Knocking in engine
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Knocking in engine
I just had to replace my oil pump on my '81 F-100, 5,0. Now there is a slight knocking in the engine. I checked the rocker arms, the push rods,etc. All tight and good. I'm clueless at to the problem. Knock's at idle, but once in gear(drive or reverse) it goes away. Grateful on any help. Thank you. 
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From: Connecticut
Could be the oil pump is not fully primed or idle is to low. This may sound like a stupid question but how much oil did you put in it? Reason Im asking most 5.0 truck motors have 6 quart oil pans. While the car oil pans use 5 quarts. did you match up lenght with old oil pump to make sure lenght is the same? theres an old farm trick to get a new oil pumpto prime pack it with vasiline and after oils filled run 30 to 40 min drain oil and replace.Vasiline will be solitified and come out with oil.
Last edited by Dungeon_Master; May 27, 2005 at 06:55 AM.
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From: Fleming Ga
Is the noise a knock or a tick? Use a stethoscope or a short piece of hose held to your ear and determine where the noise is coming from then you will have more idea what is causing the knock. You may be suprised when you find out where because it may not be the motor. Always elliminate the easiest cheapest things first. Have heard fan belts sound like an engine knock. If you had to replace the oil pump because of failure then it's very possible that you got a bearing befre replacement but find out where the knock is before diagnosing.
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From: Weston, Nebraska
Knock at idle with no load is the big end of your rod, to pin point which one take each sparkplug wire off just like checking for a miss, that'll tell you which cyl is bad, then hopefully you didn't ruin your crank.
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Originally Posted by rogue_nine_2000
I've checked all over and could not find the knock. when it has a load on it the knock almost disappers. When engine is given gas its gone. Shows up when brake is applied. 
You should be able to tell the knock is in the lower end instead of upper from behind the wheel. A knock is a knock. Once I had piston slap and it was noticable at high speeds. And once I had a knock as you are describing, mostly at idle and disappeared. It was either a rod or main bearing on the crank. I didn't go into the engine but took the dealership's word. Ordered a rebuilt engine.
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Ok. Thanks for the info. I'll look in to getting a rebuilt engine. Any type that is preferred. Thinking about building a street truck.
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Originally Posted by rogue_nine_2000
Ok. Thanks for the info. I'll look in to getting a rebuilt engine. Any type that is preferred. Thinking about building a street truck.
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I have 1986 F150, 302 which had a knock at idle and it went away when engine speed was increased. I was checking out rebuilt engines for 3 to 4K but I decided to let a mechanic look at it first. The mechanic said that he couldn't say exactly what it was until he checked it out but he said that it sounded like it ws on the top of the engine. He called me a couple of days later and said it was fixed. The engine had carbon deposit built up in a cylinder and the piston was striking it. He poured a couple cans of carburetor cleaner through the intake and blew it out. Charged me $85. Yours may be something different but I urge you to have it checked out by an honest and reliable mechanic before you make the big mistake that I almost made.
Last edited by Trial and Error; May 31, 2005 at 08:37 PM.
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From: Brentwood,CA
well what weight oil are you running and what grade i hope it is not SM rated oil and what oil filter check out www.rebuilt-auto-engines.com they have been a great company to work with
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Took the engine out and checked the bearings. Replaced the bearings. And put it back together. Still has the knock in it
. I've given up on figuring it out. Everything is tight on it. Even put new bolts and nuts on it. Nothing is cracked, flywheel is in good repair. Any ideas are helpful. Even took heads off and looked in the cylinders, just like new. Thanks for any help.
. I've given up on figuring it out. Everything is tight on it. Even put new bolts and nuts on it. Nothing is cracked, flywheel is in good repair. Any ideas are helpful. Even took heads off and looked in the cylinders, just like new. Thanks for any help.
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Sure sounds like you went through alot. Since it seems hard to figure where the knock is coming from. Have you done compression check? Pay particular attention to #4. Did you try pulling the plug wire trick, to find which cylinder?
But heres the catcher, If you replaced the oil pump, and then started getting the knock, I would say it originates there. Could be bad pump or something in the installation.
These are just ideas from what you've posted. Once I thought I had a knock on a 351W, coming from the rear of the motor, and it ended up being a pin hole in egr cross pipe that runs from head to head in rear of the motor.
But heres the catcher, If you replaced the oil pump, and then started getting the knock, I would say it originates there. Could be bad pump or something in the installation.
These are just ideas from what you've posted. Once I thought I had a knock on a 351W, coming from the rear of the motor, and it ended up being a pin hole in egr cross pipe that runs from head to head in rear of the motor.