hi rebuilding a 3.9 using parts from my old 4.0 ltr.
problem ive got is the timing cover fits ok with the camshaft sprocket plus oil pump , but the 3.9 crank is to short for the front pully.

can the 4.0 ltr crank be fitted into the 3.9 block with its own bearing.

any body done this before.

many thanks

the 4.0 crank will fit if it has the same size main bearing journals as the 3.9. some older 3.9 were the smaller type. It depends what year the 3.9 is.
Just measure them against eachother.

3.5's, 3.9's & 4.3's have the short nose crank but their journals are small (2.0in/50.8mm big end & 2.3in/58.4mm main) unlike the 4.0 & 4.6 which have large journals (2.185in/55.5mm big end & 2.5in/63.5mm main) so a 4.0L crank won't fit a 3.9 block without machining it down. the 4.0L & 4.6 also have long nose cranks hence why the 3.9L crank won't reach the front pulley when using your 4.0L cover etc.


My 3.9 is a late interim block with a 10 bolt head and the p38A block but it is not drilled for the X-bolts (but can be drilled and tapped)