Pic 02 Micrometer set 01
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Pic 03 Micrometer set 02
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Yes, these are a cheap set of micrometers from China, not top-of-the-line instruments from Starrett or Mitutoyo, but they seem to get the job done. The two more important pieces in the box are the instruction sheet on how to take a reading and the standards for checking the five gages that can’t be zeroed on themselves (like the 0-1” unit). The standards are helpful to check the instrument’s accuracy, but to verify one’s “feel” for the proper measurement before taking it in hand to make measurements. All the external dimensions were taken using these micrometers, and many of the internal dimensions were also taken using “snap” (or “telescoping”) and split-ball gages, see more below.
Crank's Main Journal Specifications, see Service Manual p. 1.7 2/15/13
Main Journal Max Wear Limit 1.7407 Inches
Front Main (Flywheel) Inches Inches
Front Perp 1.7413 Front Para 1.7413
Rear Perp 1.7413 Rear Para 1.7413
Rear Main (PTO) Inches Rear Main
Front Perp 1.7415 Front Para 1.7415
Rear Perp 1.7415 Rear Para 1.7415
Found: Crank’s Main Journals are within their wear limits. I wasn’t sure if the O-O-R and Taper was specified for just the bearing or the journal, so I measured them both. Note that it takes eight separate readings to check for O-O-R and Taper, at least the way I did it the first few times. I finally settled on taking a reading at one point and then tried to see if it “transferred” first for Taper and then Out-of-Round. If this is “cheating” so be it, but the whole trick to measuring with a micrometer (besides learning how to read it), is to develop a good, consistent “feel” for each measurement. I found that the difference between my “feel” between “tight” and “light” on a measurement was about 0.0001” so unless two reading rendered a significant difference in “feel” I took them to be identical for present purposes. I am guided by my 8th grade math teacher, an exceptional fellow, who first taught me that all measurements are approximations; but in machining the goal is to identify and remove as much as possible any ambiguity.
Pic 04 Plastigage package
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The measurements are given in SAE units on one side of the package, and in Metric units on the opposite side, although the dimension does not change from side to side.
Pic 05 Plastigage Interior shot (Marked Up)
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The Plastigage itself appears to be no more than a sophisticated, calibrated, thin strand of wax. The way it works is (1) snip off a length appropriate for the journal being measured, (2) place on journal or cap (slight pressure to make it “stick” is OK, then (3) tighten cap down to specifications. (4) Remove and examine by comparing the width of the compressed Plastigage to the gage marks on the paper sheath package: simple and effective. Not only can you get a good idea about the clearance, but any taper will be evident by varying width in the compressed wax.
Pic 06 Main Bearing from “2459” installed in “3822” Block
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Unfortunately, I couldn’t figure out a way to insert the Plastigage in the main bearing either before or after installing the crankshaft.
Pic 07 Plastigage on Main
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I was able to wiggle a bit into one end on the Flywheel end, which measured out to 0.060” –right at the 0.059” specification. All the measurements below were taken with the snap gage and micrometer.
Main Bearing Specifications and Measurements
Main Bearing Specifications in Manual for M18
Sleeve Bearing Max Out-of-Round .0005 Inches
Sleeve Bearing Max Taper .001 Inches
New Bearing Running Clearance .0049 Inches
Sleeve Running Max Wear .0059 Inches
New Sleeve Bearing I.D. (Installed) 1.7439 to 1.7461 Inches
Main Bearing Readings 02/06/2013
Front (Flywheel)
N/S Front 1.7464 E/W Front 1.7440
N/S Rear 1.7465 E/W Rear 1.7443
Rear (PTO)
N/S Front 1.7465 E/W Front 1.7455
N/S Rear 1.7466 E/W Rear 1.7460
Found: Front side of Side #1 is Out-of-Round 0.0025” well beyond the 0.0005” specification.
Note: MAX reading on sleeve is only 0.0005” out for tolerance for a NEW bearing.
Personally, I don’t see how you can keep this bearing from quickly going O-O-R both because of how it is made, and because of the way it is mounted between two halves of the crankcase. I would be happier if the engine were designed with a “pillow block” of some kind –i.e., a solid piece of cast iron or steel alloy that was bolted to the crankcase, more along the lines of the Kubota diesels that Bernie Pientka has documented on the Forum (although it need not be quite so complex as the Kubota design to satisfy me).
At any rate, it looks like I will need new main bearings fore and aft.
