A human hair is about 80 microns wide, and the smallest particle size you can see with a naked eye is about 40 microns. That seems pretty small. Can something so small you can’t even see it really cause problems? The answer is yes.
Clearance size particles do the most damage. They are small enough to get into the space between the bearing and the journal or the lifter and lifter bore, but they are too big to flow straight through without touching anything.
Particles that are smaller than the clearance between moving parts can easily flow through the clearance space without doing any damage, and the particles that are too large to enter the clearance gap are blocked out, so it is the particles that are similar in size to your engine’s clearances that you need to worry about.
When you do the math, you’ll find that .0025 vertical bearing clearance yields out a clearance space of .00125 (half of the total clearance is on each side of the journal, at least is should be). One and a half thousandths is equal to 32 microns, so particle sizes you can’t see are the ones that you need to worry about.
Here are 3 practical steps you can take during the assembly of an engine to rid yourself of these unseen assassins.
Clean your parts before installation
First, just prior to installation, wash off the Cosmoline coating that is on the parts. Driven Racing Oil recommends a foaming degreaser to lift the greasy film from the part. That film seals out moisture and keeps it from reaching the surface of the part, but it also traps fine particulate.
You don’t want an abrasive slurry working on your flat tappet lifters, so make sure the metal surfaces have been degreased before you apply the break-in lubricant.
Use an oil filter with finer microns during break-in
Second, use a finer micron filter during break-in. A production car filter will have a finer micron rating than a racing filter will have.
For example, a WIX 51061 Small Block Chevy filter has a nominal micron of 21 with a GPM flow rate of 11.
A WIX 51061R racing filter has a flow rate of 28 GPM and a nominal micron of 61. As you can see, you can use a production car filter during break-in since you are not running the engine to full engine speed (and thus don’t need more than 11 GPM).
After the initial 30 minute break-in period, change the oil filter.
Now you have removed all the larger particles that could cause problems, and you need the high flow rate filter when you start making dyno runs or go to the race track.
The tighter the micron, typically the less flow you have. Ideally, you want a micron tight enough to filter out clearance sized particles and a flow rate high enough to supply the required volume of oil to your engine.
Change the oil after break-in
The third step is to change the oil. Most of the wear metals that will be created in an engine’s life will occur during the first hour of operation. While everyone hates to throw away something that looks perfectly good, it is cheap insurance to change the oil after the initial break-in.
A high quality break-in oil is like primer for your engine. It is establishing an anti-wear film in your engine, and that is the foundation for lasting protection. It is better to get an extra coat of primer than to leave a few spots thin.
This is especially true for a hydraulic lifter engine. Any particle that gets trapped in the lifter can cause the lifter to bleed down and make noise.
The best plan of action is to use a high quality break-in oil to reduce the amount of particulate created during break-in, and then change the oil and filter after initial break-in.
Continue to use break-in oil during dyno runs, the first weekend at the track, or for the first 500 miles in a street car. After that, change to a premium oil designed for that application and follow normal change intervals.
Keeping clean, high quality oil in the engine is insurance against lubrication related problems – because what you can’t see, can hurt you.