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Fuels
Ignition
EDIS
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otherwise indicated all material is copyrighted
M Williamson 2009 |
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By Martin Williamson
The essence of the Trigger Wheel is to inform the system at position the crank is at, and what is more, the trigger wheel could be used at a later date to connect with fuel injection, so it is worth getting this part right. For the lazy amongst us, the good news is that Trigger Wheels can be bought to fit the B pulley by visiting Trigger-wheels.com, who can supply varying diameter pulleys laser-cut from 5mm steel with the 36-1 configuration and are able to offer a specific A-series pulley for the Spridget owner, too.
However, for the adventurous, a hand-built unit is possible following Matthew's guidelines below. But first some background.
It is possible to purchase an alternative genuine Ford item for approximately £13 shown below. Ford trigger wheel (Part No 1078767).
The DIY version (as created by Matthew Kimmins)
There are various ways of doing this although the preferred way would be to mill the pulley wheel and then have it balanced. Essentially the pulley edge must have 36 teeth. One tooth is removed hence 36-1. The tooth to gap ratio is 50% thus each gap between teeth equals the width of each tooth. Note as above this is not crucial so long as it is consistent around the ring. The ring must be ferrous but it doesn't need to be solid and can be made of sheet steel as shown. In addition, the trigger wheel will have to run true with little or no run-out to avoid the teeth hitting th eVR sensor. the VR sensor will sit no more than 3mm away from this trigger wheel.
As can be seen on an early car below the teeth are pretty close to the steering rack. However there is room and Matthew's trigger wheel hasn't hit the steering rack to date!
Construction
Below is a detailed plan showing how to construct the trigger wheel. Having downloaded the image use Paint Shop Pro or similar to adjust the resolution as shown. Then print it out onto a sheet of A4 using the print settings shown and it will assume the correct size. Check by making sure that the teeth extend beyond the diameter of your pulley, in other words, that the outer ring is the same diameter as the crank pulley.
Start by gluing the paper template onto a sheet of 1-2mm steel. Using tin snips you can then cut out the ring and teeth. Finish it with a file. You have to cut out the centre too which is a pain but can be done by drilling lots of 3mm holes in a circle and then punching out the centre. Paint it and you are done!
It should then look something like this.
Finally you need to bend up each tooth so that it is flush with the edge of the pulley. A small hammer makes this very easy. It can be fixed to the pulley by drilling and tapping two 3mm holes on opposite sides of the pulley face. To date we have used 2 pack metal adhesive to hold it in situ, the two small machine screws fit into the tapped holes locking it in position. Its cheap and it works. As has been said above a neater solution would be to mill the pulley specifically. It is possible Matthew can get this done so hopefully 36-1 toothed pulleys may be available in the future!
The finished article will look something like as per the photo below, where, you can see the extra clearance of a post 1976 car.
Copyright Matthew Kimmins & Martin Williamson 2007