Is the crankshaft knackered, or is it just the big end bearings? What happened to it for it to die (e.g. did you run it with no oil, or did the cam-belt snap etc.?)
If it's just the big-end bearings, the easiest/cheapest way to fix the problem is to remove the sump, then remove the crankshaft bearing caps one at a time (I guess the mechanic has already done this) and then fit new shells with the crankshaft still in place. You can tap the old ones out (they will rotate until they fall out) and then slide new shells into the gap in the same way.
The disadvantages of this method are;
a) You can't properly measure the clearance between the crank journals and the shells. If the gap is too big, the engine will still knock. If the gap is too small, the engine can seize/wear all over again.
b) If the crank journals have been worn then there's no easy way to measure it... you will be able to visually check whether there is any damage or wear marks but it will be difficult to measure the diameter of the crank journals where the bearings fit. (Same issue as above).
c) If the crank has other wear (runout, float etc.) then you can't fix that just with the crank in place.
But... you can 70% be sure the crank is okay. Fiat cranks seem to be indestructible.. and so you can just fit the same size bearing shells and see what happens... but at the end of the day it could be an expensive experiment and it might all end badly..
The second way to do it is to remove the crank from the engine .. this is quite a bit more work since you will probably (I don't know the 1.6 engine) have to remove the gearbox to extract the crankshaft, complete with rods and pistons attached, if that's possible.
Otherwise you will also have to remove the cylinder head so that you can detach the pistons/rods from the crank, remove the crank and then push the piston/rods out from underneath. It's all time and money.
But .. this way you can inspect and measure your crank journals properly, fit new bearing shells of the correct size (and a new/repaired crank, if yours is so badly damaged) and then put everything back with new oil seals, a new cam-belt, tensioner and water pump. This is the proper way to do it... but it'll cost you 3 times what the car is worth.
Third way is just to swap the engine for the other one. This is probably neither the cheapest nor the most expensive way to do it.
The advantage is that it will be almost as quick to do this as swapping the shells, if you need the car in a hurry.
The disadvantage is that to do it properly, the cost will increase; You should also change the cam-belt and water pump while you have the engine on the bench... and if it was me, I'd also have a look inside the sump to see what the bearing shells in this engine look like before I spend any money on it... (change them if needed).... so it could work out just as expensive as repairing your existing engine.
Otherwise, you could work on the basis that the new engine "was running okay when the car was driven to the scrap yard" and just fit it as it is and take the chance.. but if you're going to take a chance like that, then it's better to take the chance with your own engine, depending how bad the mechanic says it is... just fit new shells and see what happens.
Ralf S.
