Thread size

[corbal]

Hi All - came to trial fit engine sprocket and rotor today to find that the first couple of threads of the crankshaft are damaged and swollen where PO has likely used a hammer to disassemble. I need to get a die & stock or die nut to rescue it. I have measured the thread diameter which is .622 inboard but .632 where swollen at the end. Counting the number of threads in the 1/2" or so threaded portion there seems to be 9 or 10 (or was should we say before damage). Does anyone know what thread it is? I suspect its a 5/8" 20 TPI cycle thread and need to be sure before paying out probably £25+ for a die. I tried the thread guide section of Christians Archive putting in the rotor nut part number but could not make it work. If anyone's got a die/stock suitable please can I borrow it, I will happily pay for secure postage both ways.

Thanks again - Alan

[Rob Harknett]

Be handy to know what year model of bike and pt. no. without having to do detective work before trying to give an answer. 000233?? 3/4" 20tpi, 234 7/8 x20TPI. If you have an old nut, you could try cutting it in half, clamp it on the shaft with a jubilee clip, then see if with mole grips or adjustable Plumbers pliers, undo the clamped on nut to clean the thread. If you clean the hacksaw cut face of the nut on a grinder, it will cut and clean thread better.

[Rob Harknett]

Don't know where you put in a search word which did not work. Perhaps I have missed something and you can search the archives, using a word or pt. no. If at the home page click books , you will then get instruction, spares and workshop manual books, click spares then go down the list for the spares book, open it and read. If that wont work, maybe need adobe reader. So back to the home page, click adobe reader and down load the software.

[corbal]

Hi Rob - thanks for your replies, it does help if you know the model, its a 1960 M8. I know the shaft mics up at 5/8" and I have confirmation its a 20TPI cycle thread. Your idea with the split nut is really good 'old school there is always a way' - I had before reading your reply ordered a split die from RDG tools and a fellow club member can lend me a stock so hopefully I will get it sorted soon. I guess there is no rush - it's been in bits in the PO's shed since 1975.

The nut part No is 000230 and within Christians Archives is a list of dimensions of nuts, bolts and washers compiled because the parts lists only give part number and description mostly. If you click on this heading it tells you to press Ctrl F and this brings up a search box into which you enter the part no. Then click on next and it searches. It told me it was searching 43 out of 43 but the search never completed. I tried several times but no luck. It could be my ancient laptop rather than the facility.

[Rob Harknett]

Your findings were correct for pt. no. 000230, you will also find a 1960 G5 mod 8 parts book where I guided you.
000230 is an old prewar part, which converts back to pt. no. STD230, most parts starting with zero's are old parts, usually fittings. So, with these pt. numbers convert back to old part numbers, examples, 000001 = STD1 000010 = STD10, 000100 = STD 100, I am sure you follow. NOW, check out the old part number in an old parts list in the archives, say 1937 onwards WD or 1940's, These old parts list do show dimensions. You don't need to be clever to know all the dimensions, you just need to know how to find out.

[Andy51]

Thread sizes are a very complex matter. Nearly all the smaller fastenings are indeed cycle thread, 60 degree thread angle (except BA and BSF where stud screws into alloy) but a lot of the bigger stuff are specials and may use Whitworth (55 degree) thread form. Unless you are sure of your thread form use the split nut method whenever you can then you won't mix up your thread forms. It is almost impossible to measure thread angles at home although there are ways of determining angle with measuring wire or small drills and a micrometer, but as many of these threads are battered an accurate result is difficult to get.

[iansoady]

My view is that after decades of use and abuse the difference between 55 and 60 degree thread angle is academic although I know purists will shudder.