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How to tell if my crank shaft is good


MrTJ

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Any simple tips on telling if a used crank shaft is in working order? I have an extra one that seems to be in good shape, but I don't really know for sure. The bearing all seem to work well and there isn't any vertical play, though there is some play on the rods when I move it left and right. Is this normal? I was just planning on selling it but I don't want to sell faulty stuff to someone.

  I bought it a few years ago used from someone and ended up just deciding to put in a new one instead. 

 

Thanks

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clamp it in a set of v blocks and check the center bearings.  most times if the cranks have been run for a while the inner bearings are loose.  just replacing the outers with  new i'm not to sure how well that works.  i have had some come through that the rods were fine but the main bearigns were loose as heck.  i just bought a "used rebuilt" 10 mill and the main bearings on it are toast.

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I can't remember the play that the clymers has within spec, but it was a lot more then you would think.

Side clearance of the rod to the web is 0.25-0.75 mm.  Vertical movement service limit of the small end of the connecting rod is 2.0 mm.  Assembly width is 53.95 mm - 54 mm of individual web sets.  Assembly width of both web sets is 155.90 mm - 156.05 mm.  Crankshaft run out is 0.05 mm.

 

SP

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  • 3 weeks later...

pretty sure you dicked that up, no way is the radial clearance 2 mm. you might have your side clearance and radial clearance switched around. 2mm between the side of the rod and the crank web maybe, even that sounds high. but then your .25-.75 mm value for the radial clearance seems high. thats 0.007"-0.029". typically the service limit for radial clearance on crank bearings is 0.003"

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pretty sure you dicked that up, no way is the radial clearance 2 mm. you might have your side clearance and radial clearance switched around. 2mm between the side of the rod and the crank web maybe, even that sounds high. but then your .25-.75 mm value for the radial clearance seems high. thats 0.007"-0.029". typically the service limit for radial clearance on crank bearings is 0.003"

Ya, I didn't dick it up.  I think you dicked up the interpretation.  But that's all good.  I never said the radial clearance of anything was 2mm.  I said the connecting rod small end free play was 2 mm at the service limit.  It is 0.36 mm to 0.98 mm new (0.014" - 0.038").  It isn't 2 mm connecting rod side clearance, it is .25.-.75 as stated which is actually 0.010" to 0.030" which you have pretty close.

 

Happy measuring!

 

SP

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