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 on any SAE 20 crankshaft (R755, W670, R680, as well as the R760-E2). It will be necessary to remove the propeller to use this indicator, but in another article we also look at a tool that is made specifically for use with a 2B20 propeller and which can be modified for use on a Hamilton Standard ground adjustable, McCauley ground adjustable, or wood propeller.
Parts List—the protractor was purchased on eBay, everything else at Lowes
One 7” crankshaft protractor (BikeMaster p/n 15-1632 or equivalent)
One combination 2”/3” PVC general purpose drain (Oatey p/n 435793 or equivalent)
One ¼-20 x 1” machine screw
Two 3/16” x 1” machine screws and lock nuts
Modification Instructions
- Using a 2 3/8” hole saw drill out the center of the BikeMaster protractor and deburr the edges of the new hole.
- Remove the two screws that hold the chrome screen on the general purpose drain, remove the screen, and discard them.
3. Using a sanding drum or burr, remove the 1/8” lip from the drain and fit the drain on your crankshaft. It may be necessary to lightly sand the ID of the drain to allow it to slip on and off smoothly.
4. Drill and tap a ½-20 hole in the side of the drain for the nylon lock screw. Run the tap back and forth a few times to be sure the threads are loose and will not break the nylon screw when it is installed.
5. Drill all the way through the two existing tapped holes in the drain with a 3/16” drill bit.
6. Lay the protractor face down and center the drain over it. The IDs of both units should be centered over one another.
7. Using the two 3/16” holes in the drain as a drill guide, drill through the protractor with a 3/16” bit.
8. Install the machine screws through the protractor and drain, securing them against the drain and the lock nuts.
9. Check the fit of the assembly on a SAE 20 crankshaft. Lightly sand the ID of the drain if necessary to get a smooth fit. 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 on any SAE 20 crankshaft (R755, W670, R680, as well as the R760-E2). It will be necessary to remove the propeller to use this indicator, but in another article we also look at a tool that is made specifically for use with a 2B20 propeller and which can be modified for use on a Hamilton Standard ground adjustable, McCauley ground adjustable, or wood propeller.
Parts List—the protractor was purchased on eBay, everything else at Lowes
One 7” crankshaft protractor (BikeMaster p/n 15-1632 or equivalent)
One combination 2”/3” PVC general purpose drain (Oatey p/n 435793 or equivalent)
One ¼-20 x 1” machine screw
Two 3/16” x 1” machine screws and lock nuts
Modification Instructions
- Using a 2 3/8” hole saw drill out the center of the BikeMaster protractor and deburr the edges of the new hole.
- Remove the two screws that hold the chrome screen on the general purpose drain, remove the screen, and discard them.
3. Using a sanding drum or burr, remove the 1/8” lip from the drain and fit the drain on your crankshaft. It may be necessary to lightly sand the ID of the drain to allow it to slip on and off smoothly.
4. Drill and tap a ½-20 hole in the side of the drain for the nylon lock screw. Run the tap back and forth a few times to be sure the threads are loose and will not break the nylon screw when it is installed.
5. Drill all the way through the two existing tapped holes in the drain with a 3/16” drill bit.
6. Lay the protractor face down and center the drain over it. The IDs of both units should be centered over one another.
7. Using the two 3/16” holes in the drain as a drill guide, drill through the protractor with a 3/16” bit.
8. Install the machine screws through the protractor and drain, securing them against the drain and the lock nuts.
9. Check the fit of the assembly on a SAE 20 crankshaft. Lightly sand the ID of the drain if necessary to get a smooth fit. Go out and time something!
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