Guest Nic-Rebel450CA Posted October 6, 2003 Share Posted October 6, 2003 I found a couple candidate crankshafts on ebay for my project engine. In the descriptions, they say the cranks are 10/10 or .010 under/mains .030. I am not familiar with crankshafts enough to know what these terms mean. I would assume it is some sort of rebuild or machining process. Can anyone explain? Here's the crank: It's a cast 283 crank. BTW, it is going to cost about $60 to ship, how much is this worth? I have read that cast cranks are better for high rpm than forged as they wear better. Dunno if I want to try for a JY crank. Quote Link to comment Share on other sites More sharing options...
blueovalz Posted October 6, 2003 Share Posted October 6, 2003 .010" or "ten under" means the journal(s) have been reground to be .010" smaller than the factory journal diameter to clean up the surface of the journal. This term is used separately for the rod journals and the main journals. Thus 10/10 meaning both the rod and main journals are cut .010". This then means that the bearings you use for this crank must now be .010 thicker to make up for the smaller journal's size. This is not uncommon for any used crank, but .030 under is quite a bit (IMHO). Quote Link to comment Share on other sites More sharing options...
Guest Nic-Rebel450CA Posted October 6, 2003 Share Posted October 6, 2003 Does that make it harder to get bearings for it? Does this in any way compromise the strength of the bottom end? Quote Link to comment Share on other sites More sharing options...
blueovalz Posted October 6, 2003 Share Posted October 6, 2003 10 and even 20 under bearings are common, but I don't know about 30 under. How this affects the strength is a bigger question. My thoughts on this are for a low to medium build motor this amount of reduction is insignificant. I do not know enough about the dynamics of cranks to give an informed opinion on the smaller journals. Smaller journals help reduce friction in high rpm applications, but also reduce the rigidity of that journal, so how should this be looked at? Grumpy is the first person that comes to mind on providing valuable insight into this issue. Quote Link to comment Share on other sites More sharing options...
Guest Nic-Rebel450CA Posted October 6, 2003 Share Posted October 6, 2003 Ok, thanks, I'll holler at Grumpy. Based on what you have said I will probably just stick with the 10 under cranks. Sounds kind of like looking for blocks that have been bored. You just dont want too much work done to it from being too used. The one in the pic is 10 under, the one that said 30 was just pulled from someone's engine and looked like it still even had some oil on it Quote Link to comment Share on other sites More sharing options...
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