Type 1 Crank Trigger

Shown is a process to machine your crank pulley to accept a hidden crank trigger wheel.

You will need have your pulley with trigger wheel, a note pad, pencil and some 8" calipers.

First and foremost, once you have fixed the the pulley onto your chuck DO NOT leave the chuck key in the chuck. The photo is just an illustration for the process.  

Once your pulley is secure and you have removed the chuck key you can now start to zero in your pulley as shown with a dial test indicator with a resolution of at least .0005". Here is an inexpensive one if you are looking to buy one - https://amzn.to/2YMUbuT

You will want to rotate the pulley manually and find the low spot. Here we are about .002" from true. Softly tap the face of the pulley to bring this to zero. With premium pulleys it is easy to achieve a tolerance of +/- .0005". Some pulley types will only dial into +/- .0015", don't worry it isn't the end of the world. Continue on. 

This pulley came out to just under .0005" from hi to lo, that is a good pulley!

Next I will touch the the tooling to the rear pulley face and zero my dial indicator (poor mans DRO)

I then use a 1-2-3 block to find the outside edge and use this as a tooling reference.

You can do this before mounted, but it's time to write down your pulley OD. After measuring twice I found 6.7515" to be the largest.

Now measure your trigger wheel. Start with the depth moving to a 3 point measure of the OD. We will average those as a starting point. 

Now all the is done, crunch the numbers. Averaging my 3 outside measurements I came up with a OD of 6.377". 6.751" - 6.377" = .374" / 2 = .187" from the OD of the pulley.

Moving the head toward the pulley center a little over .187" (.190" for come fudge factor) I then set my 2nd dial indicator to zero. 

Taking small passes start counter boring your pulley watching the dials to make sure you stay within your limits.

Don't forget to measure as you go, it's easy to take material away but not to replace it. I'm just under the target of 6.377" so lets fit it up.

Glad I stopped early for a test fit. It slides in with a slight press fit. That is exactly what we want. Now we can check depth and make the final passes.

With a couple more measures and a very light clean up pass we are at our depth goal, -0.120".

One last check with the trigger wheel in place all is looking good!

Here is the finished product ready to remove and head to the drill press for drilling and tapping or welding. This has taken about 45 minutes to complete.

Step #2

Using a 90 degree angle straight edge, transfer the line down the side and to the backside of the pulley.

Step #3

Mark the center of your missing tooth as a reference.

Step #4

Transfer your mark from the front of your pulley to the back side and get the trigger wheel ready to insert into the counter bore that has been machined  in.

The trigger wheel should now be pressed into the pulley with a very slight press fit. It should not rotate freely. At this time verify the Key-way on the pulley and the missing tooth are on the right half of the pulley. If the missing tooth is on the lower left it's incorrect. 

With your #4 pilot drill work your way around the pulley drilling the holes through into the pulley groove.

Step #7

Use caution to not drill through into the other side of the pulley grove.

Next we are using the countersink bit to sink in the machine screws. They can't stick up otherwise they will hit the sensor. Only countersink enough to make the fasteners flush or slightly recessed. The hole has been countersunk just enough for the #4-40 Machine screw to sit flush.

Step #9

Now we need to use the 7/64" drill bit and drill only throught he remaining steel so the screw slided through freely. View next Picture. 

Step #10

With the holes prepped and the trigger wheel clearanced, we are now ready to tap the hole. Your pulley should now look like this in at least one location to prevent the trigger wheel from rotating while tapping the rest of the holes. 

Step #11

I recommend using some tapping fluid to prevent the tap from seizing. Slow and steady wins this step. Make sure your tap is kept vertical so your screw goes in straight.

Step #12

Once the first hole is tapped, install a screw and complete the remaining holes in the same manner. You may need to file the screw in the pulley groove once installed.

Step #13

After they are all complete, pull out the screws and trigger wheel. Clean away all the cutting fluid. Reinstall the trigger wheel, add a drop of blue loctite to the machine screws and torque them down. Go enjoy a beer and admire your accomplishment!

Transfer the mark down the side and onto the backside of the pulley.

Step #3

Mark the center of your missing tooth as a reference.

After the points are marked, get your die grinder ready and pull the trigger wheel back out of the pulley.

Step #7

You will want to grind both the pulley and trigger wheel at the marks. Just enough so you can get some filler material in while welding. At this time clean both the trigger wheel and pulley to prepare to weld.

Put the trigger wheel back in the pulley for the last time making double sure you get your scribe marks lined up.

Get out your tig and filler rod. I use ~75 amps and 1/16" filler.

Step #11

Hit each spot with the torch until both sides of the groove start to puddle, insert your filler material and ease off the foot pedal.

Step #12

Here is what you're left with. A pulley ready to install. You can also mask the pulley and paint the back half if you would like.