Author Topic: 396 big block knock after warmup  (Read 3175 times)

z28z11

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Re: 396 big block knock after warmup
« Reply #30 on: July 04, 2019, 08:47:53 PM »
Beware of spun bearings in big blocks causing this kind of noise. I had a 402 do this, ran fine but knocked when warm, 2 spun bearings were the culprits. Loose torque converter bolts on another 402 before, too - loud "clank" on startup more than a knock. Better pull it down before it REALLY gets worse.

Regards,
Steve
1968 Z28 M21/U17 BRG/W
1969 Z28 X77/M20/VE3 LeMans/W
1969 L78 X66/N66 Cortez/BVT
1969 Z11 L48/M35/C60/C06

olddragracer

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Re: 396 big block knock after warmup
« Reply #31 on: July 05, 2019, 12:05:46 AM »
On cars with an automatic transmission when checking for an unusual noise. The flex plate [flywheel] should be checked as a possible source. Remove the flywheel bottom cover and look up at the flex plate with a good light. Look for red rust leaking out of possible cracks. Sometimes cracks cannot be detected till the flex plate is removed. Noise from this part may only occur only when hot or only when cold. The noise can sound like a knock, a snap, a click, a clunk, or a rattle. It is the go to area to check when you have an unusual noise.

1stgen68

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Re: 396 big block knock after warmup
« Reply #32 on: July 07, 2019, 08:15:35 PM »
Thank you guys for all the info! Got up under the car today and quickly turned into a sissy to remove anything because the torq converter is really close to the flexplate and I canít get a wrench up in there because of the space to try to tighten the bolts if loose so I gave up 1 man card put the dust shield back on and going to take it to a mechanic and explain where this knock is coming from.

1stgen68

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Re: 396 big block knock after warmup
« Reply #33 on: July 12, 2019, 05:59:57 PM »
Mechanic said torque converter and flexplate are fine. Also removed the fuel pump as well, still had the knock. He said that it's in tho motor even after i bet him 20 bucks it was the flexplate.
Now to find someone that can pull the motor and check basically everything and go straight down into the financial rabbit hole and come out butt hurt.

68 Ragtop

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Re: 396 big block knock after warmup
« Reply #34 on: July 13, 2019, 01:41:54 PM »
https://youtu.be/LONT1oboJrs

Is this your mechanic?


1stgen68

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Re: 396 big block knock after warmup
« Reply #35 on: July 14, 2019, 12:02:26 AM »
That was too funny man!!!! Geez i'm still laughing at that!!! I wish that was what the problem was!!

1stgen68

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Re: 396 big block knock after warmup
« Reply #36 on: July 18, 2019, 10:37:37 AM »
Turns out that I have to have the motor rebuilt

JKZ27

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Re: 396 big block knock after warmup
« Reply #37 on: July 20, 2019, 12:03:30 PM »
Sorry to hear, man.
Just curious, what was the failed component(s)?
John
69 RS/SS Cortez Silver, L48 MC1
68 RS Ash/Ivy Gold 327EFI M20

bcmiller

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Re: 396 big block knock after warmup
« Reply #38 on: July 20, 2019, 05:20:47 PM »
Would like to know what they said was bad and pics of the items. Main bearings?
Bryon / 1968 Camaro SS 396 coupe - now old school 468 big block
1967 RS/SS 396 coupe L35/M40 - 4 generation family project
Looking for 68 Camaro with body # NOR 181016

1stgen68

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Re: 396 big block knock after warmup
« Reply #39 on: July 20, 2019, 09:16:54 PM »
Oil pump was barely inside the oil pan. Crank was really marred everywhere. Cam was rounded off. Pistons looked like $hit. Hydrolic lifters cupped really bad. Lifters mushroomed out. Saw it today for the first time and was blown away with what I saw. Threw up in my mouth a little too.

1stgen68

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Re: 396 big block knock after warmup
« Reply #40 on: July 20, 2019, 09:18:20 PM »
Spun bearings charred beyond belief too. I didnít take any close up pics. Sorry about that

maroman

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Re: 396 big block knock after warmup
« Reply #41 on: July 20, 2019, 10:05:41 PM »
Sounds like it really wasn't rebuilt or rebuilt poorly. Sorry for you! Fix it right then you will know and hopefully get some good from it.
Doug  '67 RS/SS 396 auto I know the car since new

z28z11

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Re: 396 big block knock after warmup
« Reply #42 on: July 22, 2019, 01:44:23 AM »
Amazing still that the engine ran with that much internal damage. Sounds like the builder didn't think much of oil pickup/screen clearances -

Regards,
Steve
1968 Z28 M21/U17 BRG/W
1969 Z28 X77/M20/VE3 LeMans/W
1969 L78 X66/N66 Cortez/BVT
1969 Z11 L48/M35/C60/C06

Kelley W King

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Re: 396 big block knock after warmup
« Reply #43 on: July 22, 2019, 01:56:42 AM »
Did the car have an oil pressure gauge, factory.
69 Z28 RS Scuncio Hi Performance
69 SS L78
67 SS Chevelle
64 Corvette
66 GTO Tiger Gold
77 Trans Am Special Edition

bcmiller

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Re: 396 big block knock after warmup
« Reply #44 on: July 22, 2019, 02:37:20 PM »
In my opinion, the sounds captured in the video do not seem to match up with the damage found in the engine at tear down. But that is just my opinion.

BUT, I will tell you it is surprising how long a big block will run with damage.  A 427 WILL run with 3 rods shucked out the bottom end. And I mean OUT, like onto the road out. Obviously it didn't run well, and was only left to idle for a few seconds, but it did idle. Long story...
Bryon / 1968 Camaro SS 396 coupe - now old school 468 big block
1967 RS/SS 396 coupe L35/M40 - 4 generation family project
Looking for 68 Camaro with body # NOR 181016

 

anything