Thread: Rebuild a 3.5 a 3.9 or something else?

Originally Posted by aRRon

Whenever I read these 3.9 liner stories the fear comes back. I read one not long ago that said 50k after a recondition if you're lucky, before a slipped liner will occur due to weakness in blocks, cracks and leaks behind the liner wall etc. So I'm right on 51k since a rebore and new pistons, bearings, valve gear etc inlcuding a new liner in No1 cylinder. The original liner got deeply scored by a piece of tin head gasket that failed. Hadn't slipped or suffered cracking/corrosion behind it. Now I'm sure a head asket has gone again after a mild overheat about six weeks ago (broken fan belt and gauge did not reach maximum before stopping - no loss of coolant). Gobs of cream under rocker covers, water in intake plenum, steam from exhaust.
Heads off tomorrow! Expecting the worst.

I read somewhere that the liners are marginal sometimes due to manufacturing techniques and tolerences of the parts and the ones that were measured up well went into the 4.6.

Regardless of whichever (later) motor you fit to your vehicle you will need to transfer the inlet manifold and injectors off your current engine to your replacement engine, not exactly a difficult job. That is so all your wires and EFI computer work as before, the later engines use different systems. No Disco used a flapper based EFI. You could upgrade the whole EFI system to a later one but that involves some wiring challenges.

The exhaust outlets on the heads are exactly the same for all the different engines but there are differences in the equipment bolted to the front and bottom of the engine block. Once again, you will probably have to transfer some parts off your engine to make it work. This has been done many times so the information for whatever donor engine you find is easily searchable.

Originally Posted by lidvii

The motor in my '88 RRC is in a similar condition. Worn cam, noisy lifter and blowing smoke.

If I buy a 3.5 (Flapper) motor from a Disco or RRC I'm guessing fitting the replacement motor should be straight forward? The Fuel Lines, Throttle linkage, exhaust manifolds, etc should all line up and connect in the same way?

Is that also true if I buy a 3.9 motor?

Lastly if I was lucky enough to find a 4.6 then I think I need to do more work? Will the exhaust system from my 3.5 bolt up or are mods required there?

Almost forgot. My 3.5 is dual fuel. A cheap mixer system plumbed in before the flapper. With a 'new' 3.5 or 3.9 motor am I Okay to keep the old flapper and connect to the new plenum on the replacement motor?

Paul