Thread: V8 from P6 Rover into Disco 1

AFAIK all RV8s are backwards compatible so physically it should be OK.
However whether it is a good idea is another matter.

The P6 V8s had a weaker bottom end than the later V8s in that the main bearing registers were smaller and this often resulted in cap Shuffle which caused the bolts to loosen and eventually fall out. They also had a smaller oil pump than the later 3.9 and some had rope seals.

On the other hand they could be high compression which would help a bit with power but call for premium fuel. You can check by looking next to the engine number for the CR.

Regards Philip A

Righto, thanks. Lots of things to consider.

My Disco still runs sweet with the 3.9 - but i am after a spare engine for it as it has over 400,000kms on the meter and no proof that anyone before me has ever worked on the engine!
400,000kms seems like a lot for an alloy petrol V8!

So i could hunt around for someone who is wrecking a 3.9 V8 (anyone know of any?) or i could rebuild one of these 3.5s i have sitting around. The 3.5 would be slightly more fuel efficient right? If i didn't drive it too hard it should use less fuel...

Were the 3.5 engines also used in the RRC?
By rope seals - do mean actual rope used as a gasket? :O

If you swap the front timing cover, the inlet manifold and the sump onto the early 3.5 it will work just fine. However it won't be legal due to changing emissions laws. You might get away with it for years but that depends on whether your vehicle is ever inspected for rego or roadworthy.

Ok thanks.
I only just realized after seeing a lot of discos for sale with 3.5 V8s that some actually came from the factory with the 3.5L.
It looks like there is not going to be too many Discos driving around in a few years as everyone is scrapping them instead of fixing them up.

I will pull one of the 3.5s out of one of the P6's and chuck it on the engine stand to take a look at it.
Any specifics (common weaknesses) i should be looking for? I really only build old Toyota engines...
i have no idea of the condition of the engine, but i hope as it is a P6 it wasn't thrashed or anything. I mean only old people that cruise to their holiday chateau owned P6's right?

Any specifics (common weaknesses) i should be looking for? I really only build old Toyota engines...

As I said , look carefully at the registers for the main bearings. The bearing caps should be hard to remove as they fit into a small step on each side. If loose forget it. And you may find some of the bolts already loose.
Otherwise , old alloy blocks can become porous.
3.5s have smaller valves than 3.9s also.
The heads are usually trouble free except for normal wear and tear. The blocks can warp over time and may have to be line bored.

I don't think you will find much difference in economy , as the 3.5 struggles to pull a 2 tonne plus car.

IMHO, you would be better to rebuild the 3.9. It may surprise you as your cam probably has almost no lobes left by now.LOL
Regards Philip A

Thanks.
I may hunt around for a 3.9 from a parted out disco and rebuild it.
I usually try to buy a spare engine and work on it separately than my vehicles engines, as i am still driving the disco.

Are there any reputable places that sell rebuilt 3.9 V8s? *shock*horror* I could always get someone else to to the work... but that might set a precedent!

To 1977 3.5s had smaller valve heads from then they are the same size through to the 4.6 in diameter .

The Valve stems differ through the years and volumes .

The P6 had no stem seals nor did the first bigger valved 3.5s then the flat washer type was used on the inlet and then both and then the latter normal type stem seal .

The engine number of the P6 will tell its compression ratio if it is not stamped . Factory 10.5:1 is a possible for a P6

The engine number will be stamped on the back of the engine near the firewall like what the leyland 4.4 uses or in the normal place near the dipstick on latest .

The P6 will bolt in but an SD1 has more in common with a 3.9 V belt.

If you intend to have PS , AC , Electronc Ignition , etc , the use of the block and internals and heads if your happy with the smaller valves is about all that could come from the P6 .

This would be provided your 3.9 is an early V belt engine .

If your 3.9 is a single belt serpentine type the major stumbling block is the lack of a key-way in the crankshaft to drive the oil pump .

If you just want to use the P6 3.5 as is with fan , points , oil pump etc it could be done , the PS /AC pumps could be bracketed to fit and the starters although different in size will interchange .

AFAIR I think he would have to drill the front of early 3.5 heads to fit the aircon brackets and maybe Power steer brackets.
Regards Philip A