My 69 442 has the orginal engine (400BBO), and was rebuilt 10 years ago. After the rebuild, the engine only had maybe 100 miles put on it before it was parked for nine years. All of the cylinders have good compression except for the number 7 cyclinder which has 135lbs dry and 165lbs wet (1 teaspoon of 30 weight oil in cylinder). Does this sound like a stuck ring? Here are the numbers on the cylinders:

1. 170lbs
2. 160lbs
3. 160lbs
4. 160lbs
5. 170lbs
6. 165lbs
7. 135lbs dry, 165 wet
8. 165lbs

I have read of people using marvel mystery oil in a stuck ring situation by spraying it into the cylinder and letting it sit for a week then vacuuming it out. Has anyone had any luck with this? Any recommendations on how to fix this problem? I would prefer not to have to tear the engine apart.

Would driving it like this eventually free up the ring or would this cause damage?

 

I wouldn't think you would have a stuck ring since the engine has so few miles on it and assuming the pistons were cleaned or replaced during the rebuild. The things that come to mind are a little surface rust on a valve face or valve seat from the cam holding a valve open or a cracked ring due to that #7 cylinder getting rusted a little from sitting and when you spun it over, a ring cracked. I would put an air fitting in that #7 spark plug hole and put compressed air in that cylinder and see if you hear air leaking through the exhaust, carb, crankcase or even bubbles in the radiator. Just make sure both valves are closed when you do this or remove the rocker arms on that cylinder. Since the compression improves with oil, that would usually point to a ring issue and the potential for a cracked ring. I would definitely try to solve this problem before you drive it because if a ring is cracked, you could damage the cylinder wall. Good luck with it and I hope I'm wrong about the ring.

 

Marvel Mystery Oil really helps with motors that've been sitting, but I don't know if it'll help a motor after it's been running!!
If you still want to try, squirt about 2 tbl. into the cylinder, let sit overnight with the plug in. Next day, pull the coil wire, [important!!] remove the plug in that cylinder, and crank the motor, blowing out the MM Oil. Clean as necessary!
Re-install the plug, wire, and coil wire and fire it up.
Let it get warm, and re-check your compression - hope it works!

 

Have also heard tales of Marvel Mystery Oil working...so who knows, may work as a "quick fix."

 

If you added oil and the compression went up, it is not a valve problem. It is a cylinder problem. My son bought a 68 years ago, and we had about the same problem, when we pulled the heads, one cylinder had a broken ring, and it scored the cylinder. Hope thats not your problem, but you may have to take apart to find out?

 

My hope is that it is only a stuck compression ring. I am adding Marvel Mystery Oil to the cylinder today and will give it a few days to soak. The pistons, rings, etc were replaced during the rebuild in 2000.

If it was a cracked ring I wouldn't think the compression would come up as much as it did. The car sat in a heated garage for the last nine years, not outside in the elements. I wouldn't think the rings would have rusted to the cylinder wall in a more controlled environment. I guess we will know in a few days.

 

According to my highly scientific drinking straw, I have around 3.5 inches of MMO in the number 7 hole now. I will update with the results in a few days.

 

To get that out, pull the coil wire, and 'click the key' with a rag over the hole to catch the oil!
And as much as people have said Slick 50 doesn't work, I've used it on stock motors and picked up small gains in performance and MPG.
Might be a good candidate!!

 

Okay, I couldn't wait any longer to see if the MMO had worked on what I thought was a stuck ring. I pumped out the MMO with an oil transfer pump and turned the engine over with the kill switch on to blow out the rest of the oil. Put the plug back in and warmed up the engine. Got some smoke on startup which lasted a few seconds. The number 7 cylinder read 145lbs dry.

I then pulled the valve cover off and released all of the tension off of the rocker arms on number 7 so the valves would close. Hooked up the air compressor to the cylinder at 100lbs and got some slow blow by from the valves. No air sounds from the tailpipe, carburetor or from the oil fill tube. Just slow air escaping from between the valves? Did the same thing on number 3, which has good compression, to see what it did and had the same result. Slow blow by. I had my wife turn over the engine with the kill switch on before i released the tension on the valves and the valves are moving up and down correctly.

Suggestions, comments or some pointers would be appreciated.

 

Well at this point the only thing you have to decide is, do you want to try and drive it for a while and see if it comes unstuck and take the chance of scoring a cylinder wall. Or tear it apart and see what it is!! If your going to drive it, add about 1 qt of mmo to a full tank of gas and run it out. Don't over rev it, drive like a little old lady and vary your speed from 50 - 65 and don't drive at a constant rpm for a very long time. The old fashioned breakin! If its going to settle out it will do it in a tank full of gas.