I recently picked up a 1983 F250 with the 460, and yesterday performed a compression check. All cylinders, with the exception of number 4, tested between 105 and 115psi. The truck runs, but lacks any power(I can't imagine why
Does anyone have any ideas what may be causing the zero pressure in 4? A stuck valve?
The truck had been sitting for a couple of years when I bought it, so I did all of the regular maintenance stuff...plugs, wires, distributor cap and rotor, drained the front tank, and replaced the bad fuel pump and relay. Also ran some Seafoam through the carb.
I'd appreciate any info/help I can get on this problem.
Thanks.

 

Zero compression points to something more serious than a leaking head gasket or bad rings. It sounds like you have a hole somewhere.

If the problem was an open intake valve, you would know it. You would have backfire up through the carb and it probably would barely run or not run at all.

If it were a hole in the head into the water jacket, that would be pretty obvious, and it would not be running.

If you had a hole in a piston top, you would probably have a lot of hot gas coming out of the crankcase vent. While it is running, pull the PCV valve and see if you have a stream of gas coming out.

Another possibility is a broken rocker arm or rocker stud or bent pushrod on the #4 INTAKE valve. If the intake never opens, you will not get air into the cylinder and would read a really low cylinder pressure. Pull the valve cover and crank the engine over by hand and see if the valves are moving appropriately. If they are, I would say the most likely bet would be a burnt exhaust valve/seat.

 

Thanks for the info and suggestions. I'll give these things a check and see what I find. I hope I didn't just pick up a money pit. Thanks again for the help.

 

You need to do a leak down test ...

Number 4 is ZERO .... They typically pump up some if it's rings, so the chances are it's a valve.

First thing I would do is pull the rocker cover and have a look see ... If I don't see no rockers off or bent pushrods ... on to the next test.

Either make (out of an old spark plug) or purchase an adapter that allows you to apply air pressure in the cylinder, this will point out where the leak is at, rings, intake valve, exhaust valves. Bring the cylinder to TDC on compression, apply air pressure slowly... WARNING!!!! Applying to much air pressure to a cylinder at TDC may very well force the piston down the hole, be aware and don't allow anything to be caught in rotating parts.

You may also be able to hear a valve huffing out the exhaust or intake while cranking.

-Enjoy
fh : )_~

 

Well, I have found the cause of my compression problem in 4. I removed the valve cover and found the intake valve rocker arm flapping in the breeze because the pushrod was bent. What could have caused that? What's my next step, other than inspecting the rocker arm and lifter, and replacing the pushrod?
Thanks again for all of the help!

 

When you had it running, did it have oil pressure? One thing that can happen when you bend a pushrod is that the lifter can get tossed up and out of its bore. This results in a huge oil leak and little or no oil pressure. Make sure the lifter is still in place.

I am not a 460 expert, so I don't know if bent pushrods are a common thing or not. I'm not sure how a pushrod ends up getting bent. It could have been slightly bent when new, and eventually gave in to the stress. Or something could have jammed the intake valve or rocker are causing it to bend. While you have the valve cover off, can you find a place to get some leverage with a pry bar and make sure the intake valve opens? I would suggest, if nothing else, when you put in the new pushrod turn the engine over by hand and make sure the intake valve opens and closes before you fire it.

 

Yes, I had oil pressure while it was running. My plan is to install a new push rod and crank the engine over by hand; as you suggested, and make certain that valve is opening and closing.
I used to have a '67 Falcon van back in the day, and that thing bent push rods all of the time. Here we go again!

 

Before doing anything, you need to ensure the valve works smoothly.

Like already stated take a bar of some sort and operate the valve ON THE VALVE STEM, do not push on the retainer ...
Ensure the piston is down the hole (not at TDC) before doing so ...

-Enjoy
fh : )_~

 

Well, I found that the valve isn't moving, so I'm assuming it's bent. Any tips, suggestions, or warnings on pulling the head off of this thing? Thanks again.

 

I have one other question on this truck, is it worth putting anymore money into it? It's a regular cab, 4x4, and the body is a little rough, but not too bad. It's got a topper, brush beater front bumper and a DMI Quick Cushion hitch on the rear. Everything else seems to work fine. I paid $500 for this truck, and I'm only looking to use it for getting firewood out of the mountains and doing some snow plowing around my place when I can find a plow at a decent price. I thought that this truck would be perfect for that, given the torque monster characteristics of the 460. I'm just wondering how much more of an investment makes sense.
As always, thanks for the input.

 

Well, if it is a long bed it is worth fixing. If it is a short bed.....well.... it was never worth owning in the first place :-) But kidding aside, it is the old "Beauty is in the eye of the beholder" thing. Only you can decide how much time, effort, and money you want to invest in the truck. My suggestion, before you make any decision, would be to pull the cylinder head. The $64,000 question is "Why does it have bent valvetrain parts?". Maybe the timing chain failed and the #4 piston slammed into the #4 intake valve. The PO may have replaced the timing chain, discovered that the truck ran like crap, and decided to sell it. Until you pull the head, you can't be sure how much damage there is. You may find a hole in the top of #4 piston. On the other hand, you may find that everything looks good except the #4 intake valve is bent and for a small investment a head shop can replace it. Knowing how bad the damage is will help you decide your next step. I hope things work out for you.

 

Since its been sitting a while there's a chance that its rusted the valve to the guide, there's an slimmer chance that it may have stuck shut & it popped the push rod on initial cranking when the lifter was bleed down. There's a very very slimmer chance that you maybe able to get it moving again with WD & some tap tapping. Worth a thought before pulling the head.

Generally if the valve stem tip is sitting lower than the other exhaust valves you could have a much bigger issue, but if its resting at the same height it might simply just be stuck.

Takes a fair bit of getting things out of wack with a stock cam to clobber valves.

 

The 460 is not an interference motor like the jap crap. Neither is any other Ford truck engine that I know of. I would rule out piston contact. Also if there was a hole in the piston he would have some super serious blow by coming out of the breather, alarmingly so. A stock 460 has super deep dishes in the piston tops, and the stock camshaft lift is in the .450ish lift range which is super small for a big block.

But yeah, I would try the WD-40 and tap on it to see if it unsticks. If nothing else 460 heads are cheap as hell and the only thing hard about removing one is picking one up, they weigh a lot.

Truck is worth keeping for sure. Once you get it running good you will be happy with the beast.

 

Diddo that

 

OK, here's the latest. I pulled the heads and dropped them off at the machine shop. As soon as I told the guy that the truck had been sitting for a few years, he immediately thought that the valve was stuck, and not bent. He pulled off the spring, sprayed some brake cleaner into the guide and tapped the valve out with a punch. Sure enough, it was just stuck from old gas and gunk.
Does anyone have any tips/recommendations/cautions for reinstalling the heads?
Dr. Danger, you are absolutely right about those heads being heavy. OMG! They are beasts. I decided to rent a hoist for this job since I'm doing it by myself. I'm not sure I could even imagine doing this job even with two people.