Ok, here's my problem.

I have a used '93 F-150 XL with the 4.9L inline-6. Only 84k on the truck but not well maintained by the PO's. It seems to have developed a knock in what sounds to be deep in the engine. I'm thinking rod knock. The strange thing of it is that the knock occurs only when the car has warmed up. When the car is cold, it doesn't knock at all. The knock is pretty quiet at idle, but when a load is put on it, it knocks more loudly. Also, as the engine spins down from being revved, the knock diminishes. I haven't tried grounding out the spark just yet to see if the knock's quality changes

Can an engine with rod knock not knock when cold? Or could the sound be something else?

BTW, the knock sounds like someone knocking on a piece of wood, like a 2x4 laying on the ground.

Thanks

 

anyone?

 

It could be rod knock, maybe have a rod bearing getting tired. Why worse when hot ? Oil thins out when hot, thicker when cold. Pull the pan and wiggle the rods back & forth. If one's worn bad, you'll feel it move compared to the other ones. Also, look up at the pistons with a flashlight and check them for any cracks or anything unusual. I had one break in the cylinder (at 270,000 miles, after P.O seized it up several times, too cheap to change the water pump). Amazing how much damage that rod does after running it for some 8 or 9 miles with the rod flying around in there......

 

Thanks for the reply. I was also thinking about the oil thinning or perhaps tolerances opening up as the engine warmed up.

Is it possible to replace just the one rod bearing or would it be best to just rebuild the engine or pick up a junkyard engine.

If all I have to do is drop the pan and work on one rod bearing, then that wouldn't be too bad. (unless the crank is damaged)

Thanks again.

 

Try some 20w50

Adrianspeeder

 

I have replaced main and rod bearings while still in the truck. The motor had to be tilted to get the pan off, but that was on an 83 4X4. Check for a very bad rod bearing first, and then check the mains. Remove one at a time and inspect. Check the crank journals for excessive damage.

Once I determined that there was no fatal damage, I started with the main bearings first. Remove a main cap, and push to old bearing out of the block side. Use the old bearing from the cap to get the old bearing started in the block. Use assembly lube and push the new bearing into place. Put a new bearing in the cap, lube and reinstall the cap. Torque to specs. Move on. I think there is like 5 mains in this block.

Then do the rods. Same process, but you may want to turn the motor to get the rods in a good position each time.

Don't worry if the bearings are down to the copper, or even the steel shell. The crank is steel, and is tough. As long as it's not too badly scarred up, new bearings will help, and last. My rod bearings were acytually egg shaped! Oil pressure went up immediatley, and she was quiet for a long time.

Good luck.

 

EsoxShep,

Thanks for the reply. very informative.