1973 Corvette Stingray 454 Engine Is Hiding A Big Problem!

In the last video, this 1973 Big Block Corvette Ran for the first time since the 1980's. Now with a rebuilt carburetor, maybe it will run just a little better, but something is still off. Can you guess the reason for the miss on the #8 cylinder?
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[@shadvan9494]

I have never seen a cast iron gm manifold crack. Especially a big block. Those things are practically indestructible. With the tick I would suspect a worn out exhaust cam lobe. It’s not letting the exhaust out of the cylinder #8, so when the intake opens, the exhaust is flooding back in to the intake. Which is where the carbon deposits are coming from.. that’s my 2 cents.

[@russellmooneyham3334]

Nailed it!!!

[@stevemadak6255]

He could pull the valve cover and watch that lifter. Sometimes its visible that the cam isn't pushing it. Also he can grab that rocker while running and move it. If it has a lot of play that's also a pretty obvious sign. Might get lucky and just have to tighten/adjust it down.

[@GJ-DT]

I had a sb 327 Corvette manifold with many cracks.

[@MichaelAllan01]

I must side with the worn exaust cam lobe for the carbon build up from reversion. A micrometer can effectively measure the rocker arm lift(s) for comparison. Pretty common on both SBC & BBC high mileage cars. Really like how patiently laid back & methodical you are about problems!

[@Sundance7055]

valve seals are probably leaking through.....was lucky to have 4 vettes in my lifetime am 73 years old now and have a 69.....love the videos Ben

[@TRyan-op2jo]

Worn cam lobe, bent pushrod, or pulled up rocker stud would be my guesses. Not a burnt or bent valve. There would be no compression.

[@russellmooneyham3334]

Big block Chevys do not pull rocker studs. They are screw in.

[@vanamsgarage]

I agree, valve train issue.

[@edsel1952]

Had a Buick 455 in our shop years ago trying to trace a misfire similar to yours Turned out to be a flat cam lobe.

[@robertjordan3270]

Always happy to see one of your videos in my inbox

[@paulmac9634]

The tick is either a lifter and/or could be bent pushrod. Lifter would be from sitting for a long time, pushrod would be from over-revving the engine (maybe by missing the shift to 3rd). Either way you should pull the pushrods and inspect and readjust the valves. On the strange mis-fire that's a tough one and have a similar problem with a small block in a Camaro. In any event, just my opinion, I love your channel Ben keep up the great work!!

[@russellmooneyham3334]

Most likely flat exhaust lobe on #8 exhaust. These engines, (especially the Saginaw blocks) were notorious for having off center cam journals, and lifter bores. As a result, lifters can't spin properly and wipe out camshaft. Which in turn destroys the rest of the bottom end. Also had too little side clearance on rods. So, camshaft didn't get enough sling oil at idle or low RPM.

[@tomschawe2529]

i have a 73 big block i bought new. it sat for 18 years. i fired it up and got the same results. big block chevys are good for dropping valves. i replaced the lifters, push rods, rocker arms, valve springs, keepers, retainers. it made a world of difference. it runs better than it ever did. i would not run that engine like it is. if it drops a valve she's gone.

[@Mark_Hamrick]

Possibility it is a stuck valve(bent or whatever) on the intake side. With the intake valve stuck closed it wouldn’t be able to draw in fuel, so the temp would be lower with no 🔥 burn. It could also be a lifter that didn’t pump up after sitting for a long time or a bent push rod. LOL Great Job, keep it up 👍

[@vettekid3326]

When I was redoing a 1985 Corvette I replaced the aftermarket wires, cap & rotor with Delco replacement parts along with AC sparkplugs. The engine then had a miss so I pulled the wires one at a time and found #1 not firing so I swapped the plug with the old one and it still didn't fire so I then swapped the wire and it started running on that cylinder so I put the new plug back in and it didn't run on that cylinder again. Long story short I had a bad new wire and a bad new plug on the same cylinder. Also it was common to see that carbon in the intake runners under the carb from the EGR dumping the carbon from the exhaust especially if the engine had some blow by.

[@chdurango59]

I don't know! Can You have compression still if the intake valve is not opening on cylinder 8 ? The Knock or tick could be the lifter, rocker arm, bent push rod. Good luck. Ho by the way great videos.

[@repz0611]

Enjoy watching your videos Ben. I own a 2008 Z06 and a 2019 Z06. Watching your videos has me wanting a 69-73 C3. Loved the C3’s growing up as a kid in the 70’s. Keep up the great work 🇺🇸

[@allenvaughan1]

Excellent video! Thanks for the tip on testing for vacuum leaks with pliers. Love the '68-'73 rear end. (Hate my '77 rear end--blechhh!!)

[@OldCarAlley]

I think you should check the number 8 exhaust pushrod.... if its's ok then check the lift on the camshaft. Chevrolet did have soft cam issues in that era. A worn exhaust cam lobe or bent pushrod can cause carbon in the intake. Also look for a carbon track on the number 8 terminal of the distributor cap. That knock sound, sounds like too much clearance between the fuel pump arm and its pushrod. It maybe a defective new fuel pump.

[@Jeff_Pendleton]

I will say that I have heard about a LOT of noisy replacement fuel pumps for these old GM cars recently. Had one myself and several others as well.

[@OldCarAlley]

@@Jeff_Pendleton Yes I have had it happen with a few pumps too.... not uncommon.

[@rubyred93chev]

_The LS4 for was a decent yet detuned engine from Chevrolet, sure like the 454 for 1973. Also because it's the only year C3s that had a plastic nose and chrome rear bumpers. These big blocks always baffle good mechanics, with a plethora of vacuum leaks. That said, due to the length of time the car has been sitting (and the car's age), without taking apart the engine, it could be a myriad of things. Looking forward to more videos on this Stingray._

[@jameshuban6515]

That was an LS4? My brother's 72 was an LS5. I guess you could check the engine code. My brother's code was a CSS.

[@Duey333]

Thanks for the videos Ben. I'm always learning something new about these Corvettes, the big block 73's in particular!!

[@jupiterjunk]

My dad had (built) four (9 second) Corvettes. He HATED the 454. He'd always pull them, sell them, then get a 427, tune it, then put is in ALL of his Vettes Any who... he said he'd start with... Exhaust manifold leak Dirty spark plug socket, preventing the plug from grounding Lifter not working, also if you have to replace one, then may as well replace them all. .

[@allenbonner7149]

One important thing with the fuel pump rod. There is one end specifically designed with hardened steel to go up inside the block

[@johnhere6058]

I agree - I once sold a car I thought was knocking and it turned out to be the fuel pump, that guy got many good years out of that old hotrod

[@discerningmind]

I think there's two issues here. First, is an exhaust valve that's, burnt, stuck-open, cracked. For carbon build-up to be in the first section of the induction system would have to generate from the EGR Valve gases being drawn into the intake. As far as I know that would be a cracked intake. The only other possibility of carbon turning up early in the induction system might be EGR gases entering the crankcase ventilation flow, but any reason for that would be too far-fetched for it to be the problem. I'm looking forward to the next video on this.

[@johnhouseholder7682]

Gives us more ben!! I'm starting to want a corvette, never used to care for them.thanks john from arizona

[@Steeledawg]

I really enjoy your work. As an owner of a 1 owner 67 and a 23 z06 c8 I love corvettes this model is the one that got away for me.

[@byronholt3993]

Always look forward to Corvette content! Thanks!!

[@Apache61]

I just had a similar issue on an old Ford Y-block where it wasn’t firing all the time on the front two cylinders. I hooked a timing light up to each wire and noticed they were a little sparatic. I ended up opening the gap a little on the points and it fixed the issue. Check the lobes on the distributor shaft and make sure each one is opening up the gap the same. Mine was a little smaller on the two cylinders that were giving me the issue.

[@ejp75]

The space on the spark plug is where the pinch washer goes. The original plugs had washers on them. It ensured the plugs sat at the proper depth so they wouldn’t hit the piston. With the heat shields you change the spark plugs by going through the wheel well. Remove the wheel/tire, access through the rubber curtain over the control arm. Using a long extension on ratchet remove/install plugs. Back in the day I owned a 1972 Corvette coupe 427 4-speed and did my own maintenance. I owned a ‘70 Chevelle SS 454 with the LS-6 motor so I’ve got experience with both 427 & 454 motors. Those intake manifolds never crack. They’re rock solid. I’d pull out the 454 and swap in a built 409. Then you’ll have some fun.

[@njward7511]

Hey Ben, I'm literally in the process of restoring a 1973 with a big block. I inherited the car and never heard it run but saw when I pulled the plugs that one was clean so appeared it had not been firing. I had the heads gone through and the guy sent me a video of the valve stem valley on one was completely wore out and the valve stem was floating around. Probably worth checking the valves on #8.

[@davebutler2776]

I'm a fan of the carb cleaner check engine running spray cleaner around intake engine will rev from idle that how I found carb gasket not tight enough.

[@GroundhogzGarage]

I’m in my 60s and have never heard of a cracked intake runner on a GM intake. Never. Worn cam lobes, bent push rods, pulled rocker stud, stuck valves….all day long. I’m surprised you didn’t yank the valve covers already. You’re usually right on that. My guess is a lobe is gone. Place your bets.

[@TheCorvetteBen]

You need to watch the previous video again

[@GroundhogzGarage]

@@TheCorvetteBen That was sooo long ago! 😃. I’ve been schooled, my apologies. I still think the manifold is a long shot. Smoke test. Just because I had replaced too many cams in those era GM products, I’m narrowing down my choice to the cam. I’ll be looking for the next video! Im intrigued. Love the channel!

[@geoffquinn3109]

Great vid my friend. I hope you replace those stock exhaust manifolds and make a video of it please. Im having a problem on the driver side

[@thirdcargarage2951]

I. Would pop the valve cover and do a leak down test. Pull the two pushrods for that cylinder to check. That should give you the culprit. Unless it’s a cam loan that’s shot.

[@JAFTW]

Loving the mystery of the problem, but I'm sure it's no fun for Ben. Great vid.

[@vetterfellow]

Thanks Ben, your guess is better than mine. Good Lock Buck a rue !!!.

[@TimeToBeKind]

Ben, how the heck are we supposed to install the windshield wiper cowl on a 1976 stingray? I bought one to install, and no one can figure it out at the body shop. I went over and I can’t either.

[@societyschild6055]

Spray the intake with carb cleaner, while engine is running, along the manifold where it bolts to the head, and all vacuum ports to test for cracks/leaks. Make sure the EGR is seated and the diaphragm not sucking air. The knock may be from carbon on the tops of the pistons.

[@MrSeverin420]

my friend had a 1970 Chevelle 454 SS and the Engine made also some ticking noise. We changed rocker arms, Tappets, Camshaft, pushrods. Still Ticking. On one bad day we found the reason: The Piston was tilting (right word? cant find a better translation from the German "Kolbenkipper) in the Block as the Piston shirt was worn. This day the Piston jammed, broke, the Conrod bent by approx. 70 degrees, thore a hole in the Block. Hard to verify without dismatling the Engine complete. This was the end of that Engine and I must say also for the Car. It was a beautiful car, yellow with Black interior bucket seats and black Vynil roof.

[@jumanjii1]

Start by adjusting all the rocker arm clearances- with each valve closed, adjust the rocker till it just touches the push rod, then tighten the nut half a turn, that's if the lifters are all good. You could have a collapsed lifter and in that case the intake manifold will have to be removed. You might as well replace the timing chain and sprockets to get rid of that plastic tooth sprocket that by now should be all eaten up. I did that to my 454 including replacing the cam and lifters. Also I blocked the exhaust bypass port going thru the manifold. That bypass worked with the right exhaust manifold valve that sealed off the right side exhaust and funneled exhaust to the left exhaust side thru the manifold. That system was there for fast heating of the engine and thus reduce emissions. Get rid of that EGR valve too and use a blanking plate. Could be why you have all that soot below the carb. Wash, dry and paint that intake manifold and it'll look better than any crappy easily cracked aluminum intake manifold. Good Luck.

[@xds1919]

i have not worked on many big blocks, but 120 seems a bit low, if it is low, it could be as the rest of the commenters said... anything from a bad cam lobe to just a sticky valve. i would compare it to the rest of the cylinders before i went down any rabbit holes. i have also seen the caps cause low and intermittent spark from being bad at one cylinder (or a couple). if the rotor contacts in the cap visibly look good, pull the plug wire from the spark plug and check for a good spark (like you did for the coil). also, i noticed your timing light was a bit erratic, another reason to check that cap (and the coil spark was a tad orange, yes, i watched the other video too 😉). love your videos, btw!

[@bullieboi]

So, are you thinking the intake is cracked, causing number 8 to suck air and starving the cylinder? You could spray carb cleaner along the intake and watch the RPMs. But there is also the the knock you are hearing. Are you getting a suction instead of pressure out of the PCV port on the valve cover? Could be a cracked head around the valve stem or a cracked block in the cam valley. That is a tough one to diag without a teardown!!!

[@bobbybannerman2853]

HI CORVETTE BEN GREATVIDEO WORKING ON THE 73 CORVETTE 454 BLOCK. YA ALWAYS HAVE VERY INTERESTING VIDEOS. CURIOUS TO SEE WHAT YA DO FOR THE NEXT VIDEO ON THIS 73 VETTE. TAKE CARE.

[@markf4328]

Just my thoughts, which is pretty much echoing what others have said, pull the valve covers off and check your valve's /springs, pushrods for correct function. Its easiest and you get a lot of information. Enjoy your Corvette videos, I know it's a pain to do the filming as you work, but you give out a lot of good information and your followers much appreciate it.

[@jlh8296]

This may have been addressed already, I tried looking through most of the comments? The smooth un-threaded top part of the AC spark plug is normal. It's called an un-threaded lead and helps center the plug in the hole, before the threads engage. I always remember and old timer back in the 80's telling me to run AC spark plugs because of this un-threaded lead. For whatever thats worth plus $6 will get you a cup of coffee at your favorite barista spot. LoL

[@Todd512]

It’s doubtful the intake manifold is cracked Check more than cyl 8 for compression for comparison Check for a intake leak where the intake and cylinder head meet Bad valve guides are common A broken valve spring or retainer could be the valve train noise Did you tune that replacement carb you put on? My guess it’s valve train related on #8

[@cmh2111]

Perfect car to add HEI and a Holley EFI system.

[@hildysworld]

Ben, pull the rocker cover on the right bank and spin or even pull the push rods to see if you might have one thats slightly bent. Roll them on a flat surface and before you put them back in soak them in some mineral spirits and blow them out with compressed air to free up any crud that may be blocking oil passage. If there not bent give them a shot of oil and put them back in and readjust the lifters. At least this can eliminate the ticking from the valve train. Doing both sides even better, big blocks tend to bend stock push rods depending on how it was treated prior, good luck buddy

[@flatcamvalvebarelyopening.3863]

Sounds like the cam lobe(s) for that cylinder went flat. Valve(s) barely opening causing a dead cylinder and ticking lifter(s) since the lobe(s) are so worn that the lifter can't take up the clearance making it sound like a solid lifter. Big blocks are known for their cams going flat.

[@johnschutt9187]

Very nice work!

[@ronaldwarren5220]

A co worker purchased a 73 with no options, base engine, 4 speed back in 1973. Seems like it cost him around $5,300. Of course the house I owned back then was only worth about $20,000.

[@billfunk3168]

I paid $5800 for a higher compression 350 with leather seat option.

[@dirttdude]

the black soot is from excessively rich fuel mixture, if you had a vacume leak you would have a lean condition, the only way to really know with that vintage of car is to test the emissions. Before i started tinkering with it, i would zero in on that ticking, its probably a flattened out cam lobe but hopefully just a lifter.... You can try the ATF trick and pray.

[@rooster3285]

remove the valve cover and see how much travel you have on those 2 rockers on the misfire cylinder..

[@larrycroft470]

i really wish you would post more and make your videos longer.

[@ThePerfectSeason1972]

@Larry Croft- if he did, he wouldn’t get much done. It takes an enormous amount of time to edit, produce and upload these videos.

[@Jeff_Pendleton]

Ben, I have a '75 Cadillac with a 500 that is acting very similar to your 454. Runs smooth until hot, then just a little jiggly at idle with the #8 cylinder (other side on a 500) offering very little on a power-balance test. Before I start throwing expensive parts at it (I've done everything tune-up related and rebuilt the Q-jet) I put a quart of Marvel Mystery Oil in on the oft chance it's just tight tolerances in the valve train due to dirt and sludge from sitting and lack of maintenance. One difference is I don't have that tick. So I am hoping a lazy lifter may come back with the Marvel as well. We'll see, its sort of a hail Mary, but cheap enough to try!

[@BladesRKing]

Wish I lived closer to you. I have a 79 with a noise in the back end and no one here can figure it out😡

[@michaelpeterson9479]

Just another possibility, is big block chevys were known for wrist pin/piston knock, it doesn't change anything for oil pressure, if it was a lifter or valve train, it sounds like a tick, the noise I hear sound more like a knock, which is a wristpin problem, Dosent matter either way, tear it down and build bigger and better!!! Is a vette, make it act like one!!!

[@scottwheaton9689]

Likely a cam & lifter on #8! If motor motor still has decent hot oil pressure (minimum of 15-20 psi) @ 800-900rpm idle & (min of 28-30 psi) at 2k-2,500 rpm shows bearings,crank & oil pump are still good enough to get away with just a cam & lifter replacement. I have done cam swaps with the motor still in the car without removing the motor from the car or the oil pan too! It’s not easy but it’s doable with Sbc or bbc in the car & have done both mult times over the yrs. So chk the cam 1st Warm up motor & then stop it it to Pull the pass side valve cover for #8 cyl, Next install rocker clips or all foil on rockets to slow down/deflect oil & restart motor. Now start the motor & watch the rocker send got cyl #8 to see if either of them are barely moving up/down or not at all & if yes you have a bad cam & lifter on that cyl. Also,Make sure to use oil with proper zddp/zinc & phos lvl for breakin of new flat tappet cam & lifters & post breakin too or you will over time & miles prematurely wear out another cam & lifters. Make sure to use proper assembly lube that stays put & doesn’t run off the cam lobes & lifters before firing up the motor like the thin red assembly lube does that can lead to quick cam failure esp if you crank motor too long prior to 1st start & cam breakin. Again ,use oil with proper zddp /anti wear additive lvl for breakin & after breakin too or you will eventually wipe out the new flat tappet cam & lifters too. Good luck & happy motoring! Good luck.

[@rebeccasmith3009]

The Corvette Ben I love all of the Corvette Ben videos

[@chriscatarcio2983]

Leaking EGR. Valve causing a vacuum leak block it off. Also check for broken valve springs. I have had them have enough presher to do a compression test. But not strong enough to keep the valve happy when running.

[@jigatumadre]

Hi, take out the hydraulic lifters and check the bottom for cupping if you have cupping you have a bad cam .

[@SAVERREPUBLIC1776]

How's the new shop and home coming along Ben?

[@quintonsteele2811]

Please post the fix ! I have a 70 corvette with a big block with the same knocking noise . Some lifters are pumping up and some aren't. I was thinking it may be the cam but I'm not sure . Thanks

[@vettegreaser6590]

Ben, you said the gas was brown. You didn’t have to deal with varnish in the gas tank? I have a 1970 Corvette and I’m learning from your videos

[@stephensaasen8589]

I'm with Shad Van. I bet it's a worn cam lobe. I don't know GM big blocks that well but I remember someone saying the 454 of this era had some issues with lack of oil to rear cam lobes and you could get a flat lobe on 7 or 8 cylinder. My dad had a 1973 GMC pickup with 454. It was losing 50hp on the old dyno but they couldn't tell where he was losing power. The fellow I was talking to about it said he might have had a flat lobe on 7 or 8.

[@kenfrazier616]

good start

[@crawford323]

If a valve was not seated properly, it is reasoned the compression test would not hold. Was there a leak down test performed?

[@davidbuddendorf991]

Rod knock!! U have a bent connecting rod!! I had the same thing. I had the engine machined n I rebuilt the engine.

[@mr.keepitreal2200]

Nice car again Ben! I am surely following this car because it is the same year as mine. Does the hood cowl open and close?

[@randallorr3730]

I would have to land on a bad exhaust lobe on the camshaft on number 8. Looking at the carb you pulled off, that black all over it is the exhaust gasses backing up into the intake probably when your hard into the throttle. The process if it was me is get the rocker cover back off and run the engine and see what the rocker is doing. It may be just a bent pushrod like some have said. Pulled rocker stud is possible, collapsed lifter. Typically though a collapsed lifter is not that metallic sounding but, my hearing isn't that good so take that with a grain of salt. Its a sweet car. Wish I was wrenching on it.

[@glocke380]

Broken valve spring will read normal compression unless you do a running test.

[@mzaccagnini7179]

Check the pcv valve also.

[@croozermanpro3320]

Possible rod knock. Step on brakes while in gear give it some throttle. As the engine powers up it the knock will be more pronounced. Small double knocking sound rod if it is starting to get tired

[@bullrunner8902]

Dude I learned that there is a bolt in front of motor. You take bolt out its a short one.Use the one out of the fuel pump its longer. It will hold the rod in any position you need

[@crawford323]

What're does the exhaust gases get re-injected and mixed with the intake as was the way of the '73 LS4? Could that carbon buildup be from failed EGR valve?

[@jeffsousa399]

I agree with the exhaust lobe issue. Easy fix, pull all that back off, and put a nice .500 lift hydraulic thumper cam and lifter set, and change the carb to 750 Double Pumper, and whola’ 100+ HP over stock, not even sweating it! Huge wake up Call, for DR Tonawanda!!.. (for yungins’ that’s where they built Big Blocks) :)

[@iainleverton5510]

hi great show , could you please tell me wot cc the big block 1973 corvette is please

[@bobgrob4]

Ben, did you have the numbers matching engine that was pulled? IF so, going to restore it?

[@elliottdilliplane6244]

Cam problems and rocker replacement check push rod to .maybe bad cam and lifter lobes

[@frankc1430]

Probably one of GM's notorious flat cams!

[@Buckyyyy]

Hey @TheCorvetteBen can you please find me a 1978 corvette silver anniversary edition that I can restore? Cause I can’t find any online corvette’s that are abandoned that I can’t restore. (Please make sure it’s the color Silver)

[@stevew9247]

Lifter that wont' pump up. happened to a 1973 BB corvette I had. Would happen after a warm restart. Then it would go away. Didn't like hot thinner oil.

[@blokeinacloak748]

Exhaust cam lobe on number 8 gone completely, exhaust valve staying shut. Exhaust gases entering inlet manifold via number 8 inlet valve causing the carbon build up seen in the inlet manifold. Under load number 8 is likely to ping bad, but ping on the exhaust stroke, not compression stroke.

[@xXcashXx3]

Can try running some seafoam see if it clears it up

[@ThePerfectSeason1972]

Fantastic Car!

[@riwoof]

Unrelated, but how goes it with Wifey's Pontiac? I know she's a mom and busy, but still wondering. I really like that car.

[@maniacal-s10]

Pull the valve cover(s) off , look at the rockers arms ! Have some 1 or a starter button , turn the motor over. (Hopefully not a rod )

[@jasonbuick307]

Scope number 8...carbon in the intake from pcv and blowby?

[@rmcseveney]

Guess we are never going to find out

[@markstopkey4085]

@ 12:14 Ok, no vacuum leak. Dead cam lobe?

[@harryrobert85]

I have the same car, same engine. Had wiped cam lobes.

[@johndavis1686]

Like the video looks like it’s leaking from exhaust leak.

[@robroten6446]

If the PCV enters the manifold underneath the carburetor, the carbon/soot in the intake manifold is not unexpected. Can't speak to the carburetor itself being sooted up.

[@patriotacienxciento1083]

Cuestion .. When a suitch from P to drive the carr turns off .. I have to pres the break and give some gas to don't get off . and it's the only way to drive

[@markstopkey4085]

@2:08, let me guess problem. Fuel pump cam eccentric wiped out

[@markstopkey4085]

@6:11 I lose guess. Running on fuel pump and new rod

[@johnmilner7603]

A bottle of GM EOS may fix that lifter. Also a bad EGR valve will cause carbon.

[@davidkornblatt991]

Hows the caddy?

[@markdraper4087]

I'm thinking lifter. A leak down test on every cylinder next.

[@ThePerfectSeason1972]

Redo all the heads and valves, would do a whole engine rebuild.

[@johnponthieux159]

Chang the cam and lifters and put an aluminum intake on it

[@robertbass974]

Exhaust guides and or valves. Heads need to come off!😢

[@TheAORster]

What happend to this, did you get it running properly?

[@MongoMotors352]

I’m thinking burnt or stuck valve, worn cam or lifter.

[@danielbrown4133]

Inlet manifold gasket leak between inlet manifold and cylinder head.