Head off...should I do a ring job?

ford
f150

#1

1994 Ford F150, 4.9L I-6, 164k Mi.

Recently had the head gasket go on me. Compression testing revealed the following, with max PSI attained after about 4 compressions:

1: 150
2: 170
3: 95
4: 145
5: 170
6: 170

Machine shop called today, said head isn’t cracked, but warped 0.017" and they want to do a valve job. Hone marks are still plainly evident on all cylinders. Just before HG breach became obvious, truck was going through 1Qt/5000mi, with a fair amount leaking out the oil pan, lifter gaskets, as well as around the oil pressure sensor (vs all being consumed in the engine.)

Question being: As long as the truck is “down,” what is the consensus on a ring job? I’d measure the bores for out-of-round; if they pass, I’d have effectively a top-end rebuild. (The 7 main bearings is the part of the engine I have most faith in, so I’m okay with leaving them alone.)

I guess what I’m asking is if it is good practice to leave the rings alone at this mileage, coupled with how much additional labor is involved. Can this be done with the engine in the truck (though not necc in the engine mounts)? Is it necessary to split the engine from the M5OD tranny? I think that a decent top rebuild of the engine might result in a truck that can last until I’m too old to do handyman stuff anymore.

(Or, I can patch it together and plan for a new truck and/or engine in 5 years or so…)


#2

Maybe I am reading it wrong, but it does not seem the piston rings are implicated. It would not be a bad idea to redo them, but if you are going to that expense you might consider a reman engine.

1 qt per 5k with “with a fair amount leaking out the oil pan, lifter gaskets, as well as around the oil pressure sensor” seems to indicate there is not further financial gain by doing rings.


#3

Considering your goals, the fact that you’re already getting the head redone, and the nature of your question, I’d pull the motor and finish the rebuild. If you pull the pistons to hone the cylinders and put rings in you’re going to have to check the rod bearings anyway. You’re a good deal of the way toward a total rebuild at that point.


#4

A compromise might be to just replace the rings in number 3. I’d be inclined to go in that direction if it were my truck. Unless the valves showed a problem in number 3 being the cause of the compression problem, then I’d leave the rings completely alone.


#5

Anyone else have the similar problem with a patch job, fixing only one cylander, then curiously that is the one with lowest compression again? I have.


#6

It isn’t the approach I’d take, especially since the goal is to have the truck last for many more years.

Besides, there’s no way of knowing of the low compression in that cylinder is due to the rings or due to the known warped head and/or headgasket breech. I’d bet lunch the cause is not the rings. In short, he’d be changing the rings in that cylinder for nothing.

But, hey, just because I wouldn’t take that approach doesn’t mean it isn’t a valid idea. All ideas are welcome.


#7

If anything beyond head repair is necessary I would recommend pulling the engine for a complete rebuild.


#8

@meanjoe75fan‌

My advice

Resurface the head, as needed
Do the valve job
replace the oil pressure sensor

Leave the bottom end alone

1qt/5000 miles is very acceptable . . . a ring job won’t change that

After the head job is complete, you won’t have a leaking oil pressure sensor or valve cover gasket

And your compression will probably be normal all across the board

The only leak you’ll still have is that oil pan gasket


#9

I agree with db4690 on this. I have seen too many ring jobs that didn’t last very long. Once you are into the rings, then you need to think about the bearings. Back in the 1950s, a ring and valve job was really a sloppy patch and seldom bought the owner more than about 30,000 miles.
On the other hand, my dad had valve jobs done on several of his cars without replacing rings and the cars did just fine.


#10

Okay, that sounds like a plan. I’ll take your advice on this, @Triedaq.

The tempting thing was thinking I could do this with the engine in the bay–plus, that the (presumably ok) rings have 164k on them.


#11

If oil consumption is minimal even with leaks and if hone marks are visible all around all cylinders for the visible length of the piston strokes, leave it as is. Can’t hardly be better than that if you have no doubts about the lower end.


#12

Seems like you’re already into this motor far enough that replacing the rings, honing the cylinders and replacing the bearings would be pretty easy. Replace all gaskets you can reach too. Good luck! Rocketman


#13

Did you test to find the cause of the low compression? If the cause was the head gasket I’d leave the rings alone. You were burning no oil.