Tapping sound?

I noticed for a while now the engine makes kind of a tapping or rattling sound when at idle and mostly in park, it sounds like its comming from under the pass. side valve cover. The engine runs fine and smooth but i just cant figure out what this noise is, ill try to get a audio clip up in the next few days too. kinda sucks too cause i got this nice flowmaster setup but the tapping takes away from the nice rumble sound you know?

Sounds like a loose rocker or collapsed lifter. It might also just need an adjustment and if this is the case, it could indicate a cam lobe failure in progress.

Now that you mention it, i think someone else was having a simmilar issue too, i dont think it does it when i accelerate, just at idle. would those things be a big expensive fix? or could a beginner like me dive into it?

Now that you mention it, i think someone else was having a simmilar issue too, i dont think it does it when i accelerate, just at idle. would those things be a big expensive fix? or could a beginner like me dive into it?

Do some research on how to adjust valves with the engine running (warning: this is MESSY!), before you do it. However, it is simple but DOES require starting the engine with the appropriate valve cover off to adjust the valves.

ok ill look into it

ok ill look into it

try some engine oil additive to clean the lifters... I found #8 cyl. to start to make noises first.. how does the oil look ...is it black ? or very dark ?

the oil looks like a light black, i have some of that marvel mystery oil too

the oil looks like a light black, i have some of that marvel mystery oil too


this sounds like you have a rich mixture... did you adjust the carb mixtures.....or if not that then ,,,the plugs/wires/coil are not supplying the correct spark ...


oil will get dark brown.. but if its black this is carbon ,, and will cause lifters to make noise ,,, as well as wear out the internal engine componets...


dirty air filter ? is the exhaust pipe at exit black / sooty?

The air filter is clean, the car used to shoot out black soot when i first got it but hasnt in a while now

if your oil pressure is low, or you dont have enough oil in the car, the lifters wont work.

I gotta change the oil again soon, i checked the dipstick and ther is oil, its at the add mark, so ill put some in and see what happenes

The air filter is clean, the car used to shoot out black soot when i first got it but hasnt in a while now


Hello, this reminds me exactly what my Caprice was doing when I purchased it... that rhythmic ticking noise from the left valve cover (only at idle)... I ripped off the carb, intake manifold and replaced all the hydraulic lifters, it cost about maybe $150 in total (new lifters, intake gasket and a fresh oil change)... What I had not counted on was the amount of dried up crusty black matter that was EVERYWHERE in the lifter valley - I spent about a week swearing w. a can of WD-40 in hand. I had to use miracle oil and a magnetic extension slowly 'lubing' the old clogged lifters out of their cruddy encasement.

To top it off I put a jar of Lucas oil additive to help break in the new lifters and prevent any damage from loose debris in the oil. After 2 additional oil changes (within a 2 month period), I can safely say that ticking is gone : )
However, if you can get someone to do this nasty job for you, I wouldn't hesitate to let 'em dive into the tarpit (unless your engine has been well maintained of course)

Hello, this reminds me exactly what my Caprice was doing when I purchased it... that rhythmic ticking noise from the left valve cover (only at idle)... I ripped off the carb, intake manifold and replaced all the hydraulic lifters, it cost about maybe $150 in total (new lifters, intake gasket and a fresh oil change)... What I had not counted on was the amount of dried up crusty black matter that was EVERYWHERE in the lifter valley - I spent about a week swearing w. a can of WD-40 in hand. I had to use miracle oil and a magnetic extension slowly 'lubing' the old clogged lifters out of their cruddy encasement.

To top it off I put a jar of Lucas oil additive to help break in the new lifters and prevent any damage from loose debris in the oil. After 2 additional oil changes (within a 2 month period), I can safely say that ticking is gone : )
However, if you can get someone to do this nasty job for you, I wouldn't hesitate to let 'em dive into the tarpit (unless your engine has been well maintained of course)

DO NOT REPLACE THE LIFTERS WITHOUT REPLACING THE CAM!

DO NOT REPLACE THE LIFTERS WITHOUT REPLACING THE CAM!

Silicon212, I didn't think to replace the cam, is the stock cam inherently bad in the 305 engine? My lifters were in a pretty bad state - they had very noticable depressions on the bottom where the cam lobes meet the lifter. Should I seriously consider replacing my cam now as well?

Silicon212, I didn't think to replace the cam, is the stock cam inherently bad in the 305 engine? My lifters were in a pretty bad state - they had very noticable depressions on the bottom where the cam lobes meet the lifter. Should I seriously consider replacing my cam now as well?

Yes, and the lifters again! If you see the (old) lifter is concave, think of what that cam lobe looks like. Your new lifters are already toast. The cam lobe and lifter wear into each other. If you look at the bottom of a new lifter real close, you will notice that it is not perfectly flat, but slightly convex (like a lens). Likewise, the cam lobe is not perfectly flat either, but slopes from the back down to the front at a slight angle. The whole reason for this is that when the parts are new, the lobe moving under the lifter will impart a 'spin' or slight rotation to the lifter. This rotation is CRITICAL to equalize wear. If there is no rotation, the cam lobe will eat into the lifter and the lobe/lifter will wear at an accelerated pace.

The slope on the lobes of the cam also act to thrust the cam backward in the block, so the thrust surface on the cam sprocket is pulled against the block and the cam remains properly located in the engine. This is why roller cams must either have a bolted plate on the sprocket, or a 'button' with a spring on the front of the sprocket (they don't have the angle on the lobe, don't need it).

When you replace one, you MUST replace BOTH!

If your old lifters showed any concave, that cam lobe is wiped. Running an engine with new lifters on an old cam that doesn't have the proper profile will result in immediate damage to the lifter.

The air filter is clean, the car used to shoot out black soot when i first got it but hasnt in a while now



because it was running poorly creating carbon deposits when first purchased and the oil is now black replace oil and filter and add 5oz of marvel mystrey oil. when it turns black again,,, repeat... eventually the engine will get cleaner so that your noise will stop... if not then at least the engine will be cleaner to replace any worn lifters/cam componets.....

i wouldn't replace just the lifters/cam without cleaning the entire engine of that carbon ,as carbon can rapidly wear an engine.......

Yeah ive been waiting to use the mystery oil, ill add it in the next change

Yeah ive been waiting to use the mystery oil, ill add it in the next change

if you are driving this vehicle often, you should not wait to replace this black carboned engine oil....


I would cut open the oil filter and see how much debris is in the filter media , and upon removal of filter media if i could see light pass thru it... also do not use fram oil filters........a/c, purolator pure one, wix these are good....

ok, yeah the oil has been changed three times so far since i had the car

ok, yeah the oil has been changed three times so far since i had the car


how many miles does the oil take to turn black ?

how many miles do you go on the oil change ?

I do the usual every 3k mile change, i havent wached it though

mine looks like black ink when i take it out and after a few miles of driving on new oil, it looks brown.
this engine is pretty much worthless though, so im not too worried about it.

its a 3.8, so, meh...
i usually do 2k oil intervals for the fact that if i go longer, i wont be able to see though the oil.

I think ill just change it next week even though its not at 3k yet, ill add that mystery oil in too. i was listening to it again tonight, and its a slight tap, but its not very loud or anything

I think ill just change it next week even though its not at 3k yet, ill add that mystery oil in too. i was listening to it again tonight, and its a slight tap, but its not very loud or anything

I would get a vacuum guage and check for any vac. leaks.... also at idle vac should be high and steady at 21inches.... if lower/or jumping something is wrong.... if this is 21inches and steady this is when you would adjust the mixture screws. has the mixture screws on carb been drilled out ? if so some one adjusted the mixture..


this is usually done because the engine has vac. leaks which effect idle and rather than repair vac leak these screws are adjusted .. this then causes a rich mixture..which may be your problem.....


another cause would be worn engine componets like piston rings,and excessive oil entering the combustion chamber...how much oil does this consume in 3,000mi ? if it uses 2quarts or more, then you most likely need engine work...

the vacuum gauge is a great tool to determine engine condition....as vacuum readings will narrow done whats bad inside....before buy vehicles like this it is wise to use this to determine if engine is good...

May sound like a dumb question, but where would i plug a vacuum guage too? also another issue ive been having, i notice sometimes when im at a complete stop, then go to step on the gas it sounds like the engine cuts of for a split second, and i'll feel a loss of power too...

May sound like a dumb question, but where would i plug a vacuum guage too? also another issue ive been having, i notice sometimes when im at a complete stop, then go to step on the gas it sounds like the engine cuts of for a split second, and i'll feel a loss of power too...

mounted on the intake manifold are vacuum lines... buy/get a T adapter and insert vacuum gauge on vac line to air cleaner or vacuum line from manifold to hvac vacuum ball, connect T close to manifold for accurate readings as the line you connect to may have a leak ...your engine should have many vacuum lines 5/32 sized id ...to be sure there is no leak on the line you tapped into firmly pinch the line leading to device and if vacuum increases that line/device has a leak...21 inches and steady is good ....

ok, anyone know about the power loss issue i mentioned above too?

ok, anyone know about the power loss issue i mentioned above too?

this hesitation is usually a vacuum leak....also if you find that there are vacuum leaks and someone adjusted the carb mixtures you will have to re adjust the carb mixtures....


the other thing could be timing is too retarded....

your engine should idle in gear at 500rpm so smooth you can't tell is running... when you take foot off the brake vehicle should almost not even roll forward on level surface...if you have vacuum leaks rpm has to be increased so that engine runs smoother and does not stall, and hesitate..

It does run smooth after about 5 min of a cold start, if i stomp on the gas a few times the idle will eventually knock down and become quiet. ill have it checked for vac leaks though, sound like thats what it is, i wouldnt be surprised. whats involved in fixing vac leaks? new rubber lines?

It does run smooth after about 5 min of a cold start, if i stomp on the gas a few times the idle will eventually knock down and become quiet. ill have it checked for vac leaks though, sound like thats what it is, i wouldnt be surprised. whats involved in fixing vac leaks? new rubber lines?

mounted on the intake manifold are vacuum lines... buy/get a T adapter and insert vacuum gauge on vac line to air cleaner or vacuum line from manifold to hvac vacuum ball, connect T close to manifold for accurate readings as the line you connect to may have a leak ...your engine should have many vacuum lines 5/32 sized id ...to be sure there is no leak on the line you tapped into firmly pinch the line leading to device and if vacuum increases that line/device has a leak...21 inches and steady is good ....go from line to line repeating this pinching proceedure until all leaks are repaired.... you may need several feet of vacuum/gas line hoses also any line cracked just replace....base of carb lines get brittle poor seal replace etc...

I would get a vacuum guage and check for any vac. leaks.... also at idle vac should be high and steady at 21inches.... if lower/or jumping something is wrong....

21 is an arbitrary number. There are multiple factors which determine what idle vacuum is. Engine vacuum is affected by things such as cam profile (overlap), compression etc. Normal vacuum on a stock engine is 15 to 17 inches hg @ 1,000 RPM. Mine is around 13 inches of mercury at idle speeds (high idle, 1,000 RPM) and that's due to the cam profile. It's low next to stock, but it's right for my cam. The most important thing is that the vacuum is at least 12 inches hg and that it holds steady - does not pulsate or drop.

If it holds within the 'good range' but flutters a few inches, rhythmic with the engine RPM, that could indicate a valve that is not seating. It could also indicate an intake manifold vacuum leak, or a misfiring cylinder. If it starts high and tapers off, this indicates an exhaust restriction. If it's low, this could indicate timing issues or a vacuum leak.

21 is an arbitrary number. There are multiple factors which determine what idle vacuum is. Engine vacuum is affected by things such as cam profile (overlap), compression etc. Normal vacuum on a stock engine is 15 to 17 inches hg @ 1,000 RPM. Mine is around 13 inches of mercury at idle speeds (high idle, 1,000 RPM) and that's due to the cam profile. It's low next to stock, but it's right for my cam. The most important thing is that the vacuum is at least 12 inches hg and that it holds steady - does not pulsate or drop.

If it holds within the 'good range' but flutters a few inches, rhythmic with the engine RPM, that could indicate a valve that is not seating. It could also indicate an intake manifold vacuum leak, or a misfiring cylinder. If it starts high and tapers off, this indicates an exhaust restriction. If it's low, this could indicate timing issues or a vacuum leak.



the 21 inches is reference to this engine type as built by GM... this is the vacuum reading that I get on this type of engine that has not been screwed with and has good compression and the mixture/vacuum leaks/timing are proper/correct..... 21in is what i expect to see on my engines at 700rpm not in gear...




if this is some mix/mod engine with non stock cams headers carbs and is used to drag race i wouldn't have a wild guess on what the correct vacuum would be ...... or even if there is a correct vacuum because that is not the priority in this case....