The Stovebolt Site Forums The Shop Area Engine Shop Micrometer

Getting ready to tear into one of my used 235 engines to asses it`s condition. I do not own a micrometer and need to shop for one that will work for pistons, crank etc. Planning on going non digital . Seeking input on what size mic I need and any other helpful hints. Also should I get a dial caliper or digital style for checking cylinder bore, Thanks all.

You can do a lot with a set of micrometers and those little telescopic T things. The cheap digital slide calipers are extremely handy and pretty accurate. JMHO.

I have a 0 to 6 set of offshore outside mics that i bought about 10 years ago, they were pretty cheap and have held up very well. I'm not a big fan of cheap digital calipers, my preference is a Starrett 6 inch dial caliper. Only digital caliper I've used that I really like is the Mitutoyo Absolute

Micrometers are nice, but expensive. I use a dial caliper for everything. You can buy a decent caliper for not much money, and if you drop it, it won't ruin your day! A dial caliper and set of snap gauges will let you measure every part of the engine.

Dial calipers are for making somewhat educated guesses. They are far too susceptible to making huge mistakes from applying too much or too little pressure to the handwheel, or getting the jaws misaligned while taking measurements. Even an inexpensive set of 0-6 inch micrometers from Ebay is head and shoulders ahead of a good digital caliper. I've got both- - -a 6" Starrett digital for when I want to make a pretty accurate guess, and a set of micrometers with a Vernier scale for when I want to slice a strand of hair into several equal increments. I've also got a set of inside mikes, and at least half a dozen different types of dial indicators. I use them all, regularly, and trying to make one do the job of another is a lost cause. I'm accustomed to splitting thousandths when I'm boring and honing cylinders for new pistons, and working to the same accuracy when reconditioning conacring rods. The oil clearance on a 2" diameter solid steel wrist pin in the connecting rod bushing for an 855 cubic inch Cummins Diesel is .0004"- - - -that's a strand of hair split into three equal slices. Engine machining is no place for "Measure it with a micrometer- - - -mark it with chalk- - - -cut it with an axe!"
Jerry

" They are far too susceptible to making huge mistakes from applying too much or too little pressure to the handwheel, or getting the jaws misaligned while taking measurements."

Truth! Calipers are great for layout or a quick reference but measuring +-.005 is best done with a mic.

Jerry, you forgot that the thickness of a hair depends on the the natural hair color. Redhead, blond, brunette and black.
Also the part of the body it came from!

Dial or digital calipers are not to be trusted to measure any less that +/- .005.
Even mics can not be right, if used by someone that does not know how to use one.

Don

Don, are you gonna burst my bubble and tell me that a mike can't be used as a C-clamp on a welding project????????

Jerry

Dial calipers will let you someone new to measuring find out the condition of the engine, If it needs work, the machinist will do the measuring when it comes time. You sure don't need to measure in ten thousandths to know if the engine is going to the shop or not.

Dial calipers can be zeroed out anytime they need to be checked, try that with a set micrometers when you don't have calibrated gauge blocks, and quality calipers will measure down to the .001" if you take to time to learn how to use them.

I was a machinist for 11 years working in the aerospace industry, I ran all types of lathes with all types of material. Ever machine a magnesium nose cone 14" across with tolerances +.00001 to -.00005 on a manual 50 year old lathe, I have.