Guest hodgie Posted July 14, 2004 Report Share Posted July 14, 2004 Right, I did research this a while ago, but have forgotten the specifics. Can anyone enlighten me. Having just rebuilt and instantly destroyed my newly rebuilt 3.5, I am looking at going up to 3.9. There seem to be a few 4.0 lumps around at the mo' for reasonable money. i have a new hot cam that I intend to chop across along with timing cover/ heads etc. I know that the crank is different with a longer 'nose', bu tcan this be overcome as simply as by fitting a spacer? Is there any other difference that will stop me chopping cam etc over, such as different cam bearings? I think not, although of course the pistons, rods and crank are different I understand that the rets is interchangeable. Anyone? Quote Link to post Share on other sites
andrewt Posted July 15, 2004 Report Share Posted July 15, 2004 hodgie There are two 3948cc engines. The early ones use the 3.5 crank, rods, etc but with 94mm bore instead of 88mm. These are the classic Range Rover and majority of Discovery engines if i remember correctly and are designated as 3.9. The later engine, designated as 4.0 to differentate it, is identical in bore and stroke but has the longer nose crank, larger crank journals etc. It can be used with the SD1/Tr8 timing gear by using a spacer to locate the front pulley properly. Apparantly you can also use the serpentine front end and use that in the Tr, but I have no personal experience of this. You can buy liners, pistons, rings etc and convert a 3.5 to be a 3.9, and this is in fact basically what the early factory 3.9s were. As long as the fuelling is correct this is not a problem. The problem with these engines was excessively lean mixtures from the factory Land Rover ECU (for emissions & economy) causing too much heat in the block thus causing the alloy behind the liner to crack and coolant to be pumped out by combustion gases passing round the liner. This happened to the block i have, hence the reason the previous guy sold it! Pity the exact reason wasn't clear to me until i worked out why i blew coolant out all the time but you live and learn. As a result i have an as good as new set of internals for a 3.9 short engine for sale, minus flywheel, cam, pushrods, heads & front end gear. (Block is not worth repairing as the repairs apparently tend to not last very long) The reason i am not using it is that i have fallen over a brand new 4.0 engine that i am going to use. If you are interested i could let you have this assembly. it has done 1600 miles since rebuild. At that time the rings were new, all the bearings were new, the crank was polished and the entire assembly was balanced by Basset Down balancing. There are also ARP bottom end bolts & rod bolts. You would need a linered block, your own heads, cam, pushrods etc, but these should still be ok from your old engine. My thought was to liner my old faithful 3.5 block (which needed a bore anyway) and build that up & sell it all on. However if you wanted to buy it as is I am open to sensible offers. Liner kits are £128.08 inc vat from Rimmers so could probably be found cheaper elsewhere. This way you have the best chance of a block you know is good, instead of one that could last a week, a month or a year. Drop me a mail if you want to know more. Go for it, during running in at 3000rpm i was showing 125bhp at the rear wheels with a real steel cam. This was on a very early map on my ecu, it has improved noticeably since then, but even though i have been mapping on the road it has not been back on the rollers until i got to the bottom of the coolant issue. The 3.9 is a big step up from the 3.5 i would thoroughly recommend it. Cheers Andy Quote Link to post Share on other sites
Guest hodgie Posted July 18, 2004 Report Share Posted July 18, 2004 As it happens my internals were brand new. Pistons/ rings, crank, bearings etc. Someone who shall remian nameless forgot to put water in the engine! Ouch! Ring broke up and scored the bore hence lots of smoke. Poblem is to rebore the engine to 3.9 my local shop want something silly, so figure I might as well just buy a new short block and there are a few 4.0 litres around. Quote Link to post Share on other sites
andrewt Posted July 19, 2004 Report Share Posted July 19, 2004 Ooops, of course you can always pick up a second hand 3.9 or 4.0 as well, they seem to go at around £400 - £500 second hand. Though you run the risk of picking up a cracked one like i did. Hence why i bought a new 4.0 short. I got it from RPI Engineering, though the prices are consistent from most places. Best of luck with it anyway & as i said above go for it, it is a big improvement. Andy Quote Link to post Share on other sites
Guest ajttriumph Posted July 19, 2004 Report Share Posted July 19, 2004 take the crank from leyland 4.4 engine (i think that they were in trucks in the uk) line bore the 3.9 to suit the bigger journals and yiou have just over 5litres of rover power and heaps of torque. there is a few people here in australia that have done this with much success. i have heard of a (claimed) 240KW with Haltec fuel injection with a reliable engine more if you get silly. Quote Link to post Share on other sites
andrewt Posted July 19, 2004 Report Share Posted July 19, 2004 It is the Haltech injection i am using & i have found it very easy to use. The nice thing is that fuelling changes can be made in real time so the effect can be instantly seen. The nice thing about the 3.9/4.0 option is that the stroke is nice & short meaning the engine is still quite happy to rev. Also the standard box, axle etc is happy with this amount of torque whereas i would want to change at least the box if i was running 5litres. Cheers Andy Quote Link to post Share on other sites
Guest fezman Posted August 7, 2004 Report Share Posted August 7, 2004 I would say all else equal (cost etc) the 4.0 is a better motor. IIRC it has a few structural improvements such as 6 bolt mains (crossbolted) same as the 4.6. Not to mention the fact that they are newer helps. I would say get the 4.0 and use your cam with it, and you can always throw in a 4.6 crank (or the 4.4 if you're daring) later. Quote Link to post Share on other sites
martynharrison Posted August 11, 2004 Report Share Posted August 11, 2004 This is a question addressed in the FAQ. However, it doesn't mention whether the cams are the same between the 3.9 and 4.0 families. Looking around, there doesn't seem to be two sorts of camshaft so presumably they are the same. Might be worth adding the answer to the FAQ. Quote Link to post Share on other sites
martynharrison Posted August 11, 2004 Report Share Posted August 11, 2004 Forgot to add, I'm not sure the 4.4 crank would be suitable, isn't it supposed to go in a taller block? Either way, the Australians had the 4.4 and there have been some criticism of it, a bit too long a stroke for the engine and this causes problems down the line. ISTR the five litre engines are not all that well regarded, still, they are larger than the 4.6 which is the maximum otherwise available. Quote Link to post Share on other sites
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