Honda CB750 Sandcast

crank and rod bearing sizes

Bigbilltoady

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What would be the least expensive way to size main and rod bearing sizes if the crank is not original to the cases and the rods are not original to the crank. I'm thinking to buy a pair of each size main bearing and plastigauge journals one at the time and same with the rods. That could easily mean 15 different set ups for the main journals (each journal done 3X, one with each bearing size) then the same with the rod journals. Would love to get a better idea. Thanks ( engine is 003xxx)


danyo

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Do you have access to 1" -2" micrometer? You can measure journals and pins on crank and go from there. Even if crank is not original, it should have markings , connecting rods and case also have marks. If you can find them its easy to determine what size of bearings you need unless your parts have significant wear. Of course you'll need plastigage all bearings to confirm oil clearance but I'm 99% sure if you select them according to markings, everything will be in spec. If you want get it done easier order Green bearings only. You'll find that most of them should provide you with oil clearance within wide range of Honda service limit. Please copy and paste link below to see how markings on sandcast crank look. Main journals are marked with japanese symbols (/\ and =) and crank pins with letters 3, 4. On picture you can recognize main journal #2 is marked /\, journal #3 is marked =, crank pin #2 is marked 4. Around engine #15500 Honda changed code system and moved it to side surface of the crank weight next to primary chain sprocket.   

https://drive.google.com/file/d/1RP0Xvfp3GeHksl94pBKz9Qvo6FHUYptK/view?usp=sharing