Building up a key slot on a crank shaft

admin

Hello all,In the past I have been  a few times asked by mechanics to weld pulleys on crank shafts.  This is usually when the urgent task is to get the car running.  I will space a few short beads around the joint and off it goes.  I use a 7018 rod.In the steel mills this practice was pretty common as a breakdown in production caused a backup and equipment (gear boxes, pulleys, etc. needed to get back on line immediately. I was asked a few days ago to build up around a worn out key way for a woodruff key on a crank shaft for a Geo.  I was thinking about Tigging it using a Eutectic "Tigtectic" 680 rod that I have had for about the past 10 years or so.  This is an all purpose rod for joining dissimilar iron based metals to stainless in any combination or when the composition of the steel is unknown.  I thought to use this as it safely welds high carbon, stainless, etc.What do you think?  Can I get by with regular mild steel rod or go with the high alloy stuff?Thanks,Tony
Reply:I cant speak to what is the best filler rod, but in the vw scene I have seen many people dowel pin the crank pulley to keep the keyway from shearing (the key is a protrusion forged into the pulley itself not a woodruf key in the crank itself. Not sure if that could also be done in this situation. here is a random thread about ithttp://forums.vwvortex.com/showthread.php?1598023
Reply:I've never built up crankshafts, but a little trick that got us out of some jambs in the past with worn keys in steel shafts, I would make a "key" out of brass and tap it in the keyway with a hammer, then weld up the worn portion with the mig welder and remove the temp key and cut it down on the lathe. The brasswould let u build up the shaft and not stick to the brass key. Don't know if it will help you with this repair or not
Reply:I don't think your gonna like machining the 680 mixed with steel containing any carbon at all. The 680 is similar to 312SS with similar nickel to chrome ratio and much less iron. It work hardens like crazy.Tigging it hot with E70-s2 or gas welding will prolly be your best bet. You can get very high strength nickel/chrome/silicon brazing alloys but they can be hard to machine also.Good LuckMatt
Reply:Something that might work, Devcon metal filled epoxy.  Different types for different uses.  Machinable and extremely strong.  No worries about heat distortion or machinability.  http://www.devcon.com/products/produ...Metal%20Repair"The man of great wealth owes a peculiar obligation to the State, because he derives special advantages from the mere existence of government."  Teddy RooseveltAmerican by birth, Union by choice!  Boilermakers # 60America is a Union.
Reply:Hi all,thanks for your responses.  I will go with the mild steel rod and tig.  I like the copper dam approach to build up with.  It's similar to using carbon arc rods to act as a "wall" to dam in metal that you are building up.  I think my basic question was answered which was do I go with a high alloy rod or just use mild steel.  In the past I've always used mild steel for welding on shafts.  The key slot is a small part of the entire shaft and the little material I will use shouldn't compromise the hardness of the crank shaft.  At least I don't think so.I will check out that epoxy like stuff.  Interesting approach.Thanks,Tony
Reply:Crank in what engine? Cast (nodular iron)  or steel? Use a carbon arc gouge rod, grind a same shaped key out of carbon. TIG mild steel or ni99, push puddle against carbon. Chip out carbon and no machining required. Or grind deeper and wider than key way, weld shut with ni99 and machine. Kicker is 9 out of 10 times the diameter of shaft is worn from pulley "playing" on nose. All it takes is an extra thousandth or two and the pully will work loose again. So a lasting repair requires welding diameter of crank snout and remachining, plus new or good pulley.PeterEquipment:2  old paws2  eyes (that don't look so good)1  bad back
Reply:Originally Posted by castweld. . . Kicker is 9 out of 10 times the diameter of shaft is worn from pulley "playing" on nose. All it takes is an extra thousandth or two and the pulley will work loose again.  Peter
Reply:Hi again,dsThe crank is off of a Geo (GM).  The technique described are good and is more or less how I as going to do it.  Instead of machining it, I was just going to file it down with a fine file.Thanks,Tony