Sounds Fishy

I recently took my Dart out for a test drive, and the heater core started to leak, causing my engine to overheat. I was able to get it off of the road before any major damage happened, but now when I start it, the bearings rattle for a second or two, and the then it stops while idling. They rattle more when revving the engine up. I had a mechanic pull the pan, and he said the crankshaft (it is forged), has blue heat-marks on it, and that it should be replaced. This is a big hit to my budget. All the info I can get on the net is that blue marks are normal. Will it be ok to just replace the bearings and keep rolling with the same crankshaft?

James Conn

Via email

James, I can only go by what you are telling me, and that is that you got it off the road before any major damage occurred. To me, this means that it was shut down before getting really hot. If you got it hot to where it would do damage to the crankshaft, it had to be heated to the point of nearly seizing the pistons. At that point, the oil in the engine will have been so hot, that it would be bellowing smoke from the breathers due to overheated oil. This kind of heat can cause the oil film to break down and blue the journals, and if it is that hot, the bearings will be toast, and the rings will have also likely overheated and lost tension. You are not going to get that kind of damage if you didn’t get it really hot.

I would personally inspect the journals, and see the extent of the heat damage, along with the condition of the bearings. From there you can decide whether you really have blued the journals. If so, the bearings will normally be severely heat damaged, and you will have to decide if you are willing to try and patch things up with just a fresh set of bearings, or go in for a full freshen of the engine. The bottom line is this, if the journals really did get that hot, you will be wise to go for a tear down and rebuild.

Universal Worries

I have a ’72 Charger that originally had a 318 engine and a 904 transmission. I got a 440 out of a mid-’70s motor home, and built an engine with about 500 horsepower. The engine features flat top Probe pistons, H-beam rods, Edelbrock heads, a Comp hydraulic cam, and an Edelbrock RPM intake with a Holley 950 HP carburetor. I put in a 727, and an 83⁄4 rear. The thing that has me worried is that the driveshaft has the smaller 7260 U-joints. I know the big-block cars had the big 7290 joints, which I hear are much stronger. I already have a yoke for the larger joints in my junk pile, but I am worried about the rear. Even though it is the 83⁄4, it has the small yoke. It is a 489 case, which I understand uses a crush sleeve to set the pinion bearings. I am afraid to pull the yoke and mess up the gear set up. On the other hand, I am worried about spitting out the driveshaft. I never run the car on the strip, and only tear around the streets on 275 60R-15 tires. I was told on street tires I should have nothing to worry about, but I can’t help but want to upgrade.

Frank Malloy

Via moparmuscle.com

Frank, I would definitely feel better about the bigger joints, especially if you are regularly hammering on that heavy Charger. I would bite the bullet and upgrade the driveshaft if it was my car. In fact, I would also suggest replacing the crush sleeve in the centersection at the same time with a solid spacer and shim arrangement. Although this was not a stock arrangement with the 489 case, you can get a kit for this upgrade from rear end specialists such as Randy’s Ring and Pinion. Use a high quality U-joint and you should never have a problem with this setup on street tires. The solid spacer will help the rear sustain a much greater level of abuse without failure. mm


Got a technical question you need help with? Well, we’re the guys to ask. Send you technical questions to us via www.moparmusclemagazine.com, or send your questions to our Mopar Muscle email, mopar.muscle@sorc.com. If you’re old school, snail mail your info to Mopar Muscle Magazine C/O Performance Clinic, 9036 Brittany Way, Tampa, Florida, 33619