Simple Tools For Straightening A Small Crankshaft

[Micke S]

I made a fixture today for measuring the runout of a small cranshaft. I also modified a hammer by replacing a plastic end piece with a 35 mm solid brass bar. The hammer is used to punch the crank until the runout is 0,03 mm maximum (just above a thou). I was able to get i down to about 1/3 thou after a couple of attempts. The gauge reads 0,01 mm/division.

 

[randyc]

Very nice work !

 

[rgray]

Did the brass stand up to it well? I always used a lead hammer and have to recast it when it gets to deformed.

Those little cranks are a breeze after doing twin cylinder ones.

 

[brino]

Hey Micke,

I am unfamiliar with how you straightening a crank shaft.

The upright holder you've made is for measuring only right?
How do you position and hold the shaft for straightening?

What do you mean by:

The hammer is used to punch the crank

Would the same technique apply to say horizontal mill arbours, or even bent drill bits?

The only references for shaft straightening I've seen, they mount the shaft between centres in something resembling a lathe, but then pry against the tool base.
No way would I do that on my lathe.

Thanks for any enlightenment.
-brino

 

[iron man]

I use to race moto cross when I was a kid that would have been real handy when I had to split the crankshaft on mine to replace the rod bearing nice work! Ray

 

[Micke S]

Thank you guys for the encouraging words.

Here is a video that shows how it is done. Creds to the guy who made the fine presentation.

 

[Micke S]

Hey Micke,

I am unfamiliar with how you straightening a crank shaft.

The upright holder you've made is for measuring only right?
How do you position and hold the shaft for straightening?

What do you mean by:

Would the same technique apply to say horizontal mill arbours, or even bent drill bits?

The only references for shaft straightening I've seen, they mount the shaft between centres in something resembling a lathe, but then pry against the tool base.
No way would I do that on my lathe.

Thanks for any enlightenment.
-brino

Hi !

I hope the video in the previous post answers all your questions.

I wouldn't use my lathe either to hold the crank when it is straightened. But the lathe can be used instead of the jig to measure runout if the crank is held between two centers.

 

[brino]

Thanks Micke, now I understand. It's about realigning the two part split crank on reassembly after replacing the connecting rod and/or bearing.

It's only 7:27am and I've already learned something today.

Thanks!
-brino

 

[Micke S]

Did the brass stand up to it well? I always used a lead hammer and have to recast it when it gets to deformed.

Those little cranks are a breeze after doing twin cylinder ones.

The brass wasn't deformed noticeably. It is a light crank though so it doesn't need to be hit from an over-the-head swing