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Antique Gas Engine Discussion Meet collectors of hit and miss engines, ask questions about collecting, restoring and showing antique flywheel engines.

Antique Gas Engine Discussion

Checking/ repair of bent crankshaft


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  #1  
Old 08-19-2005, 12:56:13 PM
Jim Gorter Jim Gorter is offline
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Default Checking/ repair of bent crankshaft

I am working on a vertical engine with wobble to the flywheel on one side. I can measure about 1/4 to 5/16 inch wobble. Is this something I should be worried about? If I was to correct it how do I go about determining the ammount to rebend and how do I go about rebending with out breaking the crankshaft? Any and all suggestions are appreciated. Jim.
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Old 08-19-2005, 09:54:28 PM
Chip Watford Chip Watford is offline
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Default Re: Checking/ repair of bent crankshaft

Jim,What brand of engine and what size?I have straightened several cranks on small,fairly common engines while still in the engine.While this could be risky,I have built a frame and used jacks on the main bearing caps and under the crank.I put a dial indicator on the flywheel rim to find the bend and jack slowly until I get it true.If you can get it within .010" you have done good.If it is a large crank or an engine that would be hard to find parts for then I would find a good automotive machine shop or crank shop and let them do it. My opinion,Chip
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Old 08-20-2005, 08:27:43 PM
Jim Gorter Jim Gorter is offline
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Default Re: Checking/ repair of bent crankshaft

Thanks for the reply Chip, Do you use any heat or just bend them cold? Thanks Jim. The engine is a vertical Ideal about 3 1/2 hp. but crank is pretty small. Jim.
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Old 08-20-2005, 09:48:09 PM
Neale Behm Neale Behm is offline
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Default Re: Checking/ repair of bent crankshaft

Jim,
You may also want to consider talking to one of the sponsors of this site with a machine shop (Craig Anderson, etc) about straightening it for you in a lathe. It will most likely be far less costly than damaging your engine while trying to reshape the crank yourself. It will probably be much closer to straight than you can do too.
Good Luck!

Thanks Harry
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Old 08-21-2005, 08:31:26 AM
Chip Watford Chip Watford is offline
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Default Re: Checking/ repair of bent crankshaft

Jim,Crankshafts are soft and bend easily which is how they got bent in the first place.They don't require any heat to bend that small amount.{1/4" at the flywheel rim is a small amount at the crank.}You could go to the time,trouble and expense to send it out which would undoubtedly be the safest and most accurate method but I like to figure out solutions to my own problems just like that old farmer would have had to have done!I have had good success but you have to decide which is the best route to go. Good luck,Chip
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Old 08-21-2005, 11:40:14 PM
Andrew Mackey Andrew Mackey is online now
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Exclamation Re: Checking/ repair of bent crankshaft

Are you sure the crank is bent, and not the wheel? You dare not try to straighten the wheel, as cast iron is very fickle about being bent twice!
Straightening a crank can have its hazzards too. If you try it yourself, and do not block it properly, it could end up with an offset - wheel true side to side, but now has a runout, as the cranl is now eccentric, or the crank could bend somewhere else - like in the crank journal! You could also induce stress fractures. R&T has just aquired a large DeLeval engine - stress broken crank at the crank throw journal! 6" of metal, snapped clean in two At least a professional shop will give it your best chance.
Andrew
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Old 08-22-2005, 10:04:26 PM
Jim Gorter Jim Gorter is offline
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Default Re: Checking/ repair of bent crankshaft

Thanks for the replys/advice guys. I will put a dial indicator on the shaft to see where the bend actually is. Im nervous about bending it back ,I may just try to live with the wobble. I have developed a few wobbles over the years and I still run ok. thanks again, Jim.
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