Found pistons on carpaarts.com (https://www.carparts.com/piston/dnj/...ntosku=7747772)

Will these fit the 4.9L Straight 6?

 

Maybe a less Chinese website?

 

I have a 1986 Ford F-250 with the 4.9L inline 6. While replacing the timing gear cover, I dropped a piece of gasket into the oil pan. I pulled the engine out and decided to do a cleaning and replace the other gaskets in the process. While cleaning the oil pan, I found a 1.5" chunk of piston skirt buried in sludge. The engine runs but I'm afraid if left as is, it will let go and destroy all. Can I just replace one piston with an after market piston like Professional Engine Rebuilders K1597(1).P256 piston and ring kit (https://proenginerebuilders.com/1986...-k1597-1-p256/), or will I have to replace all pistons?

 

You can't just order pistons unless you tear the engine down first and measure what you have. That engine may have been rebuilt. It may need boring, which would make it a waste of money to put new pistons in it if it needs to be bored. Even if you know that engine is original and bought new off the lot, the engine could have been replaced by the factory if it had a problem. You never know what you have till you tear into it.

 

The truck has been in the family from the beginning,and never opened up til now. I pulled the head and pan and no other damage. All internals are original and very clean considering the age.I am working with a very tight budget, but don't want to be penny wise and pound foolish.I am weighing my options and taking in all advice.

 

If you are just going to re-ring it, unless there is obvious damage just use the old pistons. You have to check the ridge on top of the cylinders. If your fingernail catches, it has a lot of wear and the bores need to be measured. If they are worn over .006, then it will be penny wise and pound foolish to try and just re-ring, it may last 10,000-15,000 miles before it is burning oil and down on power again. I am assuming that is why you want to mess with the internals of the engine?

Something like.003 wear if you cut the ridge off the top and re-ring it, will give you good service for 50,000 miles plus. A rebore with oversize pistons will give you a brand new start.