Evo Valve piston contact?
#1
Evo Valve piston contact?
I have installed a Screaming Eagle cam with 0.503" lift on my Evolution. I am looking at installing roller rocker arms with a lift ratio of 1:1.6, but I have stock heads with a James head gasket. Should I be concerned with valve/piston contact. Should I just stay with stock rocker arms
#2
I have installed a Screaming Eagle cam with 0.503" lift on my Evolution. I am looking at installing roller rocker arms with a lift ratio of 1:1.6, but I have stock heads with a James head gasket. Should I be concerned with valve/piston contact. Should I just stay with stock rocker arms
#3
It's the tdc lift you need to concern yourself with, not the overall cam lift.
However, if I understand you correctly, you're changing to 1.6 rockers, so you're actually reducing lift a fraction (stock evo rockers are 1.625), and your screamin eagle cams should have plenty of piston to valve clearance.
However, if I understand you correctly, you're changing to 1.6 rockers, so you're actually reducing lift a fraction (stock evo rockers are 1.625), and your screamin eagle cams should have plenty of piston to valve clearance.
#4
Thank you for your reply. I guess I should have been a bit clearer. Actually the roller rocker arms have a lift ratio of 1.675, which would increase spring lift slightly. I inspected my old head gaskets they were also James 0.45" thickness which is what I replaced them with. The S&E Cam has a 0.503" lift from that of stock 0.472". Flywheel, rods, pistons, cylinders, and heads are all stock spec replacement. My concern is more on the excess stress to the springs as well as the cylinder studs. My cases are stock 94 EVO and the concern is that everyone says these years are softer and weaker. Several mechanics including short block Charlie had recommended changing cases, however I opted to rebuild using the originals. Can the additional stress from constant excessive lift possibly eventually pull those cylinder studs from the cases. I was even torke shy during the head torking procedure.
Maybe I should be conservative instead of power hungry and just stick to solid rocker arms from Harley!
Maybe I should be conservative instead of power hungry and just stick to solid rocker arms from Harley!
Last edited by mbierbac; 02-14-2012 at 01:23 PM.
#5
#6
Thank you for your reply. I guess I should have been a bit clearer. Actually the roller rocker arms have a lift ratio of 1.675, which would increase spring lift slightly. I inspected my old head gaskets they were also James 0.45" thickness which is what I replaced them with. The S&E Cam has a 0.503" lift from that of stock 0.472". Flywheel, rods, pistons, cylinders, and heads are all stock spec replacement. My concern is more on the excess stress to the springs as well as the cylinder studs. My cases are stock 94 EVO and the concern is that everyone says these years are softer and weaker. Several mechanics including short block Charlie had recommended changing cases, however I opted to rebuild using the originals. Can the additional stress from constant excessive lift possibly eventually pull those cylinder studs from the cases. I was even torke shy during the head torking procedure.
Maybe I should be conservative instead of power hungry and just stick to solid rocker arms from Harley!
Maybe I should be conservative instead of power hungry and just stick to solid rocker arms from Harley!
There was a few years in the early-mid 90s, where some evo cases were cracking on the pinion shaft side near the lifter blocks. It was a bigger problem for the cases that had been bored for a big block. If your cases are good at this point, they will probably hold up with your build. Under tourquing your heads is not a good idea though, and could contribute to creating the very problems you're trying to avoid.
I'm with dj, build it to the best of your ability, and don't worry about it.
#7
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