Bearings? timing chains?

[Denver95327]

So I just bought a 93 ford ranger from a buddy of mine due to unfortunate reasons, I knew the engine needed some work due to a knock, well here I am looking for ideas of what the causes may be. It is a 4.0, When you first start truck it knocks for 1-2 seconds until oil builds pressure..then goes away. When engine gets warmed up a bit the knock comes back and doesn't go away. If you're driving along and get on the throttle the knock does go away but comes back when driving normally. I was thinking a rod bearing, but was told to do the trick of pulling each spark plug wire one at a time to see when the knocking goes away, well it never did go away . So maybe the crank bearing? The sound is hard to pin point where it is coming from, top or bottom of engine. Another issue I am having is that oil pressure does drop when engine is hot and at idle. Truck seems to have good power still and runs ok, If anyone has advice on this is would be greatly appreciated. Also, this is just a hunting truck for the woods, not a daily driver so it might not be worth dumping much money into. Thank you for your help.

 

[aspevacek]

Run som eof the seamfoam intake cleaner (or any other brand) and see if it lessens the knock. There were reports of carbon build up that would knock on startup. If you had a way to look in each cylinder at tops of pistons could be a way to check each out.

one of the quickest ways to check the main bearings to rev the engine and see if it hops around wildly was it revs. It will hop around because of excessive clearance between the bearings and the crank (too much gap allowing play).

 

[RonD]

There are "knocks" and there are "taps"
Timing chains "rattle"

Ford V6s are known for valve train "taps", especially on start up.

Yes, the spark plug test is a good one for Rod knocks
Main bearing knocks don't come and go once oil is warmed up.
I use an old broom handle(without the broom part, lol) as a stethoscope, place it on the lower block and listen, metal transfers noise pretty good and so does wooden stick , move it around to localize the area if you find a knock.

From what you have described I would think a lifter tap.
If you remove the valve covers you can feel each push rod for tightness, rotate crankshaft one full turn after first check, to close valves, to check all push rods.
If valve is closed you should be able to barely turn the push rod, but can turn it with your fingers; there, for sure, should be no up and down movement possible.
A loose push rod, easy to turn or up and down movement, means a bad lifter, there are no adjustments.

If you get a set of push rod covers, they clip on to each rocker to prevent push rod from spraying oil straight up, you can start the engine, put a towel on each exhaust manifold to prevent oil run off.
While engine is running look at each rocker, you should see oil pooling quickly in each, if you see oil coming out slowly on one then that is the faulty lifter.


You need to remove the intake to replace a lifter.
Lifters can be dirty/sticky so cleanable if you take them apart or they can have broken springs.
Oil pressure keeps the lifters tight against the push rod/rocker/valve when engine is running, but on first start up or dips in oil pressure the spring does.

When lifter is compressed to open the valve, it has to return to "normal" very quickly or will "tap" on the next rotation of the cam when it has to compress again, if piston valve setup inside the lifter is sticking then tapping is heard, high RPM tapping can be this as lifter can't recover to "normal" fast enough at higher RPM.

A slightly bent push rod could also be causing the tap, but this is usually a continuous tap, doesn't come and go like a bad lifter can.