Miffy2A Posted January 29, 2008 Share Posted January 29, 2008 Hi all, First up a quick hello as this is my first post here. I've had a few LR's over the years and currently run a 109 2A 3 Litre Weslake, and my beloved RRC '89 3.9 Efi LPG Auto SE. Have a couple more 'projects' off the road which I doubt I'll ever get round to finishing! I'm experiencing some smoke on overrun (3k revs usually when dropping speed on motorway) which I'm hoping is just the stem seals, but haven't got round to checking this yet. If it is the pistons it's not too much of a worry as I have a plan..... Currently engine (135k) has lightly ported recon-heads, Lund LE1 cam and was top end rebuilt 2 years ago (new timing, lifters, rockers etc). Heddman Hedders, K&N and a cherry bomb instead of rear box. I run mostly on LPG (single point OMVL Millenium) but use petrol for start up and when I feel like giving it real beans. This years intention is to MegaSquirt the RRC (then later the 109). Whilst thinking about this, I was looking at cranks and pistons. Am I right in assuming that the 3.9 and 4.2 pistons are the same, and that the longer crank gives the 4.2 the extra capacity? If this is true, can I straight swap the 3.9 crank for a 4.2? I know I'll have fuel issues to deal with, but I'd ideally do this after MS is setup and running with it as a 3.9 so hopefully wil be a little easier. Has anyone else done this transition before? Would you do it the same way? Any input much appreciated! Thanks Ell Quote Link to comment Share on other sites More sharing options...
landybehr Posted January 31, 2008 Share Posted January 31, 2008 Hi, at the moment I do not have a parts catalogue at hand. That would tell precisely. I cannot recall it perfectly, but I´ve thought about the same some time ago. Meanwhile I managed to get a whole 4.2 block. I think two of the three parts (crank, conrod, piston) are different. And one is the same. Maybe that´s it been the conrod that was the same. In my country buying the parts new would have been much more than finding a used block was. All the parts were fine and could be re-used after 100k miles, only new rings were necessary together with TopHatLiners Quote Link to comment Share on other sites More sharing options...
q-rover Posted January 31, 2008 Share Posted January 31, 2008 Why not just go to 4.6 if your buying new parts? Quote Link to comment Share on other sites More sharing options...
landybehr Posted January 31, 2008 Share Posted January 31, 2008 too easy to be tempting (new engine wouldn´t want to be re-linered. OTOH Turner-Eng. makes obviously very nice 4.6 with flanged liners. THAT would be the best option IMHO). BTW: yes, the conrods are the same. Pistons are different (3.9 = STC908S or STC647, dependend on C/R; 4.2 = ERR3039, or STC1191S - the latter with different offset gudgeon to reduce piston noise). Quote Link to comment Share on other sites More sharing options...
Miffy2A Posted January 31, 2008 Author Share Posted January 31, 2008 Thanks chaps, I had thought about 4.6 but don't really need to go that far, was going to replace just for 3.9 but if its a simple case of swapping bits I'll go 4.2. From what I understood 4.6 would mean a different block or more engineering? I rebuilt upwards of the pistons, but checked bores at the time and they seemed pretty good. If when I pull the block and properly check things out, if it's past it I may go straight for 43.6 block if cost is permissible. This rangie is mostly used as my runaround, for towing my landies about and long distanceUK/European road trips. I wanted that bit more power just for grin factor, which I get everytime I drive her as it is Quote Link to comment Share on other sites More sharing options...
q-rover Posted February 1, 2008 Share Posted February 1, 2008 Thanks chaps,I had thought about 4.6 but don't really need to go that far, was going to replace just for 3.9 but if its a simple case of swapping bits I'll go 4.2. From what I understood 4.6 would mean a different block or more engineering? Don't think so, again it's just the crank pistons etc. the bore is the same. I think... Quote Link to comment Share on other sites More sharing options...
Coastcard Posted February 1, 2008 Share Posted February 1, 2008 As an '89 3.9 RRC, it would be pre-serpentine engine and the 4.2's are serpentine, so you would need the front end (timing cover) from the 4.2 as well. Quote Link to comment Share on other sites More sharing options...
q-rover Posted February 1, 2008 Share Posted February 1, 2008 No you wouldn't. You just change the internals to bring it up to 4.2L. Everything else can stay the same. Quote Link to comment Share on other sites More sharing options...
jules Posted February 3, 2008 Share Posted February 3, 2008 I have a few 4.2's if you want one.. At least the 4.2's don't suffer from the problems that the multitude 4.6's did. Quote Link to comment Share on other sites More sharing options...
landybehr Posted February 3, 2008 Share Posted February 3, 2008 Or .. you could spend silly money and line-bore the 3.9 block to take the larger-bearing-journal-diameter crankshaft of the 4.6 and have all the internals in 4.6 specification. I, for a glimpse, thought about that because the engine would have kept it´s original engine number. But costs for parts and labour are prohibitive. Furthermore the local engineers didn´t like the aspect of drilling through aluminium and steel at the same time. He said one couldn´t be sure not to get out of the center line. At least there are companies who do such kind of things. Quote Link to comment Share on other sites More sharing options...
q-rover Posted February 4, 2008 Share Posted February 4, 2008 Just get a proper V8 to start with. Get an LS6. Quote Link to comment Share on other sites More sharing options...
Dunc Posted February 10, 2008 Share Posted February 10, 2008 I have a few 4.2's if you want one.. How much are they Jules? Theoretically, what else would you need to fit one in a 3.9 RRC? Just testing the water and all that... Oh, by the way, my mate took this photo at the weekend on the Wyedean. As that advert used to say, "saw this and thought of you"! Quote Link to comment Share on other sites More sharing options...
jules Posted February 10, 2008 Share Posted February 10, 2008 How much are they Jules?Theoretically, what else would you need to fit one in a 3.9 RRC? Just testing the water and all that... Oh, by the way, my mate took this photo at the weekend on the Wyedean. As that advert used to say, "saw this and thought of you"! I'm very busy at the moment If you came and take it out 4.2 engine and ecu and loom which should be all you need. To you £500 all in Quote Link to comment Share on other sites More sharing options...
Dunc Posted February 10, 2008 Share Posted February 10, 2008 £500 all in OK mate, thanks. I'll ask the wife if i can have some pocket money... Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.