Cratecruncher

I'm trying to isolate a distinct and metallic tapping noise coming from the lower left side of my engine block. I tried putting a large screw driver to my ear and the top of the rocker cover and the noise doesn't seem to be coming from there. It is loudest when I'm under the car staring up at the exhaust manifold.

The car is a '99 with only 60K MILES. It's bone stock and I've owned it since mile 1. I originally dismissed it as a mild exhaust leak but it's not that. I also have mild piston slap on cold mornings and it's not that either. The noise is a tap tap tap that is loudest at cold idle but only quiets slightly when the engine warms. It changes frequency with rpm but doesn't get any louder so the engine noise drowns it out above 1500. I haven't had any backfires or poor idle and no codes.

My plan is to warm up the car and quickly remove the rocker cover and check for excessive valve train clearance before the lifters bleed out. I'll also check for any rocker damage naturally.

Am I on the right track? Any suggestions? Should I have a new rocker cover gasket before I open her up? Can I run the engine with the rocker cover off if the problem isn't obvious?

I've read all the other threads I could find here. I'm a overhead cam guy so this pushrod stuff is kinda new to me. Any advice appreciated!!

vettenuts

Sounds like you are on the right track. With a stock car the rocker is one suspect based on history.

leadfoot4

I think you're on the right track, and technically, you could run the engine w/o the valve cover in place, but unlike the older Chevy engines, the coil packs of the LS engine sit on top of, and are attached to, the valve covers......



If you have a bad rocker arm, this could help.....

https://www.corvetteforum.com/forums...grade-kit.html

CaseyJones

A bad rocker would probably be my first bet. Get the crankshaft turned so that the offending cylinder in on TDC and check the rocker, spring, and pushrod for looseness. A worn cam lobe could also cause it if things have gotten that bad over time.

I'd also check the plug wire for spark jumping. Just in case...

Cratecruncher

Thank you for the affirmation and advice everyone. I'll open it up and get back on what I find. I can't believe I have a major internal engine failure with only 60K and no track/racing. Just mild-mannered driving and Mobil-1 when the display tells me it's time for a change. Fingers crossed it's just a failing rocker assembly but these tapping noises are apparently difficult to diagnose from what I've read here.

I'm assuming it takes at least 20 to 30 minutes for the lifters to lose hydraulic pressure after the engine is stopped. Is this correct? It will take me several minutes to remove the cover and free each valve from it's cam lobe by rotating the crankshaft manually.

Cratecruncher

Here is a Youtube video of an engine idling with the rocker covers off. The poster commented the trouble turned out to be two lifters that had rotated 90 degrees when the plastic guide trays cracked. That's why there is no tapping sound, but a metal scraping sound instead.

Cratecruncher

I warmed the engine then took the rocker cover off the left side as in the video above. Wouldn't you know the lifter shut up the minute I fired it up with the cover off. So I guess I fixed it!

Joking aside, I'm relieved it is still intermittent and my cam is ok. It gives me hope I may be able to rehab that wonky lifter without taking the engine apart. I plan to spray some B12 down the pushrods and run some engine flush through it, then change the oil and filter.

My engine looked really clean inside too. The top of the head had an even light gold tone with no deposits. Sorry, I didn't think to take a picture.

Jeff T.

As soon as you go through the work it gets quiet!

At least you got a peak inside and could see how clean everything is.

tbrowne

The car never knocks when a mechanic is listening. I thought everyone knew that! LOL!!!!

vettenuts

Just check for contact with the valve cover. Long shot but since it got quiet with the cover off might as well check it now.

Cratecruncher

I'm happy to report I figured out (ok, stumbled across) what was making that awful noise in my engine!

When the noise came back louder than ever I began fretting over what to do next. As the receipts began accumulating in my head for the imminent engine rebuild I recalled Bill Curlee suggesting in several threads that a piece of long fuel line next to the ear can help pinpoint a noise. I wanted to narrow down which cylinder was affected so I started directing my hose all over the left engine bank until I found the loudest point right next to the spark plug of the front left cylinder. What the..?

I then recalled someone else mentioning their lifter noise turned out to be just a loose spark plug. Friends, it is with much relief and a large helping of embarrassment that I report the car was fixed by tightening a stupid spark plug!!!

If anyone else has a horrible pinging which sounds like a ball peen hammer hitting an anvil check that your spark plugs are tight first. Mine had backed out about three turns.