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MAG · 09-23-2019, 04:45 PM

Tablemaker lets do a little review here:
We are working on a 4 cycle engine. Intake, Compression, Power, Exhaust, in that order.
With 1 spark plug out, observe the INTAKE Valve.
#1 Piston at the top AND when it starts down the INTAKE Valve should begin opening,i.e.INTAKE Stroke.
When the #1Piston comes up, this is the COMPRESSION Stroke. When it reaches the top (TDC) the spark plug is fired, driving the piston down,i.e. POWER Stroke.
When the piston comes back up it is on the EXHAUST Stroke and is ready to repeat the 4 cycle process when it reaches the top.

If you set the timing with the #1 Piston at the top on the EXHAUST Stroke the engine will be 180 degrees out of time and will backfire..
Have fun!

09-23-2019, 04:45 PM	#7
MAG Senior Member Join Date: May 2010 Location: Austin, Texas Posts: 925	Re: Can the TDC pin be off by 90 Degrees? Tablemaker lets do a little review here: We are working on a 4 cycle engine. Intake, Compression, Power, Exhaust, in that order. With 1 spark plug out, observe the INTAKE Valve. #1 Piston at the top AND when it starts down the INTAKE Valve should begin opening,i.e.INTAKE Stroke. When the #1Piston comes up, this is the COMPRESSION Stroke. When it reaches the top (TDC) the spark plug is fired, driving the piston down,i.e. POWER Stroke. When the piston comes back up it is on the EXHAUST Stroke and is ready to repeat the 4 cycle process when it reaches the top. If you set the timing with the #1 Piston at the top on the EXHAUST Stroke the engine will be 180 degrees out of time and will backfire.. Have fun! __________________ I noticed the harder I work the luckier I get!