You can use the TDC mark etched into your flywheel on 2003 and prior stock engines.

• 1957-2003 stock flywheels have their own TDC marks.
  • Click here for stock 57-85 TDC symbol identification.
  • Click here for stock 86-03 TDC symbol identification.
• 2004 and later (or 03 and prior engines with 04 and later Sportster / Buell crankshaft upgrades) will not have a TDC mark on the flywheel so you'll have to make your own TDC mark on these if you need one.

This will not allow you to find true TDC if that is your intentions.
However, true TDC is not always necessary to find depending on circumstance.
See also Finding TDC of the Piston in the REF section of the Sportsterpedia.

• 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. When done, it can only be regarded as an approximate setting however. The piston is only at TDC once for a very short length of time until the rod rolls back over to the down-stroke. It is difficult, if near impossible, to set exact TDC with a straw. But, unless you are creating a new timing mark or finely setting cam or ignition timing, this is an easy way to accomplish TDC.
• The straw is soft enough that you won't risk breaking anything if it gets squished between the piston and the head.
• For best results, hold the straw loosely while picking up on it periodically to keep it from getting stuck (which will affect your measurements).
• Using a straw with the engine assembled:
  • This is best handled with the bike on a lift (or at least the rear tire off the ground) and the transmission in the highest gear while rotating the rear tire in the forward direction.
• Using a straw with the primary and / or gearcase cover(s) off:
  • The rear tire doesn't have to be lifted as you can put the transmission in neutral and turn the engine over with the shaft nut on either side.
• It's also best done with two people (one turning the rear tire and one manning the straw). However, it can be done by one person watching the straw rise with the piston and then switching to one hand on the straw and the other nudging the rear tire to feel when the straw goes down.
• Caution: Turning the rear tire while the transmission is engaged will produce up and down movement of the entire bike, make sure it is tied down and secured before attempting to rotate the tire.

Straw in plug hole for single or dual plug heads 1)	Alternative location with dual plug heads (better location, less binding of the straw). 2)