Anywho, me and some other classmates were ripping my engine apart at school for an assignment, and while putting it back together, we put in one connecting rod / piston assembly and forgot to watch where the end was going. Of course the stud on the end of the connecting rod was touching the crank journal and when we tapped in the piston it dented the journal up a bit. I asked my instructor what I could do to solve this dilemna, and he said to lightly file down the high spots of the dings, and it should be alright. I don't know if I trust him on this one or not. I know crankshaft journal clearances are tight, and will the low spots of the ding have any adverse affects if I assemble it again? Will filing the high spots off be alright? Or should I go for a new crank to be safe. I don't have much money to buy a new crank with, but then again I don't want to assemble the motor and get it back in the car and have it seize up on me. Any thoughts?

 

A file would not be my first choice, but the idea is right. The area can be stoned flat to knock down the high spots), then washed and lightly polished. If the ding is at or near the center of a bearing shell, it should make almost no difference. Full grooved bearings don't make 100% contanct, so one little valley holding extra oil is not going to be a serious problem so long as the engine and oil remain clean. It debris is allowed to settle into a pocket in a journal, it could be a disaster for the crank.

 

this is why you put vacuum hoses over the studs

crappy

 

Yeah the ding is pretty small and near the center. Why use a stone versus a file (curiosity).

 

The crank is case hardened, there's a good chance it's harder than the file actually. But I think mostly because the file is big and clumsy and... well, clumsy. A stone would be a bit more delicate. If it's a small ding, just try to polish it out with 400grit wet, you don't want to scratch the crap out of it with a grinding rock.

 

yea, i would try and get in there with some pretty fine sand paper (preferrably wet too) and see if you cant smoothen it up a bit.

As long as their is nothing sticking up you wont have to worry about it chewing up the bearing!

 

Awesome guys, thats what I needed to hear. Thanks so much!

 

The reason to use a stone is to assure that the "ding" is flush with the surface. If it is above the surface, no matter how much you polish, you're going to groove or spin a new bearing. India stones can be found in very fine grits.

Once it's stoned flat, polish with whatever you like - So long as it isn't aluminum oxide sandpaper. The abrasive (aluminum oxide) is harder than even a forged steel crank, and can embed small particles in the surface of the metal. That's not going to be very friendly toward your new bearings, either. Flint paper or crocus cloth for the final polish is good, since the abrasive is relatively soft.

Oh - And as Randy suggested, next time you should use rod bolt condoms.

 

For whatever it's worth, pg 3 of this article has some good info on the surface hardening that crankshafts are subjected to... (You'll want to be careful that you don't get carried away with the abrasive...!)