The Stovebolt Site Forums The Shop Area Engine Shop Piston rings

I think i have finally learned the problem with my engine. It diesels after i cut it off and the exhaust smells like raw gasoline. I asked my buddy who's a mechanic about this. He didn't say anything, walked past me to my truck, popped the hood, pulled out the dipstick and sniffed it. He then asked me to smell it. It smelled like straight up gasoline. He said that gas was getting into my oil pan and motor oil was firing along with gasoline in the cylinder and that can only be explained by bad compression rings or piston rings or whatever. So, we are planning to take apart the engine this weekend and change the rings, head gasket and piston(he calls them journal) bearings. Before I go off and do this, I wanted to check and see what my fellow bolters had to say. Do yall think the rings are what's wrong?

In a word- - - -NO! The gasoline is getting into the crankcase from a hole in the fuel pump diaphragm, or a carburetor that's flooding severely and filling the intake with gas, which then finds its way past the rings when the engine stops.

Severe flooding can wash the cylinders down, resulting in poor ring sealing, but once the source of the gas-contaminated oil is eliminated, it shouldn't be necessary to change the rings, unless they're worn out anyway. If the carbon deposits behind the rings on a old engine get washed out by gas-contaminated oil, the compression can drop severely because the carbon was the only thing keeping the rings in contact with the cylinder walls.

Find the source of the gas, which will probably be the fuel pump, then fix it, change the oil, and run a compression test. Anything around 85 pounds or more, up to maybe 100 PSI, will mean the rings are probably OK.
Jerry

You mentioned fellow Bolters so I will answer also. I agree with Hotrod. After you do that if the comp. is good & it doesn,t have excess smoke or oil consumption, leave it alone. If it still deisels after that post it & we'll deal with that.

+1 on what Mr. Lincoln says.

The rings aren't causing the leaky gas.

Yes, to the previous responses. Beyond that, the dieseling is most likely caused by the idle speed being set too high. There are other possibilities for that, but start with lowering the idle speed. Advanced ignition timing and lean idle fuel mixture can also contribute to dieseling, although if your truck has a functioning PCV system, and there is gasoline in the oil, you most likely won't have a lean idle mixture.

Harvester

I agree with all. Pulling the motor down will not fix the problem. The gas in the oil is due to the too rich mixture washing down the cylinder walls.
Try with timimg & carb. adjustments first. I have a ford 460 cid and have to change the oil often due to rick a mixture when the motor is cold.