Compression test results & Questions

[68special]

New here on the forum. I am the 2nd owner of a 68 f250 with a 390. Bought about 5 years ago. the seller claimed the motor was rebuilt 2000mile prior to my purchase. I have no reason to doubt that based on the appearance and the way it ran. As far as i know it was a stock rebuild, the old man was cheap and mentioned his neighbor who was a mechanic did the rebuild for him......It has a 2barrell carb, i just use it for man road trips and hunting trips. My concern is reliability as when i do drive it, its not unusual to be in the middle of nowhere.

I've put 12,000 miles on it. started to tick a bit and makes a "phoot phoot" noise from exhaust randomly but often at idle. Pulled driver valve cover, #1 exhaust push rod is clearly wobbly....also notice blowby coming out above #3 and #4 cylinders. I can also jiggle that same rocker arm by hand easily. Did a compression test yesterday. Got 180 is all cylinders except for #7 which was 172. I took a photo of the plugs because the oil stain on the passenger side plugs seemed odd.

The motor runs great, just ticks a bit and also has a deeper knock (same cadence as the motor is turning) that the sounds like its coming from the back of the motor somewhere. I've listened all over with a wooden dowel and cannot pinpoint it. I haven't pulled driver side valve cover yet, but plan to replace the bent rod and check the condition of the rocker shaft.

Any comments/advice will be greatly appreciated.

[68special]

more pics

[68special]

one more

[jayb]

Sounds like you may have an exhaust leak.  I would look at fixing that so that you don't get fooled by that noise; they can sound just like an engine knock.  The knock down low would worry me, but fix the exhaust leak first and see if that cures it.

Do you have adjustable rocker arms on the engine?  I would guess probably not, in which case there should be no slop in the pushrod or rocker arm.  You may have a lifter going bad, or a bent pushrod, worn rocker arm or shaft.  Just gotta take it apart and take a good close look at the parts.

[68special]

the rockers are non adjustable. I can easily press down on the rocker arm and compress the lifter on the #1 exhaust. I didnt notice it was bent until i ran the motor with the valve cover off, as it rotates, its clearly bent but not bad enough to rub against the manifold. I have a video i will post a link too once i get it uploaded. While im pretty sure i have an exhaust leak at the manifold, the phoot phoot noice is coming from the tailpipe. The whole tailpipe shakes when the phoot noise is audible.

[cjshaker]

Where are you seeing the blowby?
The compression numbers are good. Even with #7 being a bit lower, that's still not bad numbers.

Can you press any of the other lifters down by hand? I've seen engines that you could press down hydraulic lifters by hand and others that wouldn't budge. If that's the only one that you can compress, it definitely sounds like a lifter going bad, which could explain the bent pushrod, the tick AND the slight miss out the tailpipe. If you have duals, is the sound from the right pipe? A trick to see if it's a hard miss is to hold a rag or something over that pipe. It will become very clear if it is a miss as that will amplify the pulse and sound coming out, you'll not only be able to hear it, but feel it.

I would be concerned about the knock if you're sure it's not an exhaust leak. If you can hear a steady lower knock at idle, I'd probably cut open that oil filter and see what you can find in there. That would be a good clue if something bad is happening.

[68special]

Here is a link to a video of it running. I dont have dual exhaust so i cant tell which side. Ive only had time to remove the passenger side valve cover and i wasnt able to press down any of the pushrods by hand EXCEPT the #1 exhaust.

https://youtu.be/kQQouGLvpFM

[sixty9cobra]

That has to be the driest valve train I have ever have seen. What is your oil pressure? Just cranking mine floods the rail on the head and runs over makes a big mess.

[68special]

The oil pressure gauge is almost to the middle at idle and about 3/4 when on the highway. If i rev the motor a bit with the cover off it makes a huge mess. Should i be concerned about the oil situation based on that video? Does that push rod look bent enough to be concerned? i'm not trying to make a problem here.

[turbohunter]

Does that push rod look bent enough to be concerned? i'm not trying to make a problem here.

My truck ran for a while with this push rod in it when I first bought it.
It made a bit of noise but ran from northern to southern Calif. with out a sneeze.
Tough ole engines.
That said, if it's bent you should fix it, but don't feel like you have to get it done now or the engine will explode.

[shady]

if it makes you feel better to change the lifter, you can change it without pulling the intake. you only have to remove the rocker assm. & you can fish the lifter through one of the openings for the pushrods.

[68special]

I cut open the oil filter this weekend. no sign of any metal shavings inside at all. Im going to change the lifter & pushrod after the 4th and see what happens

[cjshaker]

Hopefully that will take care of the tick and the miss. Something else you may want to glance at is the distributor cap. If it has aluminum contacts inside they can corrode and cause a miss. I've seen them get so corroded that an engine won't even fire or start. If you take a small screwdriver, pocketknife or something similar you can tell by scraping the contacts surface and see if it flakes off. The cap can still be used if it does flake off, it just needs to be addressed about once a year. Brass is much better, although more expensive also.

The blow-by doesn't look real bad, at least for a cheap rebuild with some miles on it. I wouldn't worry to much about that. The only way to address it is a complete tear-down and rebuild. I've seen worse on good running engines. It's hard to tell what kind of residue is on the plugs, looking at those pictures. It looks more brown than oily, indicating that fuel distribution may not be ideal. Kind of hard to tell without a close-up of those plugs. Do you happen to have a vacuum gauge that you can plug into the intake and see how it's acting? They can be a big help in determining what's going on inside an engine.

The exhaust leak at the manifold can be a real bearcat if the top bolts are froze, which they often are on vehicles that get used year round and sit outside.

Good luck on the work.