I have six thousand (6,000) miles on my new/rebuilt engine. It has started to make a "tapping" noise. I would guess the noise to be a valve problem. I also suspect a little loss of power recently.

Is it time for a simple tune-up? Is it customary to need to "re-tune" a new engine as it breaks in? Might it be something else?

The engine is a Chevy 400 sb. The vette is an '80. Any info would be appreciated.

Thanks, Matt

 

I'd check the exhaust manifolds (or headers) and the connections between the collector's & the pipes for (hopefully) a leak.

 

Sounds like a lifter to me, and, no, it isn't unusual to go back and tweak lifters after engine break in. I would think you would have heard it before 6K miles. :)

 

I second the exhaust manifolds. Does it only make the ticking noise while under load? If so, it most likely is the exhaust.

 

Its probably a valvetrain problem. My ticked (sounded like a high pitched ping, in a click, click, click (corresponding to RPM). Then one day I got a banging noise-it turns out I broke a pushrod thanks to a sticky rocker. I'd check it out so you don't have to go and replace the pushrod(thankfully on mine, particles didn't go everywhere.) Give it a check

 

I am voting for the exhaust leak. Typically, a valve won't require further adjustment after break-in if a hydraulic cam is used and is adjusted correctly when assembled. USUALLY the 1/4 to 1/2 turn after zero lash is sufficient to compensate for any "loosening" of the engine after break-in. The exhaust, on the other hand, can start leaking at any time due to expansion and contraction from heating and cooling. Your sig doesn't indicate whether or not you have headers or not but I would check there first regardless. Definately start with the easy things first before removing valve covers. :flag

Good Luck.

dl

 

I agree its a good idea to first confirm there are no exaust leaks. Exaust leaks will pronounce themselves most when accelerating moderatly. They are more quiet during light cruise and idle situations. If its a constant steady ticking at idle then its most likely the valve train. A very common problem on SBC is the rocker arm nuts backing off and causing a clearance gap between the rocker arm and pushrod or valve tip. Hydrualic lifters should have 0 clearence and are even preloaded .020 to make up for wear as the miles increase on the engine. If you pull the valve cover and listen to each using a piece of heater hose or the like as a stethiscope. Its easy to pinpoint the tapping that way. Tighten the rocker slowly till the tapping just stops. Then slowly tighten the rocker an additional 1/2 turn to add preload. The engine may stumble when adding the preload. It should quickly recover on its own as the lifter bleeds down to accept the new adjustment. The bummer with this method is you may set some oil splash while running the engine with the covers off. The standard crimp type factory rocker nuts are pretty much wasted after you take them off and on more than once. They loose thier grip. I switched to the poly lock style rocker nuts just recently to eliminate this problem. There is an entirely different method of setting the lifter preload with the engine off as well.

 

As has been said, sometimes an exhaust leak at or near manifold can make such a ticking sound. Also sometimes this exhaust leak ticking sound is worse when the engine is cold, and may lesson somewhat when engine is fully warmed up, due to heat expansion on metal, resulting in a smaller opening, and therefore less of a leak ticking sound. Just something to keep in mind.

If not an exhaust leak, then I'd recheck valve lash / rocker arm adjustment as has been suggested.

 

Check for pulled rocker arm studs on heads with pressed in type.
Common on higher lift cam and stock rocker studs.

 

Thanks for all the help guys. I don't think the problem is the exhaust. I have headers, but checked them tightened down. The ticking also is most prevalent at idle. It starts to get drowned out as the rpm's go up, but does correlate with rpm's.

I will check this coming weekend to see if I can find the culprit. The engine also has comp-cam, hydraulic-roller lifters, and roller rockers. It didn't mention any of this before. I don't know if that affects the prognosis at all.

Thanks again, Matt

 

Is it a "metal tapping" or a "ticking"?

If ticking, have you checked your plug wires? A loose or shorting plug wire may not tick exactly with the RPM and it could result in a loss of power.

Just a thought.

Jerry

 

rocker arm nut backed off i bet.... tighten it up some...like i said before use locking adjuster nuts and readjust all .... dont runt it with it making mechincal noise or tapping too long. it will destroy something sooner or later.