Engine dimension specs ?

jp928

jp928

Well-Known Member
In measuring the two big ends I have exposed in the 3.9L block I find a discrepancy in the manuals. In the P6B manual for crank pins I see metric specs of
50.800 to 50.812 given in inches as 2.000 to 2.0005 - using 25.4 a calculator gives 2.000472. In the later Discovery manual it gives the same metric specs, but inches as 1.999 to 2.000 . Everywhere I have looked inches to mm is always given as EXACTLY (by definition) as 25.4 - but without any trailing zeroes.
FWIW I make the big ends 50.805mm (Mitutoyo micrometer), and apart from a couple of scratches on No 1 shells, the other 3 bearings are unmarked, clean and smooth.
 
The discrepancy is in the manual data, not reality. 50.80 mm didnt change by .001" in the time between the wo books....
 
I worked for the BL/ROVER/Land Rover company for 38 years , many during the changeover from Imperial to SI units and it took years especially on old designs. I have found that the manuals often developed rounding errors between inches and mm , especially when they may cover 20 yrs of vehicles. Remember the original V8 engines were dimensioned in inches and then metric equivalents derived from that , later developed engines will be dimensioned in mm and inches calculated from that . It often creates issues with how many decimal places you calculate .
 
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