QuestionQUESTION: Sir, I am considering a rebuild of my 1971 V12 engine. Can you provide me guidance and cost ranges on the tradeoff of rebuilding my original engine vs. the potential of installing a more recent V12 from an XJ series car. I understand that I will lose authenticity but the cost and driveability may be worth it.
ANSWER: Hi Doug,
When you say "Rebuild", you don't make it clear if you are going to do the rebuild, or you are having a shop do the rebuild. As far as cost, it is probably cheaper to purchase a salvage yard engine then to have one rebuilt by someone. But either way until you open your engine up and measure everything and inspect it, you have no way to estimate cost of the rebuild. Then if you purchase a salvage engine, even with low mileage (if you could find one) you don't know the condition so you may have to rebuild that one. If you look for a late model V-12, you are talking about a fuel injected version and if you intend to use the fuel injection system you would need to get the harnesses and all the components which are vast, ECU, Relays, fuel pump etc. I have experience in this area and I can tell you it is no small task. Not to mention that the V-12 injection system had gone through several changes over the years.
I am sure you will devalue the car substantially by swapping the engine and for what purpose? For more power? You can't use what you have unless you are racing the car. What did you mean by "driveability"? If you had driveability problems you need to correct that, as going to a later engine is not going to solve that.
If it were mine I would rebuild your engine and keep the car as original as possible.
Howard
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QUESTION: Sir--your guidance is consistent with other inputs I have received. I am now committed to an original engine rebuild. I will be using a "shop" to have my work done. What are the key questions and requirements I need to look for in settling on an arrangement for such a big project? I have already worked the "top half" so I really need to go after the bottom half now. I have oil leaks, plug fouling, heat and odor problems. All classic for an engine with 145K miles Thank you for your help. Doug
AnswerGood decision, and there are some things you need to cover with the rebuilder. First are they experienced with the V-12 Jag? Even if they are not, it doesn't mean that they can't do a good job. If they are not you should get a service manual and let them use it for specs that they will not find in their normal source for crank, bore etc clearances. This is a "Wet" sleeve engine and the deck interference and other specs may not be in their reference books.
Another factor is the word "Rebuilt" is a wide range word. You want to be sure the block has all the oil galleys cleaned as well as the crank even if it don't need to be turned.
They may ask you how far you want to go. Meaning, if the cylinder bores are good and skirt clearance is acceptable do you want to just put new rings? You can compromise a little on piston to cylinder wall clearance but don't compromise any on bearing clearance.
I have a tech tip on engine rebuild. http://mg-tri-jag.net/Preamble.htm You should read it to give you some background to know what to look for.
Howard
