess. I have only ever seen straight threads used with crush washers and seals.

IMO if it doesn't leak leave it alone. Even a low profile headed drain plug will fair very poorly in 7mm wall thickness cast aluminum housing if it hits a rock.

If this were my vehicle I'd buy a spare housing. I'd TIG on some 3/4" 6061 so the bar was HORIZONTAL. Then I'd face, drill, chamfer and tap the threads HORIZONTALLY for an O-ring plug. Then I'd swap out the housing.

If the plug had to be vertical I'd make sure to recess the plug into the bung so the plug was protected from rocks and stuff. That's what the decent OEM builders do anyway.

Yeah this would have been my ideal method but the procedure to remove the transfer box is incredibly lengthy hence why I'm more keen on the preventative maintenance with it in situe. I appreciate the advice though, if I ever need to do the same mod to something in the future and can remove it easily I'll 100% take that approach.

 

[98_Martin]

My first thought on seeing that drain was it hangs too low...then I read your comment stating so.


I've added tons of drains to all sorts of components that didn't come with one. I know you said you started with work someone else had done...but aside from that...it looks pretty complicated.

My go-to for transmissions and differentials - unless they hold a bunch of oil - is to drill and tap for an 1/8" NPT allen head plug. It sits almost flush, needs little wall thickness, and is easy to manage due to its small size. A hole tapped for 1/8" NPT will drain plenty fast....go have a warm beer while you let it drain and it'll be done when you get back. If the sump holds a bunch, I might go 1/4" or 3/8" NPT.


But...NPT threads seal very well, require no washer or machined surface, and last forever, assuming you are not draining the oil every weekend.

In honesty before starting this job I'd never even heard of NPT and had to look it up, sure I'd heard of BSP with it's associated taper variant but I really didn't think I'd have the wall thickness. That and the method of filling using the same hole meant I'd be threading and unthreading multiple times during the same oil change so I wanted something that would go in easier as I had to be quick to avoid losing too much oil.

 

[Garwood]

British pipe threads come in two kinds, parallel (straight) and tapered. The copper washers are used only with the parallel threaded variety.

British Standard Pipe Thread | BSP Thread Chart | Apollo International

Nor are we talking a standard pipe seal here.

Interesting. I have only ever seen standard metric thread diameters/pitches used in such applications. I manufacture a number of different fittings using straight metric threads and BSP threads have reverse engineered a number of odd automotive connections and have never seen a BSP thread in use for pressure piping that wasn't BSPT.

 

[Joe Gwinn]

Interesting. I have only ever seen standard metric thread diameters/pitches used in such applications. I manufacture a number of different fittings using straight metric threads and BSP threads have reverse engineered a number of odd automotive connections and have never seen a BSP thread in use for pressure piping that wasn't BSPT.

My impression is that BSPT is mostly used in hydraulics these days.

But in the 1970s I did have an old Volvo 144? whose engine oil pan drain plug had a copper washer. Don't know what kind of thread it was, but Volvo used lots of British parts back then. Basically, copper-washer plugs never leaked.

One can still get these parts. The thread appears to be 3/4-16 straight, which is not a BSPP thread, but it is a standard US thread.

 

[Scottl]

If it were me I would substitute a button head allen screw (stainless would be best) with a steel/rubber drain plug gasket. Lightly face the back side of the screw head for better sealing surface and change out the washer with every lube change. If you are worried about seepage use a thin film of the blue RTV gasket maker between the washer and housing.

I would not use a taper plug as there should be no need and most drain plugs use straight threads.

CORRECTION: I meant to say copper washer, not steel with bonded rubber. The latter are OK for frequently changed oil plugs but copper will stay sealed as long as needed.

 

[jim rozen]

Copper sealing washers of any given size are easily turned on a lathe. Hold them in gas flme unti they turn briefly red-hot, quench or not. This makes them dead soft.

 

[deltap]

If this is part of a transaxle, could it be the same lubricant in transaxle and differential? If there is no provision for drain or fill on the housing, could the drain/fill be farther forward on the transaxle? I don't see how they they can build something with no provision for service.

 

[Garwood]

My impression is that BSPT is mostly used in hydraulics these days.

But in the 1970s I did have an old Volvo 144? whose engine oil pan drain plug had a copper washer. Don't know what kind of thread it was, but Volvo used lots of British parts back then. Basically, copper-washer plugs never leaked.

One can still get these parts. The appears to be 3/4-16 straight, which is not a BSPP thread, but it is a standard US thread.

Ah. I see. More speculation than fact.

IME, most all straight threads that seal a fluid or gas with a copper washer or O-ring that are not inch threadforms are straight up metric pitches. M12x1.5 is a real common metric drain bolt/banjo bolt/o-ring style connection thread. So is M16x1.5.

I have never seen BSPP in actual use anywhere, but that doesn't mean it's not out there. I just wouldn't expect it unless someone was trying to make something nobody anywhere had a tap for.

 

[CarbideBob]

Good lord.
Never heard of a siphon tube or a pump?
Talk about the hard way to go around the block.

When you thread this hole how do you know you did not push metal chips inside as that is the way standard taps work?
There is a grease trick and tap style here to minimize it.
Bob

 

[john.k]

Modern ally castings are thin wall,and a drain plug without a cast in boss will almost certainly strip after a couple of uses...if it doesnt fall out sooner.

 

[52 Ford]

Why they do they "sealed" transfer cases and transmissions - I dunno. Really dumb. For example - a Ford Explorer. The regular Explorers have a seal PTU (power transfer unit - a transfer case) BUT the police version has a drain plug. Does it REALLY cost that much more to add a threaded hole? ANY oil goes bad. Hell, I change the grease in my cordless power tools... Seriously. When I buy a new power tool, I break it in and then change the grease.

Edit - adding to the Ford Explorer thing... saw one with under 100,000 miles and the oil looked like tar. Again, no drain plug. WTF

 

[98_Martin]

Good lord.
Never heard of a siphon tube or a pump?
Talk about the hard way to go around the block.

When you thread this hole how do you know you did not push metal chips inside as that is the way standard taps work?
There is a grease trick and tap style here to minimize it.
Bob

The only accessible factory plug that I explained in the post is quickly blocked of by a driveshaft within the box and therefore a tube can not be pushed past it, if it was that easy then people would be using that method. Funnily enough that is the common method used on the rear diff as it to is without a drain but has adequate clearance inside to feed in a tube.

I absolutely used the grease trick when tapping the hole for that very reason as I didn't have the oil flowing out like I during drilling.

 

[gustafson]

Interesting. I have only ever seen standard metric thread diameters/pitches used in such applications. I manufacture a number of different fittings using straight metric threads and BSP threads have reverse engineered a number of odd automotive connections and have never seen a BSP thread in use for pressure piping that wasn't BSPT.

Yah haven't worked on British cars

Full of em

Mostly on hose related stuff


whitworth thread too, fun fun