Running in.

[Colinwatt]

In the UK you used to see "Running in. Please pass" signs on the rear of new cars as they drove slowly during their running in period.
I am putting my engine (1918) back in my tourer after a complete overhaul (rebore + rebabbeting) and I am wondering about "running in". What should I do once I have the engine running again?
Colin.

[HaroldRJr]

Just my "opinion" here, but here is what I was taught many years ago about breaking a new engine,....but first, a bit of info that might be worth considering:

You never hear of "breaking in" a new engine when you buy a new car anymore. The reason is that nowadays, engines are engineered, designed and assembled with much closer tolerances than years ago, before computers and such. Because there was greater variation in the "fit" between parts, it really did take some parts a bit of time and running "to get used to each other" for them to work together smoothly. Not so anymore, and that's why you never hear of a "breaking-in" period nowadays. But back in the '40's & '50's, here's what I was taught, mostly by my Dad, about breaking in a new engine:

Fir the first couple hundred miles, keep the speed down to pretty much city driving (before freeways) speeds. During that time, try to vary the speed as much as possible, and avoid driving for long periods at just one constant speed. And here's one point my Dad made that to this day, I think is probably most important. Very early in the running of a new engine, and every so often thereafter during "break-in", put a pretty good "load" on the engine (but don't over-rev) for a minuter or two,....sort of like making it work a bit harder than normal, like climbing a slight but very long hill, or, even when accelerating away from a stop. This puts a bit heavier load on the engine and causes higher combustion chamber pressure which causes the rings to bear a bit heavier on the cylinder walls. This is important, because the rings have to wear-in to completely seal agains cylinder walls, and this wear will be greatest when the engine is brand new, and begin to decrease as the new cylinder walls become smoother, and smoother and highly polished as the engine breaks-in.

Sorry for the long-winded "epistle" here, but I think initial "break-in" is important with these old engines, and I sincerely believe that careful and proper break-in is important. Also, one other thing, leave the "break-in" oil in the engine for quite awhile during "break-in" as this is a factor in normal "break-in", but do change the oil much sooner than you would normally change it later, as that first oil will have a much greater than normal amount of metal particles in it from initial "break-in".

Again, not saying any of this is "right", but this is what I was taught,....FWIW,.....harold

[Henry K. Lee]

Not long winded at all Harold.

Thank You for taking the time with the correct method.

All the Best,

Hank

[Henry K. Lee]

The only other thing I would add is follow what type of rings/honing grit the manufacture recommends.

Hank

[Oldav8tor]

Funny thing - with aircraft engines the rule is to run them at 75% or higher power for the first 25 hours or until the oil consumption stabilizes. The idea is to insure that the piston rings seat properly. Such a procedure is at odds with "babying" a Model T engine during it's first miles after overhaul.

[Ruxstel24]

Funny thing - with aircraft engines the rule is to run them at 75% or higher power for the first 25 hours or until the oil consumption stabilizes. The idea is to insure that the piston rings seat properly. Such a procedure is at odds with "babying" a Model T engine during it's first miles after overhaul.

I've had a few old timers say run it like you plan on driving it...some were racers.

"Drive it like you stole it"!!

Myself I baby my engines generally the first hundred miles, a little less till 500 and change oil and go. I agree with varying RPM and load, helps cam and lifters seat in also.

[Scott_Conger]

If the car was assembled with Timesaver, it is broken in. If it was bored, it is not, and the mains and rods will appreciate a little babying. If it was reamed, hard to tell condition and size of reamer and to treat as if bored.

Importantly, the oil should be changed once the engine has about 1-2 hours on the clock (my preference).