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Jaguar Technical Articles

Troubleshooting your XK Engine

So I’m sitting at a stoplight and some punk in a jacked up pick-up truck pulls up next to me, leans out of his window, and says “Hey, Grandpa, what’s that thing got in it?” I look him right in the eye and say “4.2 litre, dual overhead cam HEMI”. And I proceed to leave him in my dust! Won’t the younger generation ever learn not to mess with me??

“Harvey, wake up.” (It’s my wife Kelli calling out to me from our dual Barcaloungers). “Your favorite program on the History Channel has been over for an hour and you’ve been napping. Why don’t you go upstairs to bed?”

Damn, woke me up from a most excellent dream! But truth be known, your XK engine is in fact an overhead cam Hemi. All that Hemi means is that your combustion chamber is shaped like a hemisphere and that’s exactly what the XK engine has. So be proud and let your powerful cat loose whenever you can. But you say it hasn’t been running right lately? Or not running at all! And you’re not looking forward to the 4 figure bill it’s going to take at the local “Jag-you-are specialist” to get things right. Well, listen up because you can do some troubleshooting yourself and take control of your situation. Or at least you can deal with your chosen mechanic from a position of knowledge.

I took possession of a new E-Type a few months back. Here’s what I learned on the way to a better running car. First, a methodology is required. Certain things need to be checked first or you may just be spinning your wheels, so to speak. The general order is to address air, spark, and then fuel. Let’s break this down a little further.

First let’s talk about air. Your engine is basically a big 6 cylinder air pump. The intake valves open as the piston is moving downward and draws in a full charge of air and fuel. The intake valves close and the piston moves up and compresses the air/fuel mixture. The amount of compression is expressed as a ratio. For my 4.2 litre XKE engine its 9 to 1. As the piston nears the top of its travel (top dead center or TDC) the spark ignites the compressed charge. The resulting increase in pressure drives the piston downward on its power stroke. As it reaches the bottom of its travel, the exhaust valves open. The next time the piston comes up, the combustion gases are forced out through the exhaust valve and the exhaust system. At that point, everything starts over again. This is the basic 4 stroke cycle.

So your first chore is to assess the health of this cycle. For this you need a compression gauge (see tool list, below). Get your engine warmed up. Turn it off and remove all your spark plugs with a 13/16″ deep socket. You might want to temporarily number your spark plug leads for later re-assembly. Screw the compression gauge into the 1st plug hole. I like to pull the center spark plug wire from my distributor and lay it against the block so as to absorb the resulting spark. Place the gauge so you can see it from the driver’s seat, push the accelerator to the floor, and crank the engine. About 5 seconds should do it but you want to watch your compression gauge until it stops further upward movement. Hop out and write down the pressure number. Repeat for all 6 cylinders. A healthy engine should indicate 140 psi to 170 psi. What’s most important is that all the numbers are about the same, say within 10 psi of each other. If you have a major problem, one or more cylinders will show a dramatically lower number. If this is the case, utter your favorite swear words and clutch your wallet because it isn’t going to be cheap to get it fixed! You’ve experienced a major failure such as a blown head gasket, defective valve, or my favorite, a piston with a hole in it. They make nice conversation pieces for your desk or coffee table. Look, it could be worse. I once had a broken Porsche crankshaft on my desk at work as a conversation piece!

If you like, a leak down tester will give you a little more info. These are a little more difficult to use than a compression tester as they require a source of compressed air and also require that each piston be brought to TDC (top dead center) in order to make the check. That said, I did it and it wasn’t overly difficult. Follow the directions that come with the tool. Or ask your mechanic to perform this test. The leak down test can isolate whether the problem is valves, head gasket, or rings/piston.

So let’s assume that your compression numbers weren’t terribly bad but suspiciously low. Believe it or not but you really need to check your cam shaft timing next! The cams are a big part of proper air delivery. Because if the valves are not opening and closing at the correct times with respect to the movement of the pistons, engine performance will definitely suffer.

Gee, camshafts. Now you’re really looking around for something simpler to tackle. Like brain surgery! Come on, it’s not that bad. I’ll come over and give you a hand. You’re actually going to have a week to think about this because you need to order a $10 cam aligning tool from Terry’s or one of the other usuals. It’s a little piece of metal that serves as a template to tell you when your cams are set in the proper position. What you can do while you wait is check the TDC timing mark on your crankshaft. For the early XKE engines the stationary timing mark is at the very bottom of the crank

Timing Marks on crankshaft pulley

shaft. I understand that for later engines it is up on the sides, at the 10:30 or 2:30 position, depending on how you look at it. It’s a flat piece of metal that extends out over the crankshaft pulley. On the pulley, you need to identify the timing marks. On mine, 0 degrees and 10 degrees are marked, with 1 degree tick marks in between. You can use a 1 5/16″ wrench or socket to turn the engine manually so that the marks become visible. Clean the marks off. A little dab of white paint (Liquid Paper works nicely) on the 0 degree mark will help it show up later.

Now you need to turn the engine until the #1 cylinder is at it’s TDC position. There is a precise way and a rough way to check this. First, a bit of trivia. Since many of the Jaguar engineers were refugees from the shrinking aircraft industry after WWII, there are many quaint aspects of the aircraft business surrounding these cars. One is that the #1 cylinder, normally at the front of an engine designed by automotive engineers, is at the rear of an engine designed by aircraft engineers. Closest to the bulkhead or some such thing. Whatever, pull the plug on the #1 cylinder, that being the one nearest the passenger compartment. Turn the engine with your wrench while you use your third hand to hold a finger over the spark plug hole. If you are on the compression stroke, you will feel a little whoosh of compressed air under your thumb as the piston comes up. Once you are on the compression stroke, look down into the spark plug hole with a light and stop when the top of the piston comes into view. The precise method is to get a dial gauge with magnetic base (see tool list) and use it down the hole to determine when the piston it as high as it will go.  A slight complication is that the piston dwells at the top of its stroke for a few degrees of crankshaft revolution. Take several try’s back and forth turning the crank and stop the rotation in the approximate middle of the dwell zone. An alternate tool is available that screws into the spark plug hole. It’s also listed in the tool list. The crude method is to put a rod of some sort down the hole and just use your calibrated eyeball to determine when the piston is at its highest point. Either way, stop when you think you have the piston at it’s highest point. Hop down under the car and check the zero degree mark on your crankshaft against the stationary pointer. In some cases, you may have to adjust the stationary pointer a little bit to get it lined up correctly. Regardless, you will see that the zero mark should line up with the flat side of the pointer, not the rounded side. Now you’ll know what to look for when you are checking timing. And if you find that the pointer is substantially out of position, you may have just discovered why the ignition timing may be out of spec!

If you haven’t figured out by now, only men shaped like Gumby can get under an E-Type unless it is raised up somewhat. I made ramps out of 2×6 lumber to drive the car up onto. Two thicknesses of wood (3″) makes a big difference. Another advantage is that the hood can open fully without striking the bumper on the floor.

Gee, is that my wife that I see over there gesturing that I’ve used up my allotted space for this month! I’ve got to stop for now. Next time we’ll check those cams.

Disclaimer – Automotive work can be dangerous if proper safety procedures are not followed. In homage to our litigious society, I must state that I cannot be held responsible for any real or perceived mis-information that may be contained in this article. A good shop manual is mandatory before you attempt any work. Read the safety section of your manual. If you have any questions, contact me at hdferris@earthlink.net so we can hopefully get questions worked out before a problem is created.

Specialty Tool List
Compression Gauge- get the kind with the hose. See Summit Racing Equipment P/N SUM-900009
Leak down tester- Summit P/N SUM-900010
Cam aligning tool- Terry’s Jaguar Parts P/N C3993
Dial Gauge with magnetic base- Summit P/N SUM-900016-1
Top dead center tool- Summit P/N CCA-4795
First aid kit- priceless!

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