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???
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.
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?
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.
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...
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.
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.
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.
There are two classes of pedestrians in these days of reckless motor
traffic - the quick and the dead.
~ Lord Dewar 1933 ~
Climbing into a hot car is like buckling on a pistol. It is the great
equalizer. ~ Henry G. Felsen 1964 ~
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.
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.
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