Big end measurements for 2l - how much wear is acceptable?

[akershaw]

Hi, a garage fitted a brand new 131 2l engine to my 1800 Spider a few years ago. Seems to be from a Supermirafiori from the early '80s. Engine no: 131C4000, block 4356114 132DB.2A, crankshaft 4370092 and big end shims 5951741. I've just been checking the crankshaft for wear as part of a multi-year restoration and am getting some odd numbers. Crankpin is coming in at 50.84mm and shims are coming in at 1.50 in the centre, and 1.47 towards the ends. The official data sheet I've seen for the 131 2l shows the crankpin 50.792-50.802, and shims 1.533-1.537 (although I've seen elsewhere that they would originally have been 1.57, and in fact they're marked '157' at one of the ends). I've checked these measurements with a couple of different vernier callipers and in a couple of different places. So my question is, why is the crankpin bigger than the max of the tolerance range stated in the documentation? Does it start bigger than the tolerance range and move into it? If so, why does the documentation state a range, and not just a minimum diameter? If I need to replace my shims, how do I calculate the amount of oversizing for the replacements? Many thanks for any help with this.
Alex

[Odoyle]

Alex,

Main bearing journal standard diam. is 52.985 to 53.005mm.
Main bearing saddle bore is 56.717 to 56.730mm.
Crankpin standard diameter is defined in two classes, Class A (50.792 to 50.802mm) and Class B (50.782 to 50.792mm)

As for the rear main bearing thrust rings (standard), spec is 2.310 to 2.360mm. Thickness will taper to its lowest around beginning and end of the insert. *Side note (I just rebuilt my 1800cc and found that the the thrust rings I purchased to replace old ones (supposedly quality parts made by Glyco/federal mogul) were actually thinner at virtually every point than the 41 y/o thrust rings... concerning I know. Just goes to show, that just because something is new, doesn't make it better or even right.

[engineerted]

Alex, first off you can't accurately measure the crankshafts using Calipers. This requires Micrometers and i assume when you say "shims" you mean Bearing shells. Yes the Big end pin size is (50.787-50.807) std. bearing thickness is (1.523-1.536). Yes the bearings are tapered toward the end, this is done on purpose.

The 2l crankshaft is nitrided from the factory and typically does not wear much at all unless there is some sever scratches and grooves present. I just contribute the high number to inaccuracy of your calipers.

[akershaw]

Very helpful thank you. Good to know about the callipers, and yes I did mean bearing shells. Given the likelihood that the crankpins aren't very worn, perhaps I'll just buy a replacement set of standard bearing shells. Alex