Chainsaw Repair

I have a saw that uses a 47.95mm diameter piston (factory spec) just measured an after market replacement and it measured 47.96mm. Should I use it? Difference in diameter is .01mm or 0.0003937. That would make a reduction in piston to cylinder clearance of 0.00019685 each side. What to you all think?

what are you using for the measuring.......mic or caliper?

-joe

you may be trying measuring to tighter accuracy than the caliper can actually do.  most calipers, mics, whatever....... you end up using, show numbers outside their actual capability.

example:
in order to measure to the 0.001 inch, the instrument rounds to the last digit to the right of the decimal point, ("1").  so, if it actually reads 0.0005 it may show as either 0.001 or 0.0005, depending if it's a dial or digital.

as a rule of thumb, gauges are 100% to accurate only one number preceding the last digit they display.  digital gauges which are capable of mathematically calculating the measured result from metric to english, show digits beyond thier actual accuracy.

example:
0.01mm = 0.0003937 inch   ...........  a trusted reading of the caliper, given that displayed reading, would be 0.000 inch.  the "3937" digits are outside the capabilities of the instrument, even if they were shown on the gauge display. its common that a  micrometer is used to measure if you need measurements to the 0.001, because they are accurate out to the 0.0001.

not a fan of digital gauges, but they do have an advantage of being able to display numbers that are easy to read without a magnifying glass, can convert between metric and english.  suggest to measure with the units you need to use, and take multiple measurements.  when things are this small, even the temperature of the measuring device can alter the result.

hope it helps.
-joe

He's saying a micrometer is more accurate than your digital caliper. There is a. 0005 variation on the Mitutoyo so it could read .0005 and the true size could be  .001.   Don't think you are gonna have fitment issues with your piston, splitting hairs at this point!! Lol

He's saying a micrometer is more accurate than your digital caliper. There is a. 0005 variation on the Mitutoyo so it could read .0005 and the true size could be  .001.   Don't think you are gonna have fitment issues with your piston, splitting hairs at this point!! Lol

+1

measuring tools wear or loosen up over time.  when they are still new, i like to measure a guitar pick, and write the measurement on it with a permanent marker.  keep it in a drawer.  this way, you can always go back and measure it again to see if the tool is still reading the same.  a better idea is to use common "feeler guages" like those used to set points for example.

this is good peace of mind if the caliper was dropped on the floor, or starts to show wear marks on the slide or tips.  some low buck calipers are surprisingly accurate.

you can buy "checking standards", but a set of those costs more than an expensive caliper.  some manufactures may offer a service to recalibrate the tool.

0.01 mm is too small of a difference to be concerned about.  at about 0.05 mm,  get questionable with a caliper.

regards
-joe