Leaping Jaguar

Engine Block

Seeing this dinosaur sitting on my mechanic's work bench filled me with apprehension, I mean, this is not exactly an ideal engine for a beginner starting to learn the trade.

But there was no need to worry, it is a pretty straight forward engine, with a fairly simple design (albeit huge) and quite a few modern features, very well thought out for servicing and tune. The problem always with these engines is the restricted access, and the extra complication provided by emissions laws. The XJ12 has the dubious honour as the first UK needing EGR - Emission Control system in the domestic market plus Air Conditioning, Power Steering etc.

It took me over a week of solid work to clean the block with a very powerful detergent (my hands' skin knows all about it, use always extra strong gloves). I do not trust sand blasting or any other solid media as grit can engrain itself in the most obscure crannies and create mechanical havoc later on.

Once cleaned, all components were examined very closely; crank had virtually no measurable wear, no marks, nothing, this is astonishing! But then, this a high quality item forged in Molybdenum EN16T Steel, tuftrided for extra strength and wear resistance.

The Epicyclic oil pump (similar as found in automatic gearboxes) again was as new, its position was duly noted for later re-assembly.

I did go to the trouble of measuring the weight in all piston/rings/pins./rods assembly and found a maximum difference of 12 grammas between the lightest and the heaviest. I certainly was keen in balancing the weights, judiciously removing extra material along the forging marks on the rods. Unfortunately I did not have access to shot peening process in order to re-establish rods surface strength. Much to my chagrin, I assembled as per original condition.
I took measures to never to mismatch these piston/rod assemblies or any other reciprocating components, always keeping in separate plastic compartments. This is due to specific wear patterns that develop between inter acting parts that can be accelerated if there's a mismatch between parts of different assemblies. I made sure never to mix any part by writing down each part reference or casting number in my agenda as you can always find a particular mark in each component, otherwise we can always lightly engrave, as I did with the cylinder liners, marking 1A, 2A...6B.

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