162 replies to this topic

[DaveRob]

hey John...... im with you here......... Imagine Buying crank A from supplier A and Bolt from supplier B....... assuming the crank is std rover and unmodified .... and the bolt is the opposite..... and made to an incorrect spec.......... Just as a thought.... has anyone asked Minispares....?.... is Simon watching this thread?

by the way..... you final statement is right......... ROUND

Rob

[Dan]

as a thought.... has anyone asked Minispares....?.... is Simon watching this thread?

It's all in hand, as I said I'll post all the replies together later.

[Guess-Works.com]

IT'S NOT WHITWORTH FINE...

The thread is a Whitworth Form cut on a 5/8" O/D with 16tpi, there is no such thing as Whitworth FINE

That's like saying, a 5/8 16 UNS is UNF, and it's NOT.

This is one small concession on your behalf Nightrain, in your gloating, I told you so etc etc etc.... your actual first post was WRONG !

[DaveRob]

Slowly the truth of the matter is uncovered and brought to light .........

As in all things educational what matters is WHATS right and WHATS Incorrect

Not WHOS right and WHOS incorrect.......... This forum is an education to me and Im happy to learn.......

I await the final outcome in this discussion with great interest....... maybe the final conclusion is worthy of an FAQ.

Rob..........

[Ethel]

I don't give a monkey's who's right or wrong or what the thread is called. But it would be nice to know how well the profile of the thread in the crank mates with any bolt I put in to it and if I actually make things worse by using a tap for a different thread. So far all we know for sure about this mystical 5/8 Whitworth Fine is it's name (perhaps) and its pitch.

I'm grateful Nightrain brought it to our attention, but we've yet to establish anything useful if we don't know how to get hold of the correct tap or whether a particular chosen bolt, like some of the aftermarket socket head ones, are worth fitting.

[Nightrain]

IT'S NOT WHITWORTH FINE...

The thread is a Whitworth Form cut on a 5/8" O/D with 16tpi, there is no such thing as Whitworth FINE

That's like saying, a 5/8 16 UNS is UNF, and it's NOT.

This is one small concession on your behalf Nightrain, in your gloating, I told you so etc etc etc.... your actual first post was WRONG !

Lol, showed you the evidence, look back at the pic I uploaded and read the id of he tap what else would WF stand for ? FFS it is a special Whitworth Fine thread. ie 5/8WF.

There is really no need for you to get shirty guessworks, just count it as a learning experience. Expect there'll be something in Minimag about the revelation a certain someone has discovered as well.

You've got to remember the state of the british car industry at the time, this thread was probably used in old austin/morris/Riley's etc who knows. Why bother upgrading tooling if you've got something that will do the job.

[dklawson]

This further update came from KC regarding the callout on the crank drawings:

"It just states - '5/8" x 16TPI WHIT. Form, but quotes '0.625" drill' for the flywheel bolt thread and '0.557" drill' for the damper bolt thread - so I guess there is some lee-way in the thread form to get a 5/8" UNS tap down it. I have never seen a large amount of material removed when I chase the threads using the tap I have. KC "

The first statement clearly contains an error. The tap drill cannot be .625" for a 5/8" thread as no thread would be produced. Perhaps he was referring to a counter-drill of the flywheel bolt's tapped hole so the puller won't damage the first thread. Regardless, the callout on the drawings only identifies the size, pitch, and form without explaining what is meant by "Whitworth form".

[DaveRob]

Speaking to an old and respected engineer in this field earlier this afternoon he suggested, ( and its obviously just another nugget of information), that in bygone days, when engineers were building things in this Country, the form BSF was commonly known as Whitworth Fine. However, I can see that even this thread has the wrong TPI..... Just another thing to add to the pot.

Tin hat at the ready..... lol

Rob

Edited by DaveRob, 30 March 2009 - 04:02 PM.

[Ethel]

 Crank_thread.gif   331.94K   27 downloads

[Dan]

I was hoping to get more responses during the day so that I could put them all together but so far only 2 of the 8 or so companies I have contacted have replied.

So first off I feel that I and perhaps some others owe Nightrain an apology and also gratitude for bringing this up and for forcing us to research it. He is quite right that it is indeed a non-standard Whitworth thread (I have to go along with GW and say it can't be called Whit Fine, partly because there is no such standard and partly because the fine thread based on the Whit form is BSF and this thread is even finer still).

MED came straight back to me with this:

Dan



The thread is actually



5/8 UNF x 16 TPI



Kind regards,

Obviously some errors there but it was a vote in the Unified camp. Then Simon (and I see him watching this as I type) also replied very quickly with Mini Spares' opinion, he had to check the drawings but this was his second message:

My drawings are all Whitworth, I have just spoken to the company that make the flywheel bolts, both verto and non, and they agree.

As this was happening, Doug posted Calver's updated response. Two sets of drawings is more than enough evidence I think and personally I am prepared to accept someone's statement about the drawings without having to see them myself.

The important difference is the thread angle, and so the thread depth. The crests and troughs are a little different but not too much, I'll look it up but the formula for calculating the radius may even be the same in both. The depth is quite different though and will result in reduced thread engagement.

So then I started asking other questions, much as have been asked above. Which uprated bolts are actually going to grip the thread fully? Simon assures me that all the Mini Spares aftermarket flywheel and pulley bolts are made to Whit forms and they come from the same supplier he asked about the threadform. I have asked MED to clarify what theirs are cut to but they haven't replied so far and I have to say if they are using a Unified thread I'd think more than twice about using their bolts. I have also asked KAD, Swift Tune, the company mentioned above who make billet cranks and some others but as said I have no other replies yet. I'll keep an eye on this and report any more replies, specifically so we know what is what.

As far as I'm concerned this has called into question the professionalism of some engine builders and engineers. As Nightrain said it appears that people are assuming this thread is UNS because it's easier to find. However if you had a 5/8 16 UNS nut it would not fit on the flywheel bolt and that would tell any engineer that something was wrong. If we were to buy the expensive tap from Mini Sport would it be the right type? I must admit that I haven't contacted Mini Sport about this but if anybody knows someone there it would be good to know.

I think it's obvious now that when I described the taps before, specifically which would interfere with the other thread I had managed to confuse the two in my mind. The reason the UNS tap that so many people own runs cleanly into the Whit thread is that it simply isn't contacting most of it (I think, I may have to draw this to help my confusion). The same would go for any Unified bolts, they won't be gripping the full depth of the thread, not until you torque them and distort the thread enormously. Although bearing in mind the warning in the BMC book about not damaging the thread when cleaning it out perhaps it is best to use a tap that only skims over the surface without contact, although the angle difference would mean it wouldn't clean very effectively.

Another important question that we will never know the answer to is why on Earth were BMC messing about and using a custom pitch Whit thread for this? Was it just to stop people fitting the wrong, perhaps weaker bolt?

So GuessWorks, how about a group buy for a WhitWorth version? Maybe enough of them to supply the entire industry.

[Nightrain]

I was hoping to get more responses during the day so that I could put them all together but so far only 2 of the 8 or so companies I have contacted have replied.

So first off I feel that I and perhaps some others owe Nightrain an apology and also gratitude for bringing this up and for forcing us to research it. He is quite right that it is indeed a non-standard Whitworth thread (I have to go along with GW and say it can't be called Whit Fine, partly because there is no such standard and partly because the fine thread based on the Whit form is BSF and this thread is even finer still).

MED came straight back to me with this:

Dan



The thread is actually



5/8 UNF x 16 TPI



Kind regards,

Obviously some errors there but it was a vote in the Unified camp. Then Simon (and I see him watching this as I type) also replied very quickly with Mini Spares' opinion, he had to check the drawings but this was his second message:

My drawings are all Whitworth, I have just spoken to the company that make the flywheel bolts, both verto and non, and they agree.

As this was happening, Doug posted Calver's updated response. Two sets of drawings is more than enough evidence I think and personally I am prepared to accept someone's statement about the drawings without having to see them myself.

The important difference is the thread angle, and so the thread depth. The crests and troughs are a little different but not too much, I'll look it up but the formula for calculating the radius may even be the same in both. The depth is quite different though and will result in reduced thread engagement.

So then I started asking other questions, much as have been asked above. Which uprated bolts are actually going to grip the thread fully? Simon assures me that all the Mini Spares aftermarket flywheel and pulley bolts are made to Whit forms and they come from the same supplier he asked about the threadform. I have asked MED to clarify what theirs are cut to but they haven't replied so far and I have to say if they are using a Unified thread I'd think more than twice about using their bolts. I have also asked KAD, Swift Tune, the company mentioned above who make billet cranks and some others but as said I have no other replies yet. I'll keep an eye on this and report any more replies, specifically so we know what is what.

As far as I'm concerned this has called into question the professionalism of some engine builders and engineers. As Nightrain said it appears that people are assuming this thread is UNS because it's easier to find. However if you had a 5/8 16 UNS nut it would not fit on the flywheel bolt and that would tell any engineer that something was wrong. If we were to buy the expensive tap from Mini Sport would it be the right type? I must admit that I haven't contacted Mini Sport about this but if anybody knows someone there it would be good to know.

I think it's obvious now that when I described the taps before, specifically which would interfere with the other thread I had managed to confuse the two in my mind. The reason the UNS tap that so many people own runs cleanly into the Whit thread is that it simply isn't contacting most of it (I think, I may have to draw this to help my confusion). The same would go for any Unified bolts, they won't be gripping the full depth of the thread, not until you torque them and distort the thread enormously. Although bearing in mind the warning in the BMC book about not damaging the thread when cleaning it out perhaps it is best to use a tap that only skims over the surface without contact, although the angle difference would mean it wouldn't clean very effectively.

Another important question that we will never know the answer to is why on Earth were BMC messing about and using a custom pitch Whit thread for this? Was it just to stop people fitting the wrong, perhaps weaker bolt?

So GuessWorks, how about a group buy for a WhitWorth version? Maybe enough of them to supply the entire industry.

Very gracious dan, now form an orderly que lads........

[midridge2]

how about a sorry from all the people who said he was wrong, i think its the least some people can do to show that nightrain was trying to teach people.

[DaveRob]

It also asks the question...... If you bought a Crank pully AND a fly pully BOLT in EN24 from MED, ( guess why Im asking this question), ....... do you strip them and replace them..... andeven worse,(even more worrying, but not my problem), if you bought a high spec engine from MED what is inside it????......... I guess the answer is yes....... but where do you go from here?

Rob?????

[Guess-Works.com]

Best price for Whit form 5/8 16tpi got so far is 75 + vat + carriage on a single tap.

Now negotiating discount for volume purchase..

[Dan]

I think it's obvious now that when I described the taps before, specifically which would interfere with the other thread I had managed to confuse the two in my mind. The reason the UNS tap that so many people own runs cleanly into the Whit thread is that it simply isn't contacting most of it (I think, I may have to draw this to help my confusion).

Well I drew it, very roughly and I was right the first time and as he said above Doug agrees. A UNS tap should remove material from an internal Whitworth thread. It must be purely down to tollerances. If I draw it to a higher precision including all the correct radii I suspect I will find why there is a clearance when there shouldn't be.

Med will obviously tell you it's fine and they have built many race engines that have not had a problem. It may be that their parts are made off site by a bolt specialist who is cutting them properly and they just aren't aware of it themselves. They haven't replied to tell me what thread they do actually cut yet.