1971 454 Engine Knock
Thread Starter
Heel & Toe
Joined: May 2013
Posts: 16
Likes: 0
From: Nassau Bay Texas
1971 454 Engine Knock
New proud owner of 1971 coupe with original 454, automatic, ps, pb and AC, but not so proud right now. My wife and I were heading home after a 20 mile ride, stopped at store, wife got out, I stayed in car with it idling, no problems, she was in the store maybe 5 minutes, left store for our house (about 1 mile) and nearly did not make it, developed loud engine knock but only when touching the accelerator, not at idle. It wasnt driven hard at all on our trip, I was pretty much babying it, oil pressure is good and temperature is good. Needless to say, we idled ourselves home...any ideas where to start looking? Thanks, 
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
OUCH> knocking is never good. Start by trying to locate the source- front/back/left/right/top/bottom. With good oil pressure it gets really hard to guess. And you really don't want to run the engine and cause damage. You can justify that by the fact it's already hurt. Maybe drop the oil pan and take a look at the rods and see of one is discolored or there's a load of metal in the pan.
Is it a heavy knock or a tap-tap?
Is it a heavy knock or a tap-tap?
Burning Brakes
Joined: Mar 2010
Posts: 803
Likes: 4
From: Christchurch, New Zealand
There are other noises that can sound like a knock. It's just they never seem to happen to me. I get the bad ones. Soundalikes include exhaust manifold leak, bad fuel pump, and loose flex plate bolts. Rod knocks can be tracked down by a timing light on each plug wire until you find one that coincides with the knock. Or pulling plug leads.
Drifting
Joined: Jun 2010
Posts: 1,781
Likes: 15
From: Oxford Ohio
Often you can listen to the internals of your engine with something as simple as a long screwdriver. Use caution though. Most time I see folks do not want to accept the worse case situation and look for any number of origins of the noise. However you were looking for the most likely place to look.
I find that if I start looking at the most likely I spend less time looking. True could have gotten hot setting ther at idle, and not shown a loss of oil pressure, so you may want to check the true oil pressure with an external gauge to see if your gauge is accurate.
True it could have been a backed out bolt or a bunch of other things, but it just happened. So this reason for the knock just began, it is most likely a new issue which points to the bearing. A quick check of them tells you much of your engine and it's overall condition.
If that is your true mileage then you may be ok, just save time and start looking at the most likely. Start with the screwdriver or prybar and you'll be suprized with how clearly the sound will be, and how well you'll be able to locate the noise.
A 70,000 mile engine that wasn't maintained well can have bearing wear sufficient to create the knock
I find that if I start looking at the most likely I spend less time looking. True could have gotten hot setting ther at idle, and not shown a loss of oil pressure, so you may want to check the true oil pressure with an external gauge to see if your gauge is accurate.
True it could have been a backed out bolt or a bunch of other things, but it just happened. So this reason for the knock just began, it is most likely a new issue which points to the bearing. A quick check of them tells you much of your engine and it's overall condition.
If that is your true mileage then you may be ok, just save time and start looking at the most likely. Start with the screwdriver or prybar and you'll be suprized with how clearly the sound will be, and how well you'll be able to locate the noise.
A 70,000 mile engine that wasn't maintained well can have bearing wear sufficient to create the knock
Race Director
Joined: Jan 2002
Posts: 11,614
Likes: 350
From: No Where USA
Considering your knock may be someone elses tap and we are not there to actually hear it. It could be a cracked flywheel, loose flywheel bolt, sticking lifter. It could be a rod but I seem to think it would also tap at idle. The whole thing is you have to get an idea where it is coming from.
Could have been pinging like you said. I would start it and see what happens. If it is internal the damage is done.
Could have been pinging like you said. I would start it and see what happens. If it is internal the damage is done.
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Drifting
Joined: Jan 2011
Posts: 1,853
Likes: 81
From: Hamilton Virginia
Racer
Joined: Nov 2006
Posts: 491
Likes: 5
From: Tampa Bay Area, U.S.A. (Zombie Nation)
Our '73 454 developed a horrible knock when car was only a couple years old. Tore it down looking for cause. Never took the crank out but everything else was removed and closely inspected. Put it back together. Still knocked as before. Decided to run it hard through the gears and see what happened. After doing that it immediately quit knocking. Never knocked again. Still runs fine. To this day I don't know what caused this.
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
Take an intake rocker off and put it in the exhaust position. GM Chevy Power book says the intakes run cooler than the exhaust.
Hope that fixes your problem.
Hope that fixes your problem.