| Motor guys, check out these rod bearings |
Subject: Motor guys, check out these rod bearings by Josh on 2008/11/24 5:14:21 Well, I lost my motor last Wednesday on the dyno. Right now I'm in the midst of the autopsy and I am a little stumped, so I thought I would ask you guys. The story is as follows: 81K L98, stock bottom end. Mild mods for 80K of it's life, 100-150 HP shot of nitrous for the last 20K of it's life. I recently added a converted LT1 intake, cam, and heads. I drove the car around for about 2 weeks, made some drag strip passes, and was having a pretty good time with everything. During this span I put about 1,000 miles on the car. I finally got some free time to put the car on the dyno and dial in the tune last Wednesday. I don't know that this is relevant, but that morning I switched from conventional oil to synthetic. After the oil change, I drove the car 20 miles to the dyno and strapped it down. Everything was going fine, tune was coming along, power was starting to come up, and then... On the 12th pull on the dyno, at an indicated 6,000 RPM (which was probably more like 5700 or so because of the lazy factory tach) there was a metallic 'TINK' sound. The check gauges light came on immediately, and the oil pressure went to zero. I shut the engine off immediately. I put the car on the trailer and towed it home. Once it was in my garage I cranked the key to see what would happen. The engine fired normally, idled smooth, and had good oil pressure. Unfortunately, there was a pretty loud knocking noise coming from the bottom end. I pulled the valve covers just to make sure I hadn't lost a rocker, cranked it up again, and was able to verify that the knocking noise was coming from the bottom of the engine. Again, idle was smooth, and the engine made 50-60 PSI of oil pressure. Figuring that I had spun a rod bearing, broke a rod bolt, or something along those lines; I took the pan off tonight and pulled the caps off the rods. The bearings look abused, but none of them appear to have spun. The crank looks great on all the rod journals, and I'm a little stumped as to what was causing the knocking noise. I don't have any experience diagnosing a failure based on what the rod bearings look like, so I was hoping some of you guys that had been around the block a few times could chime in. It looks to me like the bearings starved for oil at some point, but other than that I can't make much sense of it. Here's some pictures of the bearings: |
