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Jaguar Technical Articles

Checking the Cam Timing

Tech Article 2

Troubleshooting your XK Engine – Checking Cam Timing

I’m anxiously awaiting the final decision of the judges at Pebble Beach. After all the work I’ve put into the restoration of my E-Type, could this be the penultimate moment? “And the winner of this year’s Pebble Beach Concours D’Elegance is Harvey Ferris and his magnificent Jaguar E-Type …” “Harvey, wake up.” (It’s my wife Kelli calling out to me as I nap in my hammock) “It’s time to come in and shower before dinner.” Damn, woke me up from a most excellent dream!

Now’s a good time to continue with our troubleshooting guide for the XK engine. My specific example is the 4.2 litre 6 cylinder engine in my 1967 E-Type. But the concept I am going to discuss this month, Cam Timing, can be applied to other engines too.

Last time, we checked the compression in the cylinders, in order to establish if major problems were in evidence. Hopefully, you didn’t come up with any serious issues. Last time we also discussed identification of the timing marks on your crankshaft pulley and the static timing guide on the front of the engine. We also discussed the procedure for placing your #1 cylinder at top dead center. It turns out that to check the cam timing, the #6 cylinder must be placed at top dead center. The procedure is the same, except you will be working on the cylinder closest to the front of the engine (#6) instead of the one at the rear (#1).

Here is the procedure required to determine if your cams are set to open and close the valves at the correct time. First you will need to remove the two cam covers. This will require a ½” socket to loosen the dome head nuts around the perimeter of the covers. Depending on various factors, the covers may be stuck the first time you try to take them off. You can use a rubber mallet or a hammer tapping against an intermediate block of wood to help break the seal, tapping laterally around the sides of the covers.

Once the covers are off, the intake and the exhaust camshafts will be visible. You can now see that each cam has 6 eccentric lobes spaced along the length of the cam. Each cam lobe rotates against a circular “bucket”. Although you can’t see it, under each bucket is the end of a valve stem. As the cam lobe rotates, it alternately pushes the bucket down (in the E-Type the maximum movement down is 3/8″) and then releases it back up to its relaxed position as the lobe passes. Each time this happens, the valve underneath is opened and closed. Each lobe has a different orientation such the valves are opened in a precise sequential fashion, over and over again.

You will need a 1 5/16″ socket or wrench, placed on the nut at the end of the crankshaft pulley, to rotate the engine. Make sure the tranny is in neutral. For extra safety, you might want to disconnect the ground wire at the battery or the 12V lead at the ignition coil. Go ahead and practice rotating the engine by hand. You are going to get good at it real soon!

Go ahead and use the instructions from our last article to rotate the engine until the timing marks are lined up at 0 degrees on the crankshaft pulley, corresponding to top dead center. Furthermore, establish that you are at TDC for cylinder #6. You can do this several ways. The workshop manual simply suggests that you pull the distributor cap off and make sure the rotor is pointing roughly towards the position of the #6 spark plug wire. All you are trying to establish here is that you at TDC for #6, not #1. If you are in the correct position, you will see a “notch” on the end of the camshaft adjacent to the timing chain drive gear. As you approach TDC, the notch will be roughly at a right angle (90E) to the gasket surface of the camshaft cover. If you are on #1 cylinder, the notch will not be visible at all, as it will be on the bottom side out of sight. There are notches on both in the intake and the exhaust cams. Both will have a similar alignment.

Cam timing tool in place

Assuming that you ordered your cam alignment tool as suggested in our last article, you are ready to go. The alignment tool is pretty much self explanatory when you have it in your hand. Starting on the intake (carburetor) side camshaft, use your 1 5/16″ socket to carefully rotate the engine forward until the tool just aligns with the notch on the cam. If you overshoot, rotate the engine backwards 2 or 3 pulls and the approach again in a forward direction so the slack in the timing chain is positioned correctly. Looking at the front of the XK engine, normal forward rotation is clockwise.

Now go back and look at your timing marks on the crankshaft. With perfect camshaft alignment, the 0E mark on the crankshaft pulley will exactly line up with the static pointer. Perfect is a lofty goal sometimes and yours may be 2 or 3 degrees to one side or the other. When I baselined my engine, I found the intake to be at 10E and the exhaust at 15E! Not acceptable!

Check the intake cam timing several times if you wish, to be sure you have the process down correctly. Write down the numbers you are seeing. By the way, the numbers etched on the crankshaft pulley go from zero in 1E increments up to 10E. These numbers represent degrees before top dead center. It’s possible you will fall on the other side of zero, in which case you will have to estimate your value, which should be reported as degrees after top dead center. The above process should be repeated the same way for the exhaust side camshaft.

When you are done, you hopefully will be close to zero, plus or minus a few degrees. A little bit of deviation should not result in marked degradation of engine performance. I would think that values greater than 5E would be grounds for resetting the cam timing. Unfortunately, this is a job that is best left to your mechanic or, if you feel up to it, the Bentley manual describes the procedure in great detail. I was able to do it on my engine but there was definitely a learning curve. If there was an interest in the club, this activity would warrant a hands-on technical session, lubricated with frosty beverages!

So there you have the cam timing check in a nutshell. Next time we will talk about checking the valve clearances between the cam lobes and the cam.

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. Previous Technical Articles will be posted at my website http://www.newhillgarage.com

Specialty Tool List Cam aligning tool- Terry’s Jaguar Parts P/N C3993 1 5/16″ socket with rachet or 1 5/16″ wrench (I bought a complete 3/4″ drive socket set at Agri-Supply at an amazing price. Also check out Harbor Freight.) Note that a fire extinguisher is not required for this job but is always good to have around!



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