My '39 Dodge engine needs some diagnosis...

[Don Coatney]

If your compression is 60 +- across the board you do not have a valve stuck open. If a valve was stuck open you would have a zero compression reading on that cylinder. Did you do a wet compression check, or a leak down test?

[40P10touring sedan]

Cold, dry engine. Wires are definitely on correct. I let it run for a half hour, got somewhat better, but was still very evident. I'm thinking I'll try some Seafoam in the crankcase, think that'll free up any sticky valves?

Throttle wide open while checking the compression?

Hey, can you throw a timing light on it while she's running to watch the mark for really erratic jumping...timing chain slop?{a reach, I know}

How's the plugs looking, any darker than others..maybe a fresh set of plugs and then check after running- BTW, what plugs are you running?

Edited May 29, 2012 by 40P10touring sedan

[Don Coatney]

Throttle wide open while checking the compression?

Why? Did you read my posting on how to do a compression check?

[Rodney Bullock]

I would check and replace the cap. your firing order, the rotor.

[greg g]

If your gauge is a screw in type, make sure you do not screw it in further than the spark plug would go. You could damage valves if screwed in too far.

[DodgeDan]

Let it run for an hour in the driveway, with Seafoam in the crankcase and MMO in the gas tank. Still no change. Someone had asked what plugs, they are AC Delco R45 from Robert's Motor Parts. An 81 year old neighbor of mine who grew up with these cars (had a '38 Plymouth) came over because he heard it running, he took a long handle screwdriver out of my toolbox, put the tip on the engine head and the handle up to his ear, he listened and said it sounded like a sticky exhaust valve, he told me I should run a quart automatic transmission fluid in the crankcase with four quarts of engine oil. He said that should free it up. What do you guys think?

Edited May 30, 2012 by DodgeDan

[greg g]

a sticking or partially opened valve would cause a cylinder to read low on your compression test. Have you attached a vacuum gauge to the engine they can diagnose a lot of symptoms easily.

Go to the Second Chance Garage web site and look at their section of using and inturpreting vacuum gauge readings.

Not doubting your neighbor but hearing an exhaust valve not closing seems a bit of a reach through a screwdriver....kinda like not hearing a tree fall if you get my meaning.

Edited May 31, 2012 by greg g

[46busboys]

sticking valve??

[yourpc48]

At first I was thinking water in the gas. 60 lbs of compression is low. Also firing order came to mind (I did that by accident and took me a month to figure it out). Sticky valve also. If you want to build up a little compression put a little tranny fluid in the cylinders and turn the motor over by hand. Let it sit for a day or so and then put an old towel over the entire head (big towel) and turn the engine over with no plugs in it. Crank it till you build up oil pressure and then put your plugs back in and fire it up. It will smoke for a while so do it outside and where it will not cause a problem with your neighbors. It may smoke a LOT. Dont worry till you have let it idle for a while. You can do the same with Marvels or Seafoam but the trans fluid is less expensive for a quart. That will normally clean up the buildup on anything and lube up the rings. It should also lube up your valves a bit.

Those are the things I would check and steps I would take next.

Good Luck with that.

[40P10touring sedan]

Why? Did you read my posting on how to do a compression check?

Actually.... no.

I was refering to the factory manual's recomendation.

[DCurrent]

How did this thread turn out? Does anyone know the outcome?

Darren

[michael.warshaw]

im no mechanic but on my mopar muscle cars if you have a spark plug wire on the wrong plug it will make popping noises all over the place, or a stuck valve aswel, good luck.

[garbagestate 44]

Try starting it up at night to see if you have any high voltage leaks from your plug wires.