I recently finished with a 400 rebuild and have had bad luck with it. My involvement in building the long block was none. I had a machine shop do all of the work - boring, decking, etc. and then build the long block. The owner of the shop is the only employee so I knew that I would be getting some dedicated work. After a 100 miles, the number 3 rod bearing came apart and scarred the crank. I haven't gotten the crank out so I don't if it can be saved. Anyway, when I drained the oil, the odor of gas could be smelled. The machinist is blaming the gas to be the cause of the bearing problem. After chatting with some other engine builders, I've come to the conclusion that gas in the oil couldn't have been the cause. My opinion is that it would've had to take a significant amount of gas (1 qt or more) to be the cause and my oil level never changed. If an engine is running rich, this will cause the oil to have an odor too. Logically thinking, if gas was the cause, why didn't other bearings come apart, seeing that they all use the same oil? What do you think???? Before I confront the builder, I want to know what you guys think.

Thanks

 

i witnessed a bearing problem on an fe engine a long time ago and we found the fuel pump diaphragm had allowed fuel into the crank case. the problem presented itself while on a trip on the interstate. the engine didnt spin the bearing and he was able to get it home. the pan was pulled and pan had lots of fuel mixed with the oil. the engine was a 427 side oiler and was a fresh rebuild less than 500 miles. the fuel pump was not new. hope this helps

 

I read an article a couple of years ago that said basicly the same thing. That way too rich a mixture can cause this kinda thing to happen. My quess is you would have lost other bearings had the motor run longer.

 

Fuel in the oil could definitely do it if you get enough in there. When you tear it down you should see damage all around. If everything else looks good then something was not right with the one that died.

 

I agree with what everyone has said. But, like I said, the oil level never changed. I'm just starting to take the engine out of the pickup and will know more in a few days. If that's the only bearing destroyed, then I have a strong leg to stand on when I chat with the builder. I won't take the engine back to him for repair work though. Don't trust him.

 

Before gasoline mixed in with engine oil would destroy a bearing you would have heard the lifters knocking, crank throws bouncing off the bearing saddles, and the rods pounding the hell out of the bearings. You have to remember that engine oil acts has a hydraulic fluid in the engine. If the oil got so thin that it allowed a bearing to spin, it would have to have been thin enough to cause the other troubles I listed above.

I worked has a tech rep for Valvoline Oil for a few years in Minnesota, and the only time I ever seen engine damage caused by gasoline contaminated oil was in the winter months on older, carbureted, engines. Even then this was very rare (we’re taking 1 in 50,000 oil changes). I would DEMAND that he either one- rebuilds the engine the right way, or two- pays to have the engine rebuilt correctly. If he refuses to do so then take him to court. I’ll wager money on it that you can get enough signed statements from engine shops and oil company reps to win the case without to much trouble.