Topic: Engine noises, me too...
in Forum: C3 Engines
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Hi All,
The past few runs with Ol' Blue I've heard some noise I don't really know what it is. Maybe someone can help before I start yanking things apart
At first I thought it was just an exhaust leak, but maybe not so. It seems to be coming from the top of the motor, it's got about a thousand miles on it since it was redone completely.
I've narrowed it down to possibly something under the right valve cover, exactly underneath the AC compressor. A puff - chugging sound when the car is under load, but not sitting at idle. If you rev it up, sitting in the driveway, the noise is noticable until the rpms are up, then it is quiet. Really noticiable when driving under acceleration, but not when just poking along - it is very quiet. Runs great otherwise.
I've replaced the new exhaust doughnut again thinking it was a leak around the heat riser, but same noise, hot or cold.
Ok, so I got a piece of hose and poked it along listening here and there, but I still think it is under the valve cover.
Now I think broken valve spring, rocker arm or pushrod...or something like that.... All this stuff was new.
All this stuff was new.Next, I guess is to pull the valve cover and take a look......wadda ya think?
Second noise may be easy - why would the PCV valve buzz continuously, pretty loud buzz until you yank off the vacuum line
TIA Bruce
Bruce
72 Coupe L48 4sp
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I don't know about the first noise, but I bet the PCV buzz you are getting is caused by the motor needing to breath more. Try putting a breather oil cap on, or see if it goes away when you take your oil cap off. I had the same noise...it could also be the cause of your other noise...good luck 
Do you have an EGR valve? If so, it is usually located between and just back of the carberator and valve cover on the passengers side. If you had a broken valve spring your valve would have most likely dropped into your cylinder and BANG, dead motor. If it was a broken rocker arm or pushrod, your motor would run rough, and maybe a small bang if any of the pieces got caught in any one of the other valve springs. It sounds to me, without really hearing it, that you probably have a crack in an airline or vacuum hose. Check the underside of your air cleaner also. There may be a small hole there that you may not hear at idle but at acceleration. Good luck, hope you find it and that it's easy to mend.
No EGR - too old for that ( 1972 ).
One additional clue, if I pull off the vacuum line to the pcv valve, it creates a big vacuum leak and then the engine runs rough. ( I was investigating why the pcv buzz noise).
Now the strange noise is continuous with the vacuum line off the pcv, and you can track it down easier. The engine has the proper vent from the air cleaner to the valve cover - it is bone stock and original setup.
Still sounds like it's coming from under the valve cover though. Maybe just a rocker too loose for some reason.
I doubt a leak in an air line or vacuum hose, all those were replaced with new stuff, in fact, everything is new.
I'm gonna pull the cover next week, got to eliminate something.
TIA - you guys are fantastic help
Bruce
72 Coupe L48 4sp
Custom Blue/Silver/Pearl
(Click for a larger pic)
Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
Does the engine run ok?
Does your car have the A.I.R. injection tubes that run into the exhaust manifolds? You can have a leak at the metal lines, or even the rubber hoses that come off of there, and it may make a similar noise, and it would be in the same area.
It may be just a loose rocker arm, or a lifter taking a dump...new don't mean indestructible.
Let us know what ya find when you get the valve cover off.
Does your car have the A.I.R. injection tubes that run into the exhaust manifolds? You can have a leak at the metal lines, or even the rubber hoses that come off of there, and it may make a similar noise, and it would be in the same area.
It may be just a loose rocker arm, or a lifter taking a dump...new don't mean indestructible.
Let us know what ya find when you get the valve cover off.
Joel Adams
C3VR Lifetime Member #56 
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Car runs great.
No A.I.R lines.
Thinking loose rocker arm.
I'll get to it early next week. No car stuff on the weekend.
Bruce
72 Coupe L48 4sp
Custom Blue/Silver/Pearl
(Click for a larger pic)
Ok folks an update.
I pulled the valve cover off the left side, where the noise is coming from.
Looking very carefully, I found an exhaust leak between the head and the exhaust manifold, directly under the AC compressor of course- hard to see but it is very small. Can see black soot on clean fresh orange paint.
This would be cylinder #2 exhaust port. The bolt where everything comes together, namely the heavy AC bracketry and the stud used for mounting everything probably loosened up or I did not tighten it enough. Maybe the stud broke...I'll see when I pull it apart. These were new also. All that stuff hanging on two bolts must be problems.
I had the heads trued up as well as the exhaust manifolds when the engine was redone, so nothing should be warped. I did use the gaskets there, they came with the engine gasket kit. I seem to remember someone told me that the General did not use a gasket here, so maybe I did wrong.
Now the 64 $ question, do I pull the whole mess off and take out the gaskets, and reassemble with new ones, or leave them out this time?
What is the proper torque for tightening these exhaust manifolds?
Take it apart, put it together, take it apart, getting old...
Bruce
72 Coupe L48 4sp
Custom Blue/Silver/Pearl
(Click for a larger pic)
Former Member
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Newark, CA - USA
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Vette(s): 1969 Corvette 4-speed ZZ-4 crate
Monza Red
Before you take it all apart see if it will tighten up. Might just be loose and the gasket might be ok. The torque on those bolts is 20-30 pounds.
Good luck
Good luck
Maybe not so easy. The thing looks fried out where the black soot is, and I'd rather pull it apart. Especially if it would be a long term solution not to have any gasket under each of the 4 exhaust ports anyway.
The hard part is dealing with that beast of a compressor again.....with the lines connected this time.
And BTW, it is the right valve cover.
Bruce
72 Coupe L48 4sp
Custom Blue/Silver/Pearl
(Click for a larger pic)
Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
Use header gaskets, and soak them(it) in some water for about 5 minutes before installing it. Tighten the manifold as you normally would. The "moistened" gasket will compress under the manifold, and swell a little around the port, and once dried out you should have no leaks from there again.
You didn't mess up by putting gaskets there. And it is true that there were none there from the factory.
You didn't mess up by putting gaskets there. And it is true that there were none there from the factory.
Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
in Forum: C3 Engines
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