Compression?

I have a new .060 over 390 with 20 minutes of runtime on it. I ran it just long enough to break the cam in and look for oil leaks. Later I did a compression test. with the engine cold. Cylinders 2-8 were all 148 to 150 PSI. Number 1 was at 120. I have been very OCD about this build and everything was checked and rechecked. I did not do the machine work, but I did do the install. All of the clearances are well within spec and it is assembled right. Several people have told me not to worry about it and run it. The compression did come up when I squirted oil in the cylinder. Does this mean it is the rings? I built a simple leakdown tester and I am going to try to check that tomorrow or the next day. What else should I check? I want to check everything before I tear it back down. I am open to any suggestions.

 

Is it missing or running bad? Are you sure you do not have two piston rings lined up straight perpendicular from each other? I always stagger them 180 degrees from each other. If you shot oil in the chamber then you know its the rings. Just a thought. Knuck from Indiana.

 

I am 99.999% certain. The rings came with a sheet that clearly laid out how the rings go. I really do not want to tear my engine apart. If I do a leakdown test will it tell for sure?

 

Put some road miles on it and give the rings some time to seat.

Accelerate and then back off to dry the rings and bathe them in oil, do this repeatedly.

Do a compression test on it with the engine at operating temperature after the rings have seated.

 

Before tearing it down do a compression test and a leak down test,then tell us the results.

 

I am going to pressurize the cylinder and see if it holds. It will be tomorrow before I can do this. I guess I will check cylinder 1 and 2 for comparison.

 

Break it in ! Don't know what rings,hone,clearances you used but give it some miles IF you think all was correct going together. Make sure you have no leaks, steady oil pressure, valves adjusted properly and put some miles on it , vary the speed, don't hold at a steady RPM , don't overheat and take two aspirin and call us back next week !

 

Before you prematurely take the engine apart, drive the car for a while (if it seems to be running OK), and give the rings a chance to seat. In my experience, you will be surprised at how much better the engine runs after a 1000 miles.

 

The only leaks were one fuel and one water and those were quickly fixed. 80 PSI of oil pressure at startup and 60 when warm. It will be a while before the engine goes in. The car is in 1,034,874,000 pieces.

 

def give it some time before you tear into it, fresh cylinders act funny sometimes. with the oil in the cyl was it the same as the other cyl or did it just raise a little? i had a similar issue with a 410 fe, it ended up being one of the new hardened exhaust seats was bad, luckily i caught it before it came apart and mangled a cylinder.

 

OH! "The car is in 1,034,874,000 pieces."

 

"Later I did a compression test. with the engine cold. Cylinders 2-8 were all 148 to 150 PSI " you stated. Always check compression and a leakdown when the engine is hot,Was the carb wide open when you checked compession?
Rings do need to lap in so dont be too upset with your findings.Put your efforts in putting the two million parts together to resemble the rest of the car so you can drive it.

 

All it is is that the rings in that cylinder have not fully seated yet. Don't sweat it!!

 

Like others have said, get some drive time.
Doing a leakdown can be treacherous, you are blowing unfiltered shop air into your engine via the air compressor. There will be moisture, pieces of crap from the air lines and rust flakes from the inside the tank. I have a painters filter and water seperator on one of my compressor outlets and that is what i use for leakdown testing. Even with this amount of protection i hesitate to do a leakdown, things have to be pretty grim.

 

Did you pressurize the chambers with air and check how good the valves were sealing before you fired it?
Sometimes a fresh valve job will not seal correctly and it will leak a lot of pressure by the seats.
Good luck.

Tommy

 

I did do the compression test with the carb open all the plugs pulled. It does have hardened valve seats and that did cross my mind. It seems like the car is really in that many pieces. I am not looking for a full race engine or anything, but I do want it to be right.

 

did you use moly rings or cast?

 

Assuming you're using hydraulic lifters ... pushrod length is critical on these engines. The combination of valve seat installed height & valve length is sometimes off. Years ago, all machine shops used a gauge to check height. Another 352 -390 quirk I remember - you could run 3 or 4 compression tests & get 3 or 4 results.

 

They are plain cast steel rings. If I had used Moly I wouldn't worry. Those things take forever to seat.

 

Do this just like DG says. I am normally pretty lucky and my rings seat right away but it isn't always the case.

It isn't keepin you from driving it and it won't be any harder to tear down with 500-1000 miles on it than it is today.

 

""If I had used Moly I wouldn't worry. Those things take forever to seat.""

No...Moly rings are seated by the time you finish assembling the engine [almost!]..