Rod Knock?
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Posting Guru
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Rod Knock?
I have a 1990 Bronco with the 351w, when I fire her up in the morning when it is cold I hear a knock that is somewhat loud and it doesnt go away until the truck is warm. The knocking nose increases with rpm's. What could this be? thanks for any help.
Senior User
Joined: Mar 2001
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From: gulf coast
Rod Knock?
Very well could be a rod knocking. Or could be a main bearing. A main bearing failure will give you a very "heavy" knocking sound. A rod knock is more of what I would describe as a "medium" sound that occurs at the same rate as a piston is traveling up and down. If you very slightly and quickly rev the engine while listening closely, a rod will rattle on the acceleration and decelleration. The best way to detect a main bearing knock is to put the vehicle in gear, hold the brakes and give her a little throttle. When you get it in a good strain the heavy thud of a bad main will be easy to hear. How many miles on the engine?
New User
Joined: Jul 2000
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Rod Knock?
i had a similar problem, if it sounds like a diesel at about 2500 rpms and up it is bad rocker arms. i just changed mine and the lifters. If you replace the pushrods, get them from ford. i found out the hard way that the clevite ones are too short
Posting Guru
Joined: Apr 2000
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Rod Knock?
using a mechanics stethescope or a long rod of some kind, carefully listen to the engine when you first start it up. put stethescope up to engine to try to isolate the location of the noise. this will help you diagnose it better
