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  Chicagoland MG Club:Tech Tips

Crane XR-700 Ignition System Installation

Of all the systems that enable your British automobile to keep rattling down the road, fewer are more trouble-prone than your ignition system. The main culprits are usually the contact breaker points and condenser. The usual scenarios are: 1.) the points (after too many miles since the last replacement) finally wear out the rubbing block, close up their operational gap and burn up their contact faces, 2.) (my personal favorite) the condenser finally shorts out and takes the points with it by frying the contacts.

There are other little problems like the fact that the distributor body and shaft can wear to the point that the points' cam is no longer rotating in perfect circles, but is now changing its orbit at will from circles to ellipses (and sometimes the cam opens the points completely and sometimes it doesn't). Not only does this affect the period that the points are closed (dwell) but it can effect the ignition timing as well.

The golden rule of British cars (neé Murphy's Law) now applies here; any of the above will happen to you at the single most inconvenient time of your life... usually miles from anywhere... in bad weather, when you need the car the most. Also, its going to cost you piles of gold (hence the golden rule) to get towed to the nearest town, whose local auto parts store will not have the parts you need, anyway!

Point ignition systems have been around since the dawn of the automobile age and so have failures of its basic components - the points and condenser. British Leyland recognized the shortcomings of the point type ignition systems, and in the later production runs of the MGB and TR7, these cars were fitted with electronic-type ignition systems. Unfortunately, early Lucas systems incorporated a number of flaws.

The standard Lucas System is renown for failure of the ignition amplifer unit, (the black box under the coil). It has never been a question of "will it fail", only "when". The Crane XR-700 is a less expensive and permanent solution to this problem (distributors with point systems use Moss #222-335 kit, those with electronic ignition use #222-325).

What is an "Electronic Ignition System"? It is an ignition system that uses non-mechanical means to trigger the ignition coil to fire, thereby eliminating the trouble-prone points and condenser completely, and replacing them with a system that is triggered by either a magnetic pulse or optical flash.

The Crane (a.k.a. Allison) XR-700 Ignition System works on the optical principal, with the points and condenser being replaced by an optical pick-up and a "shutter" wheel attached to the distributor shaft. The system works using a light emitting diode (L.E.D.), shining a beam of light to a photo-optic cell immediately opposite. These two are located in the optical pick-up, which has a slot through it in which the flat surface of the shutter rotates. The shutter wheel has the same number of evenly spaced slots in it as the engine does cylinders, and is fixed to the distributor shaft either by self-locating spring clips on the point type distributors, or by the original snap ring and washer when used on the later electronic distributors. As the wheel rotates, a slot will pass over the photo cell, allowing it to see the L.E.D., and in conjunction with the ignition module, signal the ignition coil to fire. The great feature is that there are no points to wear out, no condenser to short out and a L.E.D. never burns out! Also, if the shaft or body are worn in your distributor, it will have negligible effect, as the shutter wheel is still wide enough to compensate, regardless of the shaft's orbit. Because there are no mechanical parts to wear out with the Crane XR-700 installed, you will never again have to adjust your timing or dwell!

I know this sounds incredible, but in 85,000 miles on my MGB GT, my timing hasn't changed one degree. The added bonus is your future tune-ups will take less time to complete and cost less. After choosing the appropriate kit for your car, the first step is to find a location in the engine compartment to place the ignition module. These leads are sufficiently long enough to allow mounting anywhere in the engine compartment, so even you Concours fanatics can install a XR-700 and mount it out of plain sight. On the car used in this article, a '71 MGB roadster belonging to Moss' own lovely and talented Jill Jones, I chose to mount the ignition module in a empty space next to the ignition coil on the right inner fender well and across from the distributor. The kit provides two self-tapping screws in the parts bag for this task, although I used one pre-existing threaded hole and the screw in it that also mounted the wiring harness, so I had only to drill one hole to install this entire system!

The next step is to connect the various wires as dictated by the appropriate Crane diagram. Jill's car is negative ground, so the connections were straightforward, as the wires are color-coded and labeled as to the terminals they connect - practically foolproof.

Now that we have installed the ignition module on Jill's car, let's address installing the optical pick-up. The first thing to do is to set the engine so its timing marks line up on Top Dead Center, cylinder number one. If in doubt as how to achieve this, consult your workshop manual. Now follow the spark plug wire from #1 cylinder back to the cap, and mark both the cap and the side of the distributor body with a felt tip pen. On BMC series A (Midget) and B (MGB, MGA) motors, it may be easier to install the optical pick-up in the distributor if you remove the distributor from the engine first. To install the optical pick-up, remove the points and condenser, or on Lucas electronic systems, remove the old pick-up and cable conduit. On Jill's MGB we'll hang on to the plastic terminal that the low tension lead connects to; this is the part that fits into the distributor body and protrudes into the cap itself.

Next we will install the optical pick-up with its adjusting arm and mounting foot on the breaker plate of the distributor, using one of the screws that originally mounted the points. On electronic distributors, use the screw that held down the plastic conduit. Now fit the shutter wheel to the distributor shaft and slide the optical pick-up into place. Don't tighten all the screws completely until you reinstall the distributor, and make sure that there is plenty of clearance between the shutter wheel, pick-up and rotor arm, so that they don't rub anywhere. On Lucas electronic systems it may be necessary to slightly bend the studs that held down the original pick-up so that they don't contact the shutter wheel.

You'll find that on most Lucas distributors, you will have to set the optical pick-up right down on the breaker plate to get any clearance above or below the shutter wheel. Turn the distributor body so the rotor arm points at the line you marked on the body, and adjust the mounting foot so that you can slide the pick-up across the nearest slot in the shutter wheel. Run the gray cable out of the distributor body through the original grommet on Lucas electronic systems, or on earlier cars like Jill's MGB, take the original low tension insulator and drill out the bolt passing through it. You will find that the cable will just fit in the hole and with a little silicone gasket goo, you can affect a weather-tight seal.

Be sure to leave enough extra cable inside the distributor body to allow movement of the breaker plate if the distributor has vacuum advance attached. A small tie-wrap is included in the part bag for this purpose. After routing the cable out of the distributor, you can install the Molex plug, taking care to match the colors to the other half of the plug.

If you have removed your distributor, now is the time to reinstall it back in the block. Slacken the clamp bolt and rotate the distributor body until the rotor points are at the line you marked earlier and connect the optical pick-up to the ignition module with the Molex plug. Next, remove the high tension cable from the distributor cap and tape it somewhere where the end of it is about 3/8" from a good ground.

Switch on your ignition and you can make final adjustments to the optical pick-up. This is done by sliding the pick-up in a clockwise direction toward the approaching slot. As the pick-up passes the slot, the L.E.D. will see the photo cell and fire the ignition coil, resulting in a spark jumping from the high tension lead to the ground. Besides being able to see the spark, you should be able to hear it as a cracking noise. You want to slide the pick-up until the coil fires and no further, then tighten the screws to secure it. You may want to try this a couple of times until you are comfortable with its final position.

After the final adjustments of the optical pick-up make sure that nothing rubs and that the distributor cap fits with no interference. On MG T-types and Austin-Healey 100s this is very important, as the space under the cap is at a minimum. Now we can set the timing to the manufacturer's specs. on Jill's car for the last time, as the timing will never change from wear in the distributor. However, it's a good idea to check the timing, say, once a year, to see if there is any change due to timing chain wear or wear in any other components.

While we are in the neighborhood of the ignition system, it's a good idea to examine the rest of the components. On Jill's car, the distributor cap and rotor were renewed, her ignition wires were replaced with a set of Lucas Premium Ignition Wires and her tired old coil replaced with a more powerful Lucas sports Coil. Last but not least, you'll need a set of new and properly gapped spark plugs.

The end result of our labor, according to Jill, is a car that runs smoother, is more tractable, starts easier, and will require less maintenance.

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