Variable Valve Timing for the XK Engine: Part 2, It Runs!


 

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Variable Valve Timing in your Twin Cam Jaguar Future ? Part 2... the VVT XK Engine Runs!
By Harry Parkinson, Jaguar Association of New England


One of the latest innovations in automobile engine technology is the introduction of variable valve timing as a method of increasing horsepower and/or torque, improved emissions and improved economy. One of our JANE members, Gary Hagopian has designed, manufactured and assembled a variable valve timed cylinder head for a XK engine. Part One covered the design/development, fabrication, and assembly of the head. Part Two covers the installation and initial run up on an engine. Part Three will cover dynamometer testing and timing profile development while Part Four will encompass the results, final design and conclusions of the project

This is second of a series of articles covering the initial running of the motor and set up for the dynamometer runs.

Gary's design, covered in Part One, uses a mechanical method to vary the valve timing. By pushing the end of the cam shafts, the cam, is coupled to the cam gear by a spiral cut on the cam and into the cam gear hub. As the cam is pushed through the spiral, it changes the timing relative to the crankshaft. The exhaust and intake cams can be changes independently. For purposes of testing, simple threaded hubs is used at the end on the cams to provide the thrust to push the cam through the cam gear. Designed as a bolt in, a standard XK 140 head was used as the test vehicle.

Gary initially had built up a XK140 motor intending it for his 140 restoration project. It was completely rebuilt, but was an unproven motor that hadn't been run at all. The first task was to verify the rebuilt engine in stock configuration. Using an engine stand set up for Jaguar engines, on loan from SNG Barratt, the first task was to check out the engine stand. The engine stand is and a radiator with electric cooling fans ready for a Jaguar engine. The engine was fitted with side draft 45DCOE as a convenience....Webers have accelerator jets to help in cold starting and Gary had a set that fit complete with all the linkage and fuel lines. After checking the oil and filling the header tank, block, and radiator, the engine was turned over by starter with the coil disconnected. It turned over easily, oil pressure was 30 PSI and the cams had oil so the oil system was OK.

The acid test.....hook up the coil and fire the engine. It sputtered to life as the smoke cleared as the oil burned off. A short run showed several problems, but not with the engine, but with engine stand, leaks in the header tank and a battery that wasn't charging. We had to fix those problems first. The generator was checked and it had no field connection so off it went to the rebuilder, Auto Electric. The header tank had a rusty bottom so patches were soldered to repair the leaks. The rebuilt generator was installed, but still no battery charging, but at least there was voltage out of the generator. More troubleshooting called for replacing the regulator. Now the ammeter showed a plus charge so all was ready to install the Variable Valve Timing (VVT) head.

The VVT head was changed after machining a clearance cut around each combustion chamber, a condition caused by the high compression pistons sticking out to the engine block by some 0.040". After the usual tasks of changing over a twin cam XK head all was ready. The intake and exhaust cams were set at their stock position, no advance or retard in either cam. The engine was turned over by the starter to fill the oil galleys. Oil pressure was good, 30 PSI.
After all these months, mechanics Rich Mozetta and Harry Parkinson, along with Gary, were anxious and nervous, but ready......Go for it, hook up the coil and fire the engine.

It fired and ran! RPM was kept to under 1500 until the temperature reached 75 degrees C before any run up. A few quick run ups to 3000 after the temperature gauge showed 75 degrees C had a strange sound like a diesel knock or pistons hitting valves coming from the motor! A little detective work by Gary showed the sound as coming from the valve train itself. By using a screwdriver as a sounding device, it was traced to the rear of the cams. The noise was speed sensitive, more noise at lower speed and less at higher speed. Gary reasoned that the cams actually had a negative thrust component by the cam lobes was causing the cams to "hammer" the ball bearing between the cam adjuster and the cam. By shimming the ball, taking out play in the cam, the noise was reduced. With a permanent shim was made from Ertalyte, a lubricated hard plastic, the noise was almost gone. A few trials were made by adjusting the advance on the exhaust cam, and low and behold, the engine RPM increased without touching the throttle, a positive indication the horsepower and/or torque had increased. The Variable Valve Timing shows definite promise.

The VVT head is now being run at various constant RPM settings to "run in" the VVT parts. Barring any unforeseen problems, the head will be torn down after run in to check for wear on the VVT parts. Then it's off to the dyno for some test runs to develop advance curves for cam timing. So far, the VVT head is a success. Only testing will tell how much horsepower and torque can be gained with the twin cam head by Variable Valve Timing.

 

 

 

 

 

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