3.9 engines

[Pocket rocket]

Gonna show my ignorance here but what the hell

A friend has to have a rebore on his standard 3.5 RV8 so i suggested that he think about going to 3.9 - i was under theimpression that the 3.9 is just a larger bore 3.5 and since he has to change the pistons anyway...

He's been told it would require new liners - is this right?

[adamnreeves]

Rover 3.5 actually 3582cc is achieved with a bore of 3.5" (88.9mm) with a stroke of 2.8" (71.12mm)

Rover 3.9 actually 3947cc is achieved with a bore of 3.702" (94.04mm) with a stroke of 2.8" (71.12mm).


As you can see the difference is the bore requiring a over bore of some 0.202" (5.14mm), I suspect they are right, taking this amount of material out of the block requires new liners to be fitted.

My greater concern would be potential porosity issues arising from performing this. Even Rover had problems with 3.9 because the bore means that the water jacket at best is only 2.2mm from the edge of the bore!

I am not sure if the blocks were graded at this time, if they were you need the red graded block. Personally I think not worth the risk or cost. I would recommend going for the standard rebore/hone.

[Richard]

Been there, done that. Yes, you need to fit new liners, preferably "top hat" liners to reduce the risk of them slipping. There are gains to be had, but it's not worth the cost or risk. Stick with the 3.5 bore, or get a factory 3.9/4.0/4.6 block.

[katanaman]

what Richard said, my engine is a 3.5 re-linered to 3.9 works fine but can be a risk.

[softdash3.9]

I had my 3.9 block fitted with top hat liners recently, obviously same process for a 3.5 block. Had Thick liners installed so that, if I wanted I could increase piston size to @96 mm, although I never will, probably

Top hat liner also gives a better seal, i.e liner to head rather than block to head.

Would be happy to recommend the machine shop I used up north, cost @£1100 fitted, bored to suit and new camshaft bearing inc vat

[Pocket rocket]

Thanks for the replies.

Been pondering this and I think my problem was that i assumed the liners went into the same size "hole" in the block, regardless of whether it is 3.5/3.9. Presumably the bigger engine has a larger diameter "hole" to hold the liner . Makes sense when you think about it but the cold dulls my already slow senses

[katanaman]

yes the block itself is bored larger which is why it could be a risk if the block itself is a little thinner than it should be.

[adamnreeves]

Yes, the best bet is to get a 3.9 seasoned block could be cheaper as well as less risk.

yes the block itself is bored larger which is why it could be a risk if the block itself is a little thinner than it should be.

[alex]

At £1100. you are nearly up to new standard 4.6 or 4.0L short engine prices if you look around enough.

[HairbearTE]

Softdash was it B+H who did the work for you? i've spoke to the guys there but never delt with them. I might be in the market for T-hats and would have the 96mm bore too. On the other point, when building an engine i would normally agree that a "seasoned" block has its benefits. However in the case of the RV8 you can take seasoned to mean "block is cracked behind liners on back four bores!". I know the T-hats prevent movement up and down the bore by the liners but the structural damage is done to the block and surely its ability to hold an interference fit is compromised. A used block that isnt cracked behind the liners is the best starting point but you're gonna have to spend a little cash to verify this. I recently snapped up a rare 3.5 X-bolt block that shouldnt be cracked as the wall thickness behind the liner is much greater and should therefore give me an excellent base for a build up. If you do go with a new 4.6 block for your kit car or rod etc. then you should be ok without T-hats if you make ample provision for cooling and use an appropriate thermostat. The main reason 4.6's crack is that they run too hot in the cramped RangeRover engine bay while sat in traffic every day etc. The thin wall design is only part to blame. Now that the engines are being manufactured once more for spares i would love to know if any slight changes/improvements have been made to the block, anyone in the know?

[racer]

[quote="alex"]At £1100. you are nearly up to new standard 4.6 or 4.0L short engine prices if you look around enough.[/quote]

Those days and prices are long gone..if they were ever here. Since the demise of the engine..new blocks are flowing in a trickle and what is there is often beset with problems. If a 4.6/4.0 is desired, get a rebuild.

If the friend wants to keep the block (not a bad idea) AND want more power cheaply, tell him to get a stoker kit. That will add the cost of a new crank and rods to what he is already paying but add no extra labor and involve no block alterations.

It will transform the engine into a 4.3 Litre with immense torque.

racer

[alex]

As I said NEARLY.
Been looking around in interweb found
RPI std 4.6 short eng £1950 +vat+ surcharge
DJE std 4.6 short eng £1950 inc
ASHCROFT 4.6 short eng £1600+vat outright
4.0 are slightly less

If im not supposed to put prices then please edit, but these are easy to find on any websites.
It all depends on how much is enough for you.
Alex

[katanaman]

Which Ashcroft are you on about?

By the way your prices are a little off RPI is for 4.0, DJE doesn't state but its probably for the 4.0 as well (tho I could be wrong) plus he want an exchange. Add that lot together and your NEARLY twice the price.

[alex]

Ashcroft transmissions.
Looking at their newsletter.
It could be less if you have been shopping with them 3 times.
Sorry if i got prices wrong at rpi. but core charge is £100.00
DJE says 4.0/ 4.6 std as factory spec £1950.http://www.djev8.com/page11.html
Alex

[katanaman]

Ashcroft site just says POA really good price if it is 1600 all in.