The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: SimonHolyfield on 21.02. 2019 21:45

Title: Crankshaft threads
Post by: SimonHolyfield on 21.02. 2019 21:45
Chaps,

I need to clean up the oil pump drive thread on a crank I've just acquired. It looks like 9/16 - 18 BSC, left hand.

Am I right, and can anyone recommend a good way of cleaning it up?
Title: Re: Crankshaft threads
Post by: JulianS on 21.02. 2019 22:36
Should be 9/16 x 20 tpi cycle left.

I just run a die down it if the treads need cleaning.
Title: Re: Crankshaft threads
Post by: berger on 21.02. 2019 22:41
a very good way would be having a nice man with a lathe who likes to help people for a packet of park drive, before my older brother had to move house and lose his heated workshop he did one for me in his big lathe both ends where someone had been very naughty with it,  *bash* sorry mate I can't help you and don't know a man who can until we've built another shop *work* *whistle*
Title: Re: Crankshaft threads
Post by: SimonHolyfield on 21.02. 2019 23:36
If I can get it in my lathe I'll do just that. No luck finding a die!
Title: Re: Crankshaft threads
Post by: berger on 21.02. 2019 23:59
good plan even if you have to take the flywheel off *smile*
Title: Re: Crankshaft threads
Post by: Whipstrut on 22.02. 2019 04:15
I've had good results with a thread restoring file if the damage isn't too severe.
Title: Re: Crankshaft threads
Post by: BSA_54A10 on 22.02. 2019 06:23
Die is available but being an odd ball size is a bit pricey.
If you only need to clean up a bit of damage buy a new nut, they are readily available.
Cut the old one in 1/2 lengthways, file then stone the cut fact flat.
Place the 2 halves at the bottom of the thread , clamp them together then work them up the thread to the end.

If you are going to use lock jaw pliers to hold them then cut through the flats.
If you are going to use a toolmakers ( or other type ) clamp then cut through the points so you have a flat spot to hold on to.
The nuts are high tensile steel & will hold a good edge
Title: Re: Crankshaft threads
Post by: Colsbeeza on 22.02. 2019 06:51
Hi Simon,
LPR Tools in Victoria Australia have them for A$35.

https://www.lprtoolmakers.com.au/cycle-bscy-20tpi-split-button-dies-7-16-to-3-4/

In my experience they are likely to be UN, which is almost identical to BSCy.
I used one recently to clean up the thread on the clutch mainshaft. It did the job well.
Colin
Title: Re: Crankshaft threads
Post by: terryg on 22.02. 2019 07:51
https://www.rdgtools.co.uk/acatalog/20TPI_Left_Hand_Taps_and_Dies.html (https://www.rdgtools.co.uk/acatalog/20TPI_Left_Hand_Taps_and_Dies.html)

Saw this but haven't made contact to check stock. 9/16 x 20 tpi l/h cycle die is listed at about £10 + VAT.

If you can get it in the lathe there's more control over thread angle, which I like.
Title: Re: Crankshaft threads
Post by: Swarfcut on 22.02. 2019 09:18
Simon, the phrase "Clean Up" makes me think of the very similar "Just needs a little bit of welding for MO.T "

 Usual problems include a mushroomed end, caused by unprotected hammer blows to the crank end in an attempt to drive the crank through the pinion gear.  Here a lathe is a must, to establish any runout or bending. A light cut to remove the damage to the first and second threads and cut a tapered lead is a good start.
  For a pulled or crossed thread, the nut trick is a good one which works well, following a needle file to chase the thread back to the end. Cycle thread files are not very common. Starting from the pinion end, the hardened nut will realign the thread after the worst damage has been removed with a file. If you try this, just a single cut on one side of the nut may be enough to allow it to open to pass loosely over the damaged area. Clamp up, not too tight, and work it back down to the end with a dab of cutting compound. It may take several passes and successive tightenings, so keep trying a new nut and the oilpump drive until you are happy with the thread.

  Tracy Tools, in Torquay, Devon hold a good range of taps and dies, and are nice folks to deal with.

 Swarfy.

 
Title: Re: Crankshaft threads
Post by: Bsareg on 22.02. 2019 09:35
The easiest way I've found is by using a two piece die and assemble it on the flywheel end and run it outwards. Unfortunately, I'm down Penzance or I'd sort it fir you.
Title: Re: Crankshaft threads
Post by: SimonHolyfield on 22.02. 2019 09:39
I like Tracy Tools as well.

I'll have a look at setting it up on the lathe, though there is some damage to the centre drill hole which makes me think ill need a fixed steady to clean that up first...
Title: Re: Crankshaft threads
Post by: terryg on 22.02. 2019 22:02
I also like Tracy Tools but couldn't see a l/h die like the one you need in their listings.
Title: Re: Crankshaft threads
Post by: trevinoz on 22.02. 2019 22:39
Don't Tracy do a left hand in all dies at increased cost?
Title: Re: Crankshaft threads
Post by: bsa-bill on 23.02. 2019 10:27
Quote
a packet of park drive,

Good god berger that's a blast from the past
Title: Re: Crankshaft threads
Post by: kiwipom on 23.02. 2019 11:07
Quote
a packet of park drive,

Good god berger that's a blast from the past
yes it is just like Woodbines and Senior Service . I believe most of us are only alive today because we kicked them into touch years ago , cheers
Title: Re: Crankshaft threads
Post by: Greybeard on 23.02. 2019 12:00
I gave up coffin nails 40 years ago when our first child was due. Before that, I'd smoke roll-up's, Capstan Full Strength, Gauloise, Senior Service, Russian cigs, with a tube on the end that you pinched to make a filter, (anyone else remember them?) I tried a pipe for a while but the reality was horrible compared to the pleasant smell from someone else's pipe. Also, the occasional joint, in the 1960's
Title: Re: Crankshaft threads
Post by: bsa-bill on 23.02. 2019 12:15
Quote
compared to the pleasant smell from someone else's pipe

yes - funny thing that
Guy in Wooler had a tool shop, (and money losing tool club) we young lads were often in there buying tools through the club (never never, more like never ever), any way he used to give us fags "Passing cloud" fat oval things, often wonder about the fags and the guy
Title: Re: Crankshaft threads
Post by: Greybeard on 23.02. 2019 16:33
..."Passing cloud" fat oval things...
Id forgotten about oval ciggies!