Crane XR700 Ignition Installation on a Bugeye Sprite
Steve
Maas
Long Beach, California, USA
January, 2007
One
of my ongoing projects is the modification of my 1960 Austin-Healey "Bugeye"
Sprite to make it a bit more reliable and, therefore, practical for regular use.
So far, I have installed an electronic fuel pump and modified the fuel lines to
minimize any tendency to vapor lock. My second project was the installation of
an electronic ignition.
Why install an electronic ignition? The main reason, for me, is reliability. Electronic systems invariably have much lower failure rates than electromechanical ones. Another advantage is reduced sensitivity to such problems as fouled spark plugs, also a reliability advantage. Other advantages of an electronic ignition are lower maintenance, and, perhaps, slightly better fuel economy.
Two ignitions are commonly recommended for Sprites. One is the Pertronix unit. I have no first-hand experience with this unit, but many people claim that it is unreliable. The advantage of this system is its size; it fits entirely within the distributor, so there is no outward indication that the car has a nonstandard ignition. This is fine for show cars, but any concern about reliability makes it a non-choice for me. The other is the Crane XR700, which has a good reputation. The Crane uses an optical sensor to replace the points, while the Pertronix uses a magnetic one. I prefer the optical sensor over the magnetic one, even though it may be subject to failure from contamination (which seems unlikely, in any case, in the enclosed confines of a distributor). I suspect that it is considerably better in establishing accurate timing of all the cylinders. So, I got the Crane unit.
A number of Crane units are available, depending on the type of distributor you are using. I got the 700-0231, which, according to the description on the Crane web site, seems to be the right one for early Spridgets. I bought it from Summit Racing, whose price was about as good as anyone's, $95, a little over a hundred bucks with shipping. I didn't need anything else for the installation; in the worst case, you might need to get a ballast resistor. More on that in a minute.
Installation
Here I ran into some problems.
In the Crane unit, the points and condenser are removed, replaced by a shutter and electrooptical sensor. The latter is simply an infrared light-emitting diode (LED) and a light sensor. The shutter is a circular, black plastic disk with four slots that mounts on the distributor shaft just above the cam. The shutter prevents the light from the LED from reaching the sensor until a slot moves in between them. Then, light reaches the sensor, triggering the ignition.
Installation consists of removing the points and condenser and replacing them with the shutter and sensor. This is a moderately tricky thing to do, since a lot of fiddling is necessary. Don't even think about trying to do this without removing the distributor. There just isn't enough room.
The instructions for the Crane installation are pretty good. Fortunately, installation in a 1960 Sprite does not require any special considerations. The unit does require a ballast resistor in the primary circuit; if your car does not have one, or lacks an internally ballasted coil, you will have to add one. As it happens, my coil is internally ballasted. This can be determined by measuring its primary resistance, approximately 4 ohms. The measurement can be made with an inexpensive multimeter, obtainable for $7 from Harbor Freight.
A picture of the wiring diagram is shown below; it's pretty simple. Other cars might be a little more complicated. Click on a thumbnail for a larger version of this and subsequent pictures.
The kit provides a number of shutters and miscellaneous hardware for mounting the sensor. There are quite a few shutters, a couple for six- and eight-cylinder cars as well as three different four-cylinder ones. Only one shutter came remotely close to fitting the Sprite's distributor, and, frankly, it wasn't perfect. Its center hole, which should locate it on the distributor shaft, was about 0.050" too large. As a result, it wasn't centered perfectly, and a quick spin of the distributor shaft showed it clearly to be a little eccentric. I was worried about this, as it affects the timing of the no. 2-4 cylinders; once the no. 1 cylinder is in time, only the shutter keeps the other three firing when they should. If this is wrong, the other three cylinders won't be timed right. The error can indeed be substantial. With a little measurement and analysis, I determined that the worst-case timing error would be about six degrees if the problem were not fixed. That's way too much.
So, what to do? Fortunately, I have a small Sherline lathe. I used it to make a nylon sleeve to fit inside the shutter, aligning it properly with the shaft. This sleeve was not easy to make, as it was a half-inch in diameter but only 0.025" thick and 0.030" long. But, once it was in place, it fixed the problem perfectly.
Mounting the optical sensor is also a little tricky. It is important, of course, that the shutter does not rub on any part of the sensor, but also the sensor must not bind on the inside of the distributor cap when the vacuum or centrifugal advance operates. There isn't a lot of room inside the distributor, so getting everything right is a bit of a project.
Additionally, it is necessary that a slot in the shutter reach the optical sensor when the rotor connects to a plug-wire terminal in the distributor cap. Otherwise, the ignition fires when the rotor isn't connected to anything. As a result, getting the sensor into an acceptable position is something of an engineering job. I used the mounting screw from the points to mount the sensor and had to add some small washers judiciously to make sure no screws interfered with the shutter or anything else. It took most of a morning before I was satisfied with my creation.
Pictures of the distributor, with the shutter and sensor, are shown below.
You may notice, from the pictures, that I used an extra loop of cable from the sensor inside the distributor. This keeps the cable, which is actually fairly stiff, from opposing the movement of the mounting plate by the vacuum and centrifugal advance mechanisms. The instructions suggest tying the cable to the mounting plate in the distributor with a zip tie. This very likely would affect the advance mechanism, so I just made sure that the cable stayed out of the way of the shutter. I suppose it would be OK to tie it to something very loosely, just to keep it out of the way of the shutter.
The rest of the installation took about half an hour. Hooking up the electronics package was simple, and mounting it on the fender required only drilling a couple screw holes. I used regular machine screws instead of the self-tapping metal screws provided with the kit; they just seemed neater and more secure. The pictures below show the installation. Admittedly, there isn't much to see, and that's not necessarily bad.
Adjustment and Test
The unit has a useful addition: an LED, on the outside of the electronics package, that lights up when the shutter is open. This can be used to do a static ignition timing. Just set the engine on the desired timing (5 degrees BTDC is the factory spec) and adjust the distributor until the light just goes on. When this is done, timing is pretty close, so the engine should start OK. Then, a dynamic timing (which I did) is optional.
The car started right up, I timed it, and that was pretty much all I had to do. I took the car out for a spin of about 20 miles as a shake-down cruise, and all went well. No problems at all winding it up to 5000 RPM. I can't really say that it ran any differently, although it's inevitable that you will have some sense that it does. After all, a clean engine runs better, doesn't it? Something like this should be equally palpable.
New Shutter (August, 2007)
I've never been comfortable with that plastic shutter. Even with the new sleeve I made, it isn't perfect. I can see a little eccentricity, and I don't like eccentricity. I don't like imperfection in any form. Freud would have called me anal retentive, but we neurotic perfectionists are the ones who keep the world running right. So, I think I really...oops, there goes the irrelevancy alarm. Back on topic.
What to do? Make an aluminum shutter to replace the plastic one. I can make it fit the distributor nearly perfectly, and I won't have to worry about eccentricity.
I pulled the distributor and measured the plastic shutter. I copied the dimensions and modified a couple appropriately to achieve an improved fit. Most important was to make it a smooth, sliding fit over the distributor cam and to make everything concentric with the cylinder that provides that fit. On my Sherline lathe, I can hold tolerances on the order of a mil or two and angles within about a tenth of a degree. That really should do it.
Below are pictures of the finished shutter by itself and installed in the distributor. The shutter is held in place by a pair of 4-40 setscrews, which thread into the sleeve and lock it to the flat parts of the distributor cam. After taking these pictures, I colored the shutter black with a felt-tipped marker to make sure that reflections don't affect the timing. I was especially worried about possible reflections from the inside edges of the four cutouts; these were carefully blacked.
With the new shutter, it's impossible to see any eccentricity at all when I spin the distributor shaft. The eccentricity of the shutter is probably considerably less than that of the distributor shaft itself. Now I'm confident that the timing is what I expect it to be--can't be sure of that with the stock parts. My anal-retentive self is happy at last!
Below is a fabrication drawing for the shutter. Note that it requires a pair of 4-40 setscrews to attach it to the distributor cam; the screws are tightened against the flattest part of the cam. These should be 3/16 or 1/4 inch long, headless Allen setscrews, and it's not a bad idea to put a tiny dab of epoxy on them after they are tightened. Be sure they clear the sensor when the shutter rotates! The location of the setscrews depends on the installation of the sensor; in my installation, they were about 45 degrees offset from the slots, but other installations may differ. It is necessary that a gap in the shutter be located at the optical sensor when the rotor is pointed at one of the terminals in the distributor cap. This is extremely important; you don't want the ignition firing when the rotor is between terminals! Finally, it will probably be necessary to sand or file 0.025" of material off the bottom of the rotor, or it may ride too high and damage the contacts in the cap.
Disclaimer
I don't like saying this, but I suppose it's necessary, now that the lawyers have taken over American society. If you choose to do this, or something similar, but don't know enough about automobiles or electronics to be comfortable with it, get some help. In any case, I'm not forcing anyone to make this modification, so if you choose to attempt it, you take full responsibility for the results. This is just a report on my experience with these modifications. It is not intended to be a set of instructions for duplicating my work or a recommendation to do it. You're on your own.