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Old Mar 16, 2020 | 09:25 AM
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Default occasional knock

1974 454 coupe 25,000 miles.
The car starts normally most of the time but then it will occasionally start with a knock.
When it knocks (occurs in the front of the engine), the knock will go away after a few miles.
The knock will sometimes go away if I shut the car off, then restart.
When the knock goes away the car runs normally.
Any idea what could be wrong?
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Old Mar 16, 2020 | 02:38 PM
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try to determine where the knock is coming from.
use a short length of rubber hose as a stethoscope.
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Old Mar 16, 2020 | 04:38 PM
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Maybe harmonic damper slipping, causing the timing to retard ir advance?
Hard to say without knowing exactly where the knock is coming from.
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Old Mar 16, 2020 | 05:49 PM
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Does it only occur when the engine is cold or also when it is still hot?
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Old Mar 17, 2020 | 07:38 AM
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Is it a deep low pitch knock or a higher pitch tap
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Old Mar 17, 2020 | 07:49 AM
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it seems to occur after the vehicle has sat.
it goes away after about a minute or so and does not happen again till the next start.
on some starts it doesn't happen at all, runs great.
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Old Mar 17, 2020 | 07:50 AM
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tap
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Old Mar 17, 2020 | 08:23 AM
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Could the tapping noise (it comes from front of engine) be a lifter that loses it's lubrication when at rest
then taps until it gets lubricated shortly after start up?
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Old Mar 17, 2020 | 08:27 AM
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Well, a tap is quite different than a knock.
I would now begin thinking it's a lifter or your rockers need adjusting..
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Old Mar 17, 2020 | 10:37 AM
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If it's a tap when cold only it can be a lifter or even the fuel pump/pushrod.
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