SRF Engine Break-In

Introduction
EscortMotor.gif (8160 bytes)Lately, especially since the "New Car Buyers Guide" issue of SportsCar Magazine (March 1998), I’ve been bombarded (well, maybe not exactly bombarded…) with questions regarding SRF engine break-in. What follows are my thoughts on this subject.
Background
A brand-new engine is composed of brand-new parts. The concerns of many racers are how to make these parts perform to their optimum potential.

The piston rings should be the focus of break-in. The break-in of bearings: mains, rods and others can be considered to offer negligible horsepower impact. Bearings are set at correct tolerances by the engine builder and are not much of a factor for a performance oriented break-in. Piston rings, however, perform several functions. The rings should be fitted to optimize combustion sealing, as well as allowing the necessary amount of cylinder wall oiling. The top ring is the primary source of combustion sealing; the second ring serving as a backup. The lower, oil control, ring determines the amount of oil allowed to be spread onto the cylinder walls.

I once took apart an engine with exactly one hour of mild-load running time. I examined the upper ring to see how much wear/break-in actually happens in one hour of running. This ring showed almost exactly one third of its exposed surface to have made contact with the cylinder wall. This told me several things:

1. Rings take time to find optimal contact with their cylinder walls. We live in a different world than "Racing Engine Builders". Our engines are off-the-line, mass production vehicle engines. Addressing that point, I would have to say that SRF engines need a considerable amount of break-in time.
Some "Racing Engine Builders" will actually "lap" their rings in....meaning: the rings are lightly coated with an abrasive substance.. and the engine rotated numerous times, to "seat" the rings to the cylinder walls. The idea here is simple, but complex in execution.

2. Piston rings, at their optimal performance, maintain multiple functions: sealing combustion pressure as well as transferring heat from the piston to the cylinder walls. The piston, truly, has no actual contact with the cylinder wall and thereby, must transfer the involved heat to the block through....Viola! the rings!

3. New rings, when viewed microscopically, meet the cylinders (also viewed microscopically) at precious few points. Initial running of the engine will create an abrasive reaction between the rings and cylinder walls. The object of this exercise is to have the rings and cylinders meet at the largest area possible.

What I’m trying to say here is: Initial running of the engine should be designed to create optimal ring-to-cylinder wall contact.

My Recommendation
Let’s say you take a brand-new engine and drop it into your SRF and go racing...

If you choose to race a fresh engine, you will build up significant temperatures in the cylinder head and pistons. Foot- to-the-floor treatment creates load on the engine and consequently heat in the combustion chamber. This heat has to be dissipated somewhere. The only way the pistons dissipate heat is through the rings...into the cylinder walls and from the cylinder walls to the coolant.

But, the issue here is, your "fresh" rings are only partially contacting the cylinder walls. Heat builds up in the crown of the piston and tries to escape -- however the only escape is through the rings -- and the limited running surface area of the "un-seated" new rings only builds more heat in the rings.

Now, the rings are not transferring this excess heat, and , as metals will do when exposed to very high temperatures, lose their temper. In short, the rings will lose the tension pushing them outwards toward the cylinder wall.

The lower tension on the rings causes combustion sealing to decline and horsepower falls off. Glazing of the cylinder wall occurs and ultimately, ring sealing goes completely away.

So, you ask: "How do I break in my engine?"

First, whatever you do, DO NOT USE Synthetic oil during break-in. Some factions expound the use of non-detergent oil for break-in purposes. If you choose to use non-detergent oil, drain it after 60 minutes running time, and use a conventional oil.

"How long is break-in?"

"Good question", I answer, but I know you will not like my reply. Engine "break-in" is best accomplished by driving the car under various loads (none too major) and RPM’s...for, perhaps, 18 hours. These are the facts of life in our context. This procedure allows for the best ring sealing and best heat transfer from piston to cylinder wall and thereby, to coolant (water) jackets. Ultimately, this should lead to best performance. Do Not, I Repeat, Do Not race a fresh engine. There are some who believe there is a theoretical horsepower gain, involving crossover between ring drag losses and sealing compromises, but at this moment I have no answers for this equation.

Unfortunately, 18 hours of non-race break-in time is not acceptable for most amateur racers. I have to say though, that these are the facts, and, for best performance, my research leads me to believe 18 hours is a reasonable number. Sorry if I have told you things (times) you did not wish to hear. This is only my best recommendation.

It must be understood that we (the SRF community) use a mass production-based engine. In this light, we must be aware of – and live with – the limitations of racing a mass production-based engine.

Dave Liddle, Engine Department Manager/Compliance Director
SCCA Enterprises, Inc.
Rev. 2/27/98
Feedback
I welcome your comments or ideas on this information.  Feel free to drop me a line via “Comments for the Bro’s”.  

Barry

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