Help with Bosch Demolition Hammer

[Bolster]

I own a Bosch 11241EVS demolition hammer, pictured below. Recently, when trying to use it, after first turning it on, I notice it doesn't hammer for many minutes...then, when it warms up (anywhere between 5 and 15 minutes), it will start hammering.

It seems to help get the tool hammering if I lean all my weight onto the handle and force the bit down into the work for those minutes I'm waiting for the tool to actually start hammering. But I'm waiting at minimum 5 minutes before the tool starts working properly.

The demo hammer has low usage, maybe a dozen hours or less, since I bought it new several years ago. It always gets a dab of approved grease on the back end of the bit before use. I've taken really good care of it, looks in near new condition.

Any ideas what's up with the very slow startup?

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[fl18guy]

Does it have brushes that might need to be replaced.

 

[dutchgray]

It shouldn't need to warm up before the hammer starts moving, unless it was stored somewhere really cold, if you have been using grease evey use and the duration of use is not very long it could be way over greased in there, with the ones I have used and our own Makita I only add grease once what leaks out down the bit isn't much after say an hour use. Maybe every month of occasional use or if doing a lot of demo with a chisel every day.

 

[KnurledNut]

They can need up to 2 minutes to warm up if its below freezing. Not sure why yours is taking longer. Some Hiltis function in a similar way.

 

[matt_i]

It would make sense if there was a bad connection somewhere internally and it was basically arcing across a high resistance until the time it got warmed up and the surface contact improved enough to start conducting properly.

Its a pure guess. I've never opened one up to see the internals. I have a TE-5 and it doesn't seem to need a warmup period.

 

[Bolster]

Thanks. I may have to take it in for repair. I live in warm so calif, so I can't blame cold weather for the laggy hammering. I will have a look with a flashlight to see if there is caked grease in the chuck area - where the back of the bit makes contact. Instructions said a dab of grease on the back of the bit each use, and I do use mainly for chiseling, like a small jackhammer. But it's in use for a couple hours at a time, so...maybe overgreased. Had not thought of that.

 

[RTM]

I have an older 11202, and it has a weird piston in it to provide the hammer. When I got it, it was frozen solid with old dried up grease. Took it apart, cleaned it, relubed it, and it worked much better. Two years later, with minimal use, it's stiffened up again.. suspect a teardown is in its future.

Not sure if your model works the same, I don't have a good enough connection to download a parts diagram.

 

[Bolster]

Huh. Thanks RTM. So, it may be prone to this problem. I called Bosch for an over the phone diagnostic, and their top three suspicions were:

(1) Infrequent use (Yes, I use it maybe once a year for several hours at a time.)
(2) Cold weather (No, not here. "Cold" is 40F and that's rare.)
(3) Needs a "Wear and Tear Parts Set," replacement O-rings and seals. (What do you think? With <20 hours total use, could I have O-rings and seals deteriorating? I bought in 2009 so it's 10 years old.)

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[rlitman]

It shouldn't need to warm up before the hammer starts moving, unless it was stored somewhere really cold...

My Bosch 11236VS had a similar warmup issue. When I first got it, I read the instructions, and they said that the hammering would get better after as much as 2 hours of break-in. In my case, it smoked pretty badly as the grease in the hammer case got awfully hot for the first half hour or so, but it worked very well after that. However, when left overnight in a cold truck, it wouldn't hammer until warmed up again.

The problem is definitely related to grease in the hammer case. Either there is too much grease, or it is too thick. The problem is that these hammers don't have oil seals or oiling systems (like the oil reservoir in my Makita breaker), so if you put in a thinner grease, it will leak out when the machine gets hot. That, and not only does grease thicken in the cold, but when grease is heated up, it oozes oil that leaves behind a thicker base.

 

[RTM]

The parts around #840 look like my weird piston, but get too pixelated to be certain. The grease is very thick as rlitman says, so 40F is very cold to it. Mine, when warm by SF standards, took 2-3 minutes to be decent when freshly redone, now 10 is more like it. Cold day it never broke free to really work. Surprised they don't have temp spec on the grease.

 

[Bolster]

Wow -- interesting -- So (judiciously) put a heat gun on the demo hammer and warm it up before using?

I noticed at this replacement parts website, if you click the bar graph for "doesn't hit hard," or "rotates but doesn't hit," you see the most frequently purchased items for that fix. Top item is "oil reservoir."

https://www.ereplacementparts.com/bosch-11241evs-0611241739-rotary-hammer-parts-c-128_1376_1384.html

Egads! Reading around, people are reporting Bosch will charge $340 to fix!!