The 'E' Type Forum

Dear all

My understanding of why lead was added to fuel was to protect valve seats in iron cylinder heads. Thus cars with iron cylinder heads need hardened valve seats fitting as part of the unleaded conversion process. Aluminium is a soft metal so Al heads are fitted with hardened valve seats in the factory.

So, do the V12 engine cylinder heads need any kind of conversion to use unleaded fuel?



Regards

Nigel

Hello Nigel: No....by the time Jag started delivering Series 3 cars, lead free gas was becoming the norm. You could still find some leaded gas if you searched, but its days were numbered. I have a 1973 for the last 44 years and the lead free, low octane fuel has never been a problem. I have 145K miles on my car, and at 90K miles, as a matter of maintenance,I did pull the heads and freshened everything up...seats, valves, guides, etc. All was in good shape, but I thought it would be a smart thing to do if your planning to keep the car a long time.......you know, open things up and see how the engine is doing. So far so good. The absence of lead has never been a problem. FYI...additives are useless, and a waste of money.. Others might disagree, but them is da facts, as they say here in NYC. Enjoy your great car.

John

No. AFAIK they had stellite faced ( or at any rate chilled hardened ) valve seats fitted from new . Peter Crespin I think has expert knowledge of the exact details of this

I think you'll probably find that the factory was using the hardened valve seats even back in the 1950s, so the only "conversion" needed would be to adjust the timing slightly for the lower grade fuel, if at all.

Replacing the valve seats "because you want to freshen things up" may not be as good an idea as you think. The reason is that the factory will have had access to far better facilities to manufacture and install the valve seats to a closer tolerance than any aftermarket shop will ever achieve when trying to replace. Unless it genuinely needs machining work done, all you will have at the end of the day is created unnecessary risk to get back to where you already were and at your own cost.

kind regards
Marek

As usual Jag fans, Marek is spot on. I dug up the work order, and we did not change seats. Series 3 owners and fans.....I would consider Marek the 'guru' of all things Series 3 V-12's !! Learn from the best !

JC

Very kind words, but the only reason I mentioned it was that some time ago, on another forum, one chap made disparraging remarks about the tolerance specification regarding valve seat inserts to be found in the Jaguar shop manual. It was another lister, a professional who knows more about v12s than the rest of us put together, who pointed out that the acceptable standard of a "field repair" told you nothing about the standard that was originally employed at the factory at the time of manufacture. With modern computer controlled CNC mills now commonplace, we are probably now capable of repeatable workmanship which even ten years ago would have challenged most workshops.

Sadly, on my car, I'm not even convinced that the heads were skimmed by the same amount. I traced the man who rebuilt my engine and he now runs a scrapyard, which just tells me everything that I already knew after setting my verniers and calipers over his "work".

kind regards
Marek

Thanks guys, useful feedback which confirms my lifetime reading motoring mags (LJKS) has at least given me a little more knowledge than counts as a dangerous thing.

My (Reputable) engineering shop is advising me to fit ‘unleaded’ valve seats... which started alarm bells ringing in my head.

Onwards and upwards.

Cheers!

Nigel

Let me explain the situation (as you are aware) regarding repair shops who, for the most part, specialize in older sports cars, like the E, and other vintage toys..........they are desperate for work, and fighting for clients and their cars ,from an ever shrinking pool. Sad ,but true. Therefore, and this includes, sadly, world wide, the need to , even from formerly reputable shops, make up fairy tale stories about how you need to change over to "unleaded seats". Oh brother !! And this , mind you, in a world that has been over 97% lead free for over 20 years. AND !!!!! with a car that was designed to run on lead-free fuel, if need be, from the day your Series 3 left the factory.

Happy motoring !!

JC