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Jensen-Healey Engine Rebuild

Updated: Oct 26, 2022

By Les Hopkins

Originally published in the Austin-Healey Magazine, Vol. 27 4-5c

When the Healey was bought back in 1985, after having had an MGB for five years, you cannot imagine the apprehension that the sophistication of the Lotus engine caused. Especially given that it was essentially this engine that had caused much grief during the car’s advent.

However as the years passed I became used to it and the only concessions given were those of ensuring that the maintenance schedule was adhered to and using a torque wrench religiously. Much confidence was gained after stripping down the cylinder head to do a decoke in 1987 at 55,000 miles. Now another 55,000 miles had passed, and it was becoming difficult to tune accurately. Rebuild time loomed! This is the story of that rebuild.

It was deemed too expensive to send it out to a specialist, so everything I was capable of would be done by me. Only specialist operations such as regrinding/balancing the crank would be subcontracted out.

Of course the stripping down is easy, just follow the book and take care with the aluminum, as it is so easy to strip threads. The only problem that arose during the strip-down was when a retaining bolt for the water pump broke. It fortunately left about 5mm standing proud from the block which with a few taps broke the corrosion and was able to be extracted using a mole grip. The liners were extracted by turning the block upside down on the floor so it stood on the head studs, and thumping the proud part of the liner 2ith a lump hammer (with an interposed block of hardwood).

Once they had been shifted by a few millimeters, they fell onto the floor.

Notes so far:

  1. Save everything.

  2. Label everything.

  3. Clean everything.

Strip-down revealed many areas of substantial wear, notable around #4 piston where it was found that as expected, the piston/rings and liner had all worn. However, on checking with a micrometer, the gudgeon pin also was found to be worn undersize (undoubtedly the source of the top-end rattle). Also, the main and big end bearings on this piston had worn down to the backing metal (the bearings on the other pistons were substantially less worn). Remember to note when stripping down the piston/con-rod assembly, the front mark on the con-rod and the cast marks on the inside of the piston (any markings on the outside will be obliterated) as the con rod and new pistons must be assembled the same way round.

The crankshaft was sent away for grinding and balancing. Meanwhile the cylinder head was stripped, decoked and new valves, springs and collets fitted. Ensure that any debris left in the guides is removed before lapping the valves (for this I used an electronics switch-gear cleaning aerosol, as the solvent is propelled at sufficient velocity to remove any debris). New liners were then to be fitted to the block; todo this, you first have to do a “dummy” run to check that the liners stand proud of the block by the correct amount (see manual). This takes some patience, a steel rule, feeler gauges, a lump hammer and a block of hardwood.

Placing a ruler across the liner and inserting a feeler gauge between the ruler edge and the block (a-b, Fig. 1), can check the height of the liner above the block.

Using the thinnest feeler gauge between the ruler edge and the head face of both adjacent liners (c, Fig. 1), can check the relative heights of adjacent liners. Use Hylomar when finally fitting the liners, but be sure not to apply any to the ledge that the liner sits on. Otherwise, the liner will sit too high as a result of excess being unable escape (I suggest it be applied to the bores in the block).

By this time the crankshaft was ready to be collected, so I was able to obtain suitable bearings. Meantime I had obtained a new starter ring for the flywheel which had bee found to be damaged when it was removed. So the flywheel was taken in to have the old starter ring removed and the new one shrunk on. However it was suggested that the crank, flywheel and clutch cover plate should be balanced as an assembly, so this was done.

The end bushes were pressed from the con rods using a specially made die but as it was not possible to reliably insert the new ones (which also have to be precisely honed after fitting), this operation was also entrusted to the experts. New oil seals were fitted to the front and rear crankshaft covers, the front was easy (I had had to do it before when the J-Healey was first bought as it was spraying oil all over the engine bay) but the rear was much more difficult due to a combination of the size and the sharp edge on the casting. After scraping the first seal, I relented and filed a small chamfer on the outside of the housing (about 1mm wide) then by using a G-clamp, a block of wood about 80mm by 10mm cut to the diameter of the seal, the second attempt was successful. The diagram gives some idea of the arrangement.

Figure 2 (top) - Figure 3 (bottom)

If like me, you intend to rebuild the oil pump, be sure before stripping down the assembly to remove all fraze from the pump shaft around the key and circlip as the running clearance is only about .001”, and anything will damage the bore of the housing. Otherwise their assembly is straightforward.

Once the crank was ready and suitable bearings obtained, reassembly could commence. First fit a new oil pipe compression olive, ensuring that it is properly seated. The new main bearings were fitted lubricated with Graphogen, and the crank gently lowered into place, at the same time fitting the oil thrower onto the back of the crankcase and the new thrust bearings slid into place. The crank was checked o for end float with a DTI after the pistons had been removed during the strip-down. The bearing housing is then lowered onto the studs and the oil pickup pipe inserted into the hole and onto the appropriate retaining stud, taking great care that the pipe passes cleanly through the new compression olive.

This last item caused me much trouble when it did not align and had to be stripped out again and replaced with anew one. The retaining nuts are then tightened to the torque setting stated in the manual. The crankshaft can then be checked for freedom to rotate which also distributes the Graphogen around the bearing surfaces (I was happy to find that it rotated with less than 5 lb/ft of torque). The oil pipe retainer can then be refitted ensuring that it passes cleanly over the pipe and does not start moving the pickup pipe which should come up as far as the top of the circular section. The front and rear oil seal assemblies can now be fitted bolting them up to the appropriate torque setting. The manual states 7-8 lb/ft for the front and 13-15 lb/ft for the rear. In the process of torqueing up the rear, one of the bolts sheared so the assembly had to be removed and started again.

Figure 4

Before refitting, as I was suspicious of the difference of the setting with same size bolts on the front and rear, so I checked a table of shear values and found that the figure of 13-15 lb/ft is unusually high for an M6 bolt, so the rear bolts have now only been set to 7-8 as the front. (Does anybody know if 13-15 lb/ft is correct?). Refitting the auxiliary housing assembly with the oil pump is a simple procedure. The only thing to watch out for is that all the bolts are fitted in the correct position, particularly the thin headed bolt which fits under the oil filter pickup (otherwise you won’t get the oil filter on).

Now if you already have the liners in place, the piston/con-rod assemblies can be fitted ensuring that the assemblies are the correct way round (note the arrow on the top of the piston and the front mark on the con-rod). Start with no. 4, as the big-end bolts are so inaccessible on this piston. It is far easier to rotate the engine when you only have one piston in, as the livers may lift if the pistons are moved up the bore (it would be a good idea to prepare liner clamps beforehand so that you could rotate the crank without fear of a liner moving).

Once all the pistons are in and fully bolted up the cylinder head can be refitted and the nuts torqued up.

This is followed by the cam carriers which had had the valve clearances set up previously while the head was off the block. On torqueing up the second cam carrier the thread in the head on the very last stud gave way so the carrier had to come back off and a set of Helicoils obtained (M81.25 pitch) and an appropriately sized drill (8.3mm). The surrounding area of the head was blanked with paper with just holes in the paper to expose the hole and the next stud. The hole was drilled using a hand drill with a second person ensuring that the drill aligned with the next stud. The hole was tapped, all the debris removed and the Helicoil inserted-hey presto, a new thread. The cam covers can now be refitted, either the gaskets supplied or sealant, can be used to give an oil-tight joint. The only remaining apertures on the engine can now be covered and the water pump fitted, ensuring that the threads are protected by using copper grease or sealant in an attempt to ensure that the bolts do not seize again.

For the next operation, the engine had to be removed from the stand as there was not sufficient clearance to refit the flywheel and clutch. The flywheel was refitted insuring that it was running true by using a DTI attached to the block on one of the bell-housing bolt attachment holes (there must be no more that .004 run-out on the flywheel but at what radius from the center, it does not say, so I assumed at the edge). As the crank/flywheel/ clutch / cover had been balanced in a particular orientation this had to be reproduced on assembly and everything was torqued up as required.

During the rebuild, the engine bay had been stripped down, cleaned and repainted. So on refitting the engine all the ancillaries had to be refitted and I had also obtained new hoses for all but the radiator top and bottom. This included an anti-kink reinforced hose for the inlet manifold to heater. If the suppliers had to fit these themselves, they wouldn’t supply them! When I tried to fit it, I found that the hose is so rigid that I worried for the life of the inlet of the heater matrix. It also would have been impossible to remove at a later date. So I decided not to fit it and used a section from the center of the original return hose in its place. Also, during the rebuild all the wiring was cleaned, any loose tape removed and the wires rebound. So now the color of the wires can be identified, and the Laycock J overdrive that was fitted some years earlier sent away for reconditioning. So now after one month I have a power plant hopefully fit for another 100,000 miles but now fitted with latest generation parts rather than early development items.

Total cost, engine only (!!!) 1900 pounds (inclusive of services, scraped knuckles, swear box fines and lost friends).

Not what you were looking for? Don't forget you can check our back issues using the AHCUSA Magazine Index.

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