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40 engine noise mystery & compression down one cylinder I have a ’40 221 flathead engine. Last weekend after a 35 mile trip the motor started knocking and the noise sounded like a valve pecking. Here is where the confusion starts. I was in a rural area and I had to try and make it home with the motor knocking. The engine was a little down on power. I drove the car about 2 miles and the noise started to go away. Within 5 miles the noise was gone, but the car was still a little down on power and I was getting a little more blow by out of the oil filler cap when the engine was pulling hard. I drove the car 35 miles home and the noise never came back. I checked the compression and found one cylinder with 30 lbs and the others are at 90. I took the intake off and saw nothing wrong with the lifters are valves. I took the head off and saw nothing wrong with no marks on the head, cylinder, or piston. Before I took the head off I poured some transmission oil into the closed intake valve hole to see if it would leak off. It did not leak off showing a good seal. When I turned the motor over it shot the fluid about three feet out from the car. I checked the compression again after the oil came out and it was 120. After I let the engine set for a couple hours I checked the compression again on that cylinder and it was back to the 30 lbs. I don't see anything wrong and don't know how to check for anything else. What do you think? Compression ring broken or something?
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Re: 40 engine noise mystery & compression down one cylinder Bill, When you do a "wet compression test" and you attain a much higher reading than a "dry test" it indicates a bad (perhaps broken) piston ring(s).
The oil temporarily seals the bad ring(s) and allows for that momentarily higher reading. My money is squarely on a bad ring(s) in that particular cylinder. |
Re: 40 engine noise mystery & compression down one cylinder Look for a loose, broken, missing, valve seat in the block.
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Re: 40 engine noise mystery & compression down one cylinder I had a valve seat come loose and drove her home over two hours. The seat stayed under the valve at an angle, it never broke. We bored the seat relief and put in an oversized seat, and a new valve. I have driven her over 10k with no problems. But I don't think putting oil in for a compression check would bring the numbers up any if it was that. I would lean towards rings.... look the cylinders over for marks, good luck, Chuck S.
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Re: 40 engine noise mystery & compression down one cylinder Chuck, I try never to say "never" but like you, I just can;t see how a wet compression test would seal a loose valve seat. My betting money remains firmly with a broken ring(s).
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Re: 40 engine noise mystery & compression down one cylinder I go for a broken ring!
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Re: 40 engine noise mystery & compression down one cylinder I go for sticky valve or ring, mostly valve. Drizzle MMO down both sides the carb while running and the rest of the quart botlle in the gas tank. Drive it 10 miles and problem gone. Put a 1/2 pint in the tank every time you fill the tank. Don't do it for 2 tanks and problem comes back. It's this new gas it puts a thin white resin coat on the valve stems. G.M.
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Re: 40 engine noise mystery & compression down one cylinder I agree with GM, betting on sticky valve.
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Re: 40 engine noise mystery & compression down one cylinder With all this said about the possibility of a broken ring or a valve problem what would the noise in the engine for 5 miles have been? Very loud and the engine ran rough while the noise was there. When the noise goes away engine runs smooth, but not as smooth as before the noise. I can hear a little suction at times in the exhaust like a valve that is open a little. One of those deals where you can put a rag at the end of the exhaust pipe and it will suck the rag into the exhaust for a split second at times. The input from everyone is helpful to show support for my situation. Everything I do I have to do by myself with no local support. Without the imput of the Ford Barn members I only have my own thoughts to go with. Thanks
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Re: 40 engine noise mystery & compression down one cylinder For $6.00 why question the powers of MMO?? You already took the head off with all the great advise received. Try the simple things and tests before tearing things apart. G.M.
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Re: 40 engine noise mystery & compression down one cylinder You can slid a feeler gouge under the valve tappet with manifold of ,to see if it coming down fully .
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Re: 40 engine noise mystery & compression down one cylinder My thought would be a loose seat. There may be times when it stays put and runs well, then could get cocked for a bit and run lousy. A sticky valve is not going to make a knocking noise.
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Re: 40 engine noise mystery & compression down one cylinder I've never experienced it in my V8, but I have had a sticky valve make one heck of a knocking sound in my "A".
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Re: 40 engine noise mystery & compression down one cylinder With all due respect to the folks suggesting valve related issues... the fact that the wet test provided much higher readings and when allowed to sit even for a short time, those readings dropped off dramatically pretty much eliminates valve issues.
While I can imagine the slim possibility of a seat becoming loose and then seating itself (albeit temporarily) I can't imagine how a wet test would seal same. Bill, you have the valve cover off... easy to check the valves in that cylinder. Heck, if you are able, remove them. |
Re: 40 engine noise mystery & compression down one cylinder Im thinking maybe a broken ring or ring land or skirt on the piston.
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Re: 40 engine noise mystery & compression down one cylinder While I have the head off I will take the exhaust and intake valves out for that piston and see what they look like. The noise in the engine is the only thing that puzzles me as far as the broken ring idea. Maybe I'm trying to fit all the observations into one cause when I really have two problems with two different areas. I will post more when I take out the valves. I poured transmission fluid into the questionable piston today and will see if it leaks down in the morning. That could tell something about the condition of the piston rings, I would think.
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Re: 40 engine noise mystery & compression down one cylinder 4 Attachment(s)
Went in this morning and checked the fluid I poured into the pistons yesterday. All the transmission fluid had drained pass the rings into the crank case. Not sure if that is important or not. Took the valves out and could see nothing other than a little build up on intake valve outter edge. There is a small chip on the very edge of the piston at the yellow mark that could be something that is contributing to the problem. I will post pictures of the valve and piston. Any body see anything that would explain further the lost compression and the short term noise in the engine?
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Re: 40 engine noise mystery & compression down one cylinder Bill, between the information you'd provided earlier about the compression tests results and this latest info...ring(s) my friend, ring(s).
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Re: 40 engine noise mystery & compression down one cylinder I agree "RING"
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Re: 40 engine noise mystery & compression down one cylinder I'm waiting for the piston.
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