Valve noise???

Hello,
I have a 1965 Chevrolet Impala with the original 327 (300Hp) engine. I do not drive it that often. I have noticed a "tapping or rattle" noise when I
am about 2500-3000RPM. It is more noticeable when the car is maintaining a constant speed as opposed to letting off the gas or speeding up (under load). I figured it was maybe a bad lifter, so I replaced them all. Of course, it is still there. Any ideas???
Thanks,
Paul
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You don't mention the mileage but I would say that the lifters are probably varnished internally from sitting. Years ago they used to recommend that you dissemble the lifters and clean them. But if I were to take the intake off to get at the lifters I'd replace them.
Brian
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How about running the engine with valve covers, off you should be able to hear which side it is first, if you hear this in the upper valve train, pull that cover and try to see/feel which valve/rocker arm is noisey and adjust it or all of them. Were any of the old lifters badly cupped, if so the cam could be bad, now this is assuming the noise is in fact in the valve train?

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Before I replaced the old lifters with the new ones I tried to duplicate the noise with revving the engine in my garage to about 3000RPM. I couldn't duplicate it unless I was on the road. I also removed all of the belts, thinking maybe it was a pulley, etc. No luck. When I changed out the old lifters I did not notice anything out of the ordinary as far as a worn cam. You are right about "if" it is the valve train.
Thanks,
Paul
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Maybe it's NOT the valve train if you only hear it when on the road. That opens up many other possibilities. Loose baffle in muffler or Catalytic converter, fan blade(s), just to name a few of many others...

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Catalytic converter in a 1965 Impala?
I vote valve ping. Today's fuel octane is too low for that engine. Try premium fuel or a octane booster. And you may need to add a lead additive as well.

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Here are a few noisemakers that I've found over the years.
Carbon buildup on a piston Worn mechanical fuel pump Rotor hitting inside dist cap Cracked flex plate
They can all sound similar to a lifter. H
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Hairy,
All of the ones you mention are good ones to check. It is so frustrating when I can only make it happen on the road (under load). The car has a brand new rearend and rebuilt powerglide tranny. I think I will just swallow my pride, open my wallet, and take it to the mechanic. I should have done that before I replaced the lifters. I really thought that was it!! Oh well, thanks anyway.
Paul
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usually do it more at idle. The valve (if your car has one) should be on the exhaust manifold right above where the exhaust pipe bolts to it. It should move freely but if you want to test it, just slip the spring off of the pin and do a road test (make sure it opens up all the way ). I always disabled mine to keep it from rattling.
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I'm not sure whether a car this old would have any or not, but it sounds like you have a loose heat shield somewhere on the exhaust system. When one of the weld spots break, they will rattle until they eventually fall off.
Sharky
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I am thinking fuel pump.

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Scott,
I do have a spare (new) fuel pump I could swap out to check. Thanks.
Paul
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let us know.

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Scott,
I changed out the Fuel Pump. No change. Someone suggested a bad rocker arm or pushrod. My problem is I can't drive and check it at the same time. Man this is frustrating. Would a stethoscope be able to pin point a bad rocker/pushrod at idle speed? Thanks in advance.
Paul
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