Mopar Action On-line – Tech Questions
Dave Robertson , ON , Canada , 1965 Dodge Coronet 440
I have what seems to be incredible lifter noise at idle, almost like a knock. The noise was there previously, now it’s back after freshining up the engine. I used the same cam and pistons because they appeared to be fine. Cam is hyd /Crane 305H-10. I am running an old STR-14 intake (Rat Roaster 2×4 390cfm) which leaves a 2″ air gap above lifter valley pan gasket. I thought maybe it’s just valve train echo up through the top but of the motor but it can be heard with hood down 10 feet away. Oil pressure is 65 cold 30-35 hot idle. Thanks in advance for any suggestions..
Sometimes you can tell if the noise is from the bottom end or not by the frequency…top-end (valvetrain) noises are once per two revolutions, whereas bottom end noises are (usually) 1 for 1.
I have to believe that if a bottom-end component (rod bearing, piston pin, etc.) was bad enough to make this kind of noise, you’d have seen the results (read: wreckage) when you disassembled the engine. The oil pressure seems to back this thought up. I also have to believe that if a pushrod was bent or otherwise too short, you would have not only noticed it, the noise would have never gone away earlier, which your question seems to imply it did…? If I’m reading you wrong, you’ll need to check that each lifter’s plunger is depressed at least 0.020″ with that lobe on the base circle. If you have adjustable rockers, go for 0.025 – 0.030″, if nonadjustble, anything from 0.020″ to 0.075″ is acceptable (with the lower numbers providing a bit more RPM potential). This preload is mandatory. If you can’t get it you need different pushrods (Think: Manton). Also be sure none are bottomed (or nearly bottomed), that distance varies quite a bit by manufacturer, so simply test one of ’em by pushing down with a screwdriver (it may take quite a while for it to bleed down to the bottom). If this fails you may need to remove and disassemble one.
If you backed me into a corner, I’d say it’s a collapsed lifter that never properly pumped up. If you can’t see this (you may not), you can certainly feel it at idle (valve covers off), just touch the rockers. Feel near the center pivot to maintain contact. Wear decent gloves if the oil is too warm, or just use a metallic tool, the noise will telegraph right up to your hand. Also you may wanna try a mechanic’s stethoscope.