tomdoc

Help with diagnosing why I have fuel in the cylinders and and crankcase of my 68 427 L71. I went to start my motor the other day and the motor would not turn over. Thought I had bad starter so I changed it and still wouldn't crank although I could tell starter was engaging. I then tried to turn the crankshaft using the crankshaft nut with a socket and breaker bar. Still nothing the motor is locked up. I removed the spark plugs and fuel came out on a couple of cylinders. The motor then turned right over and more fuel gushed out the cylinders and finally dried up. I replaced the plugs and the motor started right up. But I noticed oil pressure dropped off right away. Only ran the motor for 20 or so seconds and shut it down. Then I checked dip stick oil level and found gas in the oil. The level was about 3 inches above the full mark on the dip stick.... quite a bit of fuel in the crankcase....... The gas tinned out the oil and I'm sure that's why no oil pressure. How did this happen and is the motor damaged or just a bit dry ??? Now let me mention this. The day before this happened I drove the car about 50 miles or so. Motor ran strong and hard like a L71 should... Not as much as a hiccup from this motor.... At the end of my drive that evening I filled the tank to the very top. Right to the filler neck (with 100 octane leaded fuel). Drove the car home from filling it up about 1 mile and parked it in the garage. The next morning the motor was bound up with fuel. Could fuel have siphoned up into the carb past the needle valve and leaked past the rings filling up the crankcase ?? The tank in the C3's sits very high. Any ideas to this mystery ???

Mike Ward

Yes, very possible and probably that this is exactly what happened. Fix the carb and change the oil before cranking the engine again. Avoid overfilling the tank too.

Not relevant but leaded fuel and 100 octane are not required for your engine.

bj1k

Chevy fuel pumps have a tendency to fail causing the gas to leak down into the oil through the seal in the back of the pump. Running it could destroy your engine . Hope it's not to late.

ignatz

As I mentioned in the other thread, be sure to prime the motor via the distributor shaft before you start. Changing the needle valves is probably a good idea too.

ignatz

I did not know that but it wouldn't explain why the motor was hydraulically locked.

Mike Ward

Didn't realize that his thread is a dupe.

Shark Racer

2nd on hydralock. The first thing I thought of when I saw "crankcase" was bad fuel pump diaphragm, but (partially) eliminated that when I saw fuel in cylinders. Doesn't mean he couldn't have a fuel pump problem and a flooding carb...

OP - What carb are you running on the motor?

tomdoc

Thanks guys, I'm running the L71 Holley 3x2 six pack. And I am running the 100 octane fuel only because I live in New Jersey. The best fuel we have here is 93 octane w/ 10 and 15% Ethenol. This motor just doesn't run well on it. I buy the 100 octane just down the street from me at a marina. I use it in my go fast boat (Twin 550inch 700hp motors)