I have "Summit" brand roller rockers. I think they are made by Crane. The are die cast aluminum, and have a typical needle bearing fulcrum and a roller tip. 1.5 ratio.

The problem is that the push rod apparently punctures the steel cup that it sits in, in the rocker, then the rocker pivots, and the end of the push rod breaks off. The result is less lift, poor idle, and "lifter" noise on that one cylinder. When I pull out the rocker, the push rod comes w/it because it is thoroughly jammed into the rocker by that point. The first one did it a few months after I installed them, and the second one a couple of days ago. (it's been a year and about 5000 miles now.) They were both exhaust valves; first on #5, the second on #6. I don't understand what is causing this.

Other info...

• stock '78 400 long block
• Stock springs
• stock push rods
• Cam; 224*/234* @.050 .465 INT / .488 EXH
• I shift @ 5000 RPM, never go above 5300.

The push rods are straight and then taper to a rounded end -they don't have the "ball" type ends. I wonder if the end of the push rod is binding in the rocker b/c of the higher (than stock) lift cam? I also wonder if I am floating my valves and the impact of the push rod coming back into contact w/ the rocker is causing the problem. But the engine doesn't miss or fall flat on it's face approaching 5000 RPM like I would expect from valve float. The power fades quick above 5000, but I'm using box stock heads and a Crossfire intake, so I expect it to be done by 5. Any ideas?

 

Tom,

Elgin also makes some of the "no name" rockers, but I don't know if they do aluminum.

Are you using hardened push rods? It's possible that the rocker material is not adequately hardened to withstand the hard push rods and extra force of your cam and springs. I'd send tham back for a replacement set or refund. The Comp Pro Magnums are forged steel, and lighter than the aluminum rockers, so that's an option as well.

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Later,
Vader
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Justice and Freedom will Prevail

 

You've got a binding/interference problem somewhere.

There are several different causes of this:

1. Coil bind. The springs you're running are stacking solid causing the damage to the other valve train parts.

2. Pusrods are binding where they pass through the cylinder head. This is a pretty common problem with higher lift camshafts and older-style heads that do not have guide plates. Those style heads also need to have the slots in the heads elongated for pushrod clearance too.

3. Valve spring retainer to guide inteference. At max lift, the retainer is hitting the guide stacking things solid.

4. Pushrod interference with cylinder block in the area of then block located between the lifter and cylinder head. Sometimes the block needs clearancing in that area to prevent the pushrod from contacting the block.

5. Piston to valve clearance not sufficient. Valve is hitting the piston causing solid stack. This probably isn't the cause though unless you've done some major mods to the engine (domed pistons, severaly decked block and/or heads, etc.)

6. Incorrect pushrod length, probably too short. It's always better to have a pushrod that much too long than one that is only a little too short.

7. Weak valve springs. At higher RPMs weak springs cannot properly control the valve. The valve hangs open because the spring is too weak to close it in time and the piston catches up with it and kisses it. Remember, the piston is always chasing the exhaust valve.

What you need to do is remove all the spark plugs to eliminate compression resistance. Then get a really bright light and get down where you can watch the valvetrain as it travels through two complete revolutions.

It would be best to find a way to turn the engine by hand, but you can get away with a hand held bump starter. .030 is the MINIMUM clearance you should see between all the parts; more if you really rev high.

Be sure to remove the fuses that control the fuel pump and the ignition.


Keep us posted on what you find.

Jake


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1986 Corvette Coupe, 415 CID, Edelbrock 6073s, ZZ9, TPIS Long Tube Headers and DynoMax Super Turbos (HATE 'em)