Author Topic: Buggered up crankshaft thread - How to fix  (Read 939 times)

Offline owain

  • A's Best Friend
  • ***
  • Join Date: Mar 2017
  • Posts: 135
  • Karma: 2
Buggered up crankshaft thread - How to fix
« on: 12.03. 2017 18:21 »
Righto, after being advised to take off the half time pinion with a puller/extractor tool (thanks muskrat); the pinion came off easily...Unfortunately, I had already done a bit of damage to the crankshaft thread from trying to hit it out with a hammer...I was feeling stupidly optimistic at the time.

Anyway, now I have a damaged thread and wondering how I can fix it...I came up with these possibilities;
  • Buy a cheap BSF tap/die kit and try to salvage the damaged part of the thread (first 2-3mm).
  • Cut the damaged section of thread off.
  • Carefully file/grind down the damage part of the thread, so that the nut can glide over it to the good thread.

Any ideas?
Sweden & North Wales
'50 BSA A10
'69 BSA A75R

Online edboy

  • Valued Contributor
  • ****
  • Join Date: Oct 2012
  • Posts: 436
  • Karma: 3
Re: Buggered up crankshaft thread - How to fix
« Reply #1 on: 12.03. 2017 18:49 »
hi , sadly youve been hammering the weakest part of the crankshaft and the crank may need crack testing before you waste any money and time on it. cracks develop at the flange of the timing side shaft sometimes. youre better off sending the crank to srm who could do all the work for you.

Online beezermacc

  • Resident Legend
  • *****
  • Join Date: Dec 2011
  • Posts: 993
  • Karma: 39
  • Not for the purist!
    • Priory Magnetos Ltd.
Re: Buggered up crankshaft thread - How to fix
« Reply #2 on: 12.03. 2017 19:27 »
I'd use a thread file.
Priory Magnetos Ltd - A10 spares, magneto and dynamo refurbs. www.priorymagnetos.co.uk

Online muskrat

  • Global Moderator
  • Wise & Enlightened
  • **
  • Join Date: Jul 2009
  • Posts: 8258
  • Karma: 106
  • Lake Conjola NSW Oz
    • Shoalhaven Classic Motorcycle Club Inc
Re: Buggered up crankshaft thread - How to fix
« Reply #3 on: 12.03. 2017 19:34 »
It doesn't look like you belted it too hard. A thread file is the quickest and cheapest way out. it's a left hand thread so not easy to get a die.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Offline owain

  • A's Best Friend
  • ***
  • Join Date: Mar 2017
  • Posts: 135
  • Karma: 2
Re: Buggered up crankshaft thread - How to fix
« Reply #4 on: 12.03. 2017 19:38 »
That would burn a massive hole in my pocket if there is a crack in the crankshaft. Hoping that it escaped unharmed!  *eek*

I didn't think of a thread file! Sounds ideal.
Sweden & North Wales
'50 BSA A10
'69 BSA A75R

Online TimK

  • A's Best Friend
  • ***
  • Join Date: Mar 2012
  • Posts: 97
  • Karma: 0
Re: Buggered up crankshaft thread - How to fix
« Reply #5 on: 12.03. 2017 21:42 »
You can get LH BSF dies from Tracy tools - (http://www.tracytools.com/taps-and-dies/left-hand-thread-taps-dies-bsf) - good luck!
Tim Kerridge
Australia

Online RichardL

  • Outside Chicago, IL
  • Wise & Enlightened
  • *
  • Join Date: Nov 2007
  • Posts: 5060
  • Karma: 48
Re: Buggered up crankshaft thread - How to fix
« Reply #6 on: 12.03. 2017 22:55 »
Owain,

Attached is a photo of my half-round miniature file laying in the timing-side thread.  (The file is from a common set.) To me, it looks like a pretty good fit (the tip of the file is not in the focal range).  I'm not swearing that this is the best (or even a good way to do it), but, if it was mine, I'd try it on a bit of the thread to see what I got. I've had some success with this particular file on even finer threads.

Otherwise, if you want to buy the die, I'd chip in 25% of the 18 GBP price if it became a forum-wide loaner.

Richard L.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Online RichardL

  • Outside Chicago, IL
  • Wise & Enlightened
  • *
  • Join Date: Nov 2007
  • Posts: 5060
  • Karma: 48
Re: Buggered up crankshaft thread - How to fix
« Reply #7 on: 12.03. 2017 23:11 »
It doesn't look like you belted it too hard. A thread file is the quickest and cheapest way out. it's a left hand thread so not easy to get a die.
Cheers

Yeah, I'm not promising (because disclaimers are a must), but I can't imagine that this minor amount of thread damage would result in cracks in the crankshaft. Interesting in hearing if there are any other takers for sending the crank for xray (or whatever they do).


Richard L.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Online JulianS

  • 1962 A10
  • Wise & Enlightened
  • *
  • Join Date: Mar 2017
  • Posts: 1006
  • Karma: 20
Re: Buggered up crankshaft thread - How to fix
« Reply #8 on: 13.03. 2017 09:21 »
You need a 9/16 x 20 tpi  British Standard Cycle (BSCY) thread left hand die. Thread form also known a CEI, Cycle Engineers Institute.

Hopefully you will only need to use it once.

You can see them on E bay.

Keep as much thread as you can there is not much to spare when the worm, lock washer and lock nut are screwed on.


Online muskrat

  • Global Moderator
  • Wise & Enlightened
  • **
  • Join Date: Jul 2009
  • Posts: 8258
  • Karma: 106
  • Lake Conjola NSW Oz
    • Shoalhaven Classic Motorcycle Club Inc
Re: Buggered up crankshaft thread - How to fix
« Reply #9 on: 13.03. 2017 09:26 »
I've seen a lot worse. The thread on my 51 was butchered by the PO. Had to remove the 1st two threads (chamfered with an angle grinder) 36 years ago. Still going.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Offline BSA_54A10

  • Wise & Enlightened
  • *
  • Join Date: May 2008
  • Posts: 2016
  • Karma: 32
    • BSA National
Re: Buggered up crankshaft thread - How to fix
« Reply #10 on: 13.03. 2017 10:01 »
If you can buy a new nut, cut he old one in 1/2 then flatten the cut end of each 1/2 starting with wet & dry and ending up on a wet stone.
Place these 2 halves over the thread at the good end, clamp with something like lockjaws and work it back off the thred.
It will clean up the buggered thread perfectly.
Bike Beesa
Trevor

Offline duTch

  • Ricketty Rocketty Golden Flashback
  • Wise & Enlightened
  • *
  • Join Date: Oct 2011
  • Posts: 4540
  • Karma: 41
Re: Buggered up crankshaft thread - How to fix
« Reply #11 on: 13.03. 2017 10:08 »
 
 Hey julian, where'd you come from, what your story?
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

Offline owain

  • A's Best Friend
  • ***
  • Join Date: Mar 2017
  • Posts: 135
  • Karma: 2
Re: Buggered up crankshaft thread - How to fix
« Reply #12 on: 13.03. 2017 20:21 »
Nice one, cheers for the advice. I've ordered a thread file to try and clean up the thread. Good homemade tip BSA_54A10..sounds a lot of work if a file does the same job though  ;)

Decided to just visually inspect the crankshaft and put it back in the bike if it looks all good. Getting the crankshaft checked is just too damn expensive. (I've set a £1000 for the quick restore/registration/sidecar).
Sweden & North Wales
'50 BSA A10
'69 BSA A75R

Offline BSA_54A10

  • Wise & Enlightened
  • *
  • Join Date: May 2008
  • Posts: 2016
  • Karma: 32
    • BSA National
Re: Buggered up crankshaft thread - How to fix
« Reply #13 on: 14.03. 2017 09:26 »
Not all that much work, about a hour if you are carefull with the cutting.
A little less if you have cut off wheels.

If nothing else do a die penetant test about $ 50 for the kit and you can do about 50 cranks with it.
I send all cranks out for nitriding without fail.
Does your budget include welding the cases when the crank lets go & send the rods through it ?
Bike Beesa
Trevor

Offline duTch

  • Ricketty Rocketty Golden Flashback
  • Wise & Enlightened
  • *
  • Join Date: Oct 2011
  • Posts: 4540
  • Karma: 41
Re: Buggered up crankshaft thread - How to fix
« Reply #14 on: 14.03. 2017 11:04 »

 Owain, I've redeemed a couple of threads with the same method as Trev suggested and it worked well for me. may be harder to find a left-hand-thread crank nut to sacrifice though. I guess it must be a 20TPI thread file?

 See i wasn't joking when I suggested;

 
Quote
Quote

    I'm having quite bit of difficulty with a hammer


    *eek* *eek* *eek*


  put the hammer down- and with your hands in the air, gently push it away from you with your foot
Modify message

   *smile*

Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia