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Original Message
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| Money to burn. |
| By Gerry Proctor - 01/19/2006 6:33:55 AM; IP 137.242.1.15 |
For option 1, the factory non-adjustable rockers will do fine.
There are a couple of scenarios where you have to go to adjustable rockers. One is obvious -a solid lifter cam. The other really depends on the cam's lift and the type of hydraulic lifter used.
Hydraulic valvetrains have a specification for lifter preload. Factory hydraulic valvetrains are designed to achieve that preload, usually 0.060" of plunger depression, in an assembly line process so there's not a lot of tolerance for custom fitting on the build. Some, but not a lot.
The things that change preload are machining specifications on the block and heads and the cam's measured lift. If you haven't done any machine work on the surfaces of the block or heads, then the preload would be the same as at the factory. If the lift of the cam doesn't significantly alter the base circle dimensions, then the preload can be achieved with stock parts.
But, if you do machine the block or heads or you use a cam with a lot more lift then you'll have to set the lifter preload with pedestal shims, or different pushrod lengths, or with adjustable rockers.
There is some wiggle room on standard hydraulic lifter preload. In other words, you won't kill the engine if you're a little off. I won't argue that there is some impact, but for the most part unless it's significatly off, no one will ever realize it.
So here you are contemplating a full aluminum roller rocker. You kind of skipped over the factory and aftermarket, like Crane, iron adjustable rockers. This is the area where you start getting opinions since that's all there really is. It would be different if you were going to a roller cam. I would say yes, you should or would want to consider going to a roller rocker. But with a flat tappet cam, you have very little to gain by going to a roller rocker setup until you get above the 400lb range on the valve springs. There is no hard and fast rule on this. Will a 500lb spring work well with an iron rocker? Sure. Can you run the roller rockers on a 300lb spring? Sure. Most of all, you want to use complementary parts throughout your rebuild. Using a roller rocker setup with end stands and heavy shafts with beefy pushrods on a relative stock rebuild isn't complementary. Neither is using the stock stuff on a roller-camed engine. It's really a matter of durability. If you're going to beat on the parts, you better use good stuff.
There is another area of consideration when you must use some type of adjustable set up. That is with anti-pumpup lifters. They have a lower preload specification, usually 0.020" and for them to run correctly, you have to be pretty close to that preload.
So, the short answer for option 2, in my opinion, is to look at the Crane iron rockers. If you have the money to burn, then go with the roller rockers. |
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