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Discussion Forum

Can rotary mower BS crank be straightened? How?

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Truck

07-15-1999 08:25:17




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A buddy gave me his shiny new push mower he had hit a rock with. It is one of those supposed mulching types, with a LOT of crankshaft extending down from the motor. I would guess there is about 3/4 inch of wobble by the time you are at the end of the crank. He was still using it until the carb shook right off....

Are we in for a new crank, or is it possible to straighten the crank with a press and v blocks and a mike? HAs anyone expeience with this?

By the way.. he already bought a new mower.. The John Deere push mower was the closest he will ever have to a JD, so he got one!( And I had 3 mowers here not doing anything at the time, too!)

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Eric Lewis

08-29-1999 10:31:04




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 Re: Can rotary mower BS crank be straightened? How? in reply to Truck, 07-15-1999 08:25:17  
Yes the shaft can be straightened if you want to expend the time and effort. I"ve staightened a few in my time and it is very laborious. Straightening a shaft of course entales removal of the shaft, meaning engine tear-down. I used an a-frame press and hydraulic jack with machined radius' to fit the particular shaft. When I thought I thought I was close to having it straighted, I mounted the crank in my lathe and applied a dial caliper. I then marked the eccentric areas and returned to the press. I was able to achieve concentricity of .062", or 1/16" out of round at the blade mounting plate end. after several attempts to correct the condition, I still was only able to bring it into within a 32nd. Being the perfectionist I am, i wanted to restore the blades running trueness. I re-attached the blade mounting plate to the shaft and returned it to the lathe. I then faced the blade mounting plate true to rotation, if this is not done, the blade will wobble up and down, that is one end of the blade will cut above the mounting center and the other end will cut below the center. I used the mower for two years after restoring the shaft and then sold it to a friend who is still using today after six years. I hope this message will give you some insight!

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gary peck

05-06-2002 10:44:02




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 roto hoe 990-2 tiller in reply to Truck, 07-15-1999 08:25:17  



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john d

07-15-1999 09:44:47




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 Re: Can rotary mower BS crank be straightened? How? in reply to Truck, 07-15-1999 08:25:17  
Yes, they can be straightened. No, it's not always (perhaps often) satisfactory.

There are two basic considerations in this. (1) Getting the crank straight enough, and (2) getting it to bend straight in the same place it bent the first time!

If you have V-blocks, a press, a dial indicator, and LOTS of patience, you can probably do it. Keep in mind that the crank will almost certainly be weaker in that area than before, and subject to fracture if it hits something again. Also, check the bearing in the lower part of the engine to see if it suffered damage when the crank bent.

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GEO

07-16-1999 14:07:05




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 Re: Re: Can rotary mower BS crank be straightened? How? in reply to john d, 07-15-1999 09:44:47  
There is a crankshaft straightener that can be bought. It claim you can straighten 7/8 and 1 inch shafts on Briggs in 7 minutes without dismantleing engine. They sell for 150.00 to 195.00.



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Mike H(MD)

08-24-1999 14:37:53




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 Re: Re: Re: Can rotary mower BS crank be straightened? How? in reply to GEO, 07-16-1999 14:07:05  
but for around $75.00 you can replace the crank and not have to worry about the shaft breaking when you least expect it



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