I'm rebuilding my boys cr250 after the piston let go, and was wandering about the crank. Its a hotrods and has no up and down movement of the rod but seems to have quite a bit of side to side. Is there a measurement I can check for that?
How to tell when crank is bad
gandgracing
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I'm rebuilding my boys cr250 after the piston let go, and was wandering about the crank. Its a hotrods and has no up and down movement of the rod but seems to have quite a bit of side to side. Is there a measurement I can check for that?
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459 Posts
using a feeler gauge, push the rod toward each side of the crank, fitting the right size into the gap between the crankthrow and the washer between the rod and crankthrow, this size should be within the spec that should be in the service manual for that bike. out of spec will cause the piston to rotate farther than it should, creating the possibility of a ring end catching a port.
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13,288 Posts
Plus make sure you check for the crank half’s twisting. Set the crank between centers or “v” blocks and check run out at both ends of the crank. New cranks or re-built ones should read less than .002” total run out (+/-.001” each side of center). Most used cranks are out of spec from .003” to .006” or more total run out.
You can get away with .003”-.004” on the small bore engines, you cannot on the BB engines…
Carlos.
You can get away with .003”-.004” on the small bore engines, you cannot on the BB engines…
Carlos.
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