what is the difference between extruded aluminum rockers, vaccum die formed and billet? any recommendations on what to stay away from and still use stock valve covers? Proform has the cheapest price in Jegs or Summit at 139.95...ok to get them? and, lastly, i have been told these rockers will not last on a daily driver, is that true
thanks guys

 

I'm not sure what difference between extruded aluminum rockers, vaccum die formed and billet is, but I would say stay away from Proform rockers I have seen one that actually came apart in a friends 355, the part where the stud goes through broke in half, about a month after he put them on. I belive you get what you pay for, so if it were my motor I would spend the extra money and get a set of Hartland Sharp roller rockers, or a set of Crane gold roller rockers.

 

Save the aluminum for custom wheels and beer cans. Use steel for rocker arms if at all possible. You can get forged steel rockers that are actually lighter than the aluminum ones and will nearly survive a direct thermonuclear assault.

If you want a little history, do a search for "aluminum + rocker + failure" .

 

extruded = squeezed through a die (like squeezing toothpaste from a tube) to get a long bar with the right shape of the rocker (from the sideview), while the almost liquid aluminum is still plastic (gooey); the hole for the main roller bearing is also usually made during the extrusion process. Once the extruded bar is made, there is still final slicing of the bar and then final machining needed to get the rocker's full shape, and to add the bearing(s) and hardened pushrod cups.

same as above, only with the extrusion zone being done in a vacuum chamber, to suck out any trapped gas bubbles;

A billet is a large metal bar that was formed by either casting (pour liquid metal into a mold, let harden) or by forging (start with a superhot casting and then pound on it with a large impact press to align the grains within the metal; this enhances the overall strength of the metal. The billet then gets sliced and machined into whatever shape you want.

Extrusion allows large numbers of the raw rocker to be made at reduced cost. The billet method involves a lot more machining, so it costs more. There are other benefiots to the billet method which I won't go into, but again, they raise the cost. The billet method is usually only done on very good (pricey) alloys, while the extrusion can be done on many alloys.

I suppose what matters most, for fairly inexpensive aluminum rockers, is the quality of the manufacture and the type of aluminum used (like 7071 alloy for example). You want a strong alloy grade of aluminum because the rocker is subjected at a harsh life, but you also have to have high quality machining and insertion of the bearings, roller tip, and wear guards.

I knew about the effects of stress on aluminum, and the interfacial galling that results from steel -to- aluminum a long time ago, before I ever saw my first aluminum roller rocker. For that reason, I won't buy them. I've also heard enough stories from people that have seen aluminum dust tracks from high shear stress locations on aluminum rockers, and that confirmed what I already knew. IMO they won't last as long as OEM stamped rockers. Readers can disagree with me -- hey it's YOUR money.

I'm also not convinced that the friction losses reduced with the roller(s) makes up for the possible increase in the valve train mass (rotary inertia for you Mech Es and Physics types) and the way that will lower the rpm for valve float. This is an item that seldom, if ever, gets mentioned but one that I've thought about.

IF I were going to buy roller rockers, I'd buy the ones made from steel, not aluminum. These cost a lot more btw. And I'd only do it if I was sure that the rpm penalty in added mass was slight (i.e. I'd analyze the rocker).

I can't, however, answer your question on how well they last because I think it has a lot to do with how stressed the rocker get (valve lift, cam profile, and how often you visit the redline), how well they were constructed, and how frequently the oil gets changed.

The above is probably more detail than you wanted to hear, but it is the facts. IMO <g> - Ken