Hello.. I registered on these forums just to reply to this post
I'm a Bronco II owner, and I love these little trucks.
First of all, let's get one thing straight: if this truck IS a 1986, it has the 2.9 V6, unless the owner has changed it to something else. The 2.9 impossible to incorrectly identify, as it actually says "2.9 EFI" in HUGE letters on the intake manifold. This is a chain-driven overhead valve engine with hydraulic lifters, but as an added bonus the valves CAN be adjusted.
Anyone who knows the Ford 2.9 will tell you that valvetrain noise is very common in these engines. There is no single certain cause, as it can be anything from worn rockers to a blown oil pump, but the most common causes are:
1) Obstructed oil pump pickup screen. Most 2.9s that I have torn apart have at least some slight buildup on the oil pump pickup, and in worst cases, the pickup tube was filled with buildup and had to be replaced. If you would like to clean the pickup, the engine can be raised a good four inches with wooden blocks, but on 4x4 models you will not get the oil pan off without pulling the engine. Trust me.
2) Worn cam bearings. Although I love this engine, I will admit that it has a horribly designed top-end oiling scheme. Oil is pumped up to the lifters via the cam bearings. If they are worn, they must be replaced, or a thicker oil must be used.
3) Poor oiling design in general. In some cases, the top-end oiling problems can be all but solved by removing the front cover and rotating the camshaft thrust plate by 180 degrees. In its default position, the thrust plate allows too much oil to escape the top-end and flow back down into the pan. Rotating this thrust plate retains adequate oil flow to the timing chain and associated apparatum, and restores proper oil volume and pressure to the top end.
Aside from these causes, the 2.9 valvetrain noise issue can sometimes be a complete mystery that is better left unsolved. I know some people who have rebuilt their 2.9s from the ground up, cranked it up, and received a hearty chunk of lifter noise. They then proceeded to drive their engines for another 200k (the 2.9 will last very long if you treat it well) with little to no negative results.
Another thing to check for is cracked heads, which are common with the 2.9. Just remove the oil cap and check for any vaseline-looking gunk. If it's there, stay away. Otherwise, flush out your cooling system as soon as you get it home.
Despite its two main annoyances, the 2.9 is a good engine with lots of torque (170lb @ 2600rpm) for its size. If you treat it well (this means using SYNTHETIC OIL ONLY. I cannot emphasize on this enough), it's also a VERY reliable engine.
Sorry for the length of this post, but I just thought I'd let you know everything that you need to know before you make this purchase.
