vetteguy75

I have a loud tapping noise coming from the top of the engine.(1975) It sounds like a value tapping (increases with speed). But here is the wierd part....if I let it sit for about 5 minutes after running it for a while...the tapping noise is NOT THERE!!! This happens sporatically....The last time was about a month ago. I just changed thermostat (180*)...the oil pressure is a little low (at idle)...about 35lb...but it increases with RPMs to about 40lbs. Any help would be GREATLY appreciated.....

Larry B.

I had a similar noise that sounded like a lifter. Several of us thought that was what it was. It was not.. It turned out to be the fuel pump push rod. The pump arm was actually stepped from wear and depending on where the push rod sat on the arm it may or may not make noise. Tough problem to diagnose.

L82-JWS

Had the EXACT same problem with a chevy 305 engine......same noise as you described, and after cam and lifter change, found it to be the fuel pump as described above...... :mad

vetteguy75

Really appreciate the input and ideas...but I forgot to add that I have a Holley Pro-Jection Throttle body fuel injectors...Sorry about that. So maybe the fuel pump idea may not be the problem....Thanks alot anyway!


[Modified by vetteguy75, 8:05 PM 7/6/2004]

marshrat99

Lifters? The place to start is to pull off the valve covers and check your valve lash. Search should give you several threads on how to adjust valve lash if you need help. If the lash looks good, the next thing I'd check would be to pull and inspect the lifters, pushrods and rockers.

I'm hoping that its not piston slap, piston rods or bearing related. Good luck.

yogi78

I have seen the rocker arm so loose that it would tap like a bad lifter. You can also check for lower end noises by pulling the plug wire on the suspected cylinder and checking to see if the noise goes away. It could also be the injectors snapping loudly while the engine is cold.

tom102

Check for an exhaust manifold leak where the manifold meets the head or a crack in the exhaust manifold, it will sound like a lifter noise and can usually get lower in volume as the temp rises. A piece of garden hose used like a stethoscope would help you locate it. Hope this helps.

gliot1

Everyone always goes deep on a tapping noise. Don't be bit by this one, it got me for awhile. The vacuum canister on the passenger side just over the valve cover. It would act exactly yhe same way. A loud tapping that sounded as if it were coming from deep within the engine. Disconnect the vacuum hose and see if it goes away. To fix mine I just had to tie wrap the vacuum line.