Measuring bearing clearance
Thread Starter
Drifting
Joined: Apr 2002
Posts: 1,716
Likes: 4
From: New Baden Illinois
Measuring bearing clearance
I am getting ready to assemble the bottom end of my engine and need to confirm that the bearing clearances are correct. I was going to follows jackson's suggestion on an earlier post, which is to measure the inside of the bearing (in place) and lock the inside micrometer, and then measure the locked micrometer with my dial caliper.
Where can I go buy an inside micrometer?
Where can I go buy an inside micrometer?
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
An inside micrometer will measure directly- what you're thinking of is commonly called a "snap gauge". Any tool supply house will have what you're looking for, or if you're just looking for something to "get by" Harbor Freight, Cummins, one of the tool wholesalers. And I'm not slamming either one.
To really measure properly, you need both an inside mic and an outside mic. But you can certainly get accurate numbers with a snap gauge and an outside mic.
To really measure properly, you need both an inside mic and an outside mic. But you can certainly get accurate numbers with a snap gauge and an outside mic.
Le Mans Master
Joined: Apr 2005
Posts: 6,350
Likes: 423
From: Seattle Area WA
I think you are referring to snap gages if you need to measure the ID and then measure that with another instrument such as a micrometer or a calipers. Preferably you want to use a Micrometer that goes out to .0001", it's more accurate than the typical calipers that only measure out to .001" A true inside Micrometer would provide the ID measurement directly.
Sometimes you can find good used mics on ebay or pawn shops. Snap gages can be found at Harbor freight for $10 as well as cheap micrometers that will do the job better than say just using plastic gage.
Sometimes you can find good used mics on ebay or pawn shops. Snap gages can be found at Harbor freight for $10 as well as cheap micrometers that will do the job better than say just using plastic gage.
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Dial bore gauge and .0001" mic is the proper way to get an accurate measurement. Check ebay you should be able to find both for around 100 bucks 
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Thread Starter
Drifting
Joined: Apr 2002
Posts: 1,716
Likes: 4
From: New Baden Illinois
Le Mans Master
Joined: Mar 2001
Posts: 6,640
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From: Ann Arbor Michigan
Drifting
Joined: Apr 2002
Posts: 1,720
Likes: 19
From: Manhattan Beach Ca
During my build I saw plasti gauge was almost always 0.0005 off (half a thou) compared to final measurements. This may not seem much but if your shooting for .002 instead of .0025 it makes a difference. All depends how much accuracy you want.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,117
From: Crossville TN
The value of Plastigage is that it "measures" the clearance of a bearing & journal in the assembled state, which is what you really want to know. It's not surprising to me that it differs from the stack-up of individual dimensions. When you put almost round things and flexible bearings together with several thousand pounds of compressive force, stuff "settles" into place. You need to start the bearing installation process with calipers and/or micrometers to choose the proper bearings, but to know what you have at the end, using Plastigage is a good idea.
Also, a .0001" micrometer is no more accurate or repeatable than a .001" set; it's just that you can get a finer result (fourth place) on its scaling. Good mic users estimate that fourth digit from the scale on a .001" mic. The micrometer mechanism for both is exactly the same [except for the vernier scale on the .0001" mic].
Also, a .0001" micrometer is no more accurate or repeatable than a .001" set; it's just that you can get a finer result (fourth place) on its scaling. Good mic users estimate that fourth digit from the scale on a .001" mic. The micrometer mechanism for both is exactly the same [except for the vernier scale on the .0001" mic].
