Bob’s 120 Restoration, part 11, by Bob Exelby


Although it’s just six months since I dismantled the engine, it seems a good deal longer. At the time, I scribbled copious notes and took plenty of photographs, but still can’t help but wonder if it would have been better left to a professional. Fortunately, there are a couple of very useful books on the subject: Dave Pollard’s Jaguar XK Engine (ISBN 1859600077) gives a step-by-step account of a rebuild and Des Hammill’s How to power Tune Jaguar XK Engines (ISBN 9781845840051) goes into great detail regarding measurement and checking for potential problems.


Between them, they provide a pretty useful layman’s guide. If you followed them to the letter, it’s possible you might finish up with as good a job as any run-of-the-mill engine builder could turn out. BUT – this assumes that you’re dealing with an engine that has not been badly worked on before, that your machine shop does precisely what it should and that all parts supplied are exact copies of the original parts.

My engine had been back to the Works Service department early in its life and I’m pretty sure had not been apart since. I’m not qualified to determine the precise quality of the machine shop’s work, but I have a good feeling about it. Alas, the supply of replacement parts is the one area that caused me some consternation, mainly because I genuinely don’t know what is or isn’t considered acceptable. Given the depth of detail contained in the aforementioned books, it would be a waste of my time and Mr Porter’s pages to attempt to produce yet another. I can however add some hopefully useful observations relating to my particular journey, from the usual carefully laid out platter of parts, to a fully-assembled engine. As outlined in Part 10, all parts required for the engine bottom half eventually materialised from the machine shop, mill and with the cylinder head components to follow a few weeks later.

In my quest for a reliable and smooth-running unit, everything that could be done to an XK block and 5crank has been done. I’ve also had all reciprocating parts – crank, flywheel, clutch and front damper – dynamically balanced. The oil scroll was removed from the crankshaft and the appropriate area machined down to 2.632 inches to accommodate an improved rear oil seal kit supplied by Classic Jaguar of Texas. A collar was also fitted to the front of the crankshaft to increase its diameter to fit inside a modern lip seal. This will, with any luck, bring to an end the ‘not welcome here’ status of all previous old cars on the pristine pressure-washed blockpaved driveways of North East England. Classic Jaguar also sent me a set of Ross forged pistons with ‘Total Seal’ rings and some very strange ‘Spirolox wrist pin retainers’ to replace the usual gudgeon pin circlips.

6First up is a careful inspection of the bare block. On at least three of my visits to the machine shop, it resided in a large tank with various fluids and sprays doing some sort of pickling and cleaning job. It certainly seems to have worked. I purchased a set of extra-long spiral brushes specifically to run through the block’s oilways and remove the very last vestige of dirt or swarf, but it turned out to be unnecessary. No matter how much pushing and pulling through the passageways, the brushes always emerged as clean as they went in. I had badgered the machine shop on this point, especially with regard to the crankshaft, after experiencing a rather dramatic seizure to a just-rebuilt Daimler V8 engine, put down to swarf left in the oilways.

The outside of the block was painted with POR15 Engine Enamel, specially formulated for very high temperature applications, but it seemed to lack the colour density of POR15 Chassis Paint and took three coats before it looked anything like presentable. The main bearing shells and thrust bearings were installed and the top half of the new rear oil seal kit was fitted. Graphogen assembly compound was liberally applied to the bearing surfaces and the crankshaft gingerly set in place. The end float was measured and was correct at just over 3 thou (0.08mm). Main bearing caps were fitted and, heeding advice from the machine shop, the original cap bolts were reused, “because it’s highly unlikely that a new set would be any better than Jaguar’s originals”. The bolts were lubricated with thin oil, then progressively tightened to 72lb ft.

7This was all done at a very leisurely rate, with the crankshaft checked for smoothness of reciprocation at every stage to ensure nothing was binding up. All very satisfying. Feeling reasonably confident that I’d got the crank installation correct, I moved on. Each piston was dunked into a bucket of very hot water to create that tiny amount of expansion to allow the gudgeon pin to slide in, attaching its connecting rod on the way. The machine shop had spent some time removing a smidgen of metal here and there from the con-rods and had managed to achieve a combined weight variation between each piston/rod set of less than two grams. The Spirolox gudgeon pin retainers were not something I’d seen before and I needed to fit two into each of the channels usually occupied by a circlip. After an hour’s fiddling, I couldn’t see how these bits of coiled sprung steel could ever be persuaded to slide in. Just before calling it a day, as it was now mid-morning in Texas, I called for help. It only takes a
couple of minutes for ‘the motor guy’ to explain the technique: expand them a little first, then push them home a bit at a time. The first one took a few minutes but I soon got the hang of it, the last of the 24 taking just a few seconds. Looking at the design of these things gives me great confidence in their inherent security. Fitting two on each side seems a little OTT, but why skimp when this is known to be the occasional cause of disastrous failure. Piston rings were fitted and the gaps (already set precisely by the machine shop) carefully positioned relative to each other, as detailed in the manufacturer’s instructions.

8The pistons were installed with the help of a very effective and previously unknown (to me) ‘wiggle’ technique I picked up from YouTube, which negates the requirement to tap them down with a hammer shaft. The big end caps were fitted and again, following advice from the machine shop, this time I used a new set of modern fasteners with no apparent means of locking; no split pins or lock tabs. Apparently the combination of a relatively fine thread and 37lb/ft of torque means they’re safe, but I couldn’t help but add a little thread lock as well, just to be sure.

9The deck of the block had been skimmed to correct the sloping 15 thou it was out of parallel with the main bearing tunnel. Measuring the height out of the block at the edge of each piston at TDC, I now found a random variation of between 26 and 31 thou. Temporarily swapping pistons between cylinders gave me a slightly different set of numbers, showing that con-rod length and crank throw must be jointly responsible; possibly I reason down to Jaguar’s original machining tolerances? Running the numbers through the spreadsheet indicates that the maximum effect on compression ratio between cylinders is 0.08, which I suppose will produce fractionally different sorts of bangs. Is this acceptable? I think it probably is, but it’s not mentioned in the books so I don’t know for sure, and that’s starting to sound a little too familiar.

Next month, things don’t go quite so well when I assemble all of those scary cogs and chains at the front of the engine and build up the cylinder head…


XK Tool Bag: The Ultimate Solution!

4 2

After spending months looking for the ideal tool bag to complement the 120, I eventually bit the bullet and had one made up to my own design. Roughly based on a very practical bag issued to GPO engineers in the ’60s, it soon became apparent from regular “Where did you get that from?” requests that a few more were needed. From there, it was a relatively short step to the formation of The Tool Bag Company.

Designed with the classic car owner/driver in mind, this handsome leather tool bag compendium will complement the boot space of even the most exotic machines, but its primary purpose is functional. Measuring 44x30x12cm, it’s neat enough not to take up valuable boot space but, when that inevitable breakdown occurs, you can be sure that your own choice of tools and spares is to hand. The top part of the bag has 21 fully-adjustable loops to hold a really good selection of tools, whilst the lower part has a useful document pouch plus space for essential spares and larger items, such as a wheel spinner hammer. It comes complete with a matching tool roll and parts box, all made from dark brown hard-wearing, dry-milled full grain leather. YKK coil zips quality buckles are used throughout.

Each bag has a unique serial numbered brass fob, which we can engrave with up to initials of your choice (NB: Tools not included). price is £260 inc carriage, Europe
€335 including Air Freight: see It is also available in from Classic Jaguar in Austin, Texas:

XK Club has negotiated for members discount off the above prices: quote offer code XKG54. ‘Superb’ is the only word needed. Congratulations, I think this is superb in every way – design, style, quality, workmanship and smell! Philip Porter


Stupid Boy!

10I’d previously spent some time cleaning the various components which make up the oil pump assembly and pickup, but not the inside of the bowl which hangs from the pump and I can’t see any way of getting into it bar cutting it open. Best thing to do is to drop it into a bucket of thinners, which will hopefully dissolve and wash out any nasty stuff within; but the strangest thing happens. Expecting it to sink to the bottom of the bucket, it doesn’t; it floats. Holding it down, it just pops up again. Only after very close inspection do I realise that it floats because it is in fact a float: the bowl is a completely sealed chamber, the pipe simply passes through it. The metal cross, which retains the gauze, perfectly conceals the end of the open pipe. Obvious really, it’s designed to float on top of the oil so that it doesn’t pick up the dirty stuff lower down.


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