Wanted a 3.9 motor

[94d90va]

Looking for a 3.9 for my 90RR.
I have a hole in my block from a thrown rod.
a whole motor would be great, or a short block.
? Could a 4.2 work ?

[mearstrae]

A 4.2L would work up to '95 RRC since they have the same computer and a distributor.

'95 R.R.C. Lwb
'76 Series III Hybrid 109
'70 Rover 3500S

[94d90va]

Is the 4.2 a bored out or a stroked 3.9 ?

[mearstrae]

Ok, the 3.9 (and the 4.0) have a 71mm (2.8") stroke and a 94mm (3.7") bore. The 4.2 is also 94mm (3.7") bore but a 77mm (3.03") stroke. So, it's stroked.

'95 R.R.C. Lwb
'76 Series III Hybrid 109
'70 Rover 3500S

[94d90va]

Cool,
Will my 3.9 heads work with the 4.2 ?
Any other accessories transferable ?
Thanks for the info,
Tom

[mearstrae]

Should all be compatable. If you're putting on new head gaskets, I suggest you use an ARP head stud kit, they're expensive but they take the stress off of the block and hold the head tighter and more even than the "Torque To Yield" head bolts, thus harder to blow head gaskets. Not everyone agrees with this, but I've never done the job twice using head studs (and all my vehicles are V-8's). i also use permatex head gasket sealer spray, also something some don't agree with.

'95 R.R.C. Lwb
'76 Series III Hybrid 109
'70 Rover 3500S

[94d90va]

thanks,
the 90RR runs a ZF4HP22 transmission...ok for the 4.2 ?
got a 4.2 short block laying around ?
tom

[Boston]

Not a problem

[94d90va]

anyone of a source for motors ? 3.9 / 4.2... used but rebuildable.

[bmoreclassic]

anyone of a source for motors ? 3.9 / 4.2... used but rebuildable.


I have a good running 3.9 out of an 95 RRC I recently converted to Diesel. Take it. It's just sitting in my shop asking for a new home. I still have the truck under construction so you're welcome to come see the vehicle it was removed from.. I've had several of these trucks and my daily driver is a second 95 RRC so I know them very well and this truck and engine are in great condition and are in Downtown Baltimore.