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Cat Man
Cat Man, Caterpillar Engine Expert
Category: Heavy Equipment
Satisfied Customers: 8870
Experience:  23 Years Caterpillar Engine experience.
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Recently rebuilt..12 CAT and NO#4 cylinder piston skirt broke appart

Customer Question

recently rebuilt a C-12 CAT and NO#4 cylinder piston skirt broke appart and proceeded to bust out the liner. Why? Defective part??
Submitted: 6 years ago.
Category: Heavy Equipment
Expert:  Cat Man replied 6 years ago.
Hi. Thanks for using JA! I will try and help you out.

Yes. I have seen this many times. The skirt suffers a fatique fracture and breaks right at the wrist pin. Its a known problem on C12 engines.

How long did it take to break after the rebuild?
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Customer: replied 6 years ago.

Driver states the engine ran great. Hauling ~50,000lbs up big hills and only dropping down one gear. Engine worked for a little over a week until he was proceeding down a hill when it broke appart. I had no problems asssembling the engine. All went togeather smoothly. I had .0015 liner heights (spec's .001-.007").

Expert:  Cat Man replied 6 years ago.
Thanks for the information.

Yeah I have seen them break like this before. The only other thing I would consider is since it broke while going down hill, I have seen drivers over speed the engine and cause a valve to hit a piston. Most of the time when this happens, there is valve to piston contact on all the cylinders. If you have signs of contact on all cylinders, the engine may have been oversped. If you do not, it is surely a defective piston skirt.