For decades now, a rotary hammer such as the Bosch 11247 have been a workhorse on jobsites. Anchors is driven into concrete with it and chases cut in brick wall. It can do things an SDS-plus drill simply cannot.
While most owners will tell you how to swap out the bit, not many are aware of how to service inner workings. The inner piston use grease to cushion against the shock of hammering. If not, the tool overheat, seizes, and then breaks.
Keeping this particular model serviced keep the impact force even and lengthens the life of the tool. It saves money from expensive repairs down the road too. Now, unlike an impact driver, a rotary hammer have a different mechanism: An impact driver rely on a sort of ratchet to produce rotational force.
How To Properly Grease Your Bosch Hammer Drill
How Rotary Hammers Work
Instead, a rotary hammer use what’s called a “pneumatic piston”, a device in which a cylinder contain a piston that goes back-and-forth inside the chamber. With each revolution of the hammer, the piston hit against anvil, creating friction and heat. Grease act as lubricant filling tiny gaps between moving piece.
This minimize wear to the piston ring. It also help the metal dissipate heat away from metal component. In effect, you want to think of the hammer mechanism as your car engine; if you drive without oil, it’ll wreck your car.
Likewise, hammering without grease will ruin this tool. The Bosch 11247 is tough, but it ain’t indestructible. Skipping on the lube make for a delicate instrument instead of a sturdy tool.
Locating the Grease Fill Hole
To clarify, you can’t just pour grease onto top of drill. That wouldn’t even get anywhere near the hammer mechanism. So what’s the deal with the fill hole?
On the Bosch 11247, it’s by the gear housing. Examine body of your drill and look for a little thread-in brass or plastic plug that is sealed in the casing. This plug seal off the interior cavity where the piston stay.
Pull out this plug and you now have direct access to the grease chamber. Some older units differ slightly from this setup, so consult your manual if you’re unclear. Basically, you want a clear shot to the inner workings.
Guessing the right spot won’t do; you might make a mess or worse, a short circuit.
Choosing the Right Grease
Use only quality lithium based grease designed for high pressure applications. Remember, grease need to be durable enough to hold up under the high frequency of impact and not wash out from either moisture or dust.
If you have standard wheel bearing grease on hand, that’ll do in a pinch, but there’s such a thing as specialty rotary hammer grease which is actualy designed with high-frequency impact in mind. That mean the grease stay put longer. It’s best to stick with specialty grease since it’s formulated specifically for the application.
Bosch even make their own, so if you go that route, use theirs to ensure compatibility. Don’t use any type of WD-40 (it’s a cleaner and doesn’t lubricate) as it will simply strip away any grease already present and leave your metal bare. Neither does motor oil, as it’s too light and will wash right through.
Use the heavy, clingy grease that stick to the walls of the piston.
Step-by-Step Greasing Process
Safety first, always unplug your tool before doing anything. Disassemble the tool and remove any bit and the chuck.
Gently remove the grease plug by unscrewing it. The plug might be snug; use a small wrench or a hex key to loosen. If no grease gun is available use a syringe to inject the grease into the tool.
Be careful not to overfill as this will cause pressure within the chamber and can harm seals. Continue until you reach resistance, but don’t overfill because too much grease create pressure that can damage seals. Re-install the plug ensuring a secure fit.
Turn on the tool for several seconds to allow the grease to spread through the system. Excess grease may escape, this is normal. Clean off any excess and confirm that the grease is circulating through the system.
Maintenance Schedule and Signs of Wear
Treat the tool according to your usage. If you are using it heavily every day, check it monthly. If using it more sporadically like weekends only then less.
Service the tool after every hundred hours of use. Rough sounds when running are a good indicator that you have run out of grease. Excessive heat is another clue, as is slowness.
Tackle this early before something fails. A well maintained tool would of cost pennies compared to replacing it. Treat the Bosch 11247 like the workhorse it is.
Grease it up and it will keep you working.