wierd knock under load....
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Elder User
Joined: Feb 2010
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From: naples, fl
wierd knock under load....
its been bugging the **** out of me since i bought the truck... what could cause what looks like a rebuilt motor to have a knock at load, but not at idle??
at idle it has a TINNYYYYY tap which i think its just the valves closing...but when i give it gas it starts to knock, and LOUD the oil is brand new, plugs, wires, cap, rotor, timing is at 10*, new battery, the knock has been preent since i bought the truck (started about 50 miles form my house as i live in Naples, fl and bought it in tampa i decided to just keep going...) and after i changed the oil it got louder..a bit..and the old oil was TTHHIICCKKKKK and blacker then the darkest night in the country
at idle it has a TINNYYYYY tap which i think its just the valves closing...but when i give it gas it starts to knock, and LOUD the oil is brand new, plugs, wires, cap, rotor, timing is at 10*, new battery, the knock has been preent since i bought the truck (started about 50 miles form my house as i live in Naples, fl and bought it in tampa i decided to just keep going...) and after i changed the oil it got louder..a bit..and the old oil was TTHHIICCKKKKK and blacker then the darkest night in the country
Laughing Gas
Joined: Feb 2010
Posts: 781
Likes: 8
From: Sanford, NC
That doesn't sound good. If the knock you describe rises and falls with the RPM of the
engine it is probably a rod bearing. You didn't say what year or engine this truck is and
what I am talking about would be a 302/351 V8 or straight 6. I don't know much about the Mod V8s.
engine it is probably a rod bearing. You didn't say what year or engine this truck is and
what I am talking about would be a 302/351 V8 or straight 6. I don't know much about the Mod V8s.
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Elder User
Joined: Feb 2010
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From: naples, fl
its a 1983 351 windsor and everything is 100% stock (aside from the ignition system)
EDIT: would i be able to just drain the oil, and change the main bearings with only removing the oil pan?? oh and i cant jum,p to WOT fro ma stop..and wit ha heavy load it bogs down BAD and i gotta pump the pedal to get it to move and its just really wierd...
EDIT: would i be able to just drain the oil, and change the main bearings with only removing the oil pan?? oh and i cant jum,p to WOT fro ma stop..and wit ha heavy load it bogs down BAD and i gotta pump the pedal to get it to move and its just really wierd...
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Elder User
Joined: Feb 2010
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From: naples, fl
i was just reading this.. it sounds ALOT like what my condition is..but it happened at 8* timing and thats why i bumped it to 10* thinking it would help...and it did help ALOT with the lugging off the line
Laughing Gas
Joined: Feb 2010
Posts: 781
Likes: 8
From: Sanford, NC
It's doubtful it is a main bearing of which there are 5 in a 302/351. It is most likely a
rod bearing of which there are 8, one for each piston/connecting rod. The way you
described the noise, the key is does the frequency of the knock rise and fall with engine
RPM? If it doesn't it could be a bad case of spark knock or detonation neither which is
good but can possibly be corrected by timing fuel mixture. I wounldn't recommend trying
to change bearings with the engine in the truck.
rod bearing of which there are 8, one for each piston/connecting rod. The way you
described the noise, the key is does the frequency of the knock rise and fall with engine
RPM? If it doesn't it could be a bad case of spark knock or detonation neither which is
good but can possibly be corrected by timing fuel mixture. I wounldn't recommend trying
to change bearings with the engine in the truck.
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Elder User
Joined: Feb 2010
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From: naples, fl
no, id take the motor out drain the oil, then do it...(i have the gaskets already haha) and the knock is non existent at idle, that as the speed/load goes up it gets louder like when i was towing my friends HHEEAAVVYY STi i had knock the second the truck started to roll... it was annoying, but i dont really have that much power loss which i find amazing!! and i dont have the +50 HP that a motor thats about to blow up has either.. but its only when im in D,2,1 (i shift the truck my self as it has a 4 barrel that the kic kdown rod can not be installed..) and i need to figure out how to fatten the mix on a holly 4 barrel carb..
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Freshman User
Joined: Jul 2009
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my dad had a loud knock in his old chevy van with a rebuilt motor and it was just a case of a poor choice of gasoline. Once that take of fuel was out and fresh stuff put in the knock went away. but of course if youve already put fresh fuel in then that takes away that thought.
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Thread Starter
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Elder User
Joined: Feb 2010
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From: naples, fl
i put 93 in last time and i know for a fact that 93 is at the carb cause i ran it for 30 min before picking up the STi, and for the 40 miles to drop it off at the shop and the 15 miles back to the house.. so 93 is at the carb and its still making the knock...im gonna check the TC maybe that is it...but i dunno cause that would be a constant knock..it really something you have to be here in the truck to hear...but its not going anywhere untill i get a new throttle cable and PS pump...but when i think about it (since i have a timing light) im gonna set it lower the 8* and then ill check for exhaust leaks...OOHHH and i just remembered my number...3 cylinder (passenger side) was colder then the rest of the pipes i fired it up, and climbs into the engine bay (maybe 15-20 secodns after starting) and started feeling pipes, starting on driver side. all 4 were really hot...and o n the passenger side th 1st 2 were really hot, 3rd was luke warm, and 4th was really hot..what makes a cylinder cold??
Cargo Master
Joined: Apr 2003
Posts: 2,057
Likes: 424
From: Too close to Houston
Open the hood and set the parking brake. Put a little load on the engine while watching it. Does it move? It could be a loose motor mount. When the engine torques up the fan gets into the shroud. If you're lucky it's a much easier fix than bearings.
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Elder User
Joined: Feb 2010
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From: naples, fl
i know its not the fan. that are no marks on the plastic around the blades and doing 200 miles home with it knocking there would be marks, and with the torque iv put on the motor and the way it lifts the front left up i dont think its a mount..
Methanoholic
Joined: Mar 2009
Posts: 6,442
Likes: 8
From: Maine (NorCal Native)
Start it, Run it up till you hear the knock, start pulling plug wires one at a time ... Does the knock change???
Loosen the wires on the cap so they are not so hard to pull first, Use insulated pliers.
-Enjoy
fh : )_~
Loosen the wires on the cap so they are not so hard to pull first, Use insulated pliers.
-Enjoy
fh : )_~
Cargo Master
Joined: Mar 2008
Posts: 2,562
Likes: 207
From: Washington
I would also do a compression test.
Jim