Nick81

I have an 81 with a stock 350 that I just replaced the valve stem seals on. It runs nice and no longer burns oil. but now... there's a pretty loud clacking noise that's coming from somewhere around cyl 8. I thought it might be the valve lash so I reset it and tested it again. I did this 6 times with both the engine running and engine off , and still clacking!! I noticed today that one of the header bolts was pretty loose. Didn't have a chance to check or tighten any of the other bolts. Could this be a cause to a noise that sounds really similar to valve clack?

Odd thing is... I've been driving this car for a month now and before the valve seal replacement, I didn't hear any clacking! And i haven't touched the exhaust...

Please if anyone has some experience with this... this noise is driving me crazy! lol

gjohnson

Just a guess but maybe you have a rocker stud coming out causing the lash to open up.I believe they are pressed in not threaded.

PeteZO6

Tighten all header bolts. They tend to loosen, and an exhaust leak can sound like clacking.

Pete

namvet6869

maybe valve spring not seated or valve keeper not seated.

Nick81

update... so i tightened all the header bolts that i could get to today and it was still clacking i'm gonna try to tighten the rest of them but i noticed also that the clacking and the engine rpm are in sync. as the car revs higher, the clacks get faster as well.. i don't know what that means but i'm hoping someone might chime in. This is really mind boggling because prior to the valve seal replacement i didn't hear any clacking whatsoever. and i checked and rechecked the valve lash adjustments several times, even over-tightening it at one point just to see if it would still clack; it did.

CaseyJones

From your description I still suspect a rocker arm but maybe not the one you really think it is. Check the adjacent cylinder's rocker arms. Also, it is true that a loose header bolt can cause a noise that sounds like a clacking noise. It would most likely be the end bolt (of course, since it's the hardest to get to). If it has burned out the gasket then that is another issue. A leaky header gasket will also change sounds with the RPM's.

It is a bunch of trouble, but find an old steel valve cover and cut a slot lengthwise that would allow you to get a socket on the adjustment nuts. Put it on and crank the car. Lower the idle if you can. Now watch and listen. The noisy one will be more obvious and you can fix it without the major mess of oil going everywhere.

Duane4238

If you change the valve seals, there's a chance that you may have over-tightened a rocker on reassembly and it cracked (broke) through the bottom of the rocker. Check all the rockers in the noisy area. Take each one off and visually check for a broken one. Good luck.
Duane

Nick81

Ok this is weird.... I pinpointed the source of the clacking... it's the exhaust valve on cyl 5. With the engine running i adjusted each valve. Loosened until i heard clacking and then tightened until it stopped clacking and then tightened 1/2 turn. Each valve worked wonderfully with this method except the exhaust on cyl 5. The only time the valve wouldn't clack is when it was on zero lash. .. slight turn forwards or backwards would make it clack. So I left it set on zero lash cause **** the clacking... now I drove about 5 minutes and the clacking came back. I don't get it! Collapsed lifter? Sticky lifter? Low headlight blinker fluid???? What gives?!

Duane4238

spend a couple of bucks and go to NAPA and get another rocker arm, ball, and lock nut. It definitely sounds like you have a broken rocker arm. You can't see it by just looking at the rocker arm. You have to take it off and clean it up and inspect it very closely to see if it is cracked. A cracked rocker arm will not hold an adjustment.
Duane

Nick81

Ok so I took the advice and went and got a new rocker arm, ball and lock nut. didn't work

took intake mani off to check lifter. It was perfectly fine, but just in case it wasn't i sprayed carb cleaner through it just to make sure nothing was clogged, took it apart to see if anything was broken inside compared to a new one, and it seemed completely fine, so i soaked it in oil over night and put it back....the cam lobe it was sitting on seemed fine too. no sign of wear.

i put everything back together & did another hot valve adjustment....and the same thing happened. rocker ticking when the nut is too loose, no sound/faint tapping when its at zero lash, and clacking past zero lash. the clacking seemed to be a different noise when compared to the rocker ticking...anyways, i left it where it wasn't making noise, put the car back together, and after driving 5 min it started clacking again...

heres the thing...i noticed while replacing the rocker arm that the valve tip was a little banged up and convex in shape. the rocker arm also showed signs of wear and was concave in shape...seemed like the valve tip sat lower than the spring retainer and was causing contact problems...new one doesn't show any wear yet...

any thoughts out there?
thanks

Super6

Are your studs pressed in? Or threaded. If pressed in, did you check to see if the stud on No. 5 is pulling out?

hugie82

If you got it to go away with adjustment and then it came back, I would say the lifter is shot! You can get the tapping to change tone by pushing on it with a hammer handle, you found the source. Look carefully at the rocker arm, it might be cracked in the cup (pivot point). Especially if you saw damage to the valve tip.
But before doing anything, double check the header gasket. I've know many people including myself that tore down a motor over a header gasket or any exhaust leak.

Guyddog

Did you fix this?

Brians1

Lifter sound's suspect here....pull it and see if it's still flat ...had same issue in my 81 and it was a combo of the lifters caved in and the cam was wiped. My symptoms were identical in that as rpm increased the popping/clanging was in lockstep with the rpms

I just replaced my can and lifters - problem solved and I got some much needed horsepower out if the swap.

Indiancreek

Put a timing light on one cylinder at a time and when the light matches the clack at least you know where to start looking. Like was said, lay a straight edge across the studs and see if any are raised.

Nick81

Hey guys really sorry about the crazy late response law school has been keeping me extra busy.

So I found out where the clacking was coming from! Yayyyy... Well actually the car told me, as the engine blew up while I was going 60 on the highway lol. I got verryyyyy lucky and managed to coast to the exit and pull over. After getting the car home I started taking it apart to look for what went wrong and after pulling the driver side head off I found something very interesting.... The clacking? That was the valve hitting against the head due to a bad valve seat, until the point that it broke off of its stem, fell down into the combustion chamber, cracked the piston, and in turn, cracked the block. The block is now a coffee table at my cousin's house.

Thankfully I found a used 350 a few hours away from me for cheap out of an 85 k20. put the block and heads from it in with the corvette's everything else. It's been running fine except for a strange coolant leak.

Just want to warn anyone out there who experiences something like this...check the valve seats!!!

If you look closely, one does not look like the others.

'75

Glad you got it fixed, but this was your clue that the valve needed to be changed / head removed. "heres the thing...i noticed while replacing the rocker arm that the valve tip was a little banged up and convex in shape. the rocker arm also showed signs of wear and was concave in shape...seemed like the valve tip sat lower than the spring retainer and was causing contact problems...new one doesn't show any wear yet..."
Seems like the rocker eventually pushed on the retainer and let the keepers out, valve dropped into the cylinder.

Nick81

Thanks man but here's the funny part... the rest of the valve (the stem) was still attached to the spring and held up by the retainers.. but you're right I definitely should have replaced the heads before this happened

TedH

I read this thread for first time today. My first thought was bad/worn guides and/or valve seats. I had similar behavior but with all of the exhaust valves. After 40k miles, the hardened seats (DART iron heads) wore out and then the guides followed. I had noisy valve train that would quiet down when I dropped it into OD... anything over 1,500rpm and I had valve clatter. Tried replacing rockers, pushrods, setting/re-setting valve lash and no improvement. Even suspected worn cam lobe(s). Solution was a full set of bronze guides and ductile iron valve seat inserts. I'm glad I got this taken care of before I dropped a few valves. I had this done back in 2013 at the time I had shop install new springs, keepers, locks and seals for the retro-roller kit. Very quiet now. Went with Comp Ultra Pro Magnum roller rockers at the same time.

What surprised me was the fact the noise started at time he replaced the valve seals; unless something 'gave out' during that procedure (such as cracked rocker as others had suggested) or perhaps with the stress removed from the valve at time that the locks were removed/installed, it didn't seat the same and wore even faster.

However, when he mentioned the valve tip was hammered and rocker looked same, I thought the valve had to be wiggling in its bore. Sorry to hear it dropped and ruined the engine.

Guyddog

So everything on the top end looked ok, nothing to give away the fact the valve was the problem? How long did it go before the valve broke?