Push rods
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Road Captain
Joined: Oct 2007
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From: Morris, Il
Push rods
Can anyone explain to me the difference between the intake and exhaust push rods. I know the intake is a bit shorter. Is this a fit issue or is there another reason. What would happen if you mixed them up. Thanks guys. Just a bit of curiosity.
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From: Phoenix '53, '88, '09 Big Twins
the length is crucial to the valve opening to the correct height.
too low, the motor doesn't make good power.
too high and something breaks
the intake valves are closer to the cam centerline ( in the middle of the motor) and the exhaust are on the outside, so farther.
the cam pushes up a lifter, which pushes up the pushrod, which pushes up on a teeter-totter ( the rocker)- which pushes down on the valve stem- opening the valve.
Springs at the valve end keep clearances close and gives tension back on the whole assembly to close the valve as the cam lobe falls away.
at high revs the springs cannot keep up with the momentum of the "lifting" parts and the valves may "float"--- and get smacked by the piston.
this is why we have rev limiters, our top ends are fine below 6000 rpms
Mike
too low, the motor doesn't make good power.
too high and something breaks
the intake valves are closer to the cam centerline ( in the middle of the motor) and the exhaust are on the outside, so farther.
the cam pushes up a lifter, which pushes up the pushrod, which pushes up on a teeter-totter ( the rocker)- which pushes down on the valve stem- opening the valve.
Springs at the valve end keep clearances close and gives tension back on the whole assembly to close the valve as the cam lobe falls away.
at high revs the springs cannot keep up with the momentum of the "lifting" parts and the valves may "float"--- and get smacked by the piston.
this is why we have rev limiters, our top ends are fine below 6000 rpms
Mike
Last edited by mkguitar; May 29, 2012 at 11:24 PM.
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Road Captain
Joined: Oct 2007
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From: Morris, Il
Think my question concerns adjustable rods. Because you adjust up from dtc the readjust the 2.5-3 full turns. At this point does the rods really matter if you adjust them properly. Guess my question reflected a fixed rod.
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From: Phoenix '53, '88, '09 Big Twins
adjusted to the correct length is same as fixed length.
too long it breaks, too short it doesn;t run right.
adjustable pushrods are easy, specific brand instructions will tell you how to adjust and lock down.
adjustable rods are usually used to save cost of labor when swapping cams- the stock rods are cut out and the adjustables can be put in place easily. fixed rods would require pulling the rocker covers off- but are generally more precise and no worries about lock nuts backing off- fixed rods may also be lighter in weight which is betterer
mike
too long it breaks, too short it doesn;t run right.
adjustable pushrods are easy, specific brand instructions will tell you how to adjust and lock down.
adjustable rods are usually used to save cost of labor when swapping cams- the stock rods are cut out and the adjustables can be put in place easily. fixed rods would require pulling the rocker covers off- but are generally more precise and no worries about lock nuts backing off- fixed rods may also be lighter in weight which is betterer
mike
Last edited by mkguitar; May 30, 2012 at 12:38 AM.
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