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Old 12-08-2017   #1
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Standard Crankshaft Dimensions

I've had my spare, spare, spare engine in bits for some time so decided to get it measured to see if it needs any machining for a rebuild. So I bought a cheap set of micrometers and set to work. I am new to this art but I do (now) know how to calibrate and read them.

The big-end journals measure up to be just very minutely worn from standard but in no way oval and fairly close to each other in dimension. But the mains, after several attempts and careful checking of my settings, appear to be just slightly under 0.5mm bigger than standard. That can't be right can it/ Or does anyone know different?

Maybe I need to spend more on my tools?
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Old 13-08-2017   #2
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Re: Standard Crankshaft Dimensions

When measuring journals on any engine that has been in bits for a long time.....

You need to remove the rust before measuring the journals

Al.
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Old 13-08-2017   #3
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Re: Standard Crankshaft Dimensions

An engine machine shop would use a "tenth" micrometer or metric equivalent to get the necessary accuracy. A tenth micrometer measures in 0.0001" increments. Not sure why but the undersides for the big ends are in 0.010" steps but the mains are in 0.2mm (0.008") steps
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Old 13-08-2017   #4
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Re: Standard Crankshaft Dimensions

I'm used to bodywork rust measuring many thousandths of a millimetre Al, but fortunately the crankshaft is still shiny. I'll have another play with it and try to get a close-up of the rogue measurement and hope someone more experienced can read it differently.
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Old 14-08-2017   #5
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Re: Standard Crankshaft Dimensions

After a steep learning curve I'm now satisfied that I obviously don't have a rogue crankshaft and I was actually reading at the wrong side of the 54mm line on the vernier. This was giving me 0.5mm in an over-read.
So the main bearings are found to be just slightly worn from standard and are not oval.

The big-ends are slightly worn from standard but are smooth and nowhere near worn enough to justify a regrind. So I have yet another engine rebuild which doesn't involve that major engineering job. My next challenge will be to measure the running clearance when I get a set of new bearing shells.

Onwards and upwards to measure the camshaft and then the cylinder barrels.
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