Evo Valve piston contact?

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Feb 11, 2012 | 05:15 PM

mbierbac

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From: Alberta Canada

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

Feb 11, 2012 | 05:18 PM

djl

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Originally Posted by mbierbac

Mock it u and check it.

Feb 12, 2012 | 01:13 AM

Mike

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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.

Feb 14, 2012 | 01:18 PM

mbierbac

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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!

Last edited by mbierbac; Feb 14, 2012 at 01:23 PM.

Feb 14, 2012 | 01:36 PM

djl

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I wouldn't worry about it; put it together and ride.

Feb 15, 2012 | 01:49 AM

Mike

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From: Centralia, Wa

Quote:

Originally Posted by mbierbac

Are you running the SE3 cams? You'll gain about 20 thousandths additional overall lift, and about 5 thousandths additional tdc lift with your rockers, not enough to be of a concern with those cams. You're still building a mild evo motor, there's nothing in your parts list that raises any concerns. If you had a bunch of money tied up in expensive componants, you might need to be looking at S&S cases, but I don't think that's the issue here.

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.