Low compression in one cylinder

[Abchoppers]

Originally Posted by Gene F

#2, and add some Marvelous Mystery Oil to the crankcase, and take her for a spin.

I’ve read that some people have good luck with that stuff, sometimes it’s worth a try!
Thanks

[Flathead Fever]

I take my five-year grandson to taekwondo, and they teach perseverance, winners do not give up, they do not tap out. That's me when working on cars, more like that used to be me. Lately my body doess not have that same spirit. I was watching an MMA fight thinking about hoiw that doesn't look that hard and then I had to practically tap out reaching for the remote with my torn shoulder (third time it's tore) so I could fast forward through the commercials. It hard working on this stuff as I get older and I'm only 61. I have the knowledge but not the body to lean over a fender for hours is gone.

I was mechanic for 30-years. Seventeen ASE certification. Master Mechanic. Master Heavy Truck Mechanic, CA State smog License. We fixed 100% of everything in house. There was no passing it on to someone else to figure out. It was coming back to you util you fixed it right. They kept them for over fifteen years so we saw everything break that could. I had the advantage of having duplicate vehicles to look at and even swap parts from that you don't have at home. Tools you don't have at home. I worked with some pretty smart guys and a few not so smart ones. I learned from both groups what to do and what not to.

Because I was a fleet mechanic and scored well on the Stats exam test I was invited by the State to be on the team of ten-guys that wrote the smog test questions for the new smog mechanics. They wanted dealer mechanics, small repair shop owners, college automotive professors and one lowly fleet mechanic on the team. I was on the bottom of the barrel in that group of guys. When we developed those test questions for the State of CA, we were told to create two ridiculous answers, a distractor answer and the real answer. When I have a tough problem, I always think back to those test questions, wouldn't it be nice if there were only four possible causes to an automotive problem and two of them were stupid choices/ Engine has low compression on one cylinder? Mechanic "A" says, it's because the radio is tuned to political station that differs from their own view. Mechanic "B" says, old cars never did have good compression in all cylinders when they were new. Mechanic "C' says, the valves have high performance valve springs with more pressure. Mechanic "D" says it could have a head gasket leak. Those tests are designed for people just starting out as mechanics. The difficulty level was designed for a beginner mechanic. They won't be good mechanics until they have years of experience. We were told 15-years ago not to create any carburetor test questions, that there were students in automotive classes that had never even been in a car with a carburetor. Some of this old technology although fairly simple will become a lost art.

My dad had old Fords, so I started with a '65 Mustang fastback I turned into a fake Shelby. Eventually I bought a real '66 GT-350. I've had fifteen early Mustangs. I had a '57 T-Bird my mom bought new. I have a bunch of unfinished flathead Ford hot rod projects. When you work as a mechanic all night long. raise two little girls during the day while building a house, the last thing you want to do is work on your own cars at home. Now, that I have all these project cars and time to work on them (somewhere around seventeen vehicles that are not finished) I can finally start working on them. I collected cars and parts for 40-years. I've had two failed back surgeries (fused vertebrates), three shoulder surgeries and I'm in constant pain. So, it is hard to get out there and work on this stuff. That's part of the reason I like sitting here helping people with their problems, it's easier on my body, until I go to stand up. Oh my god does that hurt. The longer I make my rambling answers the longer I can put off trying to stand up. My most important automotive advice, do not become a mechanic!

[cadillac512]

Flathead Fever said:


"My most important automotive advice, do not become a mechanic!"



...Now you tell me...only 50 years too late!


Terry (I agree, mostly)

[Flathead Fever]

Running compression test. This would be a test you might do if you have good compression on a static test. It might still be interesting to see what it shows on your low cylinder. This test is rarely done. This video is longer than it needs to be you can stop watching after 10-minutes.

https://www.youtube.com/watch?v=YbR7Ja2E28s&t=766s

You want to see the modern way of doing a running compression test using a pressure transducer. I couldn't cut it out in the real automotive repair world anymore, the technology has left me in the dust in just a decade.

https://www.youtube.com/watch?v=cGM6H5dz7g8

[Abchoppers]

Originally Posted by Flathead Fever

I take my five-year grandson to taekwondo, and they teach perseverance, winners do not give up, they do not tap out. That's me when working on cars, more like that used to be me. Lately my body doess not have that same spirit. I was watching an MMA fight thinking about hoiw that doesn't look that hard and then I had to practically tap out reaching for the remote with my torn shoulder (third time it's tore) so I could fast forward through the commercials. It hard working on this stuff as I get older and I'm only 61. I have the knowledge but not the body to lean over a fender for hours is gone.

I was mechanic for 30-years. Seventeen ASE certification. Master Mechanic. Master Heavy Truck Mechanic, CA State smog License. We fixed 100% of everything in house. There was no passing it on to someone else to figure out. It was coming back to you util you fixed it right. They kept them for over fifteen years so we saw everything break that could. I had the advantage of having duplicate vehicles to look at and even swap parts from that you don't have at home. Tools you don't have at home. I worked with some pretty smart guys and a few not so smart ones. I learned from both groups what to do and what not to.

Because I was a fleet mechanic and scored well on the Stats exam test I was invited by the State to be on the team of ten-guys that wrote the smog test questions for the new smog mechanics. They wanted dealer mechanics, small repair shop owners, college automotive professors and one lowly fleet mechanic on the team. I was on the bottom of the barrel in that group of guys. When we developed those test questions for the State of CA, we were told to create two ridiculous answers, a distractor answer and the real answer. When I have a tough problem, I always think back to those test questions, wouldn't it be nice if there were only four possible causes to an automotive problem and two of them were stupid choices/ Engine has low compression on one cylinder? Mechanic "A" says, it's because the radio is tuned to political station that differs from their own view. Mechanic "B" says, old cars never did have good compression in all cylinders when they were new. Mechanic "C' says, the valves have high performance valve springs with more pressure. Mechanic "D" says it could have a head gasket leak. Those tests are designed for people just starting out as mechanics. The difficulty level was designed for a beginner mechanic. They won't be good mechanics until they have years of experience. We were told 15-years ago not to create any carburetor test questions, that there were students in automotive classes that had never even been in a car with a carburetor. Some of this old technology although fairly simple will become a lost art.

My dad had old Fords, so I started with a '65 Mustang fastback I turned into a fake Shelby. Eventually I bought a real '66 GT-350. I've had fifteen early Mustangs. I had a '57 T-Bird my mom bought new. I have a bunch of unfinished flathead Ford hot rod projects. When you work as a mechanic all night long. raise two little girls during the day while building a house, the last thing you want to do is work on your own cars at home. Now, that I have all these project cars and time to work on them (somewhere around seventeen vehicles that are not finished) I can finally start working on them. I collected cars and parts for 40-years. I've had two failed back surgeries (fused vertebrates), three shoulder surgeries and I'm in constant pain. So, it is hard to get out there and work on this stuff. That's part of the reason I like sitting here helping people with their problems, it's easier on my body, until I go to stand up. Oh my god does that hurt. The longer I make my rambling answers the longer I can put off trying to stand up. My most important automotive advice, do not become a mechanic!

You’ve had an interesting career and your knowledge has helped many I’m sure, definitely helped me. It’s great how so many of you guys with real skills are willing to help out. I’m a backyard mechanic at best and I’ve already learned a ton here.
Thanks again

[Abchoppers]

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Update - I’ve adjusted all of the valves, compression on number 7 is still the same. Next I did the air pressure test. I decided to loosen both the number 7 valves until they were both closed with no rockers touching to be sure. This is where it gets tricky. I can hear the air pretty loud, but it’s very hard to determine exactly where it’s coming from. I’m using a rubber hose up to my ear. I hear a little from the exhaust tips, but also a little from the carb. Very faint on both. The oil fill I hear it the loudest with some light air blowing out, but I know that some air will always escape there. With the valve cover off, I can also hear it coming out of all of the pushrod holes. I thought it would be a lot more obvious to decide where it’s coming from, but it’s not. Maybe I’m doing something wrong? I’m using an actual leak down tester hooked to my compressor.
Thank you

[dmsfrr]

Part of the reason you're hearing the exhaust leak in several places may be the exhaust crossover inside the intake manifold.
Cyl's 2-3 and 6-7 have a common outlet in their head that is connected to the other side of the engine thru the center of the intake manifold.
The exhaust crossover also contains a heat exchanger tube for the choke mechanism on the carb that can leak into the carb if the small tube has failed from corrosion.

[Flathead Fever]

Borderline problems are difficult to diagnose. That was a good idea backing the valves off all of the way. If the exhaust valve was leaking just a little bit, it would be difficult to hear it all the way back at the tailpipe. Try pressure testing a good cylinder to see how much leakage you have from the oil fill cap compared to the bad cylinder. The rings shouldn't be leaking if that wet compression test made no difference, unless you did not get enough oil in there. Maybe gently wiggle the valve assemblies and see if that changes the valve leakage, I've never tried that one. Try the same tests on a good cylinder compared to that bad one.

When we pulled heads to verify our leaky valve diagnosis, we used to put them on their sides on the bench and fill the ports with water to see if it ran out of the valves. No way to do that on your engine.

[fordor41]

Originally Posted by Flathead Fever

Borderline problems are difficult to diagnose. That was a good idea backing the valves off all of the way. If the exhaust valve was leaking just a little bit, it would be difficult to hear it all the way back at the tailpipe. Try pressure testing a good cylinder to see how much leakage you have from the oil fill cap compared to the bad cylinder. The rings shouldn't be leaking if that wet compression test made no difference, unless you did not get enough oil in there. Maybe gently wiggle the valve assemblies and see if that changes the valve leakage, I've never tried that one. Try the same tests on a good cylinder compared to that bad one.

When we pulled heads to verify our leaky valve diagnosis, we used to put them on their sides on the bench and fill the ports with water to see if it ran out of the valves. No way to that on your engine.

I've also filled the ports but I use gas. lot of times gas will leak where water will not.

[Flathead Fever]

To be honest with you I don't t know what kind of volume of air a leak down tester puts into a cylinder. It might not be what a compression tester hose with the Schraeder valve removed, and hooked to a compressor would put in there. Maybe that would be a larger volume of air that was easier to hear.

There is another option. Originally automotive repair shops had smoke machines to find leaks in the evap system. The charcoal canister, gas cap and all the plumbing that must be a sealed system. If there is a small leak it will set a check engine light or fail the manual evap test on the smog machine. Usually, it's a bad gas cap or somebody did not tighten the gas cap all of the way on, but sometimes it's a cracked hose on top of a gas tank where you can't see up in there. A smoke machine hooks to the battery and heats mineral oil and pumps it into those hoses under very low pressure, so it doesn't damage anything, then you just have to watch for where the smoke comes out. It will stink you out of a shop. The same tool can be used to pump a cylinder full of smoke although I have never done it. Usually at the phone company when cylinders had low compression it was because the piston was in the oil pan Those drivers were pretty hard on stuff. We had a compression test we called the dipstick test. If a cylinder had zero compression, if you could take the dipstick and check the oil through the spark plug hole it failed the dipstick test. A valve job was not going to fix it.

Smoke test video. Fast forward through this guys' video to about the 15-minute spot. This is around a $280.00 smoke tester. They make them as cheap as $75.00, and you will use it once in your life at home at it still might not find the problem.

https://www.youtube.com/watch?v=48AD0P9RsHs

There are some build you own smoke machine video. Thise one is pretty clever.

https://www.youtube.com/watch?v=tixozqgSwN0

[Flathead Fever]

Originally Posted by fordor41

I've also filled the ports but I use gas. lot of times gas will leak where water will not.

I had always heard to use gas instead of water. At the phone company the fire department would not allow us to store any gas cans with fuel in them in the shop. We had overhead lube reels in each bay, each stall had a water hose so that was what we used to fill the ports. If you filled a gas can you had to empty into a vehicle (not your own) before you put the can back into the cabinet.

[Ford blue blood]

That's kind of funny? An empty gas can is far more dangerous then a full can.

[Flathead Fever]

Originally Posted by Ford blue blood

That's kind of funny? An empty gas can is far more dangerous then a full can.

We couldn't have a full gas can in the shop, but we could have six stalls with vehicles with gas tanks full of gas.

[Abchoppers]

Okay fellas, so I checked another cylinder that had good compression with the air test. Basically the same level of air noise from same places. I also did use the compression tester without the shrader valve and had the same results. I’m putting roughly 100 psi into the cylinders so it should be enough air.

When rockers are completely backed off and both valves of number 7 are fully closed, they both look like they are the same exact height. I’m thinking that the drill spinning trick might not work for me since one should appear lower if it was stuck open at all. I tried hitting both valves with a rubber mallet lightly and it didn’t seem to change anything. I’m Going to try and rig up a smoke machine because that would really show me the leaking area.

So I’m thinking the plan for now is to just drive the car. It’s definitely still
Combusting in the cylinder and overall runs really good. After summer is over my plan is to pull the head and really examine it, have it machined if needed and a new head gasket.

I’m definitely open to any other ideas, I just don’t want to keep taking up everyone’s time. You guys have been beyond helpful. I really mean it when I say I’ve learned so much and am grateful.

[cadillac512]

Excellent plan. For now, drive the car, enjoy it and monitor it's performance. If anything gets worse you can deal with it then. It'll give fair warning.
Terry

[Abchoppers]

Originally Posted by cadillac512

Excellent plan. For now, drive the car, enjoy it and monitor it's performance. If anything gets worse you can deal with it then. It'll give fair warning.
Terry

Thanks Terry, my girls would kill me if I tore the engine apart now, they’re loving it way too much!