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Discussion and questions related to the course Practical Engine Building
I disassembling old 3S-GTE (4cyl old toyota 2.0 turbo-engine 86mm*86mm) from ST215 (gen4) and found interesting(for me :) ) "half" wear pattern. Its bearing from conrod cap. Thickness measurements says that difference between "light" and "dark" halves is 3-5 microns. So it looks ok. But I still not sure. I'm going to re-use this block and crankshaft. Should I pay special attention to something because of this non-symmetrical wear pattern?
(engine was working, but all piston ring-lands are broken ))) ).
That could occur if the rods bores weren't parallel (ie, bent rod), or the crankshaft machining wasn't parallel (bent crankshaft)? Perhaps you could have your machinist check that, if they can't measure it, they might just install a bushing in the small end and re-bore the big end of the rods.
As David said, it may be due to a slightly bent connecting rod - the broken ring lands also point towards that as they usually fail due to excessive cylinder pressures, which can bend rods.
Two other possible causes could be...
A small piece of dirt/debris between the rod and the shell - the amount of large debris bits embedded in the bearing, without any 'trail' leading to them, strongly suggests the engine was assembled with little concern for cleanliness. Have a good close look at the back of the shell and the connecting rod for indications of something having been trapped between them.
The cylinder(s) being slightly off true - I understand Pontiac had a batch of V6 engines, back in the day, that had bearing problems caused by an incorrectly set boring machine on one bank.