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Engine Help
I have a 400 Ford .030 over = 406
(Its a 351 C with 1" more deck height) Stock heads mild compression bump 9.25:1 Crane Cams 524421 Lift @ .050 220 Intake 230 Exhaust Cam installed 2 degrees advanced (due to clearance issue with connecting rods) In the first build the clearance was not noticed. It ran strong for about 2 hours, until it sheared the timing keyway. Every other lobe was just sligthly contacing the connecting rods. All parts inspected and new timing set, cam, lifters, and pushrods installed. Including 1 new valve which had bent. (I don't know which cylinder, but can ask the builder). Now, I'm bending pushrods on #8 cylinder only. The failure is not during any particular hard running. This is the second time it has happened and I'd like to get to the bottom of this. Any ideas/suggestion? |
First thing to check when bending a pushrod is valve spring bind... that is, compressing the spring to the point that it can't compress anymore and passing on the "excess" to the pushrod.
Also poor alignment of the pushrod and rocker arm (guide plates?). Good luck sorting this out. - Jim - |
To bend pushrod, either alignment is off or valve springs are coil-binding. What bothers me most is if you advance cam for clearance, with timing chain wear, you may be back where you started. What cam are you running anyway? Could the base circle be wrong?
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A defective cam is a possibility, but the binding valve spring far more likely. This becomes more likely if the machine shop that did your heads installed too many spacers under the spring to boost tension. When you replace the pushrod this time, replace the valve spring too, and take a hard look at the rocker arm to make sure it's correct and intact. A more remote chance is an incorrect pushrod, but if you've replaced them more than once it becomes more doubtful...
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WADESDAD,
THIS INTERESTS ME AS I TOO HAVE BUILT A 400M BLOCK CLEVELAND WITH QUENCHED 70 4V HEADS, MOTOSPORT CAM, RHODES LIFTERS, CRANE ROCKER CONVERSIONS AND ROLLER LIFTERS. NEVER THOUGHT OR HEARD OF SUCH CAM LOBE /ROD CLEARANCE PROBLEMS. I BUILT THE ENGINE ABOUT 3 YEARS AGO AND HAVEN'T FIRED IT YET. I LIVE JUST OUTSIDE CINCI AND WOULD LIKE TO HEAR WHAT YOU FIND OUT AS TO WHAT WORKS FOR YOU TO CLEARANCE EVERYTHING AND STILL HAVE IT RUN DECENT. |
wadesdad,
I think the correct way to address the clearance issue is to remove material from the rods, or more likely the rod bolts, to correct the interference. Rebalance the rotating assembly afterward. Your engine builder should've caught this during assembly. Coil bind, or insufficient piston-valve clearance is most likely the cause for the bent pushrod. Good luck, |
Gentlemen,
Do I have "too much" cam? I copied a HotRod Mag build-up as close as practical, but they didn't mention many of the issues I've encountered. -wadesdad |
I am not a cam engineer, but..
The figures you gave seem quite mild, even for it being a SB
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Cam is about right for street use. You provided duration, but not lift.
Could be a valve hitting a piston also. Did your machine shop do any trial assembly on this setup? This should have all been checked, and caught before final assembly. |
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