Users who want custom crank wheels for missing tooth applications (either direct decoder with MS-II or 36-1 for EDIS) can have custom wheels made at a number of places.

As an example, Bruce has made up a custom 36-1 missing tooth crank wheel for a small block Chevrolet. Here are photos (the tooth edge one is somewhat blurry):

It is very easy to make, just 10 minutes with AutoCAD Light 97 and emailing the .DXF file to Waterjet Cutting Service in Lynchburg, Virginia:

(Note that the latest version of AutoCad Light 2008 is $800 - you may wish to investigate alternatives that are compatible with the .DWG/.DXF formats.)

The cost for 1/8 inch mild steel stock (0.125" = 3mm, must use a ferrous material as it must be magnetic) for 7.5 inch teeth tip diameter was US$60.00 for two wheels. They arrived in the mail two weeks later - and they did a superb job! No touch up at all required, it is ready to bolt-on and use.

Drawing up the wheel in AutoCAD took 10 minutes. The only AutoCAD commands Bruce invoked were the following:

1. Use the arc command to make up two circles, one for the base of the tooth and the other for the tooth tip.
2. Use the line command to draw the sides of one tooth.
3. Use the trim command to get rid of the outer circle other than where the tooth tip was (the trim command uses cutting surfaces you choose to define the trim edges).
4. Use the array command, set up in polar mode, and tell it how many objects (teeth) to make and to rotate them - this makes a copy of the tooth and then places them around the base circle. Delete the missing tooth (teeth).
5. Then trim again the base circle points at the tooth base.
6. Add any central holes and mounting holes as required for your installation (it helps to think about where you sensor will be in relation to the missing tooth at TDC when planning this stage).
7. Finally, export a .DXF file and you are done!

Bruce made the teeth tip match up with the sensor tip width. He is using a Magnetti-Marelli VR sensor (commonly available on eBay) and this has a ~0.175 inch (~4.5 mm) sensing element diameter.

If creating your own wheel, the wheel must be ferromagnetic - i.e., mild steel, not stainless or aluminum, etc.. You should carefully consider the tooth geometry.

In general, for the stongest, cleanest signal:

• The tooth should be as wide as the gap,
• The gap should be as deep as the tooth,
• The wheel should be at least as thick as the sensor element (not the whole tip, just the sensing element - typically ~1/8 inch).

None of these are 'set in stone' but adhering as closely as practical to them will result in a better signal.

The tooth shape Bruce choose was more experimental, especially the missing one with the shallower slope of the trailing/leading edge. Using a rectangular/square tooth works, too, and is easier to generate.

For the VR sensor, you can adapt an OEM sensor (like the ford EDIS sensor), or google the AI-TEK (formerly Airpax) VR sensors (have a look at 70085-101-001 or 70085-1010-002)

Here are some really good links on VR sensors and timing wheel tooth geometry:

www.ai-tek.net/pdf/24_PrinciplesofOperation_VR6_2001.pdf

www.ai-tek.net/pdf/25_SensorSelection_6-2001.pdf

archives.sensorsmag.com/articles/0298/mag0298/index.htm

www.integratedsoft.com/papers/techdocs/tech_9mx.pdf