Quote:
Originally Posted by nkaminar
The Model T engines were indeed "burned in." The engine was assembled with the main bearings so tight that the crankshaft could not be turned by hand. The engine was mounted on the burn in machine up side down and oil was applied by an oil can to the main bearings. The crankshaft was turned over with a large electric motor until the bearings were literally so hot that the oil was smoking. When the bearings cooled down the babbett was fitted to the crankshaft with the right clearance. The rod bearings and the rest of the engine was fitted during the breakin period.
In my experience, the bearings will tighten up when hot and when cool again will have the correct clearance. For my newly rebuilt Model T engine, I could not crank it if I stalled it when hot. I had to wait until it cooled off. These were babbett bearings. I am not sure if the same thing is true of insert bearings.
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This is a sign of poor engine machining where the journal pin is not truly round, -and/or has taper from a plunge grinding with a worn machine. Often times, engine rebuilders will assemble an engine tight like you are describing with the hopes that it will clearance itself.