Cylinder Stud Thread Profile

[Bill Thomas]

T.T. I think it comes back to what Ogrilp says with the head nuts, And once they have picked up your in trouble, I also had it with an oil pump end blank made of Alloy, Fine thread into alloy. It seems to me the trouble starts with a thread which is too tight, I have found a lot of parts are like that now, Mismatched !!, As you say, They should go on by hand. I don't know what I would do, Without my thread files and a small hacksaw, I know it's a bodge, But I have "mended " many threads with a hacksaw blade !!. Cheers Bill.

 

[clevtrev]

Well I made it near enough 55 degrees so it is whitworth no? This was a stud made and fitted by you Trev to my B Rapide. I have the original2 part studs somewhere and I will dig them ou and measure them.

Well, Whitworth form is specified on the original factory drawing.

 

[clevtrev]

I`ve pointed out the solution and the cause of nuts locking up on cylinder studs. First you have to consider the method of manufacture, the studs threads rolled ones. So if you understand a little about thread making, you can solve the problem. The root of the 9/16" x 20 TPI Whitworth form is slightly smaller than the 1/2" BSF thread that precedes it on the stud. So if the 9/16 one werte to be produced to achieve the correct depth of thread, you would have the impression of that on the 1/2" thread. So the works made sure that did not happen. So to ensure that the nuts were then able to work, the internal diameter of the nut was increased for that to happen. So if you do have a problem with your nuts, and I know some of us do, after all they would have been tapped to take a guage, maybe, just increase that hole a little bit, and all will be fine.
If you have access to a thread measuring projector, you will have the operator, staring and asking` That`s a thread ?` I`ll see if I can get some photos.

 

[Bill Thomas]

Thanks Trev, I was playing with the Poss' 560, Just doing a mockup for a laugh the other day, And had a load of trouble with some stainless nuts I have had for years, A few were ok the others were not, I then said to myself, These are going to drop me in it !!, And threw them ALL in the BIN !!, I hope they are still there !!. Cheers Bill.

 

[tatty500]

But..... the original B design had hollow studs with just the one thread size on them.... no need for Mr Trev's odd crest size then. Anyway, on a C if the 1/2 inch thread could be rolled after the 9/16 then the crests could be higher.

I ended up doing selective assembly on the B in order to get all 8 hollow studs in. I never imagined I should have marked them on removal...... but it led me to wonder whether the studs either have a different form to the crank-case holes or the same form but on minimal clearance and, in either case, perhaps put in at the works while the cases were hot.....why?, well, a good tight fit here might have stopped the oil working up from the cylinder feeds. I don't remember the brass ET158 inserts being a problem in any hole.

I have found the trouble with the big head nuts on a C is that the thread runs out about a third of a turn too soon. They often bottom out and bind just before pulling properly down and it is very tricky to spot this.

Regards,
Tatty

 

[Bill Thomas]

This should Impress Trev', Or maybe Not !!, I found some of my Stainless head nuts and with my Electric Caliper !, Found the holes vary a lot, About 502 to 504 thou, And these are the better ones !!, My old rusty nuts 509 ish, I then found a 33/64 reamer, Don't know where that came from ?,Took a chance and after running the nuts down = 519-520, That will do me. So now I should have a Shiny Comet. Cheers Bill.

 

[Magnetoman]

I came late to this thread. Has it now been determined what the thread profile is, or are micrographs and measurements still needed on an original cylinder stud? If so I can work on this, but not until tomorrow.

 

[clevtrev]

But..... the original B design had hollow studs with just the one thread size on them.... no need for Mr Trev's odd crest size then. Anyway, on a C if the 1/2 inch thread could be rolled after the 9/16 then the crests could be higher.

I ended up doing selective assembly on the B in order to get all 8 hollow studs in. I never imagined I should have marked them on removal...... but it led me to wonder whether the studs either have a different form to the crank-case holes or the same form but on minimal clearance and, in either case, perhaps put in at the works while the cases were hot.....why?, well, a good tight fit here might have stopped the oil working up from the cylinder feeds. I don't remember the brass ET158 inserts being a problem in any hole.

I have found the trouble with the big head nuts on a C is that the thread runs out about a third of a turn too soon. They often bottom out and bind just before pulling properly down and it is very tricky to spot this.

Regards,
Tatty

Use a thicker waser under the nut, it needs to be 3/32" thick.

 

[ogrilp400]

I came late to this thread. Has it now been determined what the thread profile is, or are micrographs and measurements still needed on an original cylinder stud? If so I can work on this, but not until tomorrow.

G'day Magnetoman, No a clear answer on the profile has not been ascertained. So yes please a micrograph and measurements are definitely stiil needed. Thanks.

Phelps.

 

[Bill Thomas]

I remember sending off for a Tap, Many years ago, I think there is a mistake in one of the Vin' books, Came back 9/16 x 26 !!. I now have 9/16 x 20 whit', I think there must be a whitworth " Fine " ??. Cheers Bill.