Proper bearing clearance is essential when building an engine.
That holds true for both your main bearings and rod bearings. We partnered with the Summit Racing team to cover the ins and outs of main bearing clearance earlier. Now we’ll look at the steps involved with measuring and checking rod bearing clearance.
While some aftermarket bearing manufacturers offer general rules of thumb as starting points for target bearing clearances, there is no one-size-fits-all number. Things like engine type/size, operating conditions, intended application, and lubricant selection can ultimately effect the ideal bearing clearance number.
Once you’ve established your target clearance, you can determine your existing bearing clearance by measuring the rod journals with a micrometer and subtracting the numbers from measurements taken with a dial bore gauge on the installed bearings. For the greatest accuracy, the dial bore gauge should be “zeroed” on the inside of the micrometer before measuring the bearing to ensure the measurement is the exact difference between the two.
In this video we’ll take you through the entire process, from measuring and recording the journal size and checking the final rod bearing clearance.
Follow along…
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if you are putting a new or different crank shaft in an engine how do you determine the size of rod bearings to begin with? Do you measure the rod o after the cap has been torqued down and subtract the journal size plus the clearance allowed?
The rod bearing clearance verification procedure was presented in an easy to understand manner. Well done.
I do have a question that I hope someone will kind enough to answer. If a micrometer wasn’t available for checking bearing clearances, could a high quality digital or dial caliper be used instead of the micrometer ? Would reduced accuracy be an issue ?
Thanks OAC Staff and Summit Racing.
No -use a mic and bore gauge. You are measuring to the thousands and the other gauges won’t be that accurate.
You can buy the gauges for less then $200 at Summit and they don’t wear out so you can use them for years.