# Are YOU sitting on a bomb?



## jhngardner367 (Apr 5, 2011)

I was reading the post about "speed limiter", and i recalled an article in a newspaper about an elderly man,in Florida(quite some years ago),that had been killed when his lawntractor exploded.
He had disconnected/altered the governor in order to get more speed due to a large yard. He had mowed a portion of the lawn,then,refilled the fuel,and went in for lunch.
After lunch,he sat on his tractor,and rolled it over,and,according to witnesses,it rolled a few times,then exploded,killing him. The engine was thrown on top of the carport roof,some 50 feet away.
Investigators later found,that, due to the over-revving of the engine,fuel had drained into the crankcase,and when the still-hot engine rolled over,it sloshed the fuel - diluted oil around,clogging the crankcase breather,and when the engine finally fired,it set off the fumes/fuel,in the crankcase.

So, I'm wondering...have any of you heard of other such things happening ?


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## skunkhome (Nov 30, 2008)

That is bizarre. I can't imagine enough air being in the crank case to make gasoline in the oil or for that matter a whole crankcase full of gas explode. I could see it spilling out the breather and igniting into flames but not exploding as such. I'm wondering if it were in a garage if he filled the tank and went inside. The carb float stuck filling the crankcase with gasoline and when he tried to crank it possibly in an enclosed garage the fumes from escaping gasoline spread to an outside ignition source such as a water heater and ignited explosively. I have heard of that happening after some one refueled in a closed garage and blowing up the garage.


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## jhngardner367 (Apr 5, 2011)

No,the tractor was outside.
One (1) cup of gasoline,in an enclosed space,has the destructive power of 7 sticks of dynamite.
When an engine runs,crankcase pressure normally bleeds out through the pcv valve or breather.
However,if the breather,or pcv valve is plugged pressure can build up in the crankcase,in some instances it can explode violently,if triggered by,say,a backfire,or a spark.
When I was in training as a gas/diesel mechanic,we were shown this very thing,in a controlled area. A 5hp vertical shaft engine was sealed at the breather. 1/2 cup of gasoline was poured into the dipstick tube,and the engine's governor was disconnected.
The engine started,and at WOT,it took 4 minutes,to get hot, and it blew the crankcase apart !
THAT is the scariest thing I have ever seen.


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## skunkhome (Nov 30, 2008)

Not without air! Liquid gasoline will not burn. 
I would imagine with a governor disconnected running at WOT it won't take long for the engine to self destruct even if you haven't diluted the oil with gasoline. Still the atmosphere in the crankcase is going to be far too rich to ignite. However I can see that happening, when the engine heats up and churns up the crankcase atomizing the gasoline, throws a rod, at WOT ventilating the crankcase and it all goes at once. Same thing sometimes happens in house fires...a smoldering fire fills a room with combustible molecules but won't burn until someone opens a door or window. Air rushes in and the atmosphere in the room ignites instantaneously (explosively).


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## jhngardner367 (Apr 5, 2011)

Yes,it creates a sort of "backdraft",and the superheated fuel,met with the rush of air,explodes.
As I understand it,it does get air,from the action of the piston,as some air slips past it. Otherwise there would also not be a vacuum created ,in a normally running engine.
An example: A drag engine that explodes on the strip,and sends the supercharger,and other parts flying several yards away. Same thing,here,but made worse by all the fuel in the block.
The fuel doesn't cause the explosive destruction. That is caused by the engine failing catastrophically,which THEN sets off the fuel explosion. This happens so quickly,it looks as if it all happens at once.
That,however,is NOT my point. MY point is that bypassing a governor system can have disasterous results,and should not be done on everyday machines.
By the way..liquid gasoline WILL burn,but not explode,unless there is no oxygen present(is that what you were saying?).It is in the instant that oxygen reaches the fuel,that the fuel ignites.That instant comes when the engine cracks/fails,and oxygen rushes in.


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## Cublover (Feb 20, 2011)

I've seen the fuel pump go bad on a 350 Chevy pumping gas into crankcase, then it blew the valve covers OFF when it ignited.


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## skunkhome (Nov 30, 2008)

I understand that typically when a dragster blows the blower off it is usually a result of an intake valve failing to close or floating allowing hot gas to jet into a blower housing full of compresser air and atomized fuel.
Regardless you are really asking for trouble when you defeat the governor on a small engine in use on a tractor because you really don't have sufficient load on the engine to keep it from suddenly reving dangerously above the design maximum of the engine.


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