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Original Message
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| Stock rockershafts flex with modern camshafts. |
| By Dave Shoe - 05/17/2002 12:36:22 AM; IP 63.233.226.78 |
Rockershaft flex was dealt with on the 427 by using cast iron pedestals. Iron pedestals with the slot cut into them provided clamping rigidity along the entire pedestal, so the rocker didn't seem to be standing out all that far. This worked fine back when racing valve spring technology was more primitive.
Factory aluminum pedestals don't have the capacity to clamp the shaft like the iron pedestals, partly because they don't have the slot and partly because aluminum is three times more flexible than iron.
The goal is to switch to beefier aluminum or steel pedestals, but the critical need is to get the end supports replaced because that sturdy-looking stub of a rockershaft hanging off the end is unbelievably flexible, particularly with modern camshafts which have been designed with fast ramps suitable for modern valve spring technology.
All FEs with "beyond CJ" camshafts MUST have rocker end support stands of some sort, unless you want to have a "story" to tell (I have stories, as do many others who learned the hard way). Breakage can be expected, too, so you won't have to wait too long to learn.
Stiffer rockershafts are available with thicker walls or the bogus "hardening" claim (hardening helps NOTHING in this situation), but the problem is shafts can only add thickness at the ID, and this does little to add rigidity. Even a solid steel rockershaft would tend to flex too much, so the end support stand is the only first place to look. Reinforced (thicker) shafts are a fine third line of defense.
There are several pedestal end support designs with varying cost and sophistication, but it seems they all work if you're not planning lifts beyond .650 and revs beyond 7000. You do want to look at the more expensive ones if you want to push these limits.
Sorry, I'm not knowledgeable about all the current offerings, so it might be good to ask the forum where the best place is to get some.
The second line of defense is to replace the wimpy rockershaft springs with solid aluminum dowels, and the fourth is probably to replace the center pedestals, though the details get sorta engine-specific beyond the dowels.
I seem to recall I paid about $120 for some nice FPP end supports about a decade ago. Don't know what they're going for now. Hey, $120 seemed kind of steep until I saw the mess left by the stock pedestals.
JMO,
Shoe. |
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