How to strighten a crankshaft?
- Thread starter Hilmar
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Hi Hilmar, you would probably be better off starting over sadly to say. If your crankshaft was made from several pieces you might be able to unsolder them and keep the webs, then solder in a new shaft and journals. I'm not saying that straightening a compound journal crank can not be done but you had better have a great deal of patience and a lot of time. What happened that your part got the pretzel works?
BC1
Jim
BC1
Jim
I´ve sometimes tried to do just that, with meager success. IMHO it´s way faster and way more accurate to fabricate a new crankshaft than trying to unbend a bent one. I think the Stuart crank is cast steel, so it won´t snap quite as easily as if it were of cast iron. Still, if you keep on bending it, banging it with a hammer, etc., it might develop a hairline crack (or worse). My advice: make a new crankshaft. But always willing to learn, if somebody has a miraculous cure ;D
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Hilmar,
It depends on how badly it's bent and how much patience you have. If it's a matter of being bent on the main bearing line then it's fairly easy to straighten. Mount the crank between centers on the lathe and indicate the high spot. The next step depends on how stout your lathe is. Put a small bar in the toolpost and run it against the high point and put some tension on it until it moves. It's going to spring some but only go a little at a time and then recheck it. You will get the feel of how much loading to put on it and how much it moves with that pressure.
If it's twisted, one throw to the next it won't hurt the operation of the engine it's just that the throws won't be exactly at 90*.
Like has been mentioned, if it's too far out the only option is to start over, as unpleasant as that sounds.
gbritnell
It depends on how badly it's bent and how much patience you have. If it's a matter of being bent on the main bearing line then it's fairly easy to straighten. Mount the crank between centers on the lathe and indicate the high spot. The next step depends on how stout your lathe is. Put a small bar in the toolpost and run it against the high point and put some tension on it until it moves. It's going to spring some but only go a little at a time and then recheck it. You will get the feel of how much loading to put on it and how much it moves with that pressure.
If it's twisted, one throw to the next it won't hurt the operation of the engine it's just that the throws won't be exactly at 90*.
Like has been mentioned, if it's too far out the only option is to start over, as unpleasant as that sounds.
gbritnell
As others have said, straightening a small shaft is a tedious operation. My experience is that there is always some springback and as you approach straight, you have to go past straight to allow for the spring and the result is that the bend will flip to the opposite side.
My experience is with model aircraft engines where .001" bend is way to much so it somewhat depends on what is straight enough,
My experience is with model aircraft engines where .001" bend is way to much so it somewhat depends on what is straight enough,
