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MG Midget and Sprite Technical - Threads!

Guy's addition of two grease nipples on the brake and clutch pedals to lubricate the bolt (AHA8075 photo 1) made me want to copy his idea, especially as this one too was rusty.
Ordered some UHN400 1/8th inch nipples (photo 2)and now they've arrived realised I've never actually drilled and tapped a thread before. I know, what have I been doing?
Any clues on where to start on deciding what drill size is need and which tap to use? Do I need to get hold of a thread gauge and if so which one(s) - obviously not metric but UNC & UNF or Whitworth. There is occasional reference to publications which list the thread size, drill bit and tap, any ideas where to get hold of one?
The web isn't that helpful as there is so much info it's difficult to know which is useful and which is chaff.
Help much appreciated.





Jeremy MkIII

There is a lot of info on the web but if you want a reference book this is what I use :-

https://www.rdgtools.co.uk/cgi-bin/sh000001.pl?WD=tables%20zeus&PN=ZEUS%2dCHART%2d2008%2dLATEST%2dREVISION%2d1092%2ehtml#SID=75

(well a much older edition !

Did the supplier not indicate what thread it was ?
if so look up the tapping drill size from that - if you can drill through or into a void a 'first taper' will have a gentle lead ground on it and a full thread towards the rear of the tap and you can just use the one tap, a second taper has less of a lead in and a 'plug tap' is for bottoming 'blind' drilled holes i.e into sold lumps of metal.
Remember once the tap has started cutting, go say half a turn forwards and then back off say quarter of a turn to free off the cut material then go a further half turn and back off etc etc until its threaded.
Best use a tapping lube with steel - or for the odd hole WD40 is a poor substitute and keep tap vertical !

Oh and a tap wrench size to suit square shank of tap.

Tracy Tools or RDG Tools both do mail order - I use both.
richard b

When you're done tapping the hole, make sure that there aren't burrs on the far side of the hole.
Martin

Jeremy, I am very much an amateur but get my stuff of that sort from Tracy Tools, including getting a boxed set of imperial taps and dies. I also find a little thread gauge very useful for when I don't recognise, or cannot match a thread to one of the taps in my set.

One thing you may find is that the tube wall of the pedal pivots is quite thin and you will need to check that the threaded end of the nipple doesn't protrude on the inside. I think I had to file a little off the inner ends before fitting.
GuyW

Dont know why that link does not work - its in the title Zeus Chart.

Trying again

https://www.rdgtools.co.uk/cgi-bin/sh000001.pl?WD=zeus&PN=ZEUS%2dCHART%2d2008%2dLATEST%2dREVISION%2d1092%2ehtml#SID=75


Or

https://www.buckandhickman.com/en/shop/products/details/3964575/ROEBUCK-ZEUS-CHARTS

Forgot to note on the taps when tapping blind holes start with a first then use a second (when they bottom out) and finish with a plug.
richard b

I think the thread needs to be identified first as it looks too small for 1/8" BSP and too large for 1/8" anything else and personally have have not seen a grease nipple with an 1/8" thread other than 1/8" BSP, A quick search for UHN400 seemed inconclusive as many differing nipples seemed to quote that number. What are the dimensions of the thread? The pivot bolt looks well past its best IMO, are they available new?
David Billington

I don't know if its an optical efect, but that thread looks to me as if its tapered.
GuyW

Guy,

Not an illusion, all the grease/oil/Zerk fittings I've used have had tapered threads even when not a nominally tapered standard such as the UNF ones used on spridgets.
David Billington

As David noted a 1/8 BSP is quite large - O/D is about 9.75mm (.383") and 28TPI

1/4"UNF is 28TPI and O/D of 6.35mm (1/4" !)

Can you compare it with any other nuts you have lying around or on the car that we can try to identify it for you.
richard b

Thanks for all the helpful and informative responses, much appreciated.

Thanks for the link to Zeus charts Richard and for the tip for Tracy tools Guy, I may give them a ring and explain what I'm after to see if they can help.
The nipple is definitely tapered, it came as a bundle of Mini suspension nipples.
Here's the link
https://tinyurl.com/yyum7q8z

Will ferret around and see if there's a nut which fits, measure it and post the results here.

As a process, is this how it works?

1. Choose a nipple suitable for the job
2. Count the number of threads per inch?
3. Use a chart (like the one in the image) to select the drill and tap sizes based on the thread number?
4. Drill hole, duh.
5. Tap hole, one turn forward, half backward.

Richard you mentioned several different types of tapping, I understand the plug reference I think - tapping into a blind hole but can you expand on the other two you mentioned? Thanks.






Jeremy MkIII

Half turn forward, quarter turn back.

For this application I would use a 1st taper and not cut the thread full depth onto the straight art of the tap. This will give a good thread for the nipple to screw into and the tapered thread will then tighten and seal in the slightly under cut thread formed with the tap.

If you are ever threading a blind hole you finish off with a 'plug' tap, but be careful to back it off and clear the threads several times as you get near to the bottom of the hole. I have found it horribly easy to snap a tap off in a blind hole and the remnants are so hard it is difficult then to remove the broken off bit.
GuyW

I have been thinking of getting the grease nipple size for a long time. I have several nipples and the plug the grease nipple fits into on the fulcrum pin on the front suspension. The round head pozi fasteners that are used under the bonnet to the hold the pedal box, heater blower etc. fit nicely into this. They are 1/4 20 UNC, the tapping drill is 5.2 mm or 0.2047 “ I recall they were UNC when I bought them years ago; apart from the thread depth and effective dia. 1/4 BSW are the same, makes it confusing trying to define them. More so since my ¼ UNC tap is missing and I have always found thread gauges completely useless. The 1st and 2nd taps are tapered to make starting the thread easier. Putting the plug tap in a bench drilling machine (if you have one) you can exert more pressure pulling down on the handle,and turning the chuck by HAND the tap will be perpendicular and less likely to break.
L Langley

I think this link explains the 3 types of tap better than I can !

https://www.threadtools.com/uploads/pdf/technical-specs/taps-technical-info.pdf

The number of threads per inch (tpi) only gives a part of the information - you need the thread form - whit/unf/bsp etc - as 28 tpi as I noted above can be BSP/UNF etc and the size (OD) of the thread can vary a lot. + threads are cut at differing angles BA is 47 1/2deg, whit 55deg metric 60deg etc.

When you know the thread form whit/unf etc the OD can then be refered to the table and the tapping drill size found.

Thread gauges can help to identify threads as noted but with a short thread its often a bit more difficult.

HTH at least a bit !

R.
richard b

L Langley,

I think you need to check the UNC bit as I can't think of any UNC in the body work of a spridget only UNF. The pedal box screws being 1/4" UNF.
David Billington

Thanks Richard,

that's an interesting and informative link.

I found a 7/16th nut which fitted the nipple so rang Tracy Tools (thanks Guy) and a very helpful and patient woman helped me decide what was needed, I plumped for a loose set of UNF taps from 1/8 to 1/2 inch for £20 (I think it's a mix of taper and plug taps) so we'll see what arrives.
A bit of experimentation is required now I think. Half turn then quarter turn back it is.

Didn't realise just what is involved in making a threaded hole!
Jeremy MkIII

David take one out and count the threads. ¼ UNF has 28 TPI I can count 10 or 11 on ½ of screw. Makes me think they are 20 UNC and they don’t even look like a fine thread. I have had a thread gauge for 50 years and never found it of any use. It has metric pitch at one end and TPI the other supposedly for Whitworth. Not much use for determining a unified thread. I have tried it on a known 8mm pin the 1.25 pitch fits almost as badly as the 20 TPI the other end. If I was buying a tap I would go for just one plug as opposed to a three piece set I will only use occasionally. Jeremy, I hope you will let us know how you get on.
L Langley

L Langley,

I just removed a blanking cover screw from the near side pedal box aperture and it matches a known 1/4" UNF screw from a recent job and a 1/4" UNF nyloc screws on easily. The 28 TPI thread gauge is a spot on match, 20 TPI is not even close. QED 1/4" UNF. IIRC the front suspension grease nipples are all 1/4" UNF.
David Billington

All very interesting but my advice to Jeremy would be to buy a new pedal pivot bolt, and grease it well before fitting. The originals seem to last about 40 years so a new one will see most of us out!
David Smith

David S

LOL !

Thats exactly what I did when I built up mine.

Certainly see me out !
richard b

Mr Billington I have just done the same thing you are right they are UNF. Oddly some of the captive nuts in shell are UNC the one I picked on was. But that doesn't alter the fact that my grease nipples are UNC, Have you proved yours are UNF. I am guessing that a coarse thread is used because it has a greater area for such a short thread. We would use a coarser thread in soft materials for greater strength.
L Langley

We covered this subject recently (and it was BSP(?) depending on which nipple you're referring to).

From an even earlier (2013) thread -

Les Bengtson, Arizona, USA - Posted 11 April 2013 at 18:22:28 UK time

>>A quick check can determine if the grease nipple (zerk fitting) is 1/4"-28 UNF or 1/8" BSP (also 28 tpi). Measure the {removed portion of the old} nipple. If it measures about 1/4" (.250") it is the 1/4" size. If it measures something over 3/8" it is the 1/8" BSP which has a nominal diameter of .383".<<

(I hope this helps rather than adding confusion.)
Nigel Atkins

I take your point David. The simplest route is to do as you describe but that's not the point with this task.

I admired Guy's solution to stop the bolt rusting again. It appeared simple to do but it turns out I need to learn a new skill if it's to be completed so I'm happy to continue (and acquire some new tools in the process - always a bonus).

The old bolt has cleaned up, still shows pitting from earlier, rustier times so whether its retained or replaced the grease nipples will be added and the result will most definitely outlast me.

Jeremy MkIII

Just an update on the taps. Ordered yesterday at 15.08 arrived 20 minutes ago. That's some service from Tracy Tools (and the Royal Mail) from Torquay to Lancashire.
Jeremy MkIII

The lady at Tracy tools could well have been Tracy !
richard b

L Langley,

I just checked both my stubaxle grease nipples and both are 1/4" UNF as are the holes they screw into as a 1/4" UNF screw threads in nicely. I couldn't comment on the fulcrum grease point thread as I ditched the threaded fulcrum pins in 1987.
David Billington

Haha Richard!
Well she certainly knew her stuff and was very helpful.
Jeremy MkIII

Interesting David, another mystery to solve. I was looking for a bolt to try in the threaded plug, the one I found looked like the ones under the bonnet and the one I took out was, so confirming it was a unified thread. That is another mystery why some are UNF and some UNC. I am pretty sure the other nipples on the suspension are UNC because I swap some for an angled nipple when greasing, but I will check them. Jeremy could have purchased any sort of threads on his nipple, but the one in the picture looks very much like the ones I have. They are the same overall length and looking at the scale on the rule they seem to be ¼ diameter and ¼ long, I can only see three threads (I think) not 7.
Would you tell me about ditching the fulcrum pins, never was very impressed with the thread idea? Thanks.

L Langley

https://www.metal-arts.co.uk/sprite/frontsuspmods/index.html
David Billington

Great info in here, many thanks.

I have always been a bit confused about tap types, so thanks for the link above:
www.threadtools.com/uploads/pdf/technical-specs/taps-technical-info.pdf is just all I need for selecting taps and drills for them for various car relacted jobs (I have a Zeus booklet but those who don't, that link get you going nicely).

Thanks too for the Tracy Tools tip as I have had problems buying taps - no longer get to Bills Tools in Glasgow to buy the odd tap, and not so keen on eBay as much prefer supporting a specialist and knowledgeable supplier.

I really would like a UNF and UNC tap and die set for Christmas. Any recommendations?

Cheers
Mike
M Wood

How about this set from Tracy Tools?
https://www.tracytools.com/taps-and-dies/taps-dies-wooden-box/unf2

Add postage and VAT to the shown price.
Jeremy MkIII

Thanks for that David – often wondered why something like that was not done in the first place, got the impression Issigonis designed them on the back of a fag packet after a night of inebriation. I remember those Moggies never saw many with the bonnet up but many with a collapsed wheel. The thread would seize (lack of grease) and the kingpin would snap the fulcrum pin. I think David Smith should get the BAFTA on this one.
L Langley

LOL!
thanks....
David Smith

A useful tip for cutting metric threads is that you can work out the tapping drill size by subtracting the thread pitch from the nominal diameter, it also works for other 60 degree threads such as UNF/UNC but you have to convert the TPI to pitch first.
David Billington

The taps from Tracy Tools very helpfully have the drill size stamped into them.
Will post a picture later.
Jeremy MkIII

David Billington just been looking at those wishbone mods. I didn't realize it was your own website, I am most impressed, did you market them?
L Langley

I’m impressed with that wishbone mod too. There must be a market to justify making those for sale if you don’t already?
Chris Madge

Lawrence, Chris,
David probably wouldn't say here but I'm happy to - Tim Fenna, he of Frontline Developments, 'borrowed' (my word) the original idea from David without telling him about marketing it, many years ago.

David, I think, has previously very generously said that Tim Fenna did (slightly - my word added) develope the original idea for the mark one version of the Frontline Front Suspension Kit.

So the kit is marketed already - and boy are they good at marketing and promotion, a trait of their type of person.

In the interest of disclosure, it's already very well established in the Archives here that I'm a very dissatisfied previous customer of theirs and what I think of him and Ed Braclik.

P.S. Lawrence, David Smith put the LOL and thanks as you got the wrong David before. :)

Nigel Atkins

Done!



Jeremy MkIII

Nigel - I only addressed Mr Smith once - Why is everybody named David. Looks like Frontline no longer do the fulcrum mod? I'm not in the market any longer only interested.
L Langley

Well done Jeremy, a smart looking job too.
Nigel Atkins

Lawrence,
yes I know, it used to be that when my wife told me that Dave was on the phone for me I'd have to ask which one. I also know lots of Johns, Micks, Peters, ect., names follow fashions in generations.

Sorry I don't know what a fulcrum mod is - but I do know a few years ago when I went to AVO (dampers) 3 miles from where I live and spoke with a Nigel he told I couldn't buy a damper for the kit from them as FL had the contract tied down - poacher turned gamekeeper.
Nigel Atkins

I've only made the 2 wishbones and they were for my own use, I've never made them commercially and to my knowledge no one else has done so although I did meet a guy in Kent many years ago that said he had converted many spridget wishbones to take Triumph Spitfire trunnion components and they use plastic tophat bushes so I presume the conversion was similar. At the time I did the wishbone and damper replacement I had the run of the local tech college machine shop so I had all the kit available, I then moved on did my engineering degree and got a job then moved into software. I now have the kit myself so I could do them again but am happily busy doing other things.


Jeremy,

To finish it off you could add grease nipple covers to keep them clean. Nice job.
David Billington

Jeremy, I hadnt spotted the pdf symbol on that post of yours, - nearly missed it!
Yes, nice job. I like your pedal pivot treatment too. In many ways, it's probably better than the more agricultural 'fill with weld and redrill' method. I never really understand if a weld is harder than steel, or softer. Does the hot metal temper as it cools to make it softer?

Where does one buy an oolite bush like that?
GuyW

Jeremy mentioned it's PTFE lined so it's most likely a DU bush. https://www.ggbearings.com/en/products/metal-polymer/du
David Billington

A welder told me that a weld will assume the same characteristics as the parent metal; engineering degrees I’m intimidated best keep my mouth shut, I have never been trained for anything. David, I knew about subtracting the pitch for metric not about the other, I have tried it for UNF, it does work but can’t get 30 degrees by pitch/2 /depth. Tan -1 39degrees 10min what is wrong? I worry about these things.
L Langley

Funny you should mention covers David, I've some spares from an Automec brake line kit...

Guy, the bearing was from the appropriately named World of Bearings.
Their ebay shop has the size I used
https://www.ebay.co.uk/itm/293659674906 £3.60 incl delivery.
Subsequently found it a lot cheaper at hardware kingdom (but you have to wait a month for delivery from China)
https://tinyurl.com/y63zku3o

Funnily enough originally I was going to buy an oilite bearing but saw this one and thought it might be more durable being made from steel.


Jeremy MkIII

Final pic, in situ.
Thanks for the idea Guy.

Just the easy task of bleeding the clutch now....

Jeremy MkIII

That's good Jeremy. Thanks for the acknowledgement. 😀
Why is it that these close up pictures of everyone else' car details always look so much cleaner and tidier than mine!
GuyW

Because I've cropped the untidy bits out!
Jeremy MkIII

Have you put some grease on the clevis pins?
Dave O'Neill 2

Tracy Tools often give away Drill & Tap size charts and Metric / Imperial Charts at Car and Model shows. I have several in my workshop and garage.
Alan Anstead

No I haven't Dave. TBH the thought hadn't crossed my mind mainly I suspect because the brake clevis pin is hardly worn after almost 50 years and the clutch pedal's bearing is PTFE lined.
Now you've mentioned it, I'll dab a bit on the brake pedal pin before replacing the cover.
Jeremy MkIII

This thread was discussed between 08/09/2020 and 01/10/2020

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