need4speed Posted August 26, 2015 Share Posted August 26, 2015 Bit of a bargain find.. It's not me or a friend. Just thought someone might find it handy. Grab yourself a 4.6 crank and your golden.. http://www.ebay.co.uk/itm/Range-Rover-Land-Rover-P38-4-6-v8-pistons-job-lot-water-pump-starter-etc-/331635828696?hash=item4d370927d8 Quote Link to comment Share on other sites More sharing options...
Gazzar Posted August 26, 2015 Share Posted August 26, 2015 Too soon! Too many projects! Quote Link to comment Share on other sites More sharing options...
garrycol Posted August 26, 2015 Share Posted August 26, 2015 Without severe machining and weakening of the block a 4.6 crank will not go into a 3.9 block. 4.6 crank journals are thicker than 3.9 crank journals so the 3.9 block will have to be line bored larger so the larger diameter bearings can fit. Also some machining of the inside of the block will be needed to allow clearance for the 4.6 crank counterweights. Better going for a 4.0 block that takes a 4.6 crank and is cross blolted as well. Garry Quote Link to comment Share on other sites More sharing options...
need4speed Posted August 27, 2015 Author Share Posted August 27, 2015 Sorry but that's not the case at all. No machining of the block is necessary at all. The only time you would need work done to the block is if you trying to make a 4.6 out of the 3.5 block. This is due to the 3.9, 4.0 and 4.6 all sharing the same bore. All you need to do is turn down the journals of the 4.6 crank from 2.5" to 2.3" and it fits the block like a glove. You are also wrong about the 4.6 crank weights fouling. Maybe this was a problem on very early 3.9 blocks but I doubt it. They are probably all the same. The cross-bolted block is a nice to have but it's certainly not essential. Especially on a LR. It would be more of a priority on an engine constantly at high revs like a racer. How do I know this? Through personal experience. That's exactly what I've done. I've built a 4.6 by starting off with a brand new 3.9 block that I got at a price I couldn't refuse. Fitted everything up using ARP studs to add a little strength.. Don't know how you have had the problems you mention in your post above?? Quote Link to comment Share on other sites More sharing options...
garrycol Posted August 27, 2015 Share Posted August 27, 2015 Ok so you take the journals of the crank down instead of machining the block - I would rather do that than putting in a weakened 4.6 crank into a 4.6. And you accept by your own words than some machiining may be required to some blocks to clear the weights. For sure it is possible with a 3.9 block but go for a 4.0 block and have a more reliable engine. Quote Link to comment Share on other sites More sharing options...
need4speed Posted August 27, 2015 Author Share Posted August 27, 2015 Machining the crank journals is not a problem. If it were a drag strip engine for sure you wouldn't want to do it but for normal road / off-road applications it's no trouble at all. And for folk that don't want to take my word for it, I got my advice from Ray at V8 Developments before I started my engine build. And Ray knows his oats...... Regarding the block I had a choice at the time - a used cross-bolted 4.0 or a spanking new 3.9 that was "red coded" which means it had the thickest cylinder walls that LR produced. Again, at the advice of Ray I used the new 3.9.. Quote Link to comment Share on other sites More sharing options...
Snagger Posted August 27, 2015 Share Posted August 27, 2015 The main bearing journals are a lot thicker than the bulk of the crank shaft, so it's not being weakened. Reboring the mai bearing seats in the block would weaken that, though. My concern would be the journals on the crank being prone to wear having their case hardening machined away. The bearing shells should still be much softer and sacrificial, but the shaft journals may still wear faster than normal. Quote Link to comment Share on other sites More sharing options...
need4speed Posted August 27, 2015 Author Share Posted August 27, 2015 ..My concern would be the journals on the crank being prone to wear having their case hardening machined away. The bearing shells should still be much softer and sacrificial, but the shaft journals may still wear faster than normal. Yes that's a good point. That's why it's essential that quality bearings are used. I used Michigan77 as was advised.. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted August 27, 2015 Share Posted August 27, 2015 Seems a lot of effort given the price of old P38's Quote Link to comment Share on other sites More sharing options...
need4speed Posted August 27, 2015 Author Share Posted August 27, 2015 There weren't so many cheap 4.6's around when I built this engine... The engine didn't actually cost that much to build. In fact it was very cheap. I've spent waaaay more on the megasquirt stuff.. Quote Link to comment Share on other sites More sharing options...
dangerous doug Posted August 27, 2015 Share Posted August 27, 2015 .....there is no crank in that listing. 1 Quote Link to comment Share on other sites More sharing options...
need4speed Posted August 27, 2015 Author Share Posted August 27, 2015 I did mention that in the OP.... Maybe dirtyninety will like that too! Lol What do you want for £15.50.. Quote Link to comment Share on other sites More sharing options...
garrycol Posted August 28, 2015 Share Posted August 28, 2015 The most important items in that job lot for a 4.6 are the conrods - maybe also the pistons if they are Hi Comp but low comp 4.0 (do 3.9 pistons have the same bowl volume?) in a 4.6 give a comp ratio just below Hi Comp 4.6 pistons. Quote Link to comment Share on other sites More sharing options...
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