Grease Me Up Scotty?
To grease or not to grease? That is the question! We will discuss the proper way to install rod or main bearings. This seems pretty straight forward but you would be amazed at how many calls I have received concerning just this.
First off, your going to attempt your first engine rebuild. You carefully unpack all your rod and main bearings, being extra careful not to scratch or ding any of them, right? You carefully clean them all off, getting the cardboard lint and whatever rust preventive goo off that the manufacturer so thoughtfully left behind for you, right? You carefully clean your rod and piston off and carefully oil the wrist pin good, right? Now it's time to install the bearing shells. You carefully pick them up, being extra careful again not to scratch them. You want everything to be lubed really, really good so as to prevent any metal to metal contact, right? So you now look at the rod and squirt oil in the bearing saddle and carefully rub it around so that every square millimeter of rod bearing saddle is coated with oil, you know, to prevent metal to metal contact. Now you figure, oh, I might as well smear some oil on the back of the bearing also. Couldn't hurt, right? Now you carefully line up the bearing tang with the slot in the rod and push the bearing into the saddle and rocking it back and forth to make sure it is fully seating in the rod. Oooooh, that feels real good and that bearing is never going to wear out, right? Now you carefully install the piston in the cylinder, of course with rod bolt booties on the rod bolts, you carefully tap the piston down the hole until the rod gently seats on the crank. You carefully remove the booties and slip the rod cap on, oh what a nice job you have done so far and boy how proud you are of yourself, 'cause after all, this is your first engine rebuild, right? You gently lube the rods nuts and screw them on, being extra carefully to screw them evenly. Now you get out your trusty torque wrench you just bought and ever so carefully torque the nuts down. Oh, what a superb job you did, and it's your first time too! Now for the ultimate satisfaction, you slip your socket over the snout of your crank and give it a gentle turn. What the H@*#! You turn it harder but something is seriously wrong. You start to panic as you try to turn your crank harder and harder! Finally the feeling of total failure sinks deep into your gut as you realize that no matter how hard you try, you just can't turn your crank. Where did I go wrong? That question enters you brain along with "My machinist must have machined this part wrong!" Yeah, that's it, the machinist screwed up! You now start getting madder and madder thinking of all those nasty things your going to say to your machinist come Monday morning! I'm going to give him a piece of my mind, yeah that's it, he's going to wish he never met me!
Yeah, your right, the machinist is to blame. That idiot really screwed you over, didn't he? WRONG! Fact is, you made the mistake of oiling the rod and the back side of the bearing before you put the bearing in. The film of oil completely eliminates your bearing clearance and the bearing becomes locked up on the crank! But the rod and bearing need to be lubed to prevent metal to metal contact, right? Wrong! Why do we want the bearing to spin in the rod? The last thing we want is the bearing moving in the rod or anything between the rod and the bearing. So you should always make sure the rod bearing saddle is absolutely clean and dry and free of any lint or debris. The tolarances are simply too tight for there to be anything in between. A spec of lint under a bearing shell will cause the bearing to wear out in that on spot. Clean and dry between the bearings and rod is what we want. Only lube the actual bearing face where it makes contact with the crank! Don't feel bad if this has happened to you because your not the only one and you won't be the last. We must learn from our mistakes and carry on.