Since both cam timing and magneto timing are important in order to obtain reliability and performance from any internal combustion engine, this article will demonstrate how to make an inexpensive timing indicator which will work with a 2B20 propeller. The spinner (if so equipped) will need to be removed to expose the prop cylinder.
Parts List—the protractor was obtained on eBay, the fishing leader at Bass Pro, and the rest came from Lowes.
One 7” crankshaft protractor (BikeMaster p/n 15-1632 or equivalent)
One 4” PVC closet flange, spigot fit (Oatey p/n 435873 or equivalent)
One 4” PVC coupling
One ¼-20 x 1” machine screw
Four 1/8” x ½” pop rivets
One 3/6” or ¼” female rod end (use something out of the junk box that swivels freely)
One 3/16” or ¼” bolt, one inch long to match the rod end
One 9” 30 pound test stainless steel fishing leader with 2 ounce sinker weight
3/16” or ¼” washers as needed to space out the rod end.
Modification Instructions
- Cut the 4” PVC coupling in two as shown and glue one of the halves over the closet flange. This is done to reinforce the closet flange when it is machined to size.
- Chuck the closet flange in the lathe and turn the ID of the flange to 4.315”. Leave a lip in the front part of the flange for the 2B20 cylinder to stop against.
- Drill and tap a ½-20 hole in the side of the coupling for the lock screw.
- Lay the protractor face down and center the flange over it. The ODs of both units should be centered over one another. We will be drilling through the flange in four places and installing pop rivets to mount the protractor. Align the flange on the protractor so that when the holes are drilled they miss the numbers on the face of the protractor.
- Drill four 1/8” holes through the flange and protractor for the pop rivets, then install the rivets.
- Install the bolt, rod end, fishing leader, weight, washers and nut as shown to complete the timing disc. The number of washers used behind the rod end as spacers will be dependent upon the angle at which your aircraft sits when in the three point attitude. Most tail draggers are at about 14 degrees nose up, so you will want to use enough washers to make the fishing leader just clear the protractor. Go out and time something!
Since both cam timing and magneto timing are important in order to obtain reliability and performance from any internal combustion engine, this article will demonstrate how to make an inexpensive timing indicator which will work with a 2B20 propeller. The spinner (if so equipped) will need to be removed to expose the prop cylinder.
Parts List—the protractor was obtained on eBay, the fishing leader at Bass Pro, and the rest came from Lowes.
One 7” crankshaft protractor (BikeMaster p/n 15-1632 or equivalent)
One 4” PVC closet flange, spigot fit (Oatey p/n 435873 or equivalent)
One 4” PVC coupling
One ¼-20 x 1” machine screw
Four 1/8” x ½” pop rivets
One 3/6” or ¼” female rod end (use something out of the junk box that swivels freely)
One 3/16” or ¼” bolt, one inch long to match the rod end
One 9” 30 pound test stainless steel fishing leader with 2 ounce sinker weight
3/16” or ¼” washers as needed to space out the rod end.
Modification Instructions
- Cut the 4” PVC coupling in two as shown and glue one of the halves over the closet flange. This is done to reinforce the closet flange when it is machined to size.
- Chuck the closet flange in the lathe and turn the ID of the flange to 4.315”. Leave a lip in the front part of the flange for the 2B20 cylinder to stop against.
- Drill and tap a ½-20 hole in the side of the coupling for the lock screw.
- Lay the protractor face down and center the flange over it. The ODs of both units should be centered over one another. We will be drilling through the flange in four places and installing pop rivets to mount the protractor. Align the flange on the protractor so that when the holes are drilled they miss the numbers on the face of the protractor.
- Drill four 1/8” holes through the flange and protractor for the pop rivets, then install the rivets.
- Install the bolt, rod end, fishing leader, weight, washers and nut as shown to complete the timing disc. The number of washers used behind the rod end as spacers will be dependent upon the angle at which your aircraft sits when in the three point attitude. Most tail draggers are at about 14 degrees nose up, so you will want to use enough washers to make the fishing leader just clear the protractor. Go out and time something!
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