Is top dead center both timing dots facing eachother or both dots at 12 o clock?

Slade88 · Apr 17, 2022

Hello everyone Ive heard very conflicting answers on how to set your cam and crankshaft timing. Ive heard that you want both dots facing each other and then to rotate the engine till they both point straight up and this is TDC on the compression stroke, ive also heard that both dots facing each other is tdc on the compression stroke. I recently put a camshaft in and my engine runs great in idle but in drive it lacks some serious power. I set my timing to have both dots straight up and my boss tells me im 180 out. Could anyone verify which way is correct and which isnt? I have a small block 350. I hope everyone is having a great easter!

L31MaxExpress · Apr 17, 2022

Slade88 said:
Hello everyone Ive heard very conflicting answers on how to set your cam and crankshaft timing. Ive heard that you want both dots facing each other and then to rotate the engine till they both point straight up and this is TDC on the compression stroke, ive also heard that both dots facing each other is tdc on the compression stroke. I recently put a camshaft in and my engine runs great in idle but in drive it lacks some serious power. I set my timing to have both dots straight up and my boss tells me im 180 out. Could anyone verify which way is correct and which isnt? I have a small block 350. I hope everyone is having a great easter!

Dot to Dot is TDC #6. Both at 12 o'clock is TDC #1 which is where you want it when you drop in the distributor.

GT80 · Apr 17, 2022

Slade88 said:
Hello everyone Ive heard very conflicting answers on how to set your cam and crankshaft timing. Ive heard that you want both dots facing each other and then to rotate the engine till they both point straight up and this is TDC on the compression stroke, ive also heard that both dots facing each other is tdc on the compression stroke. I recently put a camshaft in and my engine runs great in idle but in drive it lacks some serious power. I set my timing to have both dots straight up and my boss tells me im 180 out. Could anyone verify which way is correct and which isnt? I have a small block 350. I hope everyone is having a great easter!

If you were 180 out you wouldn't be driving it at all.

Erik the Awful · Apr 18, 2022

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Schurkey · Apr 18, 2022

L31MaxExpress said:
Dot to Dot is TDC #6. Both at 12 o'clock is TDC #1 which is where you want it when you drop in the distributor.

Sort of.

Cam position has NO bearing on whether the piston is at TDC or not. None. Zero. Nada. What matters for TDC is the crankshaft position, with the crankshaft timing gear "dot" straight "up".

Cam position matters if you need to be at TDC-Compression versus TDC-Exhaust. THAT matters for dropping the distributor in.

"Dot-to-Dot" is TDC-Compression for #6. Both at 12 o'clock is TDC-Compression for #1. But both #6 and #1 are at TDC in both cases. When one is at TDC-Compression, the other is at TDC-Exhaust.

Erik the Awful · Apr 19, 2022

In common parlance, when you're talking "TDC" most people are talking "TDC on the compression stroke". Typically they're trying to install a distributor. Please don't let pedantry get in the way of good advice.

Dravec · Apr 19, 2022

Not meaning to hijack, but is it the same for a big block?

Hipster · Apr 19, 2022

Erik the Awful said:
In common parlance, when you're talking "TDC" most people are talking "TDC on the compression stroke". Typically they're trying to install a distributor. Please don't let pedantry get in the way of good advice.

It pays to be specific. Mechanic to mechanic is no problem but there are many newbies that don't even know there are 4 strokes to a cycle and Schurkey threw out the most comprehensive explanation thus far. Tdc compression or tdc exhaust makes a difference and should be explained when the OP asks a question where both positions inquired about are TDC.

Hipster · Apr 19, 2022

Dravec said:
Not meaning to hijack, but is it the same for a big block?

What's being discussed here applies to any engine that has the 1-8-4-3-6-5-7-2 firing order.

Schurkey · Apr 19, 2022

Dravec said:
Not meaning to hijack, but is it the same for a big block?

Big-block CHEVY? Yes. W-block, Mk IV, Gen 5/6/7.

May not be the same for a big-block from another manufacturer.

Hipster said:
What's being discussed here applies to any engine that has the 1-8-4-3-6-5-7-2 firing order.

All those engines have #1 and #6 as companion cylinders--both at TDC at the same time.
1 8 4 3
6 5 7 2

Each vertical pair are companion cylinders--1&6, 8&5, 4&7, 3&2.

The LS firing order is 1-8-7-2-6-5-4-3.

1 8 7 2
6 5 4 3

Each vertical pair are companion cylinders--1&6, 8&5, 7&4, 2&3. Note that the pairs are exactly the same. 4/7, 7/4 same cylinders. 3/2, 2/3 same cylinders.

I won't promise that the timing sets are marked the same way (Dot-to-Dot is TDC-Compression for #6) on other engine families. Some are--some might not be.

Is top dead center both timing dots facing eachother or both dots at 12 o clock?

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