V8 from P6 Rover into Disco 1

[Finnius]

Hey folks,
I have a Disco 1 3.9 V8.
I also have a couple of V8 engines from some rover P6 cars that i am parting out.

Can i put a 3.5L Rover V8 engine from a P6 into my Disco? Are the physical dimensions, bell housing bolt patter etc the same? Can i just swap across the fuel injection manifold and all the other little bits and bobs?
Just to look at them they look very similar...

[PhilipA]

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

[Finnius]

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

[bee utey]

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.

[Finnius]

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? :)

[PhilipA]

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

[Finnius]

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! [bighmmm]

[PLR]

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 .

[PhilipA]

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

[Finnius]

Thanks for the detailed info PLR. Mine is the later single accessory belt so that would be fun getting everything to work.
Is rebuilding the 3.9s V8s that difficult? I come from the 4cyl yota engines.
I am still chasing somewhere that recons rover engines specifically - as i wouldn't trust some local guy that just does nissans with my landy engine...

[AK83]

....
Is rebuilding the 3.9s V8s that difficult? I come from the 4cyl yota engines.
....

Not that I remember, but then again I'm lazy and have never done one myself. I got a mechanic mate to do one of my P6s back in the day, but we fitted it together at my place.

In terms of finding an engine to reco, I reckon it'd be cheaper overall to find an entire V8 D1 that's no longer loved and pull motor out yourself. Once that's done resell the rest of the car minus motor.
As long as you have the room for it all that is.

Recoing the RV8 is as basic as any other pushrod v8 .. only lighter!

I've got a D2 v8 project going and it needs head gaskets, which I've decided to do myself(as the car isn't a going concern yet).
So my plan is to pull apart, take head to reco chap(he seems knowledgable in the ways of Rover v8s too, which is a bonus).
Once it's all apart, I'll then assess the condition of the block and worry that it'll turn into a full rebuild, which I don't really want to do(cost!)

I'm pretty sure there are places all over the net that sell already recoed parts for 'ya. Don't know of any in WA tho.

[PLR]

Thanks for the detailed info PLR. Mine is the later single accessory belt so that would be fun getting everything to work.
Is rebuilding the 3.9s V8s that difficult? I come from the 4cyl yota engines.
I am still chasing somewhere that recons rover engines specifically - as i wouldn't trust some local guy that just does nissans with my landy engine...


If your near or don`t mind sending to Perth , Bradtot ( username here ) is someone who could suggest an engine builder with Rover experience and someone who`s opinion rates merit in my book .

For a freshen up with rings. bearings , cam and head tidy etc , if you have the basic knowledge/experience they are an old simple design and no real difference to anything else .

Really only the lifter/tappet clearance need any special attention and that may only be a check .

Yes , if your is a serpy belt i`d think there will be easier options than the P6

[Finnius]

Thanks.

I sent a message to this "Bradtot" asking which re-builders he knows of.

If i build it myself i will get my machine work done at Harris Engines in Perth which did the machining on my little 22R.

I heard a while ago that there was a weakness in the 3.9 engines that was between the cylinder wall and a coolant passage. After time a crack can form and coolant will leak in behind the sleeve. Apparently it is often diagnosed as a head gasket problem... Anyone else heard of this?

[AK83]

and liners slipping too, hence the recommendation to go with top hat liners when rebuilding.

[Finnius]

I must be the only one who wishes the rover V8 had a cast iron block...

Apparently those top hat lines are around $100 each! :O

[PLR]

3.5s are the only ones that don`t have block coolant loss problem but can have liners move but more so after a rebore .

Brad has had a couple of 3.5s made into 3.9s which entails fitting larger diameter liners/pistons and they`re done kms .

Things tend to cost as much as you pay , someones prices may not be the same as someone else .

If your 3.9 has no coolant loss problem and it hasn`t been up high on the temp gauge the block would likely be ok .

At the age it tends to be cause and effect , like it gets very hot and then the liner problem occurs .

The ones that failed early in life have been repaired or replaced the ones that didn`t are still working unless overheated as a rule of thumb , the youngest running factory V8 are at least 12 or 13 years old now and for a 3.9 it would be at least 18 years , youngest .

Top hat liners are only as good as whoever does the job , i have a top hat block that 1 of the liners sits a full mm low in the deck so the head gasket has much trouble keeping a seal long .