MK3S Upgrading Advice  

RE: MK3S Upgrading Advice

Hi Adam, 
I think Accumulated hours figures are a potentially inaccurate... so your printer may not be as old as it appears
the printer tends to have most movement on the X and y axis so all of the wires are swished from side to side, and back and forth

you tend to get work hardening at any concentrated flexing point, typically right at the back of the extruder cable support behind the X axis travelling assembly, and just beyond the contact cover on the back of the y axis

In my experience, the things that expire first, are the wires to the Heatbed and the wires to the extruder assembly

I change the heatbed power wires to 16AWG flexible Silicone wire, as a matter of course. they are much more flexible than the Prusa original wires. 
My Pinda wires have also gone intermittent, in the past 24AWG flexible silicone wire is good for repairing the signal wires for Pinda, filament sensor and fan wires. 
the part cooling fan and extruder cooling fan bearings tend to get tired, so changing them, might be a good idea
the smooth rods and bearings also move a lot, if they were lubricated properly during assembly they can last a long time...  My oldest were installed in 2015 or 2016 (can't remember exactly when...)
If not lubricated well, you will notice lines scored into the surface of the smooth rods (lines that you cannot feel with your finger nails are normal, but if you can feel them with your finger nails, the rods are aging badly)
I have had two X or Y axis Idler bearings fail out of 8 bearings across the 4 Prusa's I have owned   first time I bought and installed a new ball bearing race, to go inside the aluminium idler roller, after the second failure I Bought after market idler rollers which have twin bearings, and I have not had a repeat failure 6mm gt2 idler rollers with 3mm bore, are available as either plain rollers or toothed rolers, on bay and amazon. I use the toothed ones bcause I don't like the rubber teeth running on smooth rollers, Mr prusa, on the other hand, has used smooth rollers for years...   (interestingly from the Mk3.9 /Mk4 prusa seem to have moved from single bearing rollers to twin bearing rollers (Still smooth)
the X and Y toothed belts may be showing wear, replacing them with genuine Gates 2gt toothed belts may be  a good idea... 
and the extruder nozzle may be showing wear... so a replacement may be a good idea

If I recall correctly, the X and Y rods are not part of the mk3s to mk4 upgrade  the Z rods change from 8mm to 10mm as part of the upgrade

Many people think that the Mk3 to Mk4 upgrade is not cost effective because a lot of the mk3 is not re used. 
the X and Y toothed belts may be showing wear, replacing them with genuine Gates 2gt toothed belts may be  a good idea... 

Mk3 to Mk4S upgrade £568  Result one mk4S and a load of spars that you probably wont use
New Mk4 Kit £682       result, a New Mk4 printer to work alongside your Mk3 printer, or a spare mk3 printer that you can sell to offset the difference between mk4 upgrade and new mk4 kit...

to be honest, 
I tend to check my printers over periodically, tighten the belts if necessary, tighten screws
clean and lube the rods and only change things if they are obviously worn... 

I generally have one of each fan, one of each thermistor, and a spare extruder heater, in stock, plus the silicone wire I mentioned
and some heat shrink tubing, on hand as spares, so that I can repair things that go wrong I make sure any joints in wires are not in the section of wire that flexes. 
If I use one of the spares, I get another spare for stock. 

I don't lube the Z axis lead screws, the plastic lead screw nuts are supposed to work without additional lubrication

good luck, what ever you do. 
Happy printing
Joan