Please forgive temporary problems with photos.
All N-Series Tractors–Ford-Ferguson 9N, 2N, and Ford 8N
You have just installed a newly rebuilt engine and discover there is next to nothing published concerning break-in proceedure. Here are my thoughts on the subject. This same procedure with minor vehicle-specific variations has worked for every engine I have rebuilt.
The second worst thing you can do to any new or rebuilt engine is let it idle or run at a steady RPM. Revving the engine splashes plenty of oil up into the cylinders. You also have to get some cylinder pressure behind the new rings to drive them into the walls. Revving the engine with a load on it takes care of that.
Most of the problems with rings not sealing and or cylinder scoring are caused by being too gentle or taking too long to tune the carb. There is no need to even tune the idle circuit until after you have taken the engine through a heat cycle. At that point your rings should have already "set". Slightly rich is better than too lean, so I always set my carb up slightly rich on the bench. For the Ford N-series Tractors, the idle mixture screw should be set 1 turn out and the main mixture screw about 1-1/4 turns out.
Now, this is how I avoid extended idling while tuning the carb on my tractor. If you prevent the engine from idling below 800 RPM it will be running off the main mixture and the idle mixture adjustment will not matter. To do that, I simply crank about two extra turns in on the idle speed screw past the normal bench setting of one turn in from throttle plate fully closed (3 turns total). For the next step, rigging a temporary foot-throttle may help or you can just use the standard hand throttle.
Crank the engine up and keep revving the throttle up and down until the temperature starts to come up. Then, the best thing you can do is put it in gear and drive it around. Continue to accelerate and decelerate the engine repeatedly with a load on it letting the RPMs get higher and higher as the temperature comes up. Run it like that for about 5 or 10 minutes watching for any serious leaks or other problems and then shut if off and let it cool.
Once it has cooled, go back and re-touque the head bolts and carefully inspect for leaks and the inevitable things like loose hardware, or dangling wiring. Then crank it up again and run it through another heat cycle with a varying load and RPM on the engine.
This is the point when I adjust my base idle and idle mixture settings. Refer to CARB TUNING for that proceedure.
Once you have your carb tuned, your tractor should be ready to work. But, for the first couple of hours, I continue to vary the RPM and load on the engine and I change the oil as soon as I see any color in it.
You may have noticed in the first paragraph that I wrote SECOND worst thing you can do. This is because the worst thing you can do is forget to put oil in it. Sadly, that happens more often than you might think. It seems like a no-brainer to me, but many people get excited and forget to check the obvious. I always work from a mental check-list that includes DUMB things like install thermostat, hoses, belts, water, oil, gas, etc. If there is any chance that you might forget something like that, WRITE IT DOWN and CHECK IT OFF as you do it!
I use this same break-in procedure for any engine that hasn't been run in a while. The best thing you can do for any engine is make sure you splash good clean oil into all the places it needs to be.
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