PM #1 crankshaft

[kmanuele]

Was making good progress on the crankshaft, running true, good fit in the base, etc., until I cut out the filler.

There must have been some built-in stresses, as the two shafts are no longer in line. Put between centers there is now about 0.012" runout at each web.

The two webs apparently tilted inward slightly when the filler was removed.

I'll finish it and see if it becomes a problem at final assembly. I can't think of a reasonable fix. Can cast iron be bent ?

Anyone else experience this?

 

[tq60]

Relieve the stress.

Put between centers.

Use a chisel and GENTLY ap the corners of the journal.

The part comes towards the chisel, the dent relieves the stress.

It is how we did real ones in the day.

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[kmanuele]

Interesting, and thanks.

Did you mean the inside corners (blue arrow) of the rod journal? After machining?

 

[tq60]

Yes, if the direction needed is upward.

It does not take much to make it move a lot.

I will guess that it may move more as it is being turned as the casting shell is removed.

So first action is to get it straight.

Not sure how you are offsetting it, likely in a 4 jaw that is offset.

First cut is reference area in the center of the journal.

Only wide enough to allow your measuring tool to make measurements.

Determine a way to hold this that will allow you to remove for measurement and return easily in correct phase.

Once you have an area that is round in the journal and good finish, remove and put back in centers and straighten as needed.

Return it to lathe, use a dial indicator on the round part to get the crank in phase with the lathe, stable zero whole turning.

Now make this area wider towards the sides, just short of the chisel marks.

Remove and straighten.

Return to lathe and do one side to face of web, repeat straighten.

Do other side and straighten.

Now you have the crank almost done.

You can either make the rod fit this size, or continue the journal to final size, just be aware it may move a bit as you turn it.

You can use a file to smooth out chisel marks.

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[benmychree]

Cast iron indeed can be bent, how much, depends on the type of alloy. tq60s advice is right on line.