Today I am going to talk to you about the importance of getting the torque correct when assembling engines. This particular engine is a remanufactured engine that was in a truck that failed prematurely because the connecting rod bolts were torqued incorrectly which caused a catastrophic failure.
Everything has to be torqued correctly or you will have this type of failure. It is probably the single most important thing, especially on these modern engines that are built to such tight tolerance. My mechanics get grilled pretty hard on torque specs. The torque specs for these engines are posted on the wall next to their work stations so that they do it correctly every single time.
This was a remanufactured engine by a fairly reputable rebuilder. You can see that the cap on the number 6 connecting rod came loose and literally snapped the bolts off. We took a standard torque wrench and checked these bolts (suppose to be torqued to 50 foot-pounds). What we do is turn the wrench up to between 60-100 foot-pounds and see if the bolt will turn at a higher torque. If it turns at a higher torque then you know that it was torqued to less than that. On these bolts, we turned this torque wrench all the way up to 100 and still couldn’t get these bolts to budge.
The reason why this happened is because of the procedures in which they use to build these engines. They use what is called a DC machine. Basically it takes these fasteners and turns them a specific number of turns. It is actually more accurate than torque in some ways. I think what happened in this case is the builder had already tightened down these rod bolts and then went to lunch or got distracted and then turned them again. There was well over 100 foot-pounds of torque on every one of these fasteners.
Unfortunately there is nothing left in this motor that is usable. The crank and motor are trashed. The one connecting rod is trashed and I wouldn’t trust the other seven connecting rods. It came out and damaged the block over here so the block is ruined. I am not one to re-use pistons. The heads are still good but they are not o-ringed. They are going have to go get rebuilt.
This motor is trashed because a very simple thing in the procedures of building the engine – not torquing the fasteners correctly. Torque the fasteners correctly and these engines will live a long time. I have seen this many times, just not paying attention to the very basic details of engine building. If you don’t know what you are doing, this is not the place to learn. These are not the engines to learn on. The parts are expensive and everything is so difficult that you will pay to learn these procedures. Of course, a reputable engine builder has no excuse except to make it right with the customer. ~Bill Hewitt