The Stovebolt Site Forums The Shop Area Engine Shop 216 blow by and crank case pressure

OK on my 216, I have have extremely rough running and excessive blow by from the road tube and the valve cover. Since the engine has been sitting for a very long time with an occasional start. I had carb issues due to ethanol eating some rubber gas lines. I am using non ethanol gas now, rebuilt the Carter YF carb, and may still have issues there. I do not have much change with turning the idle mixture screw. I have sprayed starting fluid around the base of the carb, vacuum advance, and disconnected the wiper motor line and have not found a vacuum leak. I have a gasket on both top and bottom of the new plastic carb riser. I have rebuilt this engine, it has new rings, been honed, and has a valve job. Timing was set at 5 degrees before TDC, and the engine ran great before the ethanol adventure.

I have not done a compression check yet for this issue.

I suspect either sticking valves or rings.

What are the thoughts out there on why this thing won't run properly?

The fact that the idle mixture screw doesn't have a significant impact makes me think induction. Either a goober on the rebuild or a vaccum leak that you didn't find.

Manifold-to-head gasket is likely sucking air. Use an UNLIT propane torch around that area to find it.
I you want to know what to listen for, place the UNLIT propane torch above the carburetor momentarily. This should increase the RPM similar to what will happen when you put the UNLIT torch near a manifold vacuum leak.

I tried spraying around using starting fluid and nothing happened, no rpm increase. The oil and water are not contaminated either. There is oil coming up through the dipstick hole and out the road tube.

What's the hold up on the compression check?

Getting out of this chair, grabbing almost all the tools I need and driving out to my storage location on my friends' farm. Heading that way soon

OK, so here are my Compression test results:

1 2 3 4 5 6
Dry 115 15 105 105 24 116
Wet 118 12 110 105 20 105

I have done a lot of these tests and not seen results like this

I fired the engine up right after the test, started immediately, ran for a while, then the RPM increased then quit after a short while. I couldn't get it to fire after that.

Maybe valves are stuck open on 2 and 5.

I pulled the valve cover and checked, the valves were moving. That does not rule out not moving enough and possibly stuck rings. The truck has been sitting for some time.

Broken piston ring(s) or a missing compression ring on #2 and #5 cylinders during assembly. Pull the #2 and #5 pistons and check for damage. Do a cylinder leakdown test before disassembly to confirm a pressure leak into the crankcase. If somebody else assembled the engine, RUN, do not walk away from his shop!
Jerry

I am the shop that assembled this thing. No left over rings. It ran great for a while, and had compression, then I went down the ethanol and carb hole. Once I got that fixed and it was still running good, this happened. Now the fuel pump has puked again. I am resigning myself to another tear down but it seems curious that 2 and 5 are both close in the up and down movement of the crank, and the first fuel pump failed mechanically, the pin wore on the body. In some world, could this be something with the cam shaft? I checked the numbers on the crank and cam shafts for compatibility during the rebuild, but did not mic the lobes

Excessive blowby is almost always a failure of a piston, and/or rings. It's possibly just a coincidence that the compression is low on companion cylinders, but the simplest and most effective diagnosis short of a teardown will be pressurizing the cylinders. I'd suggest locking the crankshaft in some way, like putting the vehicle in top gear and setting the parking brake and/or chocking wheels in both directions, and then loosening the rocker arm adjusters until you're sure both valves are closed. Then adapt an air hose quick connect fitting to a spark plug shell and apply air pressure to the cylinders. Listen for leakage at the carburetor, exhaust, and oil filler cap. I'm going to guess most, or possibly all of the leak will be into the crankcase. Good luck!
Jerry