{"id":1825,"date":"2018-07-14T00:10:43","date_gmt":"2018-07-14T04:10:43","guid":{"rendered":"http:\/\/maxtorqueperformance.com\/?p=1825"},"modified":"2018-07-14T00:22:47","modified_gmt":"2018-07-14T04:22:47","slug":"blueprint-series-measuring-and-setting-bearing-clearances","status":"publish","type":"post","link":"https:\/\/maxtorqueperformance.com\/staging\/index.php\/2018\/07\/14\/blueprint-series-measuring-and-setting-bearing-clearances\/","title":{"rendered":"Blueprint Series: Measuring and Setting Bearing Clearances"},"content":{"rendered":"
\n
\n
\n
\"\" <\/a> <\/div>\n

By Jeff Smith<\/a> <\/span> <\/span> July 13, 2018<\/span> <\/div>\n<\/header>\n

<\/span> <\/p>\n

<\/span><\/strong> <\/p>\n

If we had to choose one operation that epitomizes the process of engine blueprinting \u2013 we can\u2019t think of a better one than setting bearing clearance. This goes far beyond slapping a set of new bearings in the main saddles, torquing the main caps in place, and hoping the crank turns over. Blueprinting clearance means establishing a clearance that is your target number and working the components until this number is achieved. Anything else is just bolting an engine together.<\/p>\n

We won\u2019t get into establishing specific clearance goals here because that has been previously covered by EngineLabs. We can offer the standard advice that is tried and true\u00a0\u2013 multiply the crank journal diameter by 0.001-inch. As an example with a small-block Chevy main journal of 2.200-inch \u2013 then an oil clearance of 0.0022-inch would be a great place to start.<\/p>\n

This discussion will focus on main and rod bearings in a mild, street-driven performance engine that might see occasional high-RPM use, like at the drag strip. Perhaps the first bit of information worth mentioning is that this is the total clearance around the circumference of the bearing. So in the case of a 2.500-inch main bearing with a vertical clearance of 0.0025-inch, this establishes there is only 0.00125-inch clearance between the crank journal and the main bearing at the top and bottom. Under maximum load, the oil is squeezed into a very tiny area of clearance measured with five digits to the right of the decimal point\u2013perhaps as tight as 0.00025-inch. The remainder of the clearance is found on the unloaded side\u2013the top side of the main bearing or the bottom side of a rod bearing.<\/p>\n

\"\"<\/a> <\/p>\n

In order to do this job properly, you will need some accurate measuring tools. A minimum of a 2-to-3-inch inside micrometer and a dial bore gauge are necessary. Be sure the micrometers and dial bore gauges will measure down to 0.0001 inch. Cheaper tools often only measure down to 0.001 inch. This is not precise enough by a factor of 10. You will also need a torque wrench and sockets.<\/p>\n

<\/p>\n

<\/p>\n<\/p><\/div>\n

The large\u00a0amount of bearing clearance on the opposite side of the load is used to feed oil between the journal and the bearing, which is why producing sufficient clearance is so important. It is this dynamic loading of the bearings that reinforces why attention to detail is so important. There are other considerations such as bearing crush, eccentricity, and bearing materials that demand close scrutiny, but we will focus on how a DIY builder can create professional results by using high-quality measuring tools and working carefully.<\/p>\n

We will make some very important assumptions that the block and crankshaft have either been machined or carefully measured to ensure they are straight, with minimal taper, so that our measurements will pay off with a happy engine when assembled.<\/p>\n

\"\"<\/a> <\/p>\n

Creating the desired bearing clearance starts with accurately measuring the journal diameter. In this case, we\u2019re measuring a big-block crank main journal. The only accurate way is to use a micrometer that measures down to 0.0001-inch.<\/p>\n<\/p><\/div>\n

The first order of business is to measure the crankshaft. We will need a quality outside micrometer, a notebook to record the readings, and a clear, clean\u00a0work bench. The crank should be clean and ready for assembly. Assuming we\u2019re working with a V8 engine, it\u2019s important to measure the main journals in two locations and record both. If you are really fastidious, it\u2019s a great idea to measure for taper across the journal as well.<\/p>\n

Once a journal diameter is established, there are two ways to go about setting up your dial indicator to measure the inside diameter of the bearing housing.<\/p>\n

\n