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Thread: F250 / 5.4 motor has a bottom end knock

  1. #1
    Junior Member
    Join Date
    May 2006

    F250 / 5.4 motor has a bottom end knock

    Hey Guys,

    I just purchased a 1999 F250 x-tra cab 4x4. i love the truck, but the engine has a bad knock in the bottom end. It does run, but the knock doesn't go away. I've been told that several of these 5.4 mod engines have this same problem. I assume its a bearing or rod problem. I've been told that I may be able to pull the plug wire to locate the cylinder, then pull the pan and change the bearing / rod for that cylinder. Does that sound right? The truck has 110,000 miles on it. I got a price from Jasper engines for a new longblock for $3500, but I don't really have that much I can spend. I don't know too much about internal engine "stuff" so I would appreciate any help youguys can offer.

    Thanks everyone,

  2. #2
    Senior Member 390FE's Avatar
    Join Date
    Sep 2005
    S. NH
    do you know what oil was used in the motor? I have heard of guys using 10W 40 and 20W50 and all the heavy oils used in older motors. The new Mod motord 4.6L & 5.4L require 5w30(20). There is an issue with oil starviation when using heavier weight oils.

    If your trying to save a few buck and do it yourself I would try to put the truck up for a day or so. I would pull and mark all the main and rod bearings. Where you don't know much about motor internals I would than take the bearings to a reputable machine or motor shop and ask them to look at the bearings to tell you what is wrong. Tell them you have a low end knock and these are the bearings. They should be able to look at the bearings and be able to tell you a lot about whats going on with the lower end. They might even be adle to tell you what cylinder is causing the knock(hence why you need to carefully mark what bearings went to what cylinder). They may even be able to tell you of more motor work needs to be done of it just replacing a bearing would fix the problem. I put parts into individual bags and mark the bags.
    At 110K you might be able to get away with just repalcing the bearings. I would replace all of them at the same time but thats just me.

    Try to take pictures of the lower end parts without the bearings in it if possible. To show to the machine shop so they can see the condition of the metal that contacts the bearings.
    87 Toyota 4x4 -- 72 F250 -- 68 F250 -- A Ford kah -- New to Family is 07 Ranger FX4

  3. #3
    Platinum Member
    mudseeker's Avatar
    Join Date
    Feb 2006
    take it to a shop and have it checked out. it's a pain to work on the lower end with out pulling the motor, especialy if you end up changeing out rods. you have to pull the heads to do that.
    <----just your average 5.3

  4. #4
    Junior Member
    Join Date
    Jan 2007
    this might help..i had the same probelm with my motor it has well over dad's an motor rebuilder...we droped the oil pan & replaced all the ( connecting rod bearings ) which wear out way more than main bearings.....& we also replaced the oil pump.. we decied to leave the old main bearings cause of the timming chain and runs and sounds like a champ now....i hope i was helpfull

  5. #5
    Full Member
    Join Date
    Jan 2007
    Generally speaking, if it's a loud 'clack' it's a rod bearing. If it's a deeper 'knock' it's a main. This isn't cast in stone, just a hint. The engine won't run for long with a bad rod bearing, but sometimes they do with a main knock. Either way, you may as well figure on putting an engine in it before long. As soon as you fix the bottom end, something else is going to blow.

  6. #6
    Junior Member
    Join Date
    Oct 2008
    i have the same dam knock on the bottem of the motor and i was wondering how many hours would it take to take out the main and rod bearings and how could you find out what cylinder is doing it. mine is a 03 f150 x cab 5.4 L i tryed crank case **** and it made it a little quieter and how it is getting louder and it is getting colder. i realy dont want to buy a new motor

    any idea any one

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