My engine suddenly started making this tapping noise and I'm wondering if the valve lash needs to be adjusted. When the lash is out of tolerance can this tapping sound happen?

I did read on this forum that a leaky exhaust manifold can also cause this noise. I did recently check the exaust nuts and loosened/tightened them to what "felt" like 10ft-lbs. The sound started right after I messed with the nuts, but it really sounds like it is a metal to metal tap.

Any suggestions would be greatly appreciated.

S

Get a piece of hose or a mechanics stethoscope and listen around the engine until you pin-point the noise.
DD

I tried using the hose and a socket extension. It sounded like the noise was coming from the fuel pump. So...I switched out the pump with an old one (I had recently replaced a perfectly good pump ) and the noise was still there. I'm going to check the valve lash this weekend. I hope it isn't anything serious, I just bought the truck about a month ago...

It probably isn't anything major. If you just bought the truck, you probably don't know when the valves were last adjusted, so you may want to go ahead and do so. valve adjustment procedure

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks. I'll be making a hard copy of that adjustment procedure. The Haynes manual only explains how to do it on a non-running engine.

Haynes books (also Chilton, etc.) are very poor substitutes for the genuine factory service manual.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

What year is the truck / engine?
It could be a hydraulic lifter engine... with some clogged oil passages or push rods.
DD

Its in a 1980 d-150 truck. I'm assuming its the original motor so, it should have mechanical lifters right?

Took the valve cover off yesterday and found that there is a 1982 head on this engine. So there are not adjustable rocker arms. I just hope the engine is an 82 also, and not some Frankenstein.

I did find the source of the tapping sound. The #2 piston, intake rocker arm is pounding against the valve stem instead of just riding on it. With the engine running at idle I measured a .043" gap between the valve stem and rocker arm. Does this mean the hydraulic lifter has collapsed? If so is there anyway to get it back to normal without surgery?

The oil pressure is good, the gauge reads ~45-50 psi at idle. The oil is also dribbling nicely from the end of all the rocker arms. I also tried to sticking a .010 feeler gauge between all the other rocker arms and couldn't do it.

Any suggestions?

Thanks for the previous replies

You probably already know this, but the existence of a 1982 head does not necessarily mean there are no adjustable rocker arms, because the mechanical rocker assembly can be installed on the later head. Did you look and check to make sure the rocker arms aren't adjustable? As for a "frankenstein" engine, don't worry about it; there are many combinations of early + late parts that work just fine. But if you do indeed have hydraulic lifters and nonadjustable rockers, then yes, somebody probably did swap in a whole 1982 engine.
Probably so, yes.
Well, that kind of depends on how you define "surgery!" You would need to install a new lifter...

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

Yes, I checked the rocker arms, there are no adjusting nuts on them.

So, from what I've read if I replace a lifter I should replace all the lifters and put a new cam in. Is this what I'll have to do? Once a lifter collapses there is no way to pump it back up?

Given your situation, i would purchase and install one new lifter and pushrod to see if that fixes the problem.
Before installing the new parts, be sure to "pump-up" the new lifter in a small can of oil and check / clean the thru hole in the pushrod to be sure it is free of dirt.

The biggest worry is that the cam lobe is going flat or that the top of the valve stem is flattened (worn) to the point where the hydraulic lifter can no longer take-up the excess clearance.
DD

Okay.

This is a bummer since I did compression test 2 weeks ago, and the numbers were good. The cylinders were within 5psi of each other. Is it possible that the lifter just has some dirt stuck in the check valve?

If i attempt replacing the lifter, Should I pull the head or try to get it out with the head in place?

thanks,

The problem could be a piece of junk in the lifter or a clogged-up push rod.

With the correct tools, a bright light and a steady hand, you can replace the lifter with-out removing the head.
DD

You could also try running some Rislone in the engine to see if it will clean out the gunk or what ever is clogging it. After dumping in the Rislone, if it is going to clear it will clear with in 20 minutes at an idle. I have done this a few times on used rigs that were gunked up from running bad oil and or not enough frequent oil changes. Do an oil change after it frees up with a high quality high detergent oil to keep it clean.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG