A few tons on the press did nothing either.
4 got out with almost no effort
1 was stuck pretty bad, I think it was the one with the broken ring that walked out of the piston. Not sure though. Either way that one came out eventually…
And that last one was so stuck that the hammer did absolutely nothing. I think it was the white crud between piston and wall mostly; the bores cleaned up nicely and the piston top came out comparatively well (not well) when I had the skirt chiseled off. I did soak it in atf+acetone for weeks and tried acid too.
You can’t see the crud but the engine was full of all kinds of sud and deposits. The head was in the trunk for who knows how long. Stored dry.
You’re right, David, of course! I had already forgotten about that …
still a marvel, to hear about an engine destroyed and then look at a dashboard and narrow pleats seats looking almost showroom …
Great job so far! Hope that honing the cylinder really lets you get away with a new set of pistons. I would have thought about a rebore.
Keep on with that car and bring it to Lake Constance. A friend of mine did a 2.8 around 1996, it seems, and he’d be more than happy to revisit, I’m sure!
The bores look nice. There is only one spot that’s uneven far down and the crosshatching was still visible. And the coolant way down, drained…
Still not sure about 9:1 or 8:1 but likely 8:1.
I‘d be happy if we could meet with the 2.8, since I almost bought one! Is it manual?
Will regularly take the 4.2 once done, I‘m not here as often these days. Came yesterday to get some stuff and leaving again in an hour…
The press made me much more nervous. 6 tons, nothing, then I had to hammer them out from below of course and the liner did not move at all. I‘m considering myself lucky, but I guess the liner is in there tight. Can’t see it being pressed out with a normal press…
Next time I will try hot tanking it since the piston is worthless anyways. I don’t get how a hole saw would give a good result. The chisel did a nice job and I did not scratch the walls, sadly the connecting rod suffered a bit.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
29
Q for the group: Would a 1-2-3 distributor make a difference here? I understand that some of the reason that CR’s are higher today than yesteryear is because the ignition systems are far more precise and can reliably keep an engine out of detonation range.
the compression should come with the engine no. using a “H” or “S” suffix. My engine is “S”, so lower compression.
Once the head is skimmed you may be in the range of a “H” compression and are able to make use of a 1-2-3 ignition to get the most out of it without pinking.
Sorry, the 2.8l I talked about is long gone - I seem to remember it was sold on 7-7-07 for a consideration of 7777 EUR, which the former owner still likes to remember. Still, he’d be more than happy to switch from his daily driver Tesla to a SI Jag I bet.
Mine is S as well… But I wondered the same as Kirbert. Would better ignition that could be retarded quickly on a hot day and had a more suited curve etc. work better with 9:1? I bet!
Assume I paid the money I’d invest in new pistons into a set of used, known good 9:1 pistons and rods plus premium fuel, should it run there must be a break-even point that might easily favor 9:1. Then again with the block shaved I might have too much compression eventually, with the standard gasket, and I do prefer keeping it as-it-was… and compression increases don’t help too much after all.
So I think I will be buying an 8:1 set as I said.
Too bad about the 2.8, but I’ll still show up
Indeed, Kirbert - modern system has sensors to detect detonations, and back off…
The engine works best with the ignition as close to detonation as possible. But all distributors are simply too crude to do that reliably at all load and rev variations - computers are required. In the meantime we just have to accept less than optimum…
I never did the homework to really find out which changes are really involved in a high compression engine. It is a bit of a mystery as I never found any differences in performance indication given by Jaguar.
The original SI ROM only states that there are two ratios, 8 : 1 and 9 : 1, identified by engine nos suffices “/8” (for low) and “/9” for high compression ratio up to engine nos. 7G. From 7L on the suffices “L” and “S” were used. No mention of “H” - for “High” is made. At least, the ROM mentions explicitly that the difference is brought about by a different shape of the piston head.
The original SII OM makes mention of the “S” following the engine number “will denote compression ratio” and explains by “Standard”. Also the ignition timing at 8° BTDC is indicated for “S. compression ratio”. The parts catalogue mentions for 4.2 litre engines only different part nos. for piston assemblies for “Low compression ratio” and “Standard compression ratio” (“High compression ratio” only shows up for 3.4 litre cars?). Finally, the SII ROM correspondingly defines “compression ratio” “S” or “L” ,but indicates the same static ignition timing with the same distributor.
“S” cars need 97 octane fuel, “L” cars make do with 94 octane (ROM).
So, just to wrap it up: either our “S” engines are already “high” compression (9 : 1) or there are “H” engines out there with an even higher compression - maybe the “High” thing is also from E type engines which I have no knowledge about.
For the moment, I’d just restore what you’ve got - I can’t find any established superior setup - and see how it works. Depending on what you do to your head you might end up with an unwanted increase of compression which you either mitigate by a thicker gasket or you make use of it with a clever advance curve in a 1-2-3 ignition.
9:1 pistons have a larger dome on top of the pistons. I happen to have 9:1 pistons to compare to ‘upstairs’ (I am fortunate to have a cellar under a garage with another Jaguar and another engine) and my dome is definitely smaller. I have -8. Not sure if 7:1 was ever available.
Later 4.2 engines run well enough with our Super 95 and 9:1 but of course they are injected. I do think the E Type easily runs on 95 if you want it to but it is a much lighter car.
Since my cylinder head is nice and flat I will not shave it down, and in theory I would get away with it and would fare well with the higher compression. Worst case, premium fuel. With a set of rings I’m saving about two hundred euros to potentially invest into fuel if needed. Then again I won’t do it because I will always be unhappy and suspecting with the 9:1s and when driving a bit faster I prefer peace of mind.
Since the 123 can be adjusted on the fly (Bluetooth) and the curve can be adjusted very precisely, there’s only a bit of slop but it’s not relying on two approximated and old modifiers to match the timing.
There is no real need for knock sensing since we can adjust these to our liking and a small amount of imprecision is okay.
I’ll wait until Christmas or a cheap ebay find and keep the original distributor for the time being so another point for 8:1.
The old distributor has a vernier so I can tinker with it comfortably should the need arise. The rest will have to wait.
The xk engine was introduced with 9:1 compression ratio, likely regarded by Jaguar as ‘standard’ - originally specified for 98 octane. The lower compression ratio, 8:1 was intended for the vital US marked - where, at some stage ‘only’ 87(?) octane was generally available. While the xk can be re-timed for lower octane it’s full potential cannot be explored…
The performance figures quoted by Jaguar, ‘naturally’ used the higher performance of the 9:1/98 octane combo - much better ‘boast’ factor; the performance were definitely lower with other combinations were definitely lower. Ie, the original ign timing data refers to the original set-up - and cannot be used with impunity with lower octane…
And there were no factory attempt to increased compression ratio further for the general public - and likely risky to do so. Skimming the head to raise compression was a possibility tried by some on a DIY basis, but without increasing octane (like aviation fuel) the increased compression could not be used effectively anyway - and likely compromises engine integrity…
As an aside; as air is compressed in the cylinders, the temp rises - the higher the compression the higher the temp. And cylinder fill, high manifold pressure, lets in more air to be compressed. Then add temp rise due to the ignited fuel; it’s is touch and go when the temp rises to the ignition point of residual fuel - which then spontaneously detonates. And the octane rating expresses the ignition temp of the fuel…
**
When you ‘back off’ the ignition to prevent pinking, David - you also lower engine performance. There is an ideal ignition point, specific to rpms and load, tied to the engine construction - and it is as close to the detonation point as dammit. So modern ignition system, computer driven, is programmed accordingly - with sensors to back off ignition if detonation is sensed. As a last defense - which actually would be useful on our crude mechanical distributors …
Frank. The 8:1 ratio was standard and only with the introduction of fuel injection did the 9:1 become standard which adds torque and efficiency and about 10 horsepower per Jaguar IIRC.
Outside the US that is.
Backing off advance is not as efficient, yes, but drive with one tank of high octane and one tank of low octane and on hot days one would use up the low octane fuel until knocking could occur; on cold days one would get away with it and some days without fuel or very hot retard the timing a bit. Of course that would work.
And the performance increase is likely negligible. A day will come when I will be eager to drop in a late 4.2 and keep all the better parts.
I’m not sure about S2, but for S1 there were lots of high compression engines in Europe.
I have engine number 7L25380-H in our XJ6C:
And it most likely came off a 1971 Euro spec 1971 XJ6, the PO of my first car (1E76372BW) bought it from a wrecker in the Bremen area (Germany) complete with the gearbox and overdrive that went in the E-type Ser 1 2+2+ auto → manual + O/D conversion.
E-type engines were - 9 suffix as standard and many other UK / RoW engines. The later XJ was 8.75:1 rather than true 9:1.
The 3.4/3.8 XK is more susceptible to pinking at high CR than the 4.2 which needs a lower crown to achieve any given ratio. There is also a bit of squish on cyls #1,3,4 & 6, which may help prevent pinking.
1 Like
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
40
I knew a guy who race-prepared Porsches for customers. He told me once that sometimes they’d set up the engine with about 10.5:1 compression and sometimes with about 13:1. The owners invariably preferred the 13:1 cars, claiming they were faster and “more responsive” – but the lap times showed no difference at all.
