Chevy Corvette 350 small block - Knocking noise, can anyone diagnose please?

Gibbo

Gibbo

Gibbo

OcUK Staff
Joined
17 Oct 2002
Posts
38,489
Location
OcUK HQ
Hi there


My 1978 Corvette has made a knocking noise since getting it, but a few Corvette owners said they all do that, not to worry.

It has not got any worse but last night I fitted new rocker cover gaskets as it had an oil weep, just took car out on lunch break to see if the oil leak is fixed and seems the new Fel Pro blue gasket did the trick.

But having the hood up, I could hear this knocking noise:



Thankfully my phone pics up the noise crystal clear and makes it much louder than it actually is.

I can hear and feel it on drivers side.
Passenger side there is no noise and nothing to feel.

So I am thinking can the push rods under the valve cover be tweaked/adjusted as its my guess they are hitting the cover on drivers side?

Any advice or those with better knowledge on these old engines know what it is please?
 
Last edited:
Whip the valve cover off and you should be able to see if the rockers have been hitting.
The felpro gaskets might be slightly thinner than what was there before.
 
IceBear said:
Whip the valve cover off and you should be able to see if the rockers have been hitting.
The felpro gaskets might be slightly thinner than what was there before.
Click to expand...

The new gasket is thicker as the factory bolts did not want to reach, thankfully I also put in ARP studs to make changing gaskets a little easier, yep will look at removing the valve cover again, but its all buttoned up for now, a mechanic is popping by later, so will see what he has to say, it has done this since I got the car though, I just never worried about it before.

Having changed gaskets I left the engine running with hood up to look for leaks and it was then I noticed it still knocks even when warm, just quieter so I listened carefully and noticed it only comes from driver side and I can also faintly feel it in the rocker cover on that side.

Silly question but could I loosen the cover on that side to see if noise reduced or will engine oil literally attempt to go everywhere? The noise is there with revs, and is emitting from drivers side rocker cover.
 
IceBear said:
It'll weep a little but it won't spay everywhere.
Click to expand...

Thanks and yeah this video answered me that question:



So I’m hoping it is something that can be adjusted as the fact I can feel a tap in the drivers valve cover which I can't feel on passenger side tells me something is touching and making the noise. Hopefully can just be simply adjusted.

Don’t think I’ll try doing that myself though let someone who knows more about push rod engines.

It could also I guess just be an age thing and just a case of put up with it but as with all things I try to get things spot on.
 
Last edited:
IceBear said:
I wouldn't be that surprised if theres some lifter wear and your getting some slap from the push rods on that bank.
Click to expand...

Yeah my thoughts too, it is the original engine, so 43 years old and around 48,000 miles and I know these older engines don't have the longevity of newer stuff.
If it is a lifter failing, I assume to replace is an engine tear down and rebuild?

I guess its maybe why several Corvette owners have said to just accept it and not to worry about it........
 
IceBear said:
Certainly intake off to swap out the lifters.
Not a huge job in itself and certainly a lot easier today with the likes of YouTube.
Click to expand...

Not bad then.

Am I right in thinking:
Remove valve cover, run engine:
- Noise gone, adjustment needed.
- Noise still present, warn lifter or can adjustment still cure it?
- Adjustment and noise remains, then absolutely new lifter required.
 
Mechanic just came to look at it as was delivering a car back to the neighbour.

His view was nothing to worry about and if it really bothers me to pull the valve cover and adjust everything back to factory if adjustable and otherwise to just leave it alone.
 
That noise isn't normal. I'd be inclined to take the valve cover off and have a look at the pushrods and rockers before running it more. Could be a collapsed hydraulic lifter (L82 uses those, IIRC, if that's what it's got in it), potentially, too.

You might also find that, if it's got them, the oil drip tabs on the underside of the rocker covers are interfering with something. Could just require a bit of adjustment to clear the rocker that is colliding with it.
 
Last edited:
If it is something hitting the cover (which I think is probably unlikely) and making that much noise you should be able to see obvious marks on the inside of the cover...

My personal thought is as said, it is probably a pushrod or rocker with wear.
 
Lashout_UK said:
That noise isn't normal. I'd be inclined to take the valve cover off and have a look at the pushrods and rockers before running it more. Could be a collapsed hydraulic lifter (L82 uses those, IIRC, if that's what it's got in it), potentially, too.

You might also find that, if it's got them, the oil drip tabs on the underside of the rocker covers are interfering with something. Could just require a bit of adjustment to clear the rocker that is colliding with it.
Click to expand...

My mate who has several classics reckons it’s a worn lifter.

He has said to remove valve cover and run engine if still present then new lifters on that side, he says easy job as can do it from above without a full tear down using a magnet to get them out and then take it easy when running them in.

The fact I can feel it suggest to me it’s not normal especially as other side runs smoothly.

Yes it’s an L82 model.
What’s best to do remove valve cover, start it up and video it running as I’ll be honest I’ve got zero idea what I’m looking at but I guess they should all move and they should all pump oil up?
 
Hi there

Removed valve cover, to eliminate that:



The tick/tap is still there, it is a little harder to hear, but when I rev the engine it can be heard.

We think this is still a worn lifter? Am kind of hoping it is as a set of lifters is $70 and a new intake manifold gasket around $30 and its something I feel I can do myself.

No vertical movement, so I think lash is fine.
 
Gibbo said:
The tick/tap is still there, it is a little harder to hear, but when I rev the engine it can be heard.

We think this is still a worn lifter? Am kind of hoping it is as a set of lifters is $70 and a new intake manifold gasket around $30 and its something I feel I can do myself.

No vertical movement, so I think lash is fine.
Click to expand...

With the lash being fine, worn lifter is definitely looking more and more like the culprit.
 
You must log in or register to reply here.
Back
Top Bottom