The way most of us replace pistons today, is the modern way of being stupid. The only thing we do is to feed the manufacturers bank account. 95%ISH of the wear is taken care of the piston rings. If the piston has the right meassure, just go with the rings. Before the 70ies, even race teams welded scored pistons and put them up in a lathe to get them back to right specs. As said above, I wouldnt recommend this for MX (only for enduro). The more you rev, the more the piston gets beaten up.
Another thing that is kinda hysterical is air filter replacement, and for that sake ALL filters. How many of you change the filter after every practise? Probably most of you. The right thing to do is to meassure air flow and let the numbers tell you when to change it. OR oilflow if we talk about oil filters. As this is difficult on a bike I do like this. When training I change when the filter starts to look terrible, normally 5-15 hours depending on where I drive (sand, dirt etc). I dont care if the bike starts running bad at the end of a daily training. The only thing that will happen is that the filter is too dirty and the engine looses performance, idle etc. It will never run lean, only fat. Before a competition I always change filter, as I cant afford the bike to run bad.
Why do I say this?
I have worked arround filter experts my entire grown up life and Im 55. At an industry a filter can cost from $10000 up to infinity. The dirtier a filter is, the better it cleans the medium. To a point where it reduces the performance of the ment function. This is just a tip for all who hates the job with cleaning and changing air filter. And as I said, remember that the dirtier the better to a point.
Cheers
