Scratched Crank...

[Jeff Traikoff]

Putting together a completely redone 472, I put a small nick in the crank on the rod journal during a piston installation.  My machinist said all i can do is use a soft stone and some fine polishing, however that wont cut it for me i dont think.

My thoughts were to take it to another machinst and just make sure that there is no raised surface around the nick and if there is just machine it off?? Im a perfectionist so if this will have any negative effects on the on the rod or crank and cannot be resolved i will purchase another crank.

Im 19, so not used to these problems!  Thanks!

[Doug Houston]

This will depend on how hard you hit the crankshaft when you dented it. Since the crank is reasonbly hard, the ding is probably not very deep. The guys suggestion that you burnish it with a stone is good, and if you do it, youll see any raised lips on the dent, and the stone will grind them flush. Its worth a try.

[Bruce Reynolds # 18992]

Gday Jeff,

As Doug mentioned, you wont have dented it too much, and once you have removed the ever-so-slightly raised edges, you can also burnish the journal with a wrapping of 400 wetndry paper around the journal.

Actually, when the rotating mass is turning, the bearings dont touch the journal at any time as there is a layer of oil keeping everything apart.   Oil isnt just a lubricator.   It is a clearance-protector, coolant, and rubbish-removal medium.

The bearing shells are there to capture pieces of metal that might be floating around and retain them within the soft surface so they cant damage anything.

Looking under a microscope, you would be shocked as to just how rough the visually looking surfaces are.

Bruce,
The Tassie devil(le),
60 CDV

[Jeff Traikoff]

Well you guys are very reassuring... thank you for that as i am dumping most of my earnings into this car.  So as long as i get rid of those raised ridges i should be golden?  The only reservations I have about burnishing it are that I fear I make matters worse and mess up clearances around the damaged area :-(

[JIM CLC # 15000]

01-09-06
Jeff, It is VERY COMMON thing to do when assumbling an engine. I have an older Brother who rebuilt several engines and one of his tools of the trade was to always have a sheet of emery cloth, 400 or 600 grit, on hand to polish out the dings on a crank-shaft. Use motor-oil instead of water when useing either a stone or emery cloth. Wipe clean, often to check progress. I assume that the ding is near the center of the rod journey? Just take your time, and you will see where it is raised and how much you have to go. Just be sure to STOP when the Raised area is gone.
Good Luck, Jim

[Bruce Reynolds # 18992]

Jeff,

And, when you are finished burnishing, etc, make sure that all the oil galleries in the shaft are spotlessly clean.

Doing what we suggest and recommend is not going to affect the clearance tollerances, unless you attack the journal with a grinder, or something as silly.

If, as Jim mentioned, if the blemish is in the centre of the journal, then the bearings wont even touch the area, as it is a V8, and the Big Ends dont contact the full width of the journals.

All you need do is take off the sharp edges.

Bruce,
The Tassie Devil(le),
60 CDV.