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#16 Dan

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Posted 27 March 2009 - 04:26 PM

Yes it would be very odd, I think British Standards declared Whitworth as obsolete in 1960 and since then it is only really meant to be used as a lifting equipment thread (because it's massively strong and can be easily rolled rather than cut as I understand it). BA was only still in use on the Mini because it was still the 'official' standard thread for gauges, instruments and control gear.

#17 Guess-Works.com

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Posted 27 March 2009 - 04:45 PM

Right been to engineers, I'll get a price on Monday, if I get them done they will be cut from blanks on a 2nd profile and will be good enough to chase a 'bruised' thread but not suitable for cutting a new thread, well not more than once anyway... but I'm fairly sure no-one on here will be wanting to cut a new thread down a crank !

#18 Nightrain

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Posted 27 March 2009 - 06:50 PM

That's exactly what a 5/8 16UNS is


Exactly, Unified thread forms all use the same angles and peak and valley shapes. UNF is a certain pitch, UNEF is another pitch and UNC is another pitch again but if you want something that doesn't fit into a standard pitch it's a special. That's what UNS means. It's not UNF specifically because it isn't the same pitch as UNF, it's UNS.

If there was enough of a demand for them I'd get'em to run a few off, which would make them cheaper


I'd be interested if you do.

The Exact size is 5/8" WF (Whitworth Fine)


No it isn't, Whitworth threads use a different peak and valley shape from Unified and a different angle. Whitworth is 60 degrees with a radius at both the peak and the valley, Unified is 55 degrees with a radius at the valley and the peak cut square (which is exactly the same as Metric). Is there such a thread as Whitworth Fine? There's BSF but I've never encountered BSWF and I deal in Whitworth quite a bit considering it's an obsolete threadform.


LOL have a look in a proper manual one from BMC, you'll see in the text it says the thread is a special 'Whitworth Fine' thread. Theres a Tap the Correct size !

Attached Files


Edited by Nightrain, 27 March 2009 - 06:51 PM.


#19 Guess-Works.com

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Posted 27 March 2009 - 07:07 PM

Whatever you want to call it... it's a 5/8" 16tpi

I'll ask at the engineers on monday if they've ever come across Whitworth Fine

Edited by GuessWorks.co.uk, 27 March 2009 - 07:09 PM.


#20 Nightrain

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Posted 27 March 2009 - 10:28 PM

Whatever you want to call it... it's a 5/8" 16tpi

I'll ask at the engineers on monday if they've ever come across Whitworth Fine



LOL doesn't really matter if they've heard of it or not ! Not been funny or anything, but the above picture is of the proper size tap ! Just for further proof heres the extract from the BMC Blue Workshop Manual.

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  • Attached File  BMCT.jpg   18.58K   114 downloads


#21 Guess-Works.com

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Posted 28 March 2009 - 07:42 AM

Not being funny, but nowhere in the text does it say "Whitworth Fine".

#22 Nightrain

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Posted 28 March 2009 - 01:50 PM

LOL ok then guessworks my bad........ even though it says Whitworth form and there are only 2 forms of whitworth thread course and fine. Whitworth course it is definitely not, so it must Whitworth Fine. FFS I've even showed you the tap......

Edited by Nightrain, 28 March 2009 - 01:50 PM.


#23 Dan

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Posted 28 March 2009 - 04:00 PM

That's the whole point though, there aren't 2 forms of Whitworth as far as I know. Joseph Whitworth designed one thread and the main defining feature of it was the ratio of major diameter to pitch. I believe he was quite stubborn about that. The fact that the blue book states this thread is 'not standard Whitworth but of Whitworth form' essentially proves that Whitworth Fine is not a standard, or if it is a rare standard this thread is not made to it. If it were a standard thread it would simply give the thread name because engineers would understand it. Where did you get this tap marked 'WF' from (most Whitworth taps are stamped 'Whit' rather than simply 'W')? It is important to nail down for certain what this thread should be because I for one don't want to go about giving the wrong information out. I don't own a blue BMC book but I've got others and none of them state the thread for this fitting, neither do any of the Rover manuals I have. I don't appear to have any flywheel bolts at the moment either, I was planning to stick a thread gauge on one to measure the angles. It is odd that so many people get away with using a 5/8" UNS tap into this thread without removing lots of metal from the thread itself if it really is Whitworth form.

Does the blue BMC manual cover coil spring clutches at all?

#24 Nightrain

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Posted 28 March 2009 - 04:23 PM

That's the whole point though, there aren't 2 forms of Whitworth as far as I know. Joseph Whitworth designed one thread and the main defining feature of it was the ratio of major diameter to pitch. I believe he was quite stubborn about that. The fact that the blue book states this thread is 'not standard Whitworth but of Whitworth form' essentially proves that Whitworth Fine is not a standard, or if it is a rare standard this thread is not made to it. If it were a standard thread it would simply give the thread name because engineers would understand it. Where did you get this tap marked 'WF' from (most Whitworth taps are stamped 'Whit' rather than simply 'W')? It is important to nail down for certain what this thread should be because I for one don't want to go about giving the wrong information out. I don't own a blue BMC book but I've got others and none of them state the thread for this fitting, neither do any of the Rover manuals I have. I don't appear to have any flywheel bolts at the moment either, I was planning to stick a thread gauge on one to measure the angles. It is odd that so many people get away with using a 5/8" UNS tap into this thread without removing lots of metal from the thread itself if it really is Whitworth form.

Does the blue BMC manual cover coil spring clutches at all?


This is just getting comical, a 5/8" Whitworth Fine tap will go down a undamaged crank thread without removing any metal. It fits perfectly ! The tap came through a mates work, ordered a 5/8" Whitworth Fine Tap.

#25 Dan

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Posted 28 March 2009 - 04:39 PM

Err, it's not comical. I'm trying to find the answer for certain because there appear to be two equally valid opinions here. Simply because an opinion differs from yours it isn't automatically wrong. I thought you were wrong initially but the manual you have backs you up so I'd like to try to investigate further, even if you do find it amusing.

a 5/8" Whitworth Fine tap will go down a undamaged crank thread without removing any metal. It fits perfectly


Well that's kind of the point I was making above, a UNS tap fits perfectly and so a Whitworth tap shouldn't but at the same time a Whitworth tap fits perfectly and so a UNS tap shouldn't. That doesn't add up, one or the other should remove material on its way in. Since UNS is a listed threadform that has a standard description and Whitworth Fine isn't I'm inclined to believe that the Whitworth Fine you have is simply mis-described but I could well be wrong. I just find it hard to understand why there is no record of this thread in any tables or on any gauges and having checked my various catalogues this morning none of my sources list any Whit Fine taps or dies.

#26 jn1702

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Posted 28 March 2009 - 05:51 PM

Since i started this thread iv'e been doing a bit of research i took the tap to \scholar engines my local engine builder thet identified it as 5/8 16tpi but could not identify the thread. after looking at all the posts i now believe that the most likely size is 5/8 16 tpi uns which i understand is united national special. a web search revealed a supplier fpr these

http://www.engineeri...bcat.asp?id=281

67£ + vat guessworks is going to check with his people on monday as i understand it so i look foward to seeing what he comes up with thanks

#27 bigmotherwhale

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Posted 28 March 2009 - 06:35 PM

you can make a tap for cleaning simply buy cutting a notch all the way down an old flywheel bolt with an angle grinder, clean all the melted and bent bits off before you use it. if the threads are damaged you might want to consider getting a new crank.

#28 Nightrain

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Posted 28 March 2009 - 07:27 PM

Whitworth is 60 degrees with a radius at both the peak and the valley, Unified is 55 degrees


Once again this forum is proving to be much the same as the other's. Here I am trying to help people, and just like the inline engine debate, we get all the EXPERTS putting in there oar. I have told you, shown you backed what I've said up with evidence both written and photographically. What more can I do ? If your happy to carry on and shave 5 degrees of the threads to tap them UNS, go ahead.

This is your main problem, whitworth is 55 degrees and unified is 60 degrees end of story !

#29 bigmotherwhale

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Posted 28 March 2009 - 07:53 PM

youd be better off putting the bolt in without cleaning it than putting the wrong tap through, whats wrong with what i said about making one? you must have an old flywheel bolt and a dremel or angle grinder, it will do the job fine

#30 Guess-Works.com

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Posted 28 March 2009 - 08:27 PM

There's nothing wrong with using an old bolt, unless the initial tread ( peak/trough ) inside the crank has been folded over which will generally require the tapered thread of the tap to be used to remove the folded metal...

Also a crank bolt is made of a softer metal than the crank, to clean a bruised thread you need something harder to cut it, but to clean a thread of dirt etc, yes your suggestion is perfectly adequate... I use something similar for cleaning up sparkplug holes.

As for the 'debate' about the crankshaft thread.... I don't think we are disagreeing with you Nightrain, what IS important is what IS the thread down the crank tail.. You have documented evidence that is a Whitworth FORM thread, and is VERY important, as the generally accepted thread is a UNS form... and supporting this, to get my tap made, they made it using a new crankshaft bolt as the guide... and the 5/8 16UNS is what I got back...

Like Dan, none of the BMC books I have detail the thread form, erliest I have is Issue 3 ( red ring folder type ), is it possible that there are two thread forms, Whitworth for really early minis, which was later changed to the unified later ???




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