Have you ever wondered who was the masochist that designed the timing marks on early Jeep engines? The timing marks are very difficult to see, buried under the starter and viewed through a small access port in front of the flywheel. Yep, the timing marks are on the flywheel, not up front on the crankshaft pulley like on most vehicles. The heater hoses, battery cables and generator wiring makes access even worse. In this image, the cover for the access port has been swung to the side. A single screw secures the cover. There is no need to remove it completely because reinstallation is a pain. Loosen the screw just enough to swing the cover to the side and let friction hold it out of the way:
How in the world is a guy supposed to see in there with a timing light? The short answer is that you don't. It can be done, but it is not easy. A mirror helps, but only a little bit. The manual instructed you to set the timing statically, meaning with the engine not running. Manually rotate the engine until the "Ignition" mark on the flywheel is centered in the access port and then rotate the distributor so the points just open. (Remember, the ignition fires when the points open.)
Here's a close-up of the four marks present on an early flywheel. Note the references to the intake and exhaust valve action, which are not needed when setting the ignition timing. Later production flywheels only had two marks. TC for Top Center didn't change. Instead of IGN for Ignition as seen here, a 5 was used instead to indicate the number of degrees before Top Dead Center. When the flywheel is installed, you'll be trying to read these marks through a hole about the size of a quarter:
As accurate as these marks may be, access was so ridiculous that I got to thinking. One thing led to another, and before I knew it, my Jeep had timing marks up front where a timing light could be easily used. To get started, disconnect the battery ground cable for safety. With a large socket on the front end of the crankshaft, manually rotate the engine until the IGN mark is centered in the access port. A long extension, fed through the hole in the bumper for the hand crank, makes it easy to turn the engine. If desired, the spark plugs can be loosened to eliminate the resistance from compression but this is optional.
We' re going to add a small pointer bracket on the front of the timing cover. On the edge of the crankshaft pulley, we'll file a small notch to line up with the add-on bracket. With the IGN mark centered in the access port, break out a small, round needle file. Alignment is absolutely critical between the pointer and notch in the pulley. For the utmost in accuracy, determine the best location for the pointer bracket but file the notch in the pulley first. When the bracket is installed, its location can be fine-tuned to line up precisely with the notch in the pulley. For better access, it will help to remove the fan belt. Once the belt is removed, swing the generator out as far as it will go. The generator can be moved outboard beyond its normal range of travel by removing the adjuster bolt on the top.
The notch doesn't need to be very deep. Don't leave any burrs which might chew up the belt. A little dab of bright paint will make it easier to see with the timing light. Note how the fan blades have been positioned to allow a little room to work the file. Should the radiator ever be removed for any reason, that would be an excellent time to accomplish this project because access would be good from the front of the motor:
Don't move the crankshaft until the bracket is installed. The pointer bracket is made from thin sheet metal. Measure the gap between the back of the pulley and the front of the timing cover. Make the depth of the pointer bracket slightly less than this measurement to clear the pulley. None of the other dimensions are critical. At the end of the bracket is the small notch which will line up with its new counterpart on the pulley. The pointer bracket could have been formed with a single point instead, if desired:
Installation couldn't be easier. Use solvent to clean the face of the timing cover near the pulley. Mix up a small batch of quick-setting epoxy. With the IGN mark still centered in the flywheel access port, glue the pointer bracket to the face of the timing cover, carefully aligning the two marks before the epoxy sets. Tape is more than adequate to hold the bracket while the epoxy cures:
Some engines have a pulley with a double groove, leaving very little room against the timing cover. For those situations, a painted line on the timing cover will have to suffice instead of a 3-D bracket. While it will be a little harder to see, the principles are the same. Mark the pulley first and then paint the line to match.
Here's the payoff, using a timing light up front instead of cursing those blasted marks back on the flywheel. Before you ask, even though this old Actron timing light is designed for 12 volts, it works just fine with the 6 volt system:
If your engine had the timing marks on the flywheel, you can stop reading here. What if your engine doesn't have any timing marks? At some point in production, the timing marks were moved up front to the crankshaft pulley. Marks on the flywheel were eliminated, along with the access port. If your engine is a rebuild assembled from a mishmash of parts from over the years, it is entirely possible there are no useable timing marks anywhere. Or perhaps with any engine, retrofitted accessories like onboard air or a power steering pump are blocking the timing marks at the pulley. What could you do?
Fear not, for it is possible to make your own timing marks viewable from whatever angle your little heart desires. So far, all we've done is transfer an existing mark to a location that is much easier to read. The same thing can be done even if no useable marks are available as a starting point. Unlike the example above, we'll need to find Top Dead Center and then calculate how far offset the ignition mark should be for a certain number of degrees before TDC. Click here
to see one method to find Top Dead Center as our initial reference.
A little math is all that is required to calculate the offset for the ignition timing. Measure the diameter of the pulley. Multiply the diameter times pi (3.14) to obtain the circumference of the pulley. Since the circumference is a complete circle, divide that measurement by 360 to determine the width of a single degree at the edge of the pulley. Multiply this value times the number of degrees required before TDC, and the distance between the two points can be determined.
Here's the formula:
((D x pi)/360) x T = M
D = Pulley Diameter
T = Degrees Before Top Dead Center
M = Distance between TDC and IGN marks
Please note the pulley diameter and ignition timing specifications are not listed. Likely there were some changes over the years for both values so I've left them out to avoid any potential confusion. (Actually, you could scroll up
to see the timing specs but you didn't hear that from me.) Simply plug the numbers into the formula yourself. The formula would work for any vehicle, with any size pulley and any amount of timing advance, be it a Belchfire 500 or Farcel Vega.
On my Jeep, where I was simply transferring an existing mark on the flywheel, the crankshaft could be positioned at the correct number of degrees before TDC. Therefore, I aligned the pointer bracket with the notch filed in the pulley. If creating your own marks from scratch, you will be positioning the crankshaft at TDC instead. The pointer bracket will need to be offset from wherever you make the notch in the pulley. Since all Jeep engines rotate clockwise (Viewed from the front, looking aft) place the pointer bracket to the left, or counterclockwise, of the notch filed in the pulley. The amount of the offset will be determined by plugging the numbers into the formula above.
Trying to measure the offset while gluing the pointer bracket in place could be a bit tricky. Greater precision could be obtained by making a wider bracket with two notches separated by the correct distance. Glue the pointer bracket to the timing cover, aligning the right hand notch with the notch in the pulley. With that notch indicating TDC, the pointer bracket's left hand notch will indicate the correct number of degrees before TDC for setting the ignition timing.