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I got in a discussion at work today about checking push rod valves. A co-worker who I believe is very competent tells me I have been doing it wrong my entire life. I make sure the valve is closed by rotating the engine to the half way point of where the valve closed and where it begins to open. Valve should be on opposite side of cam lobe. He says it has to be TDC on the compression stroke. I say the manual will say TDC to make sure the valve is closed not because it actually has to be there. I can't see any difference but I have been wrong before. I have always adjusted my way and never any issues. Am I doing it wrong?
 

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You both could be correct. It can depend on the cam design.

To test, make your adjustment with the lobe pointing away from the valve. Then see if it changes at TDC.
 

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TDC compression is the point that both lifters are on the base circle of the camlobe for a given cylinder. Each cylinder takes two complete crank revolutions to make one cam revolution.
All valves can usually be adjusted in these 2 revolutions. Example,, set crank to 1 tdc compression, adjust both valves on #1, adjust the closed valve on all others. Rotate crank 360, adjust all the valves that remain closed. You will be able to adjust both valves on the 4th cylinder of the firing order of a 6 cylinder engine at this point.

You just have to remember that there is TDC compression, and TDC overlap for each complete cycle of power. Overlap happens as exhaust closes and intake opens at the end of the waste stroke. Ignition systems fire a waste spark here to clean up the cylinder before a new intake charge is drawn into the cylinder. preparing for compression.
At no point would both valves on any cylinder be open, so if you wanted, you could turn the crank so one valve is completely open, and adjust the other valve on that cylinder. Being careful to set it accordingly for either intake or exhaust.
You could be really anal and use a degree wheel and dial indicator.
 

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You are correct. There is no difference. TDC or any other method that ensures that your measurement and adjustment take place when the valve train is on the base circle of the camshaft lobe for that valve.
 
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Inner base circle is inner base circle. You are both correct.

An example that can be referenced for proof are most Pump Line Nozzle or Common Rail Diesel inline 6 engines. They will adjust both intake and exhaust valves using only 2 positions. The first has cylinder 1 at TDC (both I&E closed). This position then allows them to set both cylinder 1 valves, and one valve on each of cylinders 2-5. You then bar the crank over 360 degrees so cylinder 6 is at TDC and set the remaining 6 adjusters (one on each of 2-5 and both on cylinder 6).
 
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Inner base circle is inner base circle. You are both correct.

An example that can be referenced for proof are most Pump Line Nozzle or Common Rail Diesel inline 6 engines. They will adjust both intake and exhaust valves using only 2 positions. The first has cylinder 1 at TDC (both I&E closed). This position then allows them to set both cylinder 1 valves, and one valve on each of cylinders 2-5. You then bar the crank over 360 degrees so cylinder 6 is at TDC and set the remaining 6 adjusters (one on each of 2-5 and both on cylinder 6).
HUH !! :surprise::smile2:
 
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