For those of you who wonder why there is an admonition to vary speed during break in, it all relates to the engine....Each connecting rod stretches a bit and the more rpm the greater the stretch. If you were to drive at a constant speed the stretch would be constant and the wearing in of the cylinder bores by each piston would be up to a certain point, resulting in a "step" in the cylinder wall. If the engine speed is varied, then the wearing in results in no step but rather a smooth curve, from point of most wear to the point where no wear at all occurs.

So vary engine speed during the first 1000 or even more miles....No cruise control across Nebraska!! After break in you still want to use the entire range of rpm from time to time and not go hundreds of miles at one particular engine speed.

And easy on the brakes until the pads "bed" properly.

An aside, it amazes me to see people wanting a low low mileage car "off the truck" (I agree!) but then saying they will drive it 50 miles before they commit to the purchase! Huh??? Is that fair? What if everyone did that??? There are a couple of posts like this in another current thread.

 

Good advice.

 

You must have been digging in the threads - the above is 4 years old..

I love all the theories behind "break-in" periods. Way more thought goes into it than required.. When it comes down to it, just follow whatever advice (if any now days) you find in the owners manual and overall, - just drive the car/vehicle.

In a factory engine like the TL's, connecting rods are not designed to stretch under normal RPM parameters. (not to the point resulting in irregular wear). If this is occurring, you have issues other than possible break-in concerns..

Cheers

 

The context of the thread-initiating post here is that of stretching connecting rods being the reason for a cafeful and planned breakin period. This is nowhere near all that's involved in this process.. there are just a host of things which are affected by the breakin.

Primarily, it all has to do with asperities which exist throughout the engine, on all of the machined parts and mating surfaces. Piston rings, cylinders, all of the bearings, wrist pins, crackshafts, camshafts (including the lobes), followers, gears, and on and on, not to mention the transmission and transaxle. The purpose of the breakin is to smooth out these asperities properly. There are some other reasons to be sure. But asperities are item number 1.

 

"Asperities", great word Mr. Southern man. That would definitely sum up the entire break-in for all concerned parts/systems on a vehicle. We can call that the rough surface/contact mechanics theory for break-in.

Cheers

 

SouthernBoy,

I like to think of myself as at least somewhat articulate. And the truth is, I rarely if ever find a word or phrase in this forum that has me scratching my head. So it's a real delight to find a word that threw me straight into Google...and I had to find out if this word usage was proper. This is what I found:

as·per·i·ty (-spr-t)
n. pl. as·per·i·ties
1.
a. Roughness or harshness, as of surface, sound, or climate: the asperity of northern winters.
b. Severity; rigor.
2. A slight projection from a surface; a point or bump.
3. Harshness of manner; ill temper or irritability.


Now I have heard it used in the context of #3 several times, but never as listed in #2.

Congratulations, and thanks for making my daily read in here just that one iota more interesting and stimulating!

Now back on topic....

I agree completely about the ASPERITIES being the major reason for the need of a break-in period. Excellent point, and well put.

 

Hey there Smitty.. How's it going down Texas way?

The word "asperities" at first, sounds like some sort of vegetable, perhaps because it sounds like asparagus. But the fact is, asperities is really what it' all about. I've seen some of the machined parts of an engine under heavy magnification and you'd be surprised to see this little creatures (asperities) all over the surface. They are created during the machining process and appear like raised shavings, only they're attached to the surface. The breakin process, along with a "breakin" oil, hones these rough spots down. The reasons for varying speed and not pushing the engine is heat, pressure, and the varying of the mating surfaces.

 

You're most welcome. Believe me, I was not at all trying to appear pretentious by using this word. I just found it be be all-encompassing for the need at hand. It seemed to fit the entire purpose of breaking in an engine.

 

Represent ! Prof. Southernboy in da house ... LOL

 

Ok, I gotta ask. Is that a dig or an offhand compliment?

Not that I mind either as long as the first one is in good humor.