I have a major prob. I built a 6 liter using a new std block from GM and the crank from my original motor (a 2002 5.3 with 20,000miles) The crank checked within spec, but I went ahead and had it turned 10/10 just so the clearances would be perfect. I used the rods and the Diamond pistons from my last 6 liter. I had it all balanced and put it together with Federal Mogul bearings. I have put about 9000 miles on it without any issues at all. I changed the oil about 300 miles ago and the magnet had a LOT of metal on it. Yesterday I was racing my buddy and it started missing and cutting out then the check engine light came on. Had a code 336 which is crank sensor. I checked the service manual and among other things it had me look at crankshaft endplay. Sure enough, I can grasp the crank pulley and push/pull the crank about 1/4" each way!! WTF? This thing was absolutely right when it was installed. Granted, it has had a hard life, but what would cause the thrust bearing to get wiped out so soon?

 

Well, several things. The most obvious is to find out if the crank end play was checked after assembly. It's very common to check the bearing tolerences, but forget to check the clearance on the thrust surface of the middle bearing. If you don't know for CERTAIN that it was checked, assume it wasn't.

Another cause could be excessive fore-aft movement from the tranny mainshaft or the driveshaft itself (initiated by throttle on/off, rough driving surfaces and the act of shifting gears. This alone will cause a severe shock to be transmitted to the crank. Couple it with a rearend housing will excessive rotation, and you could be beating the living hell out of the crank in the horizontal, longitudinal plane.

Dirt and debris from the rebuild could be a problem, was there any evidence of problem on any other bearings?

Good luck.

 

If I remember right, the converter is a possibility. If the converter is balloning out it is going to push on the crank. I have heard of this happening but have never seen it with my own eyes. The only thing I can really think of off the top of my head if everything is good inside. The charger has a bigger pulley on the crank right? That might do something also. Just things to look at I guess.

 

Yes a converter ballooning can cause excessive wear on the thrust bearing. A trans brake can too. Stick cars are hard on thrust bearings as well.

 

I agree, but I think we're looking at a failure or install related problem which the converter ballooning would be. Trans brakes and sticks are too, but shouldn't have caused this in 9,000 miles, you think?

 

Thanks for the suggestions so far guys. Yes the endplay was checked when it went together and it was within spec. Can a converter balloon out under acceleration and then go back into shape? If so that might be a possibility. I don't think the converter is permanently deformed because there is plenty of clearance between the flywheel and the converter when it is unbolted. The converter in question is now in my other truck-the truck with the endplay problem has a new trans and new converter that now have about 20 miles on them. I think this problem has been going on for a while because of the excess metal on the drain plug when I changed the oil back on 12-3-03. If the other converter is bad, then it is currently chewing up my 5.3 and that is all I need right now! I want to figure this out so it don't happen again. I haven't pulled anything yet and probably won't for a while, so we are just speculating for now.

 

If the converter ballooned it's not usable right now.