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Sorry i missed your reply. To my knowledge big end bearings are usually the first one to go. Since the big end bearings were not in bad shape at all-no damage, no scorching etc.(we swaped them because to try to solve this issue), we didnt even check the mains in this case. Correct me if im wrong tho 🤔
depends on how the engine wears and is driven and if past owners ran out of oil at point,, ie the main heat up most when under loads ie low revs high load driving such as driving in wrong gear up hill, also many mini's were ran low on oil at some point and this over heats the main more than the big ends as such as the white metal coating or ptfe coatings get burnt off and melt and tend to destroy the crank shaft after this,, the tolerances in the bearing surfaces to crank are tiny 000.10mm clearance on a new engine common, honda engines go a step further all their engines are nearly hand built and the crank is micro metered on each journal and they have different mains sizes in each journal ie 000.5mm to 000.24mm depending on colour to ensure this clearance is as tight as can be,, reason they did this was on the Vtec engines that need high oil pressure to run the controller and also because its best way to make a engine,,, where prince engines are a cheap build done on price i would say, rule of thumb is if big ends have signs of oil starved you should treat the mains as being hurt as well,
 
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