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351w motor knocking noise

  #1  
Old 07-15-2005, 12:45 PM
blueovalboy86
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Exclamation 351w motor knocking noise

ok i have a 351 windsor and its in an 86 f150. when the motor is started cold, there is a knocking noise in the motor. a friend of mine said it was the pin that holds the piston in the connecting rod. somebody else said it was a rod bearing thats worn or loose or something but i dont know what to think. if its the rod bearing then it has to b e fixed, but i was told if its just the pin, then let it warm up before driving it. you can really hear it when the motor is at idle and you touch the gas a just a litle bit and back off then it makes the noise. whats wrong here??? thanks for the time and help
 
  #2  
Old 07-15-2005, 01:04 PM
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How many miles is on it?
If it is a wrist pin you could try and narrow it down by pulling spark plug wires one at a time to see if it lightens up or goes away (this will also narrow down rod bearings also). You could have a lifter problem also.
 
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Old 07-15-2005, 03:16 PM
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Might be a sticky valve. Somewhat related to a lifter problem. Can you can hear it under the valve cover as a knocking sound? Usually goes away after things warm up?
 
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Old 07-15-2005, 04:20 PM
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asetim-i bought the truck and it originally had a 302 but the previous owner put a 351w in it so i dont know the mileage. if it is the wrist pin, cant that scratch up my cylinder walls?
spikedog- it does go away when its warmed up well it doesnt really go away its just not as loud and you can hear the noise more if your under the motor that on top of it.
 
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Old 07-15-2005, 05:00 PM
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Another thing I would do is go down to your local parts store and buy a diagnostic stethescope (looks like the ones nusrses use but with a long metal probe on it) usually are pretty cheap
(under 20$) or you could use a screwdriver or socket extension (stay away from moving parts!). and probe the oil pan, valve covers, block etc. to pinpoint noise. If you do try the test I listed in the prevoius thread and the noise does NOT change you either have a vale train problem or main bearings (main bearings typlically make noise at all times but not always). Yes wrist pins can score cylinder walls but they have to pretty loose.
 
  #6  
Old 07-15-2005, 05:20 PM
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does it make the knock noise when traveling sat 55-60 when you let up on the gas you know sota unloading the motor ? the reson I ask is we just had a 351w that knocked cold or at hi idle warm or when you hit cruising speed and it was a loose rod bearing it did not knock under load or at normal idle warm but upon tear down we found #2 rod bearing loose and a junked crank
 
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Old 07-15-2005, 09:38 PM
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yes it still makes the noise at 55-60 if the motor isnt warm enough. but when it gets warm it goes away for the most part. when its warmed up and you get on the motor you can hear it a little bit.
 
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Old 07-15-2005, 11:02 PM
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I bought a 79 mustang one time the PO had started to install a 351w, so I
bought it without hearing it run, I sold the mustang body and the headers and
installed the rebuilt 351w in a 77 pro-street truck when it was installed it
would knock when it would idle but when I would REV it, it would slowly go
away and as soon as it would idle it would knock again. So I pulled the motor
and trans, and as soon as I sat the weight down on the engine stand I heard
the fly wheel rattled, the fly wheel was LOOSE! They had used bolts that had
a small shoulder and the bolts did not pull up tight! I replaced the fly wheel
bolts and I also pulled the pan and checked the bearings any way, there were
small gold spots on the main bearings, but I did not drive the truck with the
knock or the motor would have not pulled though!





P.S the reason I did not catch it the first time was because I just installed it
and I left the c4 that was already bolt up to the motor!
 
  #9  
Old 07-15-2005, 11:27 PM
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The wrist pin should be pressed in, so it isn't likely it is moving around. I had an FE that had the floating pins, and a couple snap rings disappeared, letting the pins rub the cylinder walls, wearing two 1/8 grooves in two different cylinders.
I also had a 76 Windsor that had a little knock, not the hard mettalic km=nock of a rod, not the dull knock of the mains, just a funny rattle like knock. About a year later, it shattered a piston. Timing of the failure couldn't have been more perfect. my ex had just taken posession of the Mustang it was in... a 79 that I had refit with the Windsor, and she took it... it blew up in short order...
Anyway, the rod bearings generally get louder when warmed up, as do mains, but the piston noise will typically go away when warm, as the crack closes. A flywheel will make a knocking noise no matter the operating temp.
 
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Old 07-16-2005, 12:38 AM
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Many different things it could be as so many have said already. First thing would be to try and narrow it down to being low in the engine or higher up. The bearings would be lower and probably a deeper sounding knock. A wrist pin would probably be higher and more of a metallic noise. You could also have piston slap which can go away as they warm up. Do some checking if you can and try to get a better handle on where it is coming from, then get back to us and we can help you trace it out further.
 
  #11  
Old 07-18-2005, 09:31 AM
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i took an extension and it seem to be coming from the top of the motor right bellow the head. is this a wrist pin then? im probably going to pull the motor anyway.
 
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Old 07-18-2005, 09:36 AM
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Sounds like it may be. I have seen wristpins work loose. Could also be piston slap.
 
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Old 07-18-2005, 10:58 AM
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if the wrist pin is too loose, than theres a chance it can score up my cylinder walls right?
 
  #14  
Old 07-18-2005, 11:17 AM
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If it worked its way out to far then yes it can score the walls.
 
  #15  
Old 07-18-2005, 01:38 PM
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see im fuc*** from every angle here because everything that everyone has said in here in bad so yea i guess ill get my motor hoist ready.... its oing to be a long long week
 

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