My friend was driving his 1996 bronco 351W just around town, started running really rough, checked plugs, wires, dist cap, coil, injectors. everything is fine. Spark isnt very good. we checked everything we can think of. did a compression check, all other cylinders are fine between 160-154 psi, but cylinder 2 didnt even move the needle on the tester.

I figure that the piston isnt even moving? any movement should cause some compression, what could be wrong here? we've heard, bad valve, collapsed lifter, bad head. we havent pulled the valve cover yet, but we're about too.

any ideas? he really doesnt have the time, money or resources to drop in an engine or rebuild the one he has now.

 

we just pulled the valve cover, no bent push rod but the cylinder in question one of the rocker arms and push rods was real loose, but the bolt was tight. we pulled the intake manifold off and checked the lifters, nothing we can see is. we are now debating to take the oil pan off to check to see if the connecting rod has snapped.

any ideas?

 

the rocker may be loose because of a bent valve. Compare the height with the others.

 

Dropped a valve seat or guide = valve not closing fully.

Just my guess.

Bob

 

You making this way too tough......

Pull the spark plug on the offending cylinder, get a straw or some other non-metal rod/stick then put it in the spark plug hole. Push it in far enough to bottom out on top of the piston. Turn over the engine by hand, watch the straw/stick to see if it goes up and down with the piston movement.

If that engine threw a rod there would be a lot more noise and issues beside rough running.

BTW.....I have never had an engine toss a rod or bend/drop a valve by "driving around town". The engine has been in the upper RPM range to cause any of that type damage. Your friend needs a better story

 

This. There would have been a loud pop/bang noise and it would sound so bad you probably would already know the engine was toast.

The next logical step to me is to pull the head.

 

My sister once had a Lincoln LS. Its a 3.9 V8, fun car, very quick. Well, one day, she said it just wouldn't start. She had been "driving around town" and then parked it, and said it just wouldn't start. Towed it to a shop, and I was checking it out. The entire left bank (or was it just two on that bank? don't remember now) had 0 compression. Maybe she meant she was "racing around town"? I'll never know, except that the engine had seem much to high of RPM! Junked that one, much too $$ to justify repair on a somewhat exotic motor.

More relevant to this OP's post. My mom drove my dad's 1987 Econoline when I was a little kid. She loved the 351, floor it, O/D came off, it downshifted, it moved. Well, the rod bolts on the older 351s weren't the strongest (says my father), and didn't stand up to RPM. My dad, suspecting my mother's driving habits of flooring it to pass people at 70mph, disconnected the "kick-down" linkage to the trans. She soon drove the van, returned home, and demanded to know "what the hell did you do to my van!" Within a year that motor kicked a rod through the block when the rod bolt finally let go, while we were en route to a family vacation, boat in tow, 120 miles from home. Haha man my dad was not happy. So next we got a van with a 4.9, not so much fun to drive like a racecar, and it lasted forever.

Most relevant yet, it definitely does not sound like your buddy's motor threw a rod. As already stated, sounds like a valve issue...much cheaper.

 

Now that's funny !!!!!!

Bob

 

we found the problem, we put it back together enough to test to see if the piston moves, so we decided it was a valve problem, so we started taking the head off and almost through taking the head off, we found that the valve spring for cylinder two (the one that seemed loose) was completely snapped and broken.

Now we have to get new head bolts and the head gasket set anyway from taking the head off.

Should we get all new valve springs while we're at it? if one broke how far away are the others from breaking? I believe the bronco has about 146K miles on it.

Anyone have a place that they have had goodluck with valve springs?

Advance Auto has a few different ones;Sure Seat; Valve Spring; Street; Non-Rotator; Seat Pressure 61-69 lbs.; OD 1.385 in.; ID 1 in.

oneSure Seat; Valve Spring; Street; Rotator; Seat Pressure 61-69 lbs.; OD 1.385 in.; ID 1 in.,

and the other is Sure Seat; Valve Spring; High-Performance Street; Non-Rotator; Seat Pressure 110-120 lbs.; OD 1.44 in.; ID 1.03 in.

We have no idea what we need here?


Also another one of my friends said now we will have to retime the valves, is this true? I would only think we would have to if we did something with the camshaft?