# How To Fix Rotary Bosch Hammer Drill 11240



## Tango

It's been a while since my roto-hammer drill stopped working right. It wouldn't hammer at all. After realizing how to fix it, I know why when you hit hard enough on the chisel point it starts to work again until the trick doesn't work any more.

There's a piston inside the case which transmits air pressure to the chisel point. The o-ring fails and oil fills the air chamber. By hitting the chisel it lets a little oil out just enough for it to work for a little while longer. 

So I ordered the service pack which ended up costing me around 80$ and took 2 weeks in the mail. Today was a good day to take this apart it was just -3C in the garage, with bare hands in rubber gloves.:biggrin:

I dismantled too many parts to figure out it would of been a 30 minute fix. I took out all the front parts, dust boot, pill bit pins, snap ring then cleaned everything and greased. So here's the short cut to the culprit. If it happens again I'll be making myself a new O-ring from my O-ring maker kit. The service pack has brushes, dust boot and more o-rings if it leaks into the motor so they may come in handy.

I wish I had a trouble shooting guide and instructions! Now you do!



Remove the 6 screws on top of the case.
Drain the oil
Pop the piston arm with a screw driver
Drain the oil from the air chamber, wipe with a clean rag
Remove the old O-ring, put a new one in with a little lube
Put the piston back in place, pop the arm back on the pivot.
I filled it with SAE 30 non detergent motor oil almost to the cover. I don't know the proper amount but enough to lube the gears.
Put the cover back on making sure you align the clutch fork and test with a chisel point.


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## OpenSights

Skimmed tonight, but I have a similar older model that needs an internal cleanup. 

Thanks! Haven’t been able to find good info...


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## Tango

Here is a few more pictures to service and clean the front end where you insert bits.

*Pull off the dust boot to find a C-clip*











*Once the clip is removed...

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*Be careful so the pills don't fall out you may never find them again. Push them out from inside the bore. Once cleaned put some grease to hold them in place.*











*Another C-clip, once removed you have a washer and that's as far as I went. After that is probably a bearing and since my service pack didn't seem to have parts of that size I reassembled everything.*


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