Photomania

I've got this clicking or tapping noise in my 1990 Corvette (L98 with manual transmission). There's no clicking when I first crank it. But after about 15 to 18 miles when the engine is warmed up, I hear this clicking/tapping noise. I can stand outside of the car and hear it well.

Another Corvette owner near me said he thinks it's a hyraulic valve lifter that's making the noise, especially since it doesn't make the noise until the engine is good and warm. He said I shouldn't drive it until it's repaired or else it may damage the cam shaft. He recommended I put Restore's Engine Restorer in the engine at the next oil change, which I did. I had gone just under 4,000 miles and 10 months without an oil change. He said the valve lifter might have gotten clogged up. I use Mobil 1.

The engine also has a brief sensation of a lapse in power when I'm driving along at a steady speed. Seems to occur around 2,000 RPM. When this happens, the RPM doesn't change any. But it feels as though I had let off the gas. It's almost as though the fuel flow was interrupted for a split second. I put a new GM fuel pump in the car less than a year ago. I've replaced the fuel pump replays.

Another mechanic told me to check the spark plugs for cracks, faulty plug wires and the distributor. I replaced the plugs and their wires less than a year ago and everything was fine for months.

Any thoughts on this.

94z07fx3

Since you can hear the noise at idle while standing beside the car you should be able to narrow it down to the exact spot with a mechanic's stethoscope. I'd do that before I went and threw any parts at it. If it is a lifter you should be able to replace it in your driveway/garage easy enough.

mtwoolford

If you believe it's a valve train issue, try pulling the valve cover(s).
It could be something as simple as a lifter that needs adjusting, or on a (almost) twenty year old engine, the stock stamped steel rocker could simply be worn out; visual inspection should reveal any physical damage.

using a mechanics stethascope or a piece of hose you'll be able, at the very least, to isolate what valve / valve train component is the offending noise maker.

scorp508

You can usually pull 1 spark plug wire at a time from the distributor to find it. I recommend wearing gloves.

PLRX

Photomania

Thanks guys for the advice.

Calderone

let us know how everything goes,my valvetrain is noisy as well

Photomania

I drove the car 10 miles to see the owner/mechanic (and friend) at an auto repair shop so he could listen to the clicking.

But the clicking noise was completely absent. He was very busy anyway. But he talked with me about rocker arms, valves, etc. and said absolutely don't drive the car anymore until the source of the problem is found. If a rocker arm is broken or loose, additional damage could occur to the engine. He was very emphatic about this.

I tried to get a ballpark figure from him about how much he would charge if he did the work himself and he said he couldn't come up with a figure.

He asked me if the oil light had come on, and I said no.

So I drove the car home and by the time I reached mile 15, the clicking noise was in full swing. So, I made up mind that I would at least remove the rocker arm cover on Friday if there is no rain. I would have done it today, but it rained.

The pulsation was bad and the engine seemed to run rough. It may need new fuel injectors, which is something else I'll eventually tackle, based on encouraging info from Jon at fuelinjectorconnection.com. Basically I can replace all 8 fuel injectors for $200. Whereas a Chevy dealership was going to charge me $540 to replace just one. It's a very time consuming job.

I got a hose as someone suggested and I put it over each cylinder and listened like a doctor and his stethoscope. I'm almost positive it's cylinder No. 7, which is the cylinder closest to the driver.

I just wish I knew why the noise doesn't occur until the engine is hot.

94z07fx3

Post up some pics of what you find under the valve cover. It's not a major PITA at all to pull them off of an LT1 but I have no idea how buried they are on your L98.

Photomania

Only four bolts come out of the valve cover and off it comes. Fortunately, the noise is on the driver's side and that side is much easier to access than the passenger side.

I'll take some photos, and see if I can post them. I have dialup and sometimes I can't even get logged onto the CF. Verizon stopped at my neighbor's house and won't bring high speed any closer. We've begged Verizon for years for high speed.

coupeguy2001

I would get #7 on compression, and wiggle the rockers. you will know which one is loose. If you don't mind cleaning up the mess, the absolute best way to adjust a rocker is while it's running. I have had the locking feature on some rocker nuts just lose tension, and I changed the nuts, and adjusted the valves, and that engine went another 87,000 miles.

Photomania

Sounds like the way to go, but I've never adjusted rocker arms. If one is loose, I understand I should turn the crankshaft with a breaker bar and bring the piston to top dead center and tighten the rocker arm. It must be challenging to adjust the valves. Is that something I should leave for a professional or is it something that a backyard mechanic can do if he proceeds with caution?

I was in the middle of removing the valve cover today when storms came. It's been raining for hours. I managed to remove the four valve cover bolts and the part of the serpentine belt and the spark plug wires, which I tagged. The valve cover is surrounded closely by hoses, and other things. I could almost lift the cover out of the way, but that will have to happen tomorrow if the weather clears up.

5abivt

I had a clicking sound from my ls1 camaro last week. I checked all the plugs and 1 was a little loose. Don't overlook the simple possibilities like I did.

Calderone

Its not difficult to adjust the valves,its time consuming and the bolt head is not long enough to get the socket securely so it will slip one time or two or more but be patient,this is the best part !
Im sure you can do it ! remove the spark plugs as well,that will let the compression out and it will be 60% easier to turn.-

Now do yourself a favor and take pics of every step you do !
i didn't do this when i removed everything 2 years ago and i was banging my head on the wall to assemble everything back in place
i did it succesfully thanks to the board members who helped me bigtime ! gotta love this board ! so take a pic and save the pics and you can post them here as well so we can join the fun and assist you if you have doubts and so that way you make us part of the process !

Good luck ! Hope to know more from your new adventure !
C.

powerpigz-51

Adjusting the valves is not that hard, and I have never done it with the engine running (too messy). If you breaker bar the engine clockwise starting at number 1, keep going until the intake valve is all the way closed, and then a hair further. Tighten rocker arm until you can barely spin the pushrod. Do the exhaust one next. The just follow around the firing order, 1-8-4-3-6-5-7-2. I always spin it one more time to double check. Keep in mind that even though they seem tight when you are doing it, pressure will bleed off the lifter so they will seem more loose than the first time. After that, turn all the nuts a quarter turn....some people go a half turn, I would check the consensus on that. This has never failed me.

powerpigz-51

Having a plug wire crossed also makes a ticking noise that sounds like a bad lifter. This would explain some of your other symptoms as well. Just a shot in the dark!

pletzvet

There has been a lot discussion in this thread about a valve train issue being the source of the noise that you are hearing. I'm not disagreeing entirely, but it seems odd that the noise develops after the engine has been running for some time and is well within operating temps. Typically (although not always) a sticky or leaking hydralic lifter will make most noise at start up, especially if the engine is cold. No harm in checking your valves for adjustment, however I would also be suspicious of a failing injector(s), especially since you have described a performance issue happening when you hear the noise. Some injectors are known to be prettty noisy - just another perspective.

Calderone

i had a miss,and it was an injector,it started to fail once it reached normal temps

powerpigz-51

I forgot to mention, when adjusting your rockers, make sure they are all the way loose when you start out........

Photomania

OK, I removed the valve cover on the driver's side today and spent a long time closely examining everything. The noise seemed to be coming from cylinder No. 7 and the rocker arms there are no different from the other rocker arms.

In fact, all eight rocker arms are identical in every aspect. The only movement they will make is a tiny bit of movement from side to side, but not up and down. This movement from side to side is ever so slight. Seems like normal movement.

I didn't see any cracks in anything. There was plenty of oil all over the rocker arms, valve stems, etc. I didn't see any sludge. In fact, it was a beautiful sight to behold and I can only imagine how all those rocker arms looked while in operation.

Yes, it does seem odd that the loud clicking noise occurs only after the engine warms up and the car has been driven 15 to 18 miles. I'm beginning to think it can't be anything in the valve train.

I took photos, but I can assure you they won't show anything unusual.

So, what should I do now? Is there anything else I should look for or check? All of the rocker arm nuts seem tight. I counted three threads above each rocker nut.

Should I go ahead and see if I can give the nuts a turn?
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