One bad dog Posted October 12, 2012 Share Posted October 12, 2012 What will cause a crankshaft to break that's two cranks broke in same place thanks Quote Link to comment Share on other sites More sharing options...
David Posted October 13, 2012 Share Posted October 13, 2012 When ever someone ask Dave George, the famous truck drive line re builder from Binghamton, NY, what caused something to break? His answer was always "material fatigue or operator abuse". 1 Quote Link to comment Share on other sites More sharing options...
staxx Posted October 13, 2012 Share Posted October 13, 2012 Crankshaft alingnment or vibration . Quote Link to comment Share on other sites More sharing options...
Lmackattack Posted October 13, 2012 Share Posted October 13, 2012 let me guess ....300 maxidyne and it broke either near the rear of the block or the nose where the damper is located? Quote Link to comment Share on other sites More sharing options...
One bad dog Posted October 13, 2012 Author Share Posted October 13, 2012 Yep 300 maxidyne Quote Link to comment Share on other sites More sharing options...
Lmackattack Posted October 13, 2012 Share Posted October 13, 2012 It was a known issue but it can be caused from Lugging the Engine a lot, Vibration, block not line bored correctly. I have seen a few bad cranks and all were in trucks that were used in good service for 15+ years. So who knows if its was just worn out or over stressed? If I recall some mack mechanics said to check the block for stress cracks near the back. I dont remember what year they updated the blocks for more stiffness but that was an issue as well.?I would line bore the crank journals or try to at least check to see if its true.hopefully a mack tech can chime in with more info. Quote Link to comment Share on other sites More sharing options...
staxx Posted October 13, 2012 Share Posted October 13, 2012 Could be a line bore issue main caps not true or straight , something out of balance this would include rods which come in differant weights defective damper, flywheel clutchnot bolted up correctly or flywheel housing not true to block and crank , cracks in block up around rear main caps , loose main caps or alot of lugging the engine will do this also. You will need to do a thorough inspection of componets to see what realy happened . Where did it break and is this a dump, highway , logg truck etc ? Quote Link to comment Share on other sites More sharing options...
One bad dog Posted October 13, 2012 Author Share Posted October 13, 2012 Right behind second main cap on throw same place as last time.i ran the truck years hauling dirt no problems started haul sugarcane and broke two cranks in the same place. Thanks Quote Link to comment Share on other sites More sharing options...
One bad dog Posted October 13, 2012 Author Share Posted October 13, 2012 Right behind second main cap on throw same place as last time.i ran the truck years hauling dirt no problems started haul sugarcane and broke two cranks in the same place. Thanks Quote Link to comment Share on other sites More sharing options...
staxx Posted October 13, 2012 Share Posted October 13, 2012 When you broke the first crank what other components did you change? Quote Link to comment Share on other sites More sharing options...
Maddog13407 Posted October 13, 2012 Share Posted October 13, 2012 237's and 300;s were known for that. have a 237 sittin in my yard right now with a broke crank. only reason its still sittin is someone canabolized it, stole the flywheel and oil pan and the turbo is wore out otherwise id probably put a crank it it. cant see it right now for a hobby truck Quote Link to comment Share on other sites More sharing options...
Maddog13407 Posted October 13, 2012 Share Posted October 13, 2012 gotta make sure you put a new balancer on with a new crank also. Quote Link to comment Share on other sites More sharing options...
One bad dog Posted October 14, 2012 Author Share Posted October 14, 2012 I had put a used crank and balancer Quote Link to comment Share on other sites More sharing options...
fjh Posted October 15, 2012 Share Posted October 15, 2012 I had put a used crank and balancerPUT A NEW BALANCER on it ! you aleady have a used one the balancer is likly the issue! the blocks rarely have issues unless the engine has been cranked up! then they tend to crack near the starter and you will find the main bolts in the pan! Quote Link to comment Share on other sites More sharing options...
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