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

[Gibbo]

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?

 

[Gibbo]

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.

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.

 

[Gibbo]

It'll weep a little but it won't spay everywhere.

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.

 

[Gibbo]

I wouldn't be that surprised if theres some lifter wear and your getting some slap from the push rods on that bank.

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........

 

[Gibbo]

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.

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.

 

[Gibbo]

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.

 

[Gibbo]

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.

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?

 

[Gibbo]

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]

sounds like lifter tick to me, has it been run a lot in the last 12 months ? my old bmw used to have lifter tick with so many short runs.

Not really, been the kind of car it is, I am also a little afraid to now take it anywhere just in case it is something serious, plus the PS leak I fixed is now back big time, seems the pump itself is now leaking big time, guess it found next weakest link, as such I have a new pump/reservoir on the way which after that will only leave the module as only unchanged item in the PS system so any luck will be on top of that.

Back to the engine got lots to look at, getting a lot of mixed messages from US side.

Some say at idle oil should be squirting everywhere from rocker arms and some argue that mine is absolutely fine, so its a case of do I have an oil flow issue or is that normal. Oil pressure is good, but good oil pressure does not equal good flow necessarily.

Many are also saying worn lifter and or camshaft and check #6 cam lobe first as it gets most wear.
Also a few have said they had same issue and it was not engine but things like crank pulley bolts backing out and catching and a new favourite is the TH350 transmission could have a cracked or broken flex plate, so I am gonna remove transmission cover and check that out with it running.

Also been told to listen to fuel pump as supposedly they can make a similar tapping noise too and are generally noisy.

Another one is to check exhaust manifold gasket on that side also, could be reason, so there is a lot to look and listen to before doing more engine work.

Its in a local garage Monday, who have a good reputation and understand classics somewhat, so gonna see what they thinnk and let them know all feedback I've had from US side. Also a guy I know in Stoke put me in touch with his mate who owns a garage and has good understanding of classic and Chevy small and big blocks, so he is my next stop.

Its really difficult as many say its fine, drive it, otherwise have no clue but don't want to look at it and then finding someone you actually trust who actually knows what they are doing is not easy.
I could do the lash, pull the lifters and it could still be present, hence gonna let some mechanics with better hopefulyl better understanding take a look before I start pulling it to bits, though I can now get the valve covers off in about 5 mins per side and intake manifold seems an easy affair to remove....

Unfortunately for me my hearing is very tuned into car noises, I hear a squeak, knock I have to fix it, most people who have seen the Corvette are just wowed by it and can't even hear the engine knock, I think there is absolutely a problem and maybe with more use it could go away, but it could also get worse and result in a major engine rebuild or replacement which would be a shame on a matching numbers car to drop a crate motor in it.

 

[Gibbo]

What oil is in it @Gibbo? Reasonably high zinc content?

It had 10-40W Millers classic with zinc in it and I changed it too the 20-50W version with zinc a month ago which had no real impact on the noise, maybe marginally quieter.

Ive added some lifter additive, so far no change but I’ve not driven car yet only let it idle.

I am gonna set valve lash over weekend just to rule that out, gonna set it with engine running so loosen rocker until it clatters, tighten until it stops and then tighten an additional 1/4 turn. I doubt this will fix it but best I do that and rule it out than pay someone.

I’ll also get the trans inspection cover off just into the trans plate is cracked or broken and I’ll have a good listen to fuel pump and inspect crank bolts just to rule those out.

No expert, but isn't US fuel different to ours? If you've used v-power or similar could that be the difference given its not got modern efi.

Some knock noises can actually be from a cracked exhaust/manifold too. Worth investigating if you haven't already.

Sounds like it needs a once over with some expert eyes. I can imagine outside of some guess work you'll end up replacing peace of mind items like the rockers, lifters pushrods etc but could still end up hearing it.

US fuel is same as ours but can tend to be a lower octane but I just put basic unleaded in this, I did try Vpower but again no difference.

 

[Gibbo]

A better video, you can really hear it at the start:

Hope it’s dry at weekend so I can investigate further.

 

[Gibbo]

Lifters or cam BUT.... for some reason on yank muscle lifters always go they have the same problem on the newer 2011+ MDS 6.4 hemi SRT's mate, and everyone goes literally every engine now.

HOWEVER... TBH though, that sound if it is a lifter is a little deep sounding to me, lifters in my experience are a higher tappet sound literally like tappets rather than a low down knock. Tough one, can't add anything but would be interesting to see how this one goes, good luck fell! I wonder if this is like the HEMI tick, which people here but there is simply nothing anyone can do... wonder if it's that kidna thing and no one knows why it occurs!!!

Really no idea listened to lots of 350’s online which have similar sounds and they don’t seem to be complaining or worrying about it.

I feel there is absolutely an issue the question is discovering how serious or not.

Part of me hopes it is a lifter or worn cam as that will be an excuse to put a new cam in that gives some extra power, some roller rockers and a tune up should make it good for 300 horses with those basic mods.

not had a chance to work on it today, miserable weather and for obvious reason I don’t like running it in the garage.

 

[Gibbo]

Hi there

I’ve set the valve lash today. Did the engine running procedure and doing this also does seem to have increased amount of oil flowing to the top as it made quite a mess lol.

I slackened off each rocker nut until the rocker arm started clattering and then tightened until it stopped so at zero lash, I then gave an additional quarter turn very slowly.

I did notice as undoing a few oil flow to the rocker arms improved, even got a few squirting and car was at idle.

Buttoned it all back up and car is quieter and the tapping I could feel on the valve cover has reduced and is near none existent.

Id say they were all set to between 1/2-3/4 turn before I started and I’ve set them all to just 1/4 turn for a touch more power and hopefully better flow.

Took car out and it also felt smoother and a touch peppier.

Car is in garage tomorrow so will see what they have to say, they are experts with classics and land rovers, so see what their opinion is and let them check the fuel pump, crank pulley and transmission for excess noise.

 

[Gibbo]

Having compression and not hanging valves open will tend to do that!

Yep I think a lot of people think they should turn them more as I’ve seen some recommend one full turn once at zero lash but there is equally many who say as you said, 1/4 turn and let engine give its best and if they back off and clatter again then just readjust as it’s an easy job, just messy.

But I guess how worn the cam also plays a part also, will report back on what garage says in week.

 

[Gibbo]

Dropped car of this morning, spotted @paradigm also, hope your well mate.
Mechanic says the engine noise is tappets and he says in his oppinion they are pretty quiet (car is much quieter now since I did lash), he said I did the correct thing only making 1/4 turn on the rocker arms.
He is gonna give the car a thorough checking over and fit the new steering pump, sort the alignment and centre the steering box/wheel.

He said if engine gets noisier then he will do a proper cold lash adjustment and check all the parts for wear and replace if necessary.

 

[Gibbo]

Watch out for the higher ethanol content of regular unleaded.

Yep I only put E5 unleaded in, if in future only E5 becomes super unleaded then I will put super in.
I know that for engine oil it must contain zinc and to avoid E10 fuels.

 

[Gibbo]

I've always thought if you are going to buy a second had car buy it off Gibbo as it is probably in better condition than when new, the exact opposite of my car ownership journey!

defo buy after gibbo

My head works in a way that I want to enjoy a used car when its performing its best. Hence why I tend to freshen suspension / bushes and just make sure everything is functioning spot on. Like my S2000, its had a full bush refresh, many were fine as its only got 50k miles on it, Ohlin suspension and I've changed all fluids, but won't be selling that for a long time, bit like the Corvette they are keepers.

I am considering selling my M5 though, it was always a tick box, I've now tick the box, also spent a few grand in running cost in the process also, but I am hardly driving the car so I might as well move it along in the near future.

 

[Gibbo]

Hi there

Collected Corvette today.

Mechanic after having car a couple of days, cold starts and driving it has said the engine has piston slap and hence the noise that tends to be present on cold starts and fades as it warms and the noise then heard is tappets.

He has however told me not to worry and to do nothing as in his opinion from other 359 small blocks and several Ford performance engines he said it’s the kind of issue that can remain as is and not get any worse for a very long time and as such he said to not worry and enjoy the car.

He said if it gets to a point where it’s piston slapping all the time and loud is the point where it’s time to sort it and it’s something he could do and be happy to sort.

He fitted new PS pump, confirmed the car now has zero PS fluid or oil leaks so my valve gasket cover change sorted that and new pump has sorted that.
He fitted all new belts, new track rod ends, new rear camber arms, he also regressed every suspension nipple.

He said most of the underpinning LDS of the car look brand new and confirmed all fuel lines are spotless with half been new and other half in hood condition, confirmed zero rust or rot.

He was able to confirm the car has been painted and whoever did it that it was done to a very high standard and that the car shows zero signs of ever been in an accident so is totally straight.

He was able to align it back to factory specification and centre steering box too. He ask me the story of the car and said it’s very lucky to not only find such a good quality car but one that is so original and in such good condition. He said leave the engine and enjoy as he believes it will never be an issue and if it ever does then it’s worth fixing to keep a numbers matching car.

He said it drives superb and on the drive home the alignment and suspension refresh has really tightened it up even more and made it feel quite confident inspiring. Car definetely pulls better since I did the valve lash too, I’d need to time it but 0-60 feels like it’s easily around 6s, not bad for something so old.

Gonna enjoy it now with only mods planned of rear composite spring and maybe 1” front lowering springs to get it sitting really nice as I’ve got 8” adjustable bolts in rear so can adjust height but front is convention springs so I’d either need to cut 1/3-1/2 a coil of each one to get around 1” drop or see what lowering spring options there is.

Oh and he did say as the AC does not work and Re gas to newer gas would no doubt leak out he suggested it’s probably worth pulling all the AC kit out, I’ve had a look online and the AC stuff all removed is like 60-70kg out the car, a rear composite spring will save 15-20kg too so I think I may do that as 100kg more or less out the car will improve it even more.

 

[Gibbo]

Yeah that sounds more like it, definitely could tell it wasn't lifter tick.

If it was me, I'd get it done later in the year, get the bits imported and sort it. it's a nice car and presumably one you want to keep for a while.

Yeah I’ve done some reading up and found quite a few post on forums and Facebook of people complaining about with some getting it even on new engines with around 1000 miles, supposedly the L82 are more susceptible to it due to the forged parts and some ignore it and have no issues and others think in time it will get worse at which point sort it.

I’ll keep a listen out for it getting worse and when Winter comes look at maybe getting the parts needed and sorting it during the colder months.