Radiator drain tap - tapered or straight fit?

[Colin Lindsay]

My drain tap, one of the wing-type in the picture has just dumped about 5 litres of coolant all over the floor, one drip at a time over the last two days or so. It's not cheap stuff! I tightened it until it felt tight, in fact very tight, so I didn't want to wring the fitting right out of the radiator body and stopped short of a complete nut to body seal. It hadn't dripped at all for over a week, then off it went. Now I'm wondering if it is a straight fit, not tapered, and so needed a little bit more pressure to seal. Anyone know?

[Paul H]

Here’s mine . Vitesse radiator - longer thread

Paul

[Pete Lewis]

most would be tapered thread  , a splosh of sealant should work

but you know when you need to use it it will be seized and the wing falls off 

 

Pete

[Ian Smith]

It might be tapered, at 1/4" BSPT.

"Where's my bl**dy Zeus when I need it? 

Ensuring the threads (both male & female ) are clean & OK, try putting a couple of threads of PTFE on the joint. If it's a parallel thread into a straight thread, it'll either bottom out, or foul at the top on the female side. 

Finally, are the block & radiator drains of the same thread gauge? I'm still pretty sure it's still 1/4" BSP, or 1/4" BSP Taper)  which (should) be 12 degrees on the taper. 

Check I've got it right, however. 

[PeteH]

From Memory, the taper is around 1.5 degrees?

[Colin Lindsay]

I thought it was tapered so stopped just before Gorilla force, and the fibre washer I used was about 2mm off the radiator body. It's now soaked and the coolant is all over the floor...  I think I'm going to have to take the rad off again and fit it on the bench so I can monitor closely. Another step backwards but I suppose the floor needed the wash.

[Patrick Taylor]

Did/do these have a fibre washer? I've never seen/replaced one, having assumed they 'just' sealed through being an interference fit.

[Colin Lindsay]

Probably not, but in any case it wouldn't have provided any kind of seal given how far off the radiator the tap stopped. Later in the week I'll remove the rad again and see what the setup is, and how to prevent leaks in future. At the very least I can retap the rad threads.

[Ian Smith]

On 02/01/2022 at 02:14, PeteH said:

From Memory, the taper is around 1.5 degrees?

Please check my previous posts, folks. Imperial taper is 1-48, whilst metric taper is 1-50. Although it's close, the differing angles are enough to   mess up the job, especially if we're down to the smaller sizes. I still can't remember where my Zeus  booklet is, but everything is available via Google. 

I'd respectfully suggest that a full, 100% quality check is performed on a new drain plug. I've seen some wonderful things on 'bay, which are nowhere near close. 

 

As a slight aside, on some fixings on water systems need a full-plug tap to finish off. A normal tap has a lead in; usually, first, second, and bottom. Some taps, however, require no lead whatsoever, going to the full depth in one pass. In appearance, it'll look like a headless bolt, with a set of grooves up the side. If you need to have one, grind the 'lead' off the tap. Like the Zeus, I can't find my copy, but that's how I've made mine before. 

However, please, please, check the veracity of both this post, and my previous post.   

Cheers,

Ian.

[Colin Lindsay]

On 01/01/2022 at 20:52, Ian Smith said:

It might be tapered, at 1/4" BSPT.

"Where's my bl**dy Zeus when I need it? 

Ensuring the threads (both male & female ) are clean & OK, try putting a couple of threads of PTFE on the joint. If it's a parallel thread into a straight thread, it'll either bottom out, or foul at the top on the female side. 

Finally, are the block & radiator drains of the same thread gauge? I'm still pretty sure it's still 1/4" BSP, or 1/4" BSP Taper)  which (should) be 12 degrees on the taper. 

Check I've got it right, however. 

I'll try to borrow a 1/4 BSP tap for the radiator later today. I can obtain replacement drain taps but the radiator itself needs a bit of care, the brass threads are slightly distorted so a cleanup will only help.

[Wagger]

47 minutes ago, Colin Lindsay said:

I'll try to borrow a 1/4 BSP tap for the radiator later today. I can obtain replacement drain taps but the radiator itself needs a bit of care, the brass threads are slightly distorted so a cleanup will only help.

Colin. If it is of any use, a 1/2in UNF tap has a TPI of 20. 1/4in BSP is same diameter, but 19 TPI. I know that the thread angles differ, but, if you can find a 'Taper' tap, careful use will clear the thread. I have used Metric coarse to clear whitworth where the thread gauge 'Fits' over a 3/8 in length. We called this method 'Anti vibration' on our Triumph motor bikes. We used 24 TPI bolts in 26 TPI holes for mudguards.

[Colin Lindsay]

Thanks for that; I know what you mean about the threads and length and the radiator drain looks to be around 1/2 inch or so. I had thought however that the radiator is untapered, but a parallel thread, and the actual drain tap is the tapered bit? I'll be over at the Engineering Works later today and will see what they have.

[Pete Lewis]

its much easier to control the taper diameter of a male fitting and use a straight  parallel  tapped hole   its always been that way 

and is as used on sumps gearbox and diff plugs 

to use a parallel male you need a flat face to seal with a washer etc.you wont find that on a radiator tapping 

Pete

 

 

[Ian Smith]

In certain circumstances, you might try a 'Dowty' washer.  As Pete has mentioned, sealing off a joint is prone to leaking, as over-tightening  the leading thread will cut through a rubber washer. to resolve that, pass a file over the leading thread, to get  the flat face joint. 

 

[Pete Lewis]

i dont get the confusion rad drain taps have been a tapered thread since god made apples until they deleted the nasty things 

by design you fit a tapered tap to a open parallel holed type  and you need a faced tap to seal with a washer on a flat face 

if you mix and match its sure to give you a problem 

a faced fitting is Nipped up the washer does the sealing on its faces 

  on  a  taper you do it up Tight  and the threads seal  not the face ,  bit of thread sealer if you fancy some 

pete

 

 

[Wagger]

Pete is absolutely correct.

Dunno if these were ever made of copper, but it is softer than brass. In the past I have lightly 'Tinned' the tapered thread with Lead/Tin solder. This is soft enough to form in the threaded hole absorbing discrepancies. I used the old red Hermatite in case it worked loose.

I have seen many a Sump cracked as a result of Gorilla force on tapered plugs. Had to use 150lb ft to undo one on a Mini!

[Pete Lewis]

there is this idea that uncontrolled  Gorilla action solves everything.....................Wrong 

tis unfortunate  there is a lot of it about 

 Pete

 

[daverclasper]

I guess with sump plugs, it's maybe worry about it coming undone (rather than just sealing). I have to say to myself "not too tight", then, sort of hope it's ok. Maybe I should use a torque wrench, or is that obvious?.

[Wagger]

1 hour ago, daverclasper said:

I guess with sump plugs, it's maybe worry about it coming undone (rather than just sealing). I have to say to myself "not too tight", then, sort of hope it's ok. Maybe I should use a torque wrench, or is that obvious?.

If the plug has a square head, drill a hole through it and wire it to prevent it turning. Usually, a bit of gasket goo will stop it.

[Pete Lewis]

the only plugs ive seen missing are when the guy refilling the sump after a drain down has forgotten to refit the plug first

and Dave  a good hand pull on  a normal spanner will get you a good night sleep     so worry less drive more  

happy new year Pete

[daverclasper]

Cheers Pete. Happy New year to you, too

[Colin Lindsay]

17 hours ago, daverclasper said:

I guess with sump plugs, it's maybe worry about it coming undone (rather than just sealing). I have to say to myself "not too tight", then, sort of hope it's ok. Maybe I should use a torque wrench, or is that obvious?.

I'm happy enough with diffs and gearboxes, they're heavy enough to withstand considerable torque, and the sump to a lesser extent in case I pulled the drain part clean out of the metal - it can be thin enough - but it's worse with the radiator which is just brazed in. I've swapped that one for another spare and won't be using it until I've checked it over and probably refurbished. 

[Peter Truman]

The one that always worried me is the drain cock on the engine block the cock is a parallel thread into the block and has a tapered wedge plug passing thro the body of the valve, which keeps its seal to the body of the valve using a mild steel spring which rusts and could (never has!) loose the seal/tension on the tapered plug! the spring and tapered plug is held in with a washer and split pin which also rusts!

Surely a simple brass plug with fiber washer into the block was easier and safer. 

[Chris A]

46 minutes ago, Peter Truman said:

The one that always worried me is the drain cock on the engine block the cock is a parallel thread into the block and has a tapered wedge plug passing thro the body of the valve, which keeps its seal to the body of the valve using a mild steel spring which rusts and could (never has!) loose the seal/tension on the tapered plug! the spring and tapered plug is held in with a washer and split pin which also rusts!

Surely a simple brass plug with fiber washer into the block was easier and safer. 

I know what you mean, not long after I got my 13/60 I went out for a drive and the engine temp rose to the red! After carefully removing the rad cap the water level had dropped way down. Luckily I pulled up close to a bar and they gave me enough water to refill. I had been cleaning the engine and I must have caught the tap and opened it by accident. The tap must have been kept closed by dirt and grit as it now opened far too easily ! I quickly ordered a plug and replaced it.

[Colin Lindsay]

1 hour ago, Peter Truman said:

The one that always worried me is the drain cock on the engine block the cock is a parallel thread into the block and has a tapered wedge plug passing thro the body of the valve, which keeps its seal to the body of the valve using a mild steel spring which rusts and could (never has!) loose the seal/tension on the tapered plug! the spring and tapered plug is held in with a washer and split pin which also rusts!

Surely a simple brass plug with fiber washer into the block was easier and safer. 

Both of my drain taps have broken due to the spring rusting out; they're otherwise perfect but now there's nothing to hold the tension and jeep the brass wedge in the tap body. In the estate I'm just using a brass plug, screwed straight into the block; it came with one of the cars in the past and I suppose it's as easy to use as the tap.