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#1 piston at T.D.C ?
- Thread starter SCguy
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Bruno_69z28
Senior Member
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Larry,
Is the head on?
Bill
Is the head on?
Bill
Bruno_69z28
Senior Member
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Larry,
I should first ask, do you want it exact or aprox..
Bill
I should first ask, do you want it exact or aprox..
Bill
Bruno_69z28
Senior Member
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Larry,
Sorry, misunderstood. I thought you wanted to find TDC.
While turning the crank, you will see #1 intake valve open and then close. Keep turning until you come to TDC. You will be at #1 TDC.
Bill
Sorry, misunderstood. I thought you wanted to find TDC.
While turning the crank, you will see #1 intake valve open and then close. Keep turning until you come to TDC. You will be at #1 TDC.
Bill
77_MG_Midget
Jedi Trainee
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Keep in mind, there are actually 2 different TDCs, and depending on what you are trying to do, it may or may not matter.
Most people think of TDC as being, as stated, when the #1 intake valve opens, then closes. This TDC is close enough for general timing of an engine.
But, TRUE TDC is different. It is the difference in degrees between when the #1 piston reaches TDC and when the piston leaves TDC. This difference is because when the piston is at TDC, there are degrees of crank "Float" that must be accounted for. Crank float is basically when the crank starts to "roll over" and begin it's downward motion. In the case of my 1500 motor, there were 16 degrees of float, where the piston remains at the top of the cylinder, before beginning it's downward motion. This is important if you are trying to degree in a cam. You need to split this difference (8 degrees in my case) using a degree wheel to find TRUE TDC.
Most people think of TDC as being, as stated, when the #1 intake valve opens, then closes. This TDC is close enough for general timing of an engine.
But, TRUE TDC is different. It is the difference in degrees between when the #1 piston reaches TDC and when the piston leaves TDC. This difference is because when the piston is at TDC, there are degrees of crank "Float" that must be accounted for. Crank float is basically when the crank starts to "roll over" and begin it's downward motion. In the case of my 1500 motor, there were 16 degrees of float, where the piston remains at the top of the cylinder, before beginning it's downward motion. This is important if you are trying to degree in a cam. You need to split this difference (8 degrees in my case) using a degree wheel to find TRUE TDC.
Hello all,
77's post above does highlight the difficulty of determining TDC (top dead centre) and I would add that you also need a dial indicator to accurately measure piston position. Also do it two or three times to minimise error.
I would disagree that:-
"Keep in mind, there are actually 2 different TDCs, and depending on what you are trying to do, it may or may not matter."
there is only one TDC and with engines of even number of cylinders there are normally two pistons at TDC simultaneously.
Alec
77's post above does highlight the difficulty of determining TDC (top dead centre) and I would add that you also need a dial indicator to accurately measure piston position. Also do it two or three times to minimise error.
I would disagree that:-
"Keep in mind, there are actually 2 different TDCs, and depending on what you are trying to do, it may or may not matter."
there is only one TDC and with engines of even number of cylinders there are normally two pistons at TDC simultaneously.
Alec