PowerPlus rotary hammer drill teardown and rebuild.

Had this for a good few years and other than a knob that broke a few years ago it's been absolutely faultless until recently.
Every now and again while drilling, the bit would stop spinning even though the motor was working fine.
Easing the pressure on the bit would sometimes get it to spin just enough to retrieve it from the hole, fortunately everything I've been drilling lately has been to weaken it ready to break it up so if a bit got stuck I could always retrieve it eventually.
Thought I'd try and see if I could find out what was wrong with it so set about it with my tools this morning.
Before starting (obviously):

Casing removal pt1:

Motor housing off:

Casing removal pt2:

"Nose piece" removal:

This is the piston which creates the hammer action. For those unfamiliar with how these work, this piston travels back and forth inside a bore, the air it displaces causes another loose piston to strike a flat ended thingy (can't think of the best word to describe it) which is attached to the opposite end of the chuck.

The actual piston and conrod:

For anyone wincing at the above photo, the vice isn't done up tight, it's just very lightly nipped up to hold the motor upright.

Gearbox split:

The pin inside the gear on the right disengages the hammer action when that black plastic lever is flipped, it pushes up inside the bore in the photo below

The business end:

^This is the mechanism to engage/disengage the rotation. As it's shown there, the rotation would be disengaged, it's held together by a spring and those cutouts on the left side of that gear.

Annoyingly I couldn't find anything obviously wrong with it but I regreased and reassembled everything and upon testing it does seem to be working fine though I'll know more when I put it to proper use again.
If it happens again I suspect it might be something inside the nose piece so will attempt to strip that part down further, it may even be a piece of grit or something causing the rotation stop mechanism to stick disengaged.

 

Just thought I'd follow this up as I've been using it quite a bit lately.
It still doesn't like drilling holes but chisels fine but.... today it decided it didn't like the motor cooling fan and threw it out of the cooling slots in small pieces.
Unfortunately it looks like it's not available as a spare part, it comes attached to the motor armature.
I can't complain really, it's a good few years old and has done a fair amount of hard work since I bought it. It still runs ok but obviously I'll have to be mindful of how long I run it for and give it time to cool down.
I recently treated myself to a 15kg breaker so it will only get used for very light stuff now anyway.

 

My 15kg one is MacAllister, I know it’s not in the same league as the pro stuff but it’s a proper beast with serious grunt and will do me fine.
I borrowed a Makita one to knock out a few fence posts but it had a fault and would only run intermittently then it stopped working completely. Fortunately the owner said he’d been having trouble with it. Rather than hire one I thought I might as well buy one.