Jaguar XK engine, unleaded fuel
Discussion
Does anybody know, as far as can be known for definite, whether the 4.2 Jaguar XK engine will run unleaded fuel without the need for additives.
I understand that the fuel injected engines were introduced for the US market in 1978 and some, if not all, of those used catalytic converters. Therefore, I presume those are unleaded-friendly. I also understand that the fuel injected engine was later adopted for the UK market with the Series 111.
Was this UK engine the same spec (valveseat wise) the same as the US versions? What about the earlier 4.2s?
I've posted on jaguarforum, but not had a definite answer, so over to the PH boys.
I understand that the fuel injected engines were introduced for the US market in 1978 and some, if not all, of those used catalytic converters. Therefore, I presume those are unleaded-friendly. I also understand that the fuel injected engine was later adopted for the UK market with the Series 111.
Was this UK engine the same spec (valveseat wise) the same as the US versions? What about the earlier 4.2s?
I've posted on jaguarforum, but not had a definite answer, so over to the PH boys.
Valve reccesion occurs over 4000 rpm, so with the XK engine being a torquey beast, short shift. No problem.
To be honest, in the days of leaded petrol, the XK engine would close up its valve gaps over 10/20,000 miles anyway. So on unleaded it wil happen a bit faster.
The in-line tin catalyst things DO help - so I would use one of these, keep an eye (or ear) to the tappet clearances and not venture over 4000 rpm too often.
To be honest, in the days of leaded petrol, the XK engine would close up its valve gaps over 10/20,000 miles anyway. So on unleaded it wil happen a bit faster.
The in-line tin catalyst things DO help - so I would use one of these, keep an eye (or ear) to the tappet clearances and not venture over 4000 rpm too often.
Huntsman said:
INteresting question, according to VSE website, they replace the exhaust valve seats for this reason.
I wonder, if the more important matter is going to be dealing with ethanol.
Thanks folks. I agree that ethanol is yet another thing to look forward to I wonder, if the more important matter is going to be dealing with ethanol.
VSE? Vintage Sports Engines, Wales? If so, I wasn't aware of them, but am now, and have had a look at their site.
A hoary old question that crops up from time to time. Please don't quote me on the exact year, but I think it was around 1964 that California went unleaded, yet Jaguar made no changes to the production head and no problems were found to occur. As A8HEX says, being an alloy head inserts were always needed. Mentioned above is a rev limit which I've never before heard mentioned, and since my 3.8 engine is now 90,000 in from its last rebuild and has been thrashed on track days and rallies yet only burns oil at the rate of one litre per 3,000 miles I bweg to differ. I would also mention that even with a 9:1 compression I still use 95RON unleaded with no pinking although the vernier screw is retarded about a degree to cope. I guess though that if I was rebuilding a cooing engine today I'd probably go for 8:1 since few people use the car to its full capability. As regards short-shifting, taking a Jaguar engine over 4,000 has only been necessary in racing terms, since the torque makes revs pointless. I can drive my car from 12mph in top with no vibration.
tonys said:
Does anybody know, as far as can be known for definite, whether the 4.2 Jaguar XK engine will run unleaded fuel without the need for additives.
Absolutely no problem running unleaded with all Jaguar 4.2 XK 6-cylinder engines. The main reason clearances could close up to any significant degree over time may be because a previous owner has bodged things. Bodgers will set clearances by either grinding the tops of valve stems or shims. Valve stems and shims are hardened but it is possible to grind past the hardened surface layer. I have even come across a bodged job where slivers of shim steel (possibly offcuts of feeler gauges) were inserted on top of shims
XJ13 said:
tonys said:
Does anybody know, as far as can be known for definite, whether the 4.2 Jaguar XK engine will run unleaded fuel without the need for additives.
Absolutely no problem running unleaded with all Jaguar 4.2 XK 6-cylinder engines. The main reason clearances could close up to any significant degree over time may be because a previous owner has bodged things. Bodgers will set clearances by either grinding the tops of valve stems or shims. Valve stems and shims are hardened but it is possible to grind past the hardened surface layer. I have even come across a bodged job where slivers of shim steel (possibly offcuts of feeler gauges) were inserted on top of shims
USA went ALL unleaded in 75/76 - most UK cars that were being exported to the USA would most likely be OK for unleaded fuel in UK (Rolls Royce definately, Jaguar most probably) - if one has any doubt perhaps knock total timing back a degree or two. Shell Vpower Super Unleaded DOES inrease performance (if only by 1 to 2%) - it certainly helps stop my engine (10.5 c/r) 'running-on'
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