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Problem with FP Diesel/Federal-Mogul 400 series rod bolts??


pirlbeck
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We are rebuilding a 986 D-436 engine and when we went to torque the rod bolts, once they started getting close to the final torque, they would snap, crack and jump. Everyone we tried would do this. This was with plenty of 30W engine oil being used for lube. We then tried the old rod bolts and they torqued normally.  We then purchased a new set of OEM rod bolts and they torqued just fine also. We did another 986 in March and the rod bolts came from the same engine parts distributor,  but I am not sure who supplied those bolts to the distributor, but they likely were FP Diesel too and we did not notice any problems with them.  The bolts would thread into the rods with fingers until they started to get tight and then the binding started, so it was not mis-cut threads.

My tech that does most of our engine rebuilds feels like something was wrong with the under side of the head causing them to have excess friction when they started to get tight.

Anyone ever seen this?

Thanks!

 

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Obviously the bolts shouldn't break, but I've had things like that happen before.  I did not think it felt right while torquing.  As it turned out, my torque wrench was either broken, or way out of calibration.  Sent it in for repairs and got it fixed.  Snap-On torque wrench, not a cheapie.  I get my clickers checked now and again after that incident.  Digitals are not supposed to require checking.... but I'm skeptical.  I've never had my digital checked but it still feels accurate. 

When was the last time you had your torque wrench checked?  

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Just to clarify, the bolts are not breaking, the cracking I mentioned refers to the noise they make while being torqued.

As far as the torque wrench being used, it is a fairly new Snap On Digital Tech/Angle. This is the style that keeps track of the rotation after the initial torque is reached for torque turn fasteners. The problem has NOTHING to do with the torque procudure or the tools we are using and is all about the cap screws being supplied by FP Diesel/Federal-Mogul.

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They didn't screw the hardness(Heat treat) up on a batch did they causing funky things to happen when under load(Stretch)?  I would think if their was a machining problem on the bottom of the bolt head a eye would catch it when compared to a known good one.  

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37 minutes ago, Missouri Mule said:

^^ my thoughts as well. 

From my screw machine and heat treat classes in College there is volumes to understand about fasteners, they are not as simple as they seem, and I know the knowledge I learned there is only the top of the ice berg that goes a long way under the water.

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And this is the reason on most of my builds I am still using stock rod bolts...if they torque up I send it.

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