Sooo today I brought in a quad that was making a CLACK CLACK CLACK noise every time it turned over and wouldn't start. All of the mechanics including myself thought rod bearings were to blame for it. So I took the top end off of this 4-stroke quad...
We were wrong...
That's the cylinder I pulled off. Note the very nice scoring on the wall of it. As well as the melted metal slag welded to the top of it.
That would be the piston that caused it. Notice the brilliant up and down striations caused by the lack of lubrication and very high heat that it caused, as well as 3 of the 4 oil holes welded shut. Then if you look a little closer, you'll see that all of the rings are still in place.
That is the top of the piston where it was hitting the head of the cylinder. When the piston melted to the wall the engine was still running, so the piston went back down, bending in the skirt as will be shown in the next picture, making the piston slap the head of the cylinder every time it turned over. That mark is approximately 1/16th of an inch down into the piston itself.
That's the nicely bent/melted piston from the side. For non-mechanics, both sides of the piston should be PERFECTLY parallel. And just to see how far in that piston is bent, look at the grids on both sides of it. Both were even when the piston started life.
Don't mind the pudgy fingers on top of it... lol
Now what does that kind of thing do to bolts holding the cylinder together? It tightens them up, making them very hard to get off. Hence the wrench I broke while disassembling the stupid thing.
As a note, this came out of a 1999 Yamaha Grizzly 600, air-cooled 600cc 4 stroke quad with a fan-forced oil cooler on it. No one I've talked to at the shop has ever seen one fail, much less to this degree. Because of the extensive damage, even the crankshaft is damaged, and parts alone for this job are 4500 dollars, and another 1000 in labor. It's literally cheaper for him to buy a new quad.
Keep oil in your engines people!