See related procedures for Finding TDC of the Piston in the REF section of the Sportsterpedia.

This is not accurate enough to find True TDC.
However, true TDC is not always necessary to find depending on circumstance.
You can use a straw through the spark plug hole to measure when the piston is close to TDC with the rocker box on or off.
The straw is soft enough that you won't risk breaking anything if it gets squished between the piston and the head / valves.
See procedure and cautions for Finding TDC with a straw in the REF section of the Sportsterpedia.

A straw in plug hole for finding TDC 1)

Engine calibration and set-up kit: Includes a piston stop, gauge extender, adapters and a TDC whistle. (piston stop shown installed) 2)

Find Compression Using a TDC Whistle.
Basically, you install whistle in the spark plug hole, rotate the engine and wait for the whistle to blow.
There is a distinct difference in the sound of the whistle between the 2 TDCs from your finger.
Just like the finger method above, a TDC whistle only works when disassembling.
(or rather only works if the pushrods are installed)
It doesn't work when assembling.
Every up stroke has compression when assembling and the valvetrain isn't hooked up and working.

How it works:

• When at TDC (exhaust):
  • Both valves are open slightly.
  • The force of the piston pushing air is sent thru enough orifices that there will not be much pressure going to the whistle although you may hear slight air or audible sound coming from it.
• At TDC (compression):
  • Both valves are closed.
  • This leaves the whistle as the main outlet for the air which drastically increases the sound it emits.

1. Engine Prep:
   • Remove both spark plugs (1 from each cylinder with dual plug heads) so the engine rotates freely without compression.
2. Establish how the engine will be rotated.
   Caution: Turning the rear tire while the transmission is engaged may produce up and down movement of the entire bike.
   Make sure it is tied down and secured before attempting to rotate the tire.
   • With the transmission in high gear, rotate the rear wheel in the forward direction (bike on a jack or lift).
     • This is easily done with one person;
       • Rotate the rear wheel slowly while listen for the whistle to sound off.
   • With the transmission in neutral, rotate the crank shaft or pinion shaft with a wrench.
     (no compression to put undue stress on the pinion shaft)
3. Install the whistle into the spark plug hole.
4. Rotate the engine forward until you hear a loud audible tone from the whistle.
   • Stop rotating the engine when you hear the whistle sound off.
   • Be careful not to rotate the engine past this TDC.
     • If you continue to rotate through and past the sound of the whistle, you've went too far. Rotate through the next cycle.
     • If your not sure if the tone you hear is the correct tone, continue rotating the engine until you get a feel for it.
5. Anticipate to rotate the engine forward to the nearest TDC from here:
   • This will be your ending point of rotation at TDC (compression).
   • Slowly rotate the engine until the TDC mark is in center of the timing hole.
   • Or you can use a straw inserted into the spark plug hole to measure when the piston has reached the top.

14 mm and 12 mm TDC whistles 3)	12 mm TDC whistle 4)

For Dial Indicators and Piston Stops:

You can break the ceramic out of a spare spark plug and drill / tap the side walls for screws.
Then insert a 1“ dial indicator in the middle of the plug.
The indicator is a slip fit in the middle of the hole and then snug the screw up against it to lock it in place. ⁸⁾