importance of TDC when torquing rocker arms - Mustang Evolution

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Old 08-05-2009, 09:52 AM   #1
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importance of TDC when torquing rocker arms

I'm pretty sure I got all my rocker arms torqued down to the proper tightness while it was at TDC on the compression stroke.

However, I'm having a hard time understanding WHY it had to be TDCocs when you're basically tightening a bolt pretty dang tight which holds something that moves. If the rocker arm is going to go through its full range of motion anyway, why does it matter what place the it was in when you started?

And what symptoms will it exhibit if I messed it up? : )

Thanks!
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Old 08-05-2009, 09:55 AM   #2
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Re: importance of TDC when torquing rocker arms

I think you raise them to TDC due to how the rocker arm pivot point touches the lifter. It is not always on the same spot on the lifter. If you have them to tight you can probably get issues with the valve not closing/opening fast enough and additional wear on the cam and if its to loose they can not move fast enough either as the rocker will not be tight enough to hold itself to pivot correctly.

If you have enough clearance from the pistons then your issues might just be rough running/valve train noise (some noise in the morning is normal)
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Old 08-06-2009, 11:03 AM   #3
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Re: importance of TDC when torquing rocker arms

The piston must be at top dead center (TDC) of the compression stroke in order to adjust the valves for that cylinder Valves are adjusted when they are completely closed and hopefully (if adjusted correctly) there is no pressure from the cam on them

Too much clearance = clicking. Too little = low compression and burnt valves

Rotate the engine in its normal direction of rotation (clockwise) and watch the exhaust valve on that particular cylinder. When the exhaust valve begins to open, stop and adjust that cylinder's intake rocker arm.

To adjust, back off the intake rocker arm adjusting nut and remove any tension from the push rod. Wait a minute or two for that hydraulic lifter to return to a neutral position. The spring inside the lifter will move the push rod seat up against the retaining lock, if you give it time to do so.

Twist the intake push rod with your fingers while tightening down the rocker arm. When you feel a slight resistance to the turning of the push rod, you are at "Zero Lash". Turn the adjusting nut down one half to three-quarters of a turn from that point for street applications. Use 1/8 to 1/4 turn for race applications. Lock the adjuster into position. The intake is now adjusted properly.

Continue to turn the engine, watching that same intake valve/rocker you just set. It will go to full open and then begin to close. When it is almost closed, stop and adjust the exhaust rocker arm on that particular cylinder. Loosen the exhaust rocker arm and follow the same procedure described before in steps 3 and 4 to adjust this rocker arm.

Both valves on this cylinder are now adjusted, and you can move on to your next cylinder and follow the same procedure again.
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Old 08-06-2009, 11:35 AM   #4
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Re: importance of TDC when torquing rocker arms

Which is the exhaust valve and which is the intake valve? There are 2 valves per cylinder and I can't find any pics to tell me which is which.
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Old 08-15-2009, 02:20 AM   #5
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Re: importance of TDC when torquing rocker arms

It doesn't REALLY matter. If one is open, then the other should be closed. Otherwise, if you're rotating the engine through a few revolutions, the intake will open, then close, then the exhaust will open, then close, then neither will move for a while. The first one that opens should be intake, followed promptly by the exhaust one.
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