The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: owain on 12.03. 2017 18:21
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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?
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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.
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I'd use a thread file.
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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
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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.
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You can get LH BSF dies from Tracy tools - (http://www.tracytools.com/taps-and-dies/left-hand-thread-taps-dies-bsf) - good luck!
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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.
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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.
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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.
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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
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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.
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Hey julian, where'd you come from, what your story?
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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).
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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 ?
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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
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*
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Trev's tip sounds like a good'un.
"sounds a lot of work if a file does the same job though"
Using Trev's method there's every chance a lot of the distorted thread can be persuaded to reform. A file is only going to remove metal.
I've had success in the past using a small chisel and very small (!) hammer, to gently push deformed metal back into place, rather than file it away. Not so good for major distortion though.
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Don't blame me, it was a "penny fix" from 1949
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If you saw a post here that is no more, it's because I reconsidered how much thread damage there might be. Is it more than just the lead in and next thread after that?
Richard L.
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Not that I can tell RichardL. It just seems to be the lead and a thread after that. I'm waiting on the file to arrive to clean it up and make it usable!