In the final instalment of our two-part Jaguar XK engine rebuild, we follow the experts at SNG Barratt as they assemble a 4.2-litre unit.
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WORDS AND PHOTOGRAPHS:
ROB HAWKINS
We follow the experts as they build up Jaguar’s legendary XK straight-six, double overhead cam engine.
In the last issue of Classics, we followed P&K Thornton Restorations stripping a 3.8-litre XK engine from an XK150S. The time required to properly reassemble this engine, once any machining has been completed, can easily take around two working weeks (80 hours), which makes it impractical to follow, so we asked SNG Barratt to demonstrate the main stages of reassembly on one of their test engines that is frequently stripped and rebuilt.
Our photographs and 44 steps over the following pages provide an overview of what’s involved, but remember this is quite a complicated engine to assemble. For instance, it’s important to know how to time it up. The timing marks on these Jaguar engines can be found in one of three positions. Early engines had timing marks on the flywheel, accessed through a small window in the top of the bellhousing. Middling engines have a pointer mounted on the sump at the six o’clock position with TDC marked on the circumference of the harmonic damper. This required you to roll around on the floor to check the timing, so at about the start of E-type S2 production in 1968, the pointer was moved to the left side of the timing case and the marks on the damper altered to suit so that they could be read from above.
However, Peter Sant, Product Design and Development Head Technician at SNG Barratt, also adds: 'These timing marks are OK for ignition and basic checks, but there is an amount of adjustment on the pointers so they are too vague for valve timing. I determine my own marks by making a stop for the piston and using a timing wheel.' So do check your workshop manual carefully to ensure your timing data matches the engine you are working on, and note that we will also be running a general feature later in the year on valve timing. And do remember that it is also important to work in a clean environment, to fit new components such as gaskets and bearings and to not cut corners on reusing components that may be worn.
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…the ends of each head stud protrude into the coolant chambers of the engine block, so they are at risk of corroding. Consequently, it’s worthwhile trial fitting them with the core plugs removed to look for rust.
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If the cylinder head studs have been removed, or even if they haven’t been, it’s worthwhile checking that the ends of them can wind fully into the engine block. Why? Well…
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With all the main caps fitted but not fully tightened, rotate the crankshaft again to check it moves with consistent resistance. Fit the lower rear seal with two 3/16in Allen key bolts.
3
New core plugs should be fitted into the engine block. Use a suitable size of socket (28mm is being used here, but sizes vary depending on the outside diameter of the socket) to evenly seat each core plug in position with a hammer.
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Note that the centre main bearing cap has two thrust washers on the cap side. A support bracket for the oil pickup pipe also needs to be fitted, but only on the 4.2- litre XK engine.
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Next, fit the front and rear main bearing caps with new bearings and assembly lube, fitting their bolts and lock tabs on the front cap, but don’t fully tighten the bolts at this stage.
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Check the crankshaft is spotlessly clean before lowering it onto the base of the engine block. Apply more engine assembly lube over its bearing journals before and after fitting it.
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Insert and rotate an oil seal sizing tool (part number JD17B – the JEC hire them out) in an anticlockwise direction from the rear to squeeze and seat the seal so that it will bite into the crankshaft.
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Rotate the crankshaft to check for any inconsistencies in resistance. It will be stiff due to the new rope seal, but the amount of effort required to turn it should be consistent.
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Soak a new rope seal in engine oil, then add a little Graphogen assembly lube before fitting both halves of the seal housing and the rear main cap into position like this.
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Continue to fit the other main bearing caps with new bearings and assembly lube. Fit new bolts and lock tabs or support brackets for the oil pickup pipework.
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Once the main bearings have been fitted into the bottom of the engine block, add a generous squirt of engine lube to the exposed surfaces of the bearings.
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Turn the engine upside down and dry fit the main bearings onto the engine block. There’s a tang on each bearing which sits in a corresponding recess in the block.
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You can now tighten the 3/4in main bearing cap bolts to 83lb.ft, but start to progressively tighten them to 50lb.ft, before finishing off with the final torque figure. Then bend over the lock tabs to secure them in position.
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If there’s an arrow on the top of each piston, this should point towards the front of the engine (the water pump end). If you are reusing the old pistons, these should have been marked or checked during stripdown.
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The conrods and big end bearing caps should also have been marked and numbered to ensure they are correctly fitted. Remember that on this engine, number one is for the cylinder nearest the back of the unit (the flywheel end).
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A piston ring can be trial fitted into the cylinder bore to check there’s a sufficient gap between its ends. On the 4.2- litre XK engine the bores are 3.5in in diameter, and we can measure a 14-thou gap for the piston ring, which is sufficient.
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When lowering a piston into the engine block with the ring compressor tool wrapped around it, use the wooden or nylon handle of a hammer to knock it further down, leaving the tool behind.
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Once the piston is seated inside the engine and the end of the conrod is in position around the crankshaft, fit the big end bearing cap with a new bearing and finger-tighten the nuts.
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Lowering a piston through the engine block risks damaging the crankshaft due to the exposed threads on the ends of the conrods, so fit rubber tubing to protect the crank.
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We’re now ready to fit the pistons, conrods and big end bearings. Make sure all these components have been assembled and are in the correct order.
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Fitting the piston rings around the pistons is fiddly, but a pair of piston ring pliers makes it easier. This pair costs just £15.98 from Machine Mart.
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When fitting new bearings into the conrods and their caps, add engine lube afterwards and make sure the tangs for both bearings meet.
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Apply lots of engine oil around the walls of each piston prior to clamping a compressor tool around it and lowering it into the engine block.
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After fitting each piston and big end bearing cap and tightening its nuts, rotate the crankshaft again to check that it moves with a consistent amount of resistance. If all is okay, continue fitting the remaining pistons.
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Pack a new or old oil pump with petroleum jelly, then fit it with three 1/2in bolts and lock washers. Two of the bolts have dowelled shanks and are fitted to the outer mounting points. Once tightened down, bend the lock tabs over.
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Loosely fit the two timing chain guides and a tensioner, followed by a Woodruff key on the crankshaft, then the timing chain gear, which is fully seated on the crankshaft.
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Rotate the crankshaft to check the piston moves freely, then tighten the big end bearing cap nuts to 37lb.ft. Use 1/2in double- hex nuts instead of the older castle nuts and split pins.
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Fit the timing chain assembly with two upper chain guides secured with two bolts on each side to locate each tensioner, including splash plate and spacers.
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Fit a lock washer into the recess for the Woodruff key and then a 7/8in securing nut. Bend the lock washer over using water pump pliers to lock the securing nut.
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Fit the oil pump and distributor drive gears with the thick bevelled edge to the engine block, although some drive gears don’t have this.
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The distributor drive can be fitted next, but it’s quite involved. Start by manoeuvring it into position so that the bottom of it is offset as shown here.
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A washer and drive cog need to be fitted over a Woodruff key, tapping them into position with a hammer whilst squeezing an Allen key in at the other end.
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Fit the oil pickup pipe and feed pipe with new O- rings and a gasket. Some components are secured to brackets attached to the main bearing cap bolts.
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Fit a Woodruff key on the front of the crankshaft, drifting it into position with a hammer and metal bar as shown here.
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On early engines, fit a splash guard onto the crankshaft, a seal with nonsilicone sealant and finally a round seal track before fitting the front cover in the next step. On later engines, fit these after the cover.
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Turn the engine upside down and fit the sump with a new gasket. Progressively tighten the 26 1/2in bolts threaded into the engine block and the four 1/2in nuts around the timing cover.
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With the engine timed up, adjust the tension on the upper timing chains using a special tool (which costs around £20), then tighten the 11/16in nut on the upper tensioner.
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Refit the rocker covers and continue to fit the engine ancillaries. Do note that these steps have been an overview of the work assembling an XK engine, and are not a complete workshop manual!
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Release the lower chain tensioner, then tighten the 1/2in bolts for the lower guides. The right guide needs to be parallel but 1mm off the chain. The left guide can touch the chain.
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Make sure the engine and head are correctly timed up. Carefully lower the cylinder head onto the engine block. Secure the ends of the cams to the cam sprockets.
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Fit the front timing chain cover with new gaskets, blue silicone sealant and five 9/16in bolts and one 1/2in bolt (up to seven bolts may be fitted in some cases).
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Fit the cylinder head studs (there are 10 long studs and four short ones) with a light oil applied to the threads and tighten them with a stud extractor.
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Progressively tighten the cylinder head nuts to 54lb.ft, working from the inside out. Start with around 30lb.ft, before finishing with 54lb.ft.