sunbeam - In summary of the last few posts, at least how I would summarize it. You do not need to buy shims. At least until you ACCURATELY measure clearances. Because the likelihood is that most or all clearances will be in spec, and you won't need to change shims. And even if you were out of spec by a very slight amount, and you changed the shim and put it back to the CENTER of tolerance ... therefore you made the clearance PERFECT, I seriously doubt you'd even notice the difference (by noise, by mpg, by power, by any means). Rendering it not worth buying shims.
However, if you measure clearances accurately, and find a spot or 2 out of spec, I forget how this works exactly, but yank a bucket, measure that current shim, figure what shim would adjust your clearance to nominal, buy 1 or 2 shims as necessary, and be done with it. Don't concern youself with having a whole supply of shims up front.
Those shims are so expensive because they are in low demand. And, they must be stamped, then machined / ground to a certain thickness, checked to see it's actual measurement, then maybe coated so they don't rust, then packaged and set on a shelf until someone decides they need it. All that work to make them (via machine) is not cheap. And they're not made by the ton, so that's why they're expensive for their size.
This all comes from memory. I changed a shim once. On a 1995 Kawasaki ZX6-R racebike. I found 1 out of spec, replaced it. And never knew the difference. Now, that bike did run really really well. 15k rpm redline, 16k rev limiter. I was not a small guy then either. I was a linebacker in college, and I ran that 600cc in the Novice-Production class (stock exhaust, no mods). And it would out pull string-beans in Novice-Supersport (unlimited fuel and exhaust mods). Was it because of that shim? Maybe 0.4% due to the shim. But I just kept the bike maintained well, all systems running nominally, early oil changes (when the bike was new), every bolt tightened to factory torque spec, spark plugs indexed. But that was a race bike. Good maintenance and good ears is all that is needed for a street machine.
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View my fuel log 2020 Mirage ES 1.2 manual: 42.4 mpg (US) ... 18.0 km/L ... 5.5 L/100 km ... 50.9 mpg (Imp)