SEPARATE PARTS

551 903 17 SEPARATE PARTS is usually a seal kit for one of the smaller hydraulic cylinders on the rig – maybe for a feed cylinder, or a boom swing, even a drill rod changer. Its job is pretty straightforward: keep the hydraulic fluid where it belongs, inside the cylinder, so you get proper pressure and movement. Without good seals, that fluid just slips past, and your cylinder won't hold its position or extend with full force.

When these seals start to go, you’ll usually notice a few things. The most common is cylinder drift – you extend something, like a boom, and it slowly sags or retracts on its own. Or, if it’s a feed cylinder, you might see inconsistent feed pressure, or the drill head just doesn’t hold position as well as it used to. Sometimes, you’ll even hear a slight internal bypass noise, a sort of faint hiss, as fluid leaks past the worn seals under load.

Replacing these seals isn't usually a huge job, but it’s critical to get it right. Always clean the cylinder bore thoroughly before installing new seals – any grit or old fluid residue will chew up the new ones fast. And don’t forget to check the piston rod for any nicks or scoring; a damaged rod will just ruin your new seals in no time, no matter how carefully you install them. Lube them up proper before assembly too.