Having already assumed that it will be OK for re-use without re-grinding, I'm trying to get to grips with measuring my 650 crankshaft, just for peace of mind. I know I should take it to the machine-shop for a verdict and that my digital calipers can't achieve the accuracy of a micrometer; but I'm an awkward so and so and want to do it myself. But I can see the comparative sizes of the journals and identify that they are not oval.
The issue is that one of the main bearings appears to be 0.05mm bigger in diameter than standard; but I'm going off the specifications in my 500 manual.
Please can anyone confirm the standard journal sizes, 650 engine, from a source other than Haynes for the Fiat 500.

Thinking back, I surprise myself that I rebuilt my 500 engine, which has proved to be totally sound and reliable, without measuring any of this. I did replace the big-end bearings and had it re-bored with new pistons, but the mains were simply cleaned and popped back in.

Photo of the 500 crank:
KNO_6869 by Peter Thompson, on Flickr

Morning Peter;
I have a FACTORY work-shop manual---I will copy out the appropriate pages and put them into the post to you.

The sizes shown in the Haynes manual are all a match for the official Fiat specifications & data apart from the max main bearing undersize which should read 0.8 and 1.00 mm not 0.9 mm but having said that I have never seen 1.00 mm bearings anywhere. If your mains are larger than 54.050 mm on the internal diameter then they are outside the tolerances.

Toshi 975 said:

If your mains are larger than 54.050 mm on the internal diameter then they are outside the tolerances.

Click to expand...

Thanks for that offer Tom I regret selling a 126 manual I used to have but that's me...the Clearout Kid!

Dave, that is useful to know. My measurements are taken of the crankshaft journals. I am fitting new bearings in any case. It is obviously most likely to be my measuring "technique" or a badly calibrated, almost brand-new, Lidl vernier gauge, as having a worn crank that is bigger than spec. seems unlikely.
It's just that the gauge seems accurate when measuring other known dimensions.

Hi Peter;
The letter, with copies of the appropriate pages, was put into the post this morning (1st Class)--you should get it tomorrow, or Monday at the latest.

Thanks Tom....first class all round; you, the Royal Mail and the information.
So it's pretty conclusive that I must be measuring incorrectly.
I give in and will take it all down to our very precision engineers in Inverness for an experienced opinion.

A flash of inspiration:idea:
With Tom's factory dimensions and the brand new camshaft supplied by the great Toshi:worship:, I was able to calibrate my vernier gauge properly. Common sense really; I needed to use more force in gripping the journals between the calipers. So I found the camshaft had spot-on measurements, as should be expected. Returning to the crankshaft, based on the difference between the average of two measurements taken at right angles to each other on the journals and on the median of the specified tolerances for a standard crankshaft, I find that the rear main is worn to 0.040mm and the front main to 0.010. The big ends are worn 0.057 and 0.083mm. There is minimal ovality so I feel authorised to proceed onto initial assembly.