Hi all
After almost 5 years, finally got around to doing a burr set replacement on my M4 (thanks Chris!)

Why now?
Well, having stripped it down for cleaning multiple times and noticing increasing notches and nicks, and a general 'smoothness' as I ran a nail across the teeth, I wondered if it was getting close.

But I also had noticed some signs of bluntening similar to the machine tools from my woodworking days - the grinder was struggling to maintain a consistent grind setting (I seemed to be constantly correcting/overcorrecting) and adjustments required were much larger. Where when the grinder when new it could be adjusted by 1/8 a micro turn one way to the other to go from gusher to drip, more recently this would take 1-1.5 turns to do the same thing. But also, I was finding that the tamp was 'sinking' much more than it used to…

So over the weekend I swapped to a new set. Pretty easy job - remove top carrier, three screws, clean it and replace in reverse order. Nice tight tolerances on the top carrier so no real probs locating the burr set.

Bottom carrier was a fraction more involved. Piece of soft timber through the chute to stop bottom carrier turning, three screws, clean everything, replace. The only gotcha was that there was some play in the locating of the bottom burr set - so easy for the burr to be tightened up off centre (easily visible to the eye when spinning by hand).
Unfortunately I haven't got a dial gauge or similar - so had to make do! Used three toothpicks to wedge the burr equally off the three 'exit arms?' (the little sweepers for ejecting the grounds out the shoot) and kept spinning the bottom carrier until it seemed as true as I could get by eye. I might ponder a way I could improve this for next cleaning shift - any ideas?

However…
Working beautifully

My observations as to the improvement? (to be taken with a grain of salt - required for reducing possible placebo effect!)

First thing I noticed - the aroma off the grinder. Seems more potent.
Under tamping? Far less 'compaction' for the same pour result - feels much less compressible - more like sand, rather than flour. I would put this down to a more consistent size across the board - less coarse to fines ratio?

In the cup? Not as pronounced a change - still getting lovely coffee. But maybe a little cleaner in taste and stronger in aroma? But completely subjective I know.

But for me, well worth the effort. Kinda like getting new tyres on the car - there might have been a few more k's in the old ones, but new ones are nice

Have a great week everyone
Matt