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rod bearing confusion

6.9K views 14 replies 10 participants last post by  engineguy  
#1 ·
I posted question earlier about rod bearings and have a question.I currently have .010 bearings in my engine and my clearance is not enough.It is .010-.015 and im wanting to get at least .001 more clearance.I was thinking since I have a .010 turned crank I would want to go with a .011 bearing to get the more clearance.I had another person tell me I would need to go with the .009 bearing to get the extra clearance on my .010 crank..Need correct info if you can help..IN my mind Im thinking go with the .011 since its bigger which seems to me gives you more clearance.
 
#5 ·
By your reasoning a 30 over bearing would be way too loose. In actuality, it would be locked up tight. A crankshaft is turned down or made smaller to remedy damage or wear. That requires a thicker bearing to accommodate the material removed from the crankshaft. Polishing the crankshaft would benefit the clearance desired.
 
#12 ·
If the crankshaft journal is turned .010", a .009" bearing will give .001" MORE clearance and a .011" bearing will give .001" LESS clearance that the -10 (.010") bearing will. These bearing shells (.009", .010", .011") can be mixed to achieve .0005" more or less oil clearance on each journal. In this example, you can mix shells of .009" and .010" OR .011" and .010" shells to arrive at your desired vertical oil clearance, but never a .009" and .011" shell. Hope this makes sense.

Usually target oil clearance on crankshaft bearings is about .0018" to .0030" and exact clearance may be achieved by mixing one shell of one size with one shell of the next thicker, or thinner bearing shell - per above notation.
 
#15 ·
I think the OP was confused about his measurements. Hopefully he has gotten some help with the project . . . . . . . .