Author Topic: Crankshaft repair  (Read 2087 times)

Offline unclemeat

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Crankshaft repair
« on: 23.05. 2007 19:48 »
I'm in the process of having a crank reground and the left hand thread repaired where the oil pump worm drive and lock nut screw on.

Q: What are peoples thoughts on preheating the crank before laying weld down. Would it be necessary ? What temp would be required ?

Q: After the thread had been repaired, would the crank need to be stress relieved due to the irregular thermal signature of the welding process ?

Q: Or am I getting cranky by over stressing myself !? *roll*
BSA A10 GOLDEN FLASH 1954
CHANG JIANG COMBO 1968
TRIUMPH THRUXTON 2007

Offline LJ.

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Re: Crankshaft repair
« Reply #1 on: 23.05. 2007 22:17 »

No idea, sorry Uncle... But I like the Stressed Cranky bit! Hey someone will be along soon to answer your questions! Hope all goes well. *smile*
Ride Safely Lads! LJ.
**********************
1940 BSA M20 500cc Girder/Rigid- (SOLD)
1947 BSA M21 600cc Girder/Rigid-Green
1949 BSA A7   500cc Girder/Plunger Star Twin-(SOLD)
1953 BSA B33  500cc Teles/Plunger-Maroon
1961 BSA A10  650cc Golden Flash-Blue
1961 BSA A10  650cc Golden Flash-Red

Online Brian

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Re: Crankshaft repair
« Reply #2 on: 23.05. 2007 22:41 »
What part of the thread is damaged? if its only the part that the lock nut screws on its not a big problem. I had this on one of my motors because some twit had belted the end of the crank with a hammer. I set the crank up in my lathe and machined off the damaged thread down one size and then re-cut a new thread. I made a new locknut for it and it all went together perfectly and had done many thousands of miles since. I would avoid any form of welding on the crank unless its absolutely necessary. If this is possible on your motor any machine shop could do this. Could you locate another crank?

Offline unclemeat

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Re: Crankshaft repair
« Reply #3 on: 24.05. 2007 23:52 »
Thanks for the comments.
The crank is out of my hands and is most probably on its way back to me now. Wish i'd thought of turning the end down, as you say, it is the end bit where the lock nut screws on. I'v done a bit of reading on the net and there are some very clever people out there when it comes to crankshaft know-how. As the horse power output of the A10 engine isn't massive, i dont think there is too much to worry about. Saying that, it is pretty universal when it comes to good radii of the correct size on the journals - the point where most stress is concentrated on the firing stroke. Also important is to chamfer the edge of the oil holes that feed the big ends. The reason is so the feed oil is squished and nicely lubricates the shells, if there is little or no chamfering then the oil is scraped and lack of lubrication occurs.
Any comments on crank repair in general most welcome.
BSA A10 GOLDEN FLASH 1954
CHANG JIANG COMBO 1968
TRIUMPH THRUXTON 2007

Offline dpaddock

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Re: Crankshaft repair
« Reply #4 on: 24.05. 2007 23:55 »
There's nothing so special about the A-10 crankshaft that won't permit the usual procedures for its reconditioning. Find a good engine rebuilder, check that he's done similar work, and give him your specs. See the factory Service Sheet No. 207 for the regrind info.
As for the boogered thread, Brian's suggestion is good.
David
'57 Spitfire