How do I find Top Dead Center (TDC) on a Mazda RX-7 FB engine?

Finding Top Dead Center (TDC) on a rotary can be tricky, especially if you suspect your front pulley was reinstalled incorrectly by a previous owner. On the FB RX-7 (whether you have a 12A or a 13B), there are a few ways to verify true TDC.

Difficulty: Easy to Moderate

⚠️ CRITICAL WARNING: If you need to adjust or remove the front pulley to fix your timing marks, do not remove the large central eccentric shaft bolt unless you know exactly what you are doing. Doing so can cause the needle thrust bearings inside the front cover to drop, which requires pulling the engine apart to fix ¹. If you need to take the pulley off, only remove the four 10mm bolts.

Here are the most reliable methods to find TDC on your FB, based on community consensus:

Method 1: The Flywheel Inspection Plate (Most Accurate)

Because front pulleys can be bolted on wrong, the community generally relies on the flywheel to find true TDC.

1. Locate the side inspection plate on the passenger side of the engine, right behind the exhaust manifold where the engine meets the transmission ¹.
2. Remove the plate and shine a flashlight inside.
3. Rotate the engine by hand until you see the flat side (or "skinny part") of the flywheel.
4. Align that flat side of the flywheel with the flat side of the engine block. You are now at true TDC ⁶.

Method 2: The Front Pulley & Keyway

If your engine is completely assembled and you trust the pulley hasn't been messed with:

1. Rotate the crank pulley until the yellow notch lines up with the timing pin on the front cover ¹.
2. As a secondary check, when the pulley is at TDC, one of the four 10mm pulley bolts should be facing straight up at the 12:00 position ².
3. If your pulley is already off, look at the eccentric shaft keyway. At TDC, the keyway will point exactly to the 9 o'clock position (towards the exhaust manifold) ¹¹.

Method 3: The Wire Trick

If you can't access the inspection plate easily because of your exhaust manifold, you can use a physical check inside the rotor housing:

1. Remove the rear leading spark plug (L2).
2. Poke a thick piece of wire into the L2 spark plug hole.
3. Carefully hand-crank the engine until you feel an apex seal touch the wire.
4. Back the engine off just a bit. Your front rotor is now at or extremely close to TDC ².

Once you have established true TDC using the flywheel or wire method, check your front pulley. If the timing marks don't line up with the pin, remove the four 10mm bolts, rotate the pulley until the yellow mark aligns with the pin, and bolt it back down.

If you're doing this to drop the distributor back in, make sure you align the dimple/dot on the distributor gear with the notch on the bottom of the distributor shaft before inserting it, being careful not to let it jump a tooth on the way in ¹.