i have a 1990 f250 with a 351 and it has 106 thonsand miles om it. after the engine warms up it starts to knock prety bad. if you push the clutch in it will stop and sound normal. if anyone has any ideas on what the problem could be please let me know.

 

If its an engine knock it could be your main bearings going out. When the oil is cold its thick taking up space between the mains and the bearings, when the oil heats up it thins out causing the bearings to knock.

If its a tranny knock, then maybe your throw out bearing is going out on you.

 

with the motor running take a broom stick to your ear and put the other end in different places on the motor. this will help determine were the sound is coming from. could be lifters, rod bearings or just piston slap. hook up a mechanical oil gauge this will tell you what your pressure really is also a compression test would also be a good idea

 

what i dont understand is why the noise stops when i push the clutch in

 

because there is no drag on the motor. thats why im starting to think rod bearings. if you let the clutch out then rev the motor does the knock get worse with rpm or go away?

 

the knock goes away when i rev the motor up

 

ok that sounds like rod bearings then. when there is a load on the motor the rods take up the slack . but when you slow the rotation of the motor (idle) that gives the rods a chance to move back on forth on the crank. this will also cause serious wear to your crank and probably score your cylinder walls to.

 

is there anything i can do so i can get more miles out of it without pulling the motor and rebuilding it.

 

run 30w oil

 

Autozone carries a product made by Lucas Oils that you add to your oil. It is a high viscosity additive that will cling to your main and rod bearings giving them protection from wear. That and some 30w or 20w50 oil and you should be good for awhile.

 

i was driving today and noticed when i came to a complete stop and it was ideling the oil pressure would drop to none when i reved it up it went back to normal

 

thats because ford gauges suck. get a mechanical gauge that way you really know what you have

 

I'll tell you how simple that may be, if it doesn't knock when cold, but knocks when hot, it could either be bad fuel wherever you are buying it, or could be the simple thing of needing to slightly hand retard your distrubutor by hand till the rpms drop about 20, then drive it and tell me what happens, because what most people never realize is this, when engines get over 80k miles, all parts have just a little wear or slack would be a little in an engine with 109k miles, so forget the timing light, just "time it down 20 rpm and see if that fixes it, or it may be simple in the way, crank it and remove the battery ground cable, let it run 2 minutes, then go kill it, everything is dead now, then reconnect the battery ground, and let the computer RE READ your system, and that may fix it, but an engine that has timing advanced too far, will not knock when out of gear or nuetral or park at idle, but drive it hot, and bingo, listen to them clatter, many of these fuel stations have underground tanks that have 2 feet of water underneath the gasoline that floats on top, after a few people get gasoline the water mixes in and we get a small percentage of water, because most of the time if an engine has a problem it will knock while idling in park, if i was there i would be able to define wrist pin clatter knock from main bearing and even rod at crank knock or thust crank bearing area knock under uphill conditions, but anyway, thry those two littlle things i told you of and get back with me.also be sure you're using the right type oil filter, let me tell you something, i have seen many an engine ruined by using the wrong filter!!! Use an Autolite or a Motorcraft, those two makers are forced to always keep Ford Mercury Lincoln engines in consideration when they make them, as to where AC filter or Fram does not...Janet

 

Yeah, I'm pretty sure there are a million electrical warnings against running any motor with the battery cable disconnected. That has a tendency to fry electrical stuff including your alternator. If you want to erase the memory just take the neg cable off and let it sit for ten minutes.

Be careful about not trusting the gauge too. You should get the mechanical gauge and test it BEFORE you run the engine. You wouldn't be the first to lose an engine to low oil pressure, who didn't believe the gauge.

 

I didn't notice anyone in here saying to drive around with the ground cable disconnected, but i wouldn't be afraid to disconnect the battery ground at idle to make sure my alternator was working, but then i would shut the ignition off before replacing the ground, a person has to disconnect the ground to change a bad battery??? running an engine for only a few moments without the ground, then shutting it off first and then reconnecting, will not fry any system..Janet