checking pushrod length?
02-24-2011, 06:29 AM
#21
i installed the stock length pushrod,colored valve stem with a sharpie,properly adjusted the rocker and turned the motor over til the rocker went up and down twice.I then pulled it back apart and checked to see where my mark was.with the 7.2" pushrod the mark was off toward the exhaust port.i then adjusted the pushrod checker .50 at a time til i got it where i thought it should be.7.00" seemed to be the magic number and put the line in the center of the stem and i tried on different studs to see if the outcome was the same,like i said ive never done this before and i could be doing something wrong.when the rocker is adjusted with the 7.00' pushrod the set screw sticks out of the polylock when tightened down which makes me question if i did it right.
02-24-2011, 08:19 AM
#23
A couple of years ago, I tinkered with this in depth and this is what I found.
First off the best way to check PR length is to use a solid lifter or convert a hydro lifter into solid for testing purposes. I tried the soft valve spring and it always gave inconsistent results because the piston in the lifter would always move some tiny amount. IMO, its worth pulling the intake and using the solid lifter to ensure the measurements are spot on accurate. I remember way back, when using the soft spring testing, the 7.050" PR length looked to be correct for my motor. When I did the solid lifter testing more recently, the ideal PR was 7.150" and that is what I am running today with great results.
Second dont use a Sharpie because the markings dont wipe off easily enough to reveal the pattern. Instead, use a dry erase marker (whiteboard marker) and the patterns will be much more clear and readable. The best stuff to use IMO is ring and pinion gear pattern grease because that stuff provides the best pattern period but not everyone has it sitting in the toolbox.
Third the ideal scenario is to have the sweep pattern as thin as possible and dead center on the valve tip. You will quickly learn that this is not easily achievable so one must compromise. I personally believe that thin sweep slightly trumps being dead center because the bigger the sweep, the more parasitic loss (friction) at the rocker roller thus robbing power. Also you dont want the pattern to be too close to the edge of the valve or you risk excessive valve guide wear due to the valve being biased when moving up and down in the guide.
IIRC, my current roller sweep is around .040" with the pattern being around .030" off center on the valve. If I run the pattern dead center of the valve, the sweep increases to around .090" or so. Without some serious mods to the heads and valvetrain, it is impossible IMO to have .040" of roller sweep while having the pattern dead centered on the valve so again, you must compromise. I have also gotten the sweep down closer to .020" or so but the pattern was dangerously close to the edge of the valve.
My 2 cents.
First off the best way to check PR length is to use a solid lifter or convert a hydro lifter into solid for testing purposes. I tried the soft valve spring and it always gave inconsistent results because the piston in the lifter would always move some tiny amount. IMO, its worth pulling the intake and using the solid lifter to ensure the measurements are spot on accurate. I remember way back, when using the soft spring testing, the 7.050" PR length looked to be correct for my motor. When I did the solid lifter testing more recently, the ideal PR was 7.150" and that is what I am running today with great results.
Second dont use a Sharpie because the markings dont wipe off easily enough to reveal the pattern. Instead, use a dry erase marker (whiteboard marker) and the patterns will be much more clear and readable. The best stuff to use IMO is ring and pinion gear pattern grease because that stuff provides the best pattern period but not everyone has it sitting in the toolbox.
Third the ideal scenario is to have the sweep pattern as thin as possible and dead center on the valve tip. You will quickly learn that this is not easily achievable so one must compromise. I personally believe that thin sweep slightly trumps being dead center because the bigger the sweep, the more parasitic loss (friction) at the rocker roller thus robbing power. Also you dont want the pattern to be too close to the edge of the valve or you risk excessive valve guide wear due to the valve being biased when moving up and down in the guide.
IIRC, my current roller sweep is around .040" with the pattern being around .030" off center on the valve. If I run the pattern dead center of the valve, the sweep increases to around .090" or so. Without some serious mods to the heads and valvetrain, it is impossible IMO to have .040" of roller sweep while having the pattern dead centered on the valve so again, you must compromise. I have also gotten the sweep down closer to .020" or so but the pattern was dangerously close to the edge of the valve.
My 2 cents.
