4.7 loud knock. Most likely problem? To mechanics. - JeepForum.com
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post #1 of 7 Old 02-17-2020, 05:30 AM Thread Starter
car6car
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4.7 loud knock. Most likely problem? To mechanics.

This is a question for Jeep mechanics.
Which knocking reason has highest chance? which is #2? #3?
thanks.
I didn't diagnose it yet.
Valve seat fell out?


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post #2 of 7 Old 02-17-2020, 07:52 AM
Double E
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To some, a knock could be a broken bolt or 2 on the driver's side exhaust manifold. To others, a knock is something metal trying to get out of the block in a hurry.
We need a sound clip, location of the noise or something diagnostic like a comp check and bore scope image to assist.
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post #3 of 7 Old 02-17-2020, 08:18 AM Thread Starter
car6car
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Quote:
Originally Posted by Double E View Post
To some, a knock could be a broken bolt or 2 on the driver's side exhaust manifold. To others, a knock is something metal trying to get out of the block in a hurry.
We need a sound clip, location of the noise or something diagnostic like a comp check and bore scope image to assist.
Thanks.
Some engines have specific problems. as far as I know 4.7 drop valve seats.

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post #4 of 7 Old 02-17-2020, 08:58 AM
smokeyyank
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My loud knock was a dropped valve seat. How many miles? Does the knock seem louder from up top or down below?
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post #5 of 7 Old 02-17-2020, 09:06 AM
Bigrigr
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I have seen several 4.7's with rod knocks, one is on my engine stand in the shop right now. I have never seen one with a dropped valve seat-but its super popular to discuss in this forum(see sticky) and online. Next knock noise i have never seen but heard of is bad cam followers(lifters).

If it's a rod knock, you can narrow it down to the culprit cylinder by removing the spark from each cylinder while the engine is idling, the offending rod will get quieter when the cylinder stops firing. Also may be able to narrow it down with a long screwdriver to the ear pressed to the oil pan(or mechanics stethoscope) while engine is running.

Compression test will reveal drop valve seats. Valve cover removal should reveal noisy cam followers(idle engine without valve covers on to hear)
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post #6 of 7 Old 02-18-2020, 04:10 PM
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My engine had a dropped valve seat and the seat was impacting the top of the piston because the seat was caught between the valve and the head. The impact noise from the piston hitting the valve is pretty significant.

As indicated above a compression test will help diagnosis.

If it is not a dropped seat piston rod bearings are an option.

Unfortunately to really fix either one the engine should be removed and torn down. I am sure some have successfully replaced a cylinder head for a dropped seat without replacing the piston but I wouldn't recommend it.

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post #7 of 7 Old 02-18-2020, 06:14 PM
Darnice
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Simple, if you were driving and it was fine, then shut if off, went int a store and came out and it was knocking, its a valve seat
If it a knock that started slow and has gotten louder, its something else.
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