Calling all metrologists! (more bearings...)
 

Been trying to get the hang of my newest tool.. a Starrett 0-1" outside mic. I got it because it had removable ball anvils. For fun I have been trying to measure the thickness of my used main bearings. I feel pretty good about my measurements, it is just a lowly friction mic, and I am trying to use a light touch.

However.... I seem to make a little divot in the frosty coating of the bearing from the tip of the ball end anvil.. in fact I can scrape that coating with my fingernail. No matter how lightly I do it, I always seem to leave a mark. Something to worry about? I really don't care about these, since they are old bearings, but what gives me pause is that soon I will have new bearings and I presume I will be wiggling my bore gauge anvils against them as I assemble my engine.. I guess they are just going to get a little marked up?

Pic is just for the heck of it. Not demonstrative of a measurement or anything.

http://forums.pelicanparts.com/uploa...1388284597.jpg

My $.02: If you're marking the face of the bearing/coating then I would not use this tool on a bearing I plan to run in the engine after inspecting. If you're checking QC for the manufacturer and plan to toss the bearings in the trash after then I would say proceed... otherwise use the plastigage method for bearing clearance to crank measurement.

When I bought new genuine bearings you can see where they measure each one during quality control.

I would venture to say that you have nothing to worry about.

Spot-on.

From another thread regarding soft bearing surface.

Thanks all for your advice! Those articles on bearings were pretty interesting.. I will get some plastigauge when the time comes and use that as a backup, although I know many here say not to rely on it. And I won't worry about the tiny marks from measuring, nice to get some reassurance on that.

The articles made me think that after the car sits for a long time it might be worth turning the engine with the fuel pump relay disconnected to get the bearings primed the way you might with a freshly rebuilt engine.. I wonder how many people bother doing that in the spring.. something I will consider for the future.

So for "fun" last night I tried measuring the thickness of my used main bearings.. 66k miles. I took six measurements on each shell / half bearing. And I wrote them all down. I took a cursory look in the book of Wayne and he doesn't list a tolerance for the bearings themselves, but I think I figured out the range of acceptable thicknesses based on the specs given for the bore and for the bore with the bearings installed.

Takeaways.. mostly that it's hard to measure bearings with a micrometer.. they are so soft you can really plant the anvil end in there by several ten thousandths of an inch if you are not careful. I am glad I gave myself the practice though. I already feel much more confident handling the micrometer, applying it on a workpiece, and reading the scale.

So these are slightly worn by my calcs.. out of the acceptable range. I didn't bother to calculate what hypothetical clearances these old bearings would give me on an in tolerance crank but that might be fun to try too. At any rate.. going to shop for some new bearings for my rebuild and see what they look like.

http://forums.pelicanparts.com/uploa...1388425226.jpg


<img src="http://forums.pelicanparts.com/uploads22/photo+21388425257.jpg" style="image-orientation: 90deg;" />

What temperature were the shells when you measured them?

Room temp.. I would say around 68 deg. I took the liberty of doing this at the kitchen counter and not in the garage, and all the materials and tools had been inside for several days as well. I tend to run pretty hot.. so I was wondering if even my brief handling of the tool and the material would have any effect.. do you think it would? Not sure what the coefficients of expansion for bearing material and micrometer material would be.

I have never ever seen anyone measure bearings like that.....

To add to the statement , I have seen machinists size rods, then assemble the rod with the bearing, set torque specs and then measure for concentricity.

Never meant to imply that this was an accepted practice of any kind at all in any aspect of engine building and I hope no one interprets it as such. I think the point of me posting this was really just noticing how soft bearings are, familiarizing myself with their dimensions, and wondering if I stand to damage them with a bore gauge. It sounds like I don't need to worry about it. It's also a rough baseline to go on for when I purchase new bearings.. I can compare the thickness for a little quick and dirty QC to see if they are really out of whack before I go to the trouble of inserting them in the case. With all the crazy stories I have read about bearings I just feel like I will benefit from approaching this task with an abundance of care and caution, even if it's all from a novice perspective.

I used to do that on my race motors.