Jensen-Healey Engine Improvements

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I've now got my rebuilt engine and it's a beautiful piece of engineering. I'd reviewed what people in the JHPS forum had done and suggested in rebuilding their engines and I have rebuilt the engine to a fairly high-performance specification, stopping just short of porting and polishing the head.

I've rebuilt the engine using the longer stroke crank from 2.2 liter engines and using high compression pistons and a high compression head with wider inlet passages. I also obtained a set of stainless steel valves and will use a pair of the "104" specification cams driven by a set of adjustable HTD type cam gears running in a set of later Excel cam carriers to prevent oil leaks. I've installed a set of new cylinder liners as well as the expected new bearings and seals throughout. I've had the crank, pistons and flywheel dynamically balanced. A new water pump has been fitted as well as a new, high voltage coil and an electronic distributor. I've also got a gear-reduction starter for it. And it was assembled using stainless steel hardware where suitable.

I've used a later Elite 907 block instead of my early one. I understand that there are no significant differences in the block castings, but since I had this as a "spare" it allowed me to have the engine worked on while the car was still nominally drivable.

The cross-drilled 2.2 crank and bearings. This is reputed to give the car a significant increase in useable torque and to be one of the most useful upgrades. These are also available without the cross-drilling but I opted for the better lubrication thinking it would be better for the higher performance modifications I'd  make throughout the engine.

I've got a set of 10.9:1 higher compression pistons and a later, high compression head. (a “912” casting) There seem to be a variety of possibilities for the head- the stock low compression one, a higher compression one with unimproved inlet runners, the one I'm using that is a higher compression head with improved inlet flow and the "Zeus" head as fit to the very latest of the engines- heads that are both rare and expensive. And any and all of these could be ported to achieve even better air flow.

I've a set of 104 cams for both Intake and Exhaust, though I also had a pair of 107s I’ve opted for the more powerful choice. I'm going to use the existing cam lifters, having kept them in their original bores as required, and the necessary shims will come from the original set and a motley collection gathered from other people's stripped engines. From the JHPS I have a set of stainless steel intake and exhaust valves. I've acquired the later set of HTD type cam gears that provide a more reliable engagement with the drive belt. These are complemented with a set of aftermarket adjustable gears so the cam timing can be fine-tuned as necessary. Oddly enough, the gears didn't come with the normal alignment markings so I've had these gears marked by my engine builder so that they may easily be timed.

The engine also benefits from using a set of later cam carriers from an Excel. These provide a much better seal and stop the endemic oil leaks for which the 107 engine was notorious. These also look very impressive with their red crinkle paint. They carry the Lotus name, much as I'd have liked to have kept the Jensen-Healey name the better oil retention was highly desired, even with the limited driving I've done the oil leaked excessively, leaving the central valley with the spark plugs soaking in oil.

My all new Ignition System: Electronic distributor, High Voltage Coil & high performance wires. This too is from an after-market source and is something of an experiment. Its settings seem to be good for my application but how well they work in practice remains to be seen. But the great advantage of having a system that avoids points and having to regularly replace and adjust them is obvious giving the awkward position of the distributor.

My initial plan is to leave the fan off and use an electric one mounted behind the radiator if there's room- or in front if not.

I've installed twin Dellorto 45s- spec 10- these have the accelerator pumps and were used on the later, highest performance Lotus engines.

I'll wait until it's in the car before I mount the trumpets and air cleaners. I've a set of Foam ITG ones that will fit and I'd thought I'd try those. I also have the proper Lotus air box and cleaner and may well use that, but it takes more room, and the ITG ones do look more racy....

I plan on using the old exhaust manifold. Its been sandblasted and painted with heat-resistant flat black paint, not that anyone is likely to see it unless I run over them. The design seems pretty efficient and should be adequate for my requirements. The previous owner acquired a "Tony Low" high performance exhaust system from there back and it is in excellent shape. I've investigated whether a custom header would be useful but it seems that would be overkill, and would actually reduce performance for anything short of a race-specification engine.

All I need do now is put it all together and get it into the car.....

Problems:

A highly sophisticated and exotic (for its time) engine like this can hardly be rebuilt without encountering the odd problem or six, and this rebuild was no exception:

I bought a set of high compression pistons- genuine Lotus items, but they were marked "A" and "B"; with three of one and one of the other. This concerned me, for these represent manufacturing tolerances with one grade being slightly bigger than the other, and presumably Lotus would have installed matched sets... I spoke with my engine builder and they measured the pistons and determined that these were a useable set and would be matched to the liner's bores (with new liners each then could be honed to provide exactly the desired clearances for each individual piston) so that proper tolerances would be maintained. Looking at the old, low compression pistons was a revelation, for the engine originally carried two of each grade- so the inference is that Lotus didn't install matched sets and may possibly have similarly tried to match pistons to bores... or they could have just been a little sloppy....

Second problem: One of the connecting rod end caps wasn't useable so a new set of connecting rods was in order. Why not just replace the one? Well, there were apparently 10 different grades of connecting rods used, and a full, matched set is required. The likelihood of getting exactly the grade needed was small, and vendors don't like breaking sets, either...

Third problem: My nice, shiny new valves came with nice, shiny new valve guides. You'd think these would slot right into the head. But no, the head too allowed for variations in the OUTSIDE diameter of the guides with standard, 1, 2 and even 5 thousandths oversize valve guides. The head I had used the largest of the oversized guides, and the standard ones were nowhere close to being useable. Ouch.

Fourth Problem: The auxiliary housing that contained the oil pump was cracked and had been repaired using epoxy on the inside. A new housing was readily to hand from the original engine (and I even had another spare), and the best oil pump was assembled from the pieces of the three available to get the best fit and end-clearance.

Fifth Problem: The new light-weight steel flywheel from a Turbo Esprit needed machining for the clutch and pressure plate to fit. The spigot (pilot) bearing too was the wrong size for the 5 speed Lotus transmission and no one seemed capable of supplying one that would fit. One of the tight ones was then machined to fit and installed. A further issue was the size of the pressure and clutch plates- these needed a "shim" between the pressure plate and flywheel to allow their fitment so that the plate would have clearance for releasing the clutch disk.

Sixth Problem: The oil pick up was damaged and the mesh pick up unusable. A Lotus one was acquired and found to be too deep. Its good pick up head was removed and transplanted onto the Jensen-Healey pipe and everyone lived happily ever after, we hope....