Possible causes for connecting rod failure?
10-07-2002, 11:35 AM
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Possible causes for connecting rod failure?
I had a rod fail on my boat this weekend on a 454 that only had 40 hours after a rebuild. Cranks was polished and rods were reconditioned by the machine shop with new hypereutectic pistons installed. Oil pressure has been a solid 40 lbs all season at any rpm over 3000. I have only spun the engine to 4700 rpm and followed a natural oil and the synthetic break in procedure. The engine was running great with oil temps in the 215 degree range and engine temps around 170. I haven't disected the motor yet and won't be able to for at least two weeks. Any input is greatly appreciated!!
10-07-2002, 11:40 AM
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Piston pin seizure is a common cause of connecting rod failure. It the rod bolts/nuts are still intact the pin probably seized in the piston bores. Of course, I run wood through a machine for a living so I could be all wet. 
Sorry to hear of your grief though.
Sorry to hear of your grief though.
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10-07-2002, 12:23 PM
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Like cord says, could be hydrolock. The last motor we had in the baja had the same thing. It had a bad riser gasket and got water in one of the cylinders. Didn't think nothing about it, Over the next 2 months it worked that rod where it was bent over and over again.. then finally 2 1/2 months later the rod let go at 3500 and made the same funny hole in the oil pan like yours 
The rod was broke right in the middle where it was bent from the hydro lock. just a thought.. I hate those little oil pan holes 
The rod was broke right in the middle where it was bent from the hydro lock. just a thought.. I hate those little oil pan holes
10-07-2002, 12:34 PM
#5
I had a rod break right where the flat was filed in for the rod bolt.
My hole in the pan was alot larger!! I believe it failed from over revving. It was also a small block 350. Sleeved block, got new rod, piston and crank and was back in biz.
Make sure when you disassemble engine that you take your time and look at everything very closely. Kind of treat it like a crime scene
Dave
My hole in the pan was alot larger!! I believe it failed from over revving. It was also a small block 350. Sleeved block, got new rod, piston and crank and was back in biz.
Make sure when you disassemble engine that you take your time and look at everything very closely. Kind of treat it like a crime scene
Dave
10-07-2002, 04:00 PM
#6
Geronimo36
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Rod Bolts
I hope your engine builder used new rod bolts? If he did, you need to torque them in a special proceedure to set them correctly.
The rod bolts if they were "used", got stretched and broke. Secondly if they were new, they could have been over torqued, or even under torqued.
Complete rod failure is also a possibility, which was already mentioned here.
The rod bolts if they were "used", got stretched and broke. Secondly if they were new, they could have been over torqued, or even under torqued.
Complete rod failure is also a possibility, which was already mentioned here.
10-08-2002, 06:18 PM
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Rod Bolt broke or don't rule out detonation.
Detonation can cause the bearing to spin and seize then break the rod.
Have you taken it apart yet?? If the bottom of the rod is OK the piston could of hydro locked or froze in bore. You need to check it out.
Detonation can cause the bearing to spin and seize then break the rod.
Have you taken it apart yet?? If the bottom of the rod is OK the piston could of hydro locked or froze in bore. You need to check it out.
10-09-2002, 09:56 AM
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Originally posted by Gearhead99
Rod Bolt broke or don't rule out detonation.
Detonation can cause the bearing to spin and seize then break the rod.
Have you taken it apart yet?? If the bottom of the rod is OK the piston could of hydro locked or froze in bore. You need to check it out.
Rod Bolt broke or don't rule out detonation.
Detonation can cause the bearing to spin and seize then break the rod.
Have you taken it apart yet?? If the bottom of the rod is OK the piston could of hydro locked or froze in bore. You need to check it out.
10-09-2002, 11:16 PM
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were the rods GM ? shot peened to reduce the chance of stress cracks? new bolts pressed in and not beat in with a hammer? 3/8 or 7/16th's bolts? what was the original hp of the engine so the type of rod can be determined? were they magnafluxed? pressed or floating pins and were they replaced? how long have you been dealing with that machine shop? i think they may have missed something.
