Swapping a 3.5 for a 4.6

[simon]

I've been offered a 4.6 rover engine short engine. Can I just swap over my 3.5 heads and ancilliaries?
Thanks
Simon

[tonym]

You certainly can assuming the front ends are the same, the 4.6 probably has a serpentine front end, check to see if this comes with the short engine, if not then your 3.5 front end will probably fit, although to get some hp gains you might want to upgrade your heads, just my opinion :thumb:

[kev]

Probably not.
3.5 front end won't fit on a 4.6, the crank is longer on the 4.6, a spacer is needed.
3.5 heads are 36cc, 4.6 heads are 29cc, so your cr will be shot to bits.
Sump is different, you'd need to check.
Fuelling will be totally different so it very much depends on your intakes.
Ignition on the 4.6 is 4 coil lost spark, 3.5 it's single coil and distributor.

The swap can be done but you'll need to spend some money, main issue is the front end/ignition, they are interdependent.

Kev

[tonym]

Originally Posted by kev

Probably not.
3.5 front end won't fit on a 4.6, the crank is longer on the 4.6, a spacer is needed.
3.5 heads are 36cc, 4.6 heads are 29cc, so your cr will be shot to bits.
Sump is different, you'd need to check.
Fuelling will be totally different so it very much depends on your intakes.
Ignition on the 4.6 is 4 coil lost spark, 3.5 it's single coil and distributor.

The swap can be done but you'll need to spend some money, main issue is the front end/ignition, they are interdependent.

Kev

Mmmm, i was under the impression the front cover of a 3.5 fitted a 4.6 block but agree a spacer will be required to bolt the damper down. the c/r on the heads will be ok if you use tin gaskets rather than composite. fuelling will be anyway you want depending on which carb/efi route you take. ignition will be single coil and dizzy if you use the 3.5 front cover OR 4 coil/lost spark with an aftermarket ecu on efi (megasquirt etc.) so i still think it can be done

[craggle]

3.5 front cover should fit straight on.
Spacer is needed to stop the pulley going too far on the crank.
3.5 sump will fit as long as you have the 3.5 front cover. Spin the engine over to check for crank clearance before starting!
Use a cam shaft that has the space to fit the original 3.5 distributor drive gear on the front and stick with the original distributor. Forget the coil packs.

If you are offered a cheap 4.6 engine ask why. These were only fitted to Range Rovers and they had a habit of getting too hot. Bad fuel maps for economy, small radiators and owners not checking the water level often enough led to overheating. A 4.6 engine is well known for cracked liners or liners that have dropped down the bore slightly allowing cooling water to seep past the liner into the bore. The only permanent fix is to have the block re-sleeved with top hat liners. This can cost more though than buying a new 4.6 short engine from one of the specialist V8 dealers.

Be careful

Craig.

[osgood]

Originally Posted by simon

I've been offered a 4.6 rover engine short engine. Can I just swap over my 3.5 heads and ancilliaries?
Thanks
Simon

Simon The old front end will fit on a 4:6 block with no mods, as said the nose of the crank is longer so a spacer will have to be made up. Once the old front is fitted your old sump will also fit with no modifications required together with your old oil pick up pipe.

Osgood

[osgood]

Originally Posted by simon

I've been offered a 4.6 rover engine short engine. Can I just swap over my 3.5 heads and ancilliaries?
Thanks
Simon

Simon I will stand corrected on this but I don't think you will find any difference in the combustion chambers, the 4:6 heads are pretty much the same as the 3:5, 3:9. 4:00 & 4:2 with the same size valves,The CR is controlled by the piston dish in comparison with the bore size, I have recently fitted 8:4.1 pistons in my 4:6 ready for supercharging.There is however a bit more space within the inlet and exhaust ports but the exits & outlets are the same size. Just fit your old ignition system (Dizzy coil etc)and all will be okay. As said inlet manifold will also fit but require a bigger carb W.H.Y. I have built many Rover engines of all sizes and most all parts interchange Osgood

[kev]

Originally Posted by osgood

Simon I will stand corrected on this but I don't think you will find any difference in the combustion chambers, the 4:6 heads are pretty much the same as the 3:5, 3:9. 4:00 & 4:2 with the same size valves,The CR is controlled by the piston dish in comparison with the bore size, I have recently fitted 8:4.1 pistons in my 4:6 ready for supercharging.There is however a bit more space within the inlet and exhaust ports but the exits & outlets are the same size. Just fit your old ignition system (Dizzy coil etc)and all will be okay. As said inlet manifold will also fit but require a bigger carb W.H.Y. I have built many Rover engines of all sizes and most all parts interchange Osgood

If you use the 3.5 heads on the 4.6 block you should use the tin gasket otherwise you'll lose 05:1 off your cr. Rover took about 20thou off the head to reduce the combustion chamber size to compensate for the thicker composite gasket.

Kev

[osgood]

Originally Posted by kev

If you use the 3.5 heads on the 4.6 block you should use the tin gasket otherwise you'll lose 05:1 off your cr. Rover took about 20thou off the head to reduce the combustion chamber size to compensate for the thicker composite gasket.

Kev

Yes I sand corrected Kev, same size chamber but not so deep Osgood

[osgood]

Simon on the subject of heads again it may well be more advantageous to have 20-30 thou skimmed off so you can use a composite gaskets instead of using the old tin ones, not a bad idea to have the heads licked over anyway on a rebuild.

As regards camshaft if you were going to upgrade to fast road / sports etc, as no stuff is available for the 4:6 I had the cam I used last time machined at the end so I could use the 4:6 retaining plate to keep cam in check. Just copy the recess from the old 4:6 cam re your local machine shop.

Hope this helps Osgood.