Ever wondered what happens when a connecting rod decides it’s had enough abuse? Typically it’s hidden inside the engine until until it decides to exit stage left and take a chunk of engine block with it. We’ve all seen plenty of engine carnage photographs with pieces of block missing and a twisted, mangled connecting rod hanging out of the hole.
Not this time, as the guys at Project Farm [1] decided to make it easy for us to see what happens by taking a Briggs & Stratton lawnmower engine and cutting a huge hole in the crankcase to provide unfettered viewing of the engine in operation. This particular engine already had mechanical issues including a previously-existing rod knock. This made it the perfect candidate to see what happens when an internal combustion engine is run without oil.
[2]Look to the right of the laser–that’s the broken connecting rod at the moment of destruction.
A quick diagnosis of the rod knock was performed prior to the experiment, and it was determined that the aluminum connecting rod material doesn’t mix well with the steel crankshaft when there is no oil supply. Since small engines like these don’t use a rod bearing between the large end of the rod and the crankshaft journal, oil supply is an absolutely-critical part of the equation to prevent failure.
With the window into the engine’s depths opened up, the engine was fired up and run until it seized up again. At this point it did not have a major mechanical failure, although it lasted just shy of three minutes and created a lot of smoke and a lot of heat–nearly 500 degrees by the laser thermometer employed in the test. The engine was allowed to cool for one hour, broken loose, and fired back up again. It only lasted a short time until the end of its lifespan occurred–with connecting rod chunks flying everywhere. The video offers an interesting perspective of the failure. Check out the carnage!
[3]