How to braze cast iron?

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Hi,This is the ring gear from a riding lawn mower engine.  It's what connects the starter motor to the flywheel.  It's cast iron.  I started to drill a 3/32 hole in it, and it made a powdery dust from the drilling, no shaving or chips.I have an O/A setup with "low fuming bare bronze" rods, and brazing flux.  The only thing I've brazed before is 2 pieces of re-bar, just to see how it worked.This is what I plan to do:1. Heat up several pounds of sand in an oven to about 350 degrees.2. Grind out a U shaped notch on both sides of the gear.  Each notch will be about 1/3 the total thickness of the gear.  Then clean all the surfaces thoroughly3. Place about half the hot sand on a tray, and put the gear on top of the sand.4. Use a torch to heat up the entire gear.  5. Braze both sides of the gear, then cover it with the other half of the sand, and put it back in the oven at 350 degrees.6. Let it slowly cool down, then grind it smooth.Is this going too far overboard with the preheating and postheating?  Or could I just simply put the 2 U shaped notches on both sides and then braze it, skipping the entire involvment of sand and my toaster oven?Any tips or advice is appreciated. Attached ImagesHH187Harris O/AInfrared thermometerHalf a dozen angle grinders
Reply:Ok please take some advise from an engine guy, DONT DO IT!! You have no idea what the material is, you have lost your fit to the flywheel, and you dont want to be around if it comes off. Go find a good flywheel, or a replacement ring gear and do it right.P.S. it looks like a PM part ( Powdered Metal ) so again.....dont mess with it.
Reply:Torching on top of sand isn't a good idea either.
Reply:You can skip pre/post heat on edges and ends. Treat this as welding ends, because of small cross section and the ability of the rest of the ring to expand and contract freely. Grind almost through leaving minimal material to hold in alignment. How much it goes oval will determine if it will work. What broke it? Did someone try to hammer it on cold? Heat the whole gear to 300-400 degrees and drop it on.After its on try to drive it off. If it does not move with moderate hammer blows it might work.Good luck.PeterPS- tigged some steel ones before and it worked, but never a cast one. I'd give it a try!
Reply:I'm with makoman, if you can get another 1 do so, if it is a fairly late model briggs or kohler or other popular engine it should be readily available used. I know dealers kill you on new replacement parts but that thing is already weakened , heating and cooling, refitting with no balance ++ 3600 RPM is a bad combination. You could get and backside or face full of schrappnell."Si Vis Pacem Para Bellum"Lincoln Idealarc 250 AC/DCMillermatic 251   Syncrowave 300   30A spoolgunLincoln MP210Hypertherm 45(2) LN 25(2) Lincoln Weldanpower 225 CV(4) SA200   1 short hood    SA250    SAM 400
Reply:Hi Paul your best bet rather than trying to repair the gear and take a later chance of it flying apart is to get a new gear. A good place to check for parts would be http://www.jackssmallengines.com/  they are cheaper than any dealer. Their site is well organized. If you have the Make of engine and serial number you'll have no problem locating a replacement part.Co-Own CNC shop:Miller :1251 plasma cutter, MaxStar 700 TIG/Stick, & XMT 456 Multiprocess Welder.&  2 Hypertherm HPR260's Plasma CutterSorry I had a bad stroke but now I am back.
Reply:i worked for CTI-Cryogenics in mansfeild maand no we did not freeze waltbut they had metololiagest the spellingis wrong but its a phd in metal and thebest is ni-44 filler to tig weld cast ironwe got it from Middlesex Gases Tech.
Reply:Well that's one guys opinion.....providing the part is actually cast iron. Many aren't nowdays, PM ring gears are real common, and any kind of welding or brazing attempt on them would be pointless. I'm all for saving parts, and work on a LOT of antiques.....but not something like this. Scrapyard, Ebay, all places to get a good used wheel. What engine is it off of? Maybe one of us has a spare even.
Reply:Can you braze the ring gear to the flywheel?  One of the whole points of brazing is that it takes the base material out of the question because you aren't melting the filler into the base.  I say go for it, it's  a freakin' lawnmower.  If it breaks down in the middle of your lawn what is the worst that happens?  The neighbors call the home owner's organization to report a derelict lawn mower?  If the gear does scatter the thing has a bellhousing, right?  That should contain the pieces.For the subject of preheat and cooling.  You're getting a little too complicated.  Preheat and postheat are for constrained parts that will create internal stresses as they shrink away form the parts that weren't heated.  The ring gear you pictured is flexible in all directions the braze could pull the part.  It's not going to fail during cooling.  Don't even worry about preheat or postheat.Let me say one more thing about cast iron welding.  Cast iron welding causes cracks.  There are many techniques you can use to reduce the size and number of cracks that form like nickel fillers, preheat/postheat, peening, etc...  A successful cast iron weld is basically a weld that has few enough or small enough cracks that they don't compromise the strength or function of the repaired part.  Brazing on the other hand fuses the parts without getting too involved with the metullurgy.  Brazing is usually the best repair method.  Welding should only be performed if the wear resistance or heat resistance of the braze are in question.Last edited by 76GMC1500; 03-18-2010 at 02:56 AM.
Reply:I've seen these things fixed A LOT at a Golf Course that I used to work at when I was younger.  Those OLDER Style mower's and such had REALLY weird parts in them and those guys were always brazing parts back to life.Considering it's a 'riding mower' I think you'd likely be fine, even if that thing let's go, but assuming it does, what other damage might occur?  I suppose that's how you'll guage whether or not you want to take that risk...Personally, I'd BRAZE the sucker and see what happens (I just wouldn't be cutting around the Neighbors Kids !! .  Just eliminate about 95% of the flux crap that's on the LFB rod and use White Handy Flux instead.  I find that REALLY helps it flow better onto porous metal and is nowhere near as sticky as that crap that they put on the rods.  Also, you'll find that when you Grind down a 'Braze' using 'GOOD FLUX' you'll notice that there are no pinholes!Cheers,/J...Miller Diversion 165120 amp Buzz BoxVictor Oxy/Ace Oxy/LPGSmith "Little" Oxy/LPGHypertherm Powermax 30Lot's of Misc. tools n' crap....
Reply:I go with makoman on this one.  It's not cast iron, but powdered metal.  Think about the manufacturing process . . . a casting would be a very expensive way to make this part.  Ring gears will be powdered metal or machined from tubing, with individual gears sliced off after the teeth are cut.  Jim
Reply:I looked for a replacement part at various online sites (including Jackssmallengines and Ebay).  They are around $154 plus shipping.  This is for a new flywheel and ring gear.  The individual ring gear is not available by itself, I'd have to buy the flywheel too.  It's a Kohler 22hp v-twin.  It was manufactured in May of 2007 with a 2 year warranty.  I've contacted Kohler and am waiting on their reply.4sfed, I can see how this gear would have come from a tube.  First they would cut out the gaps for all the teeth, then cut off each individual gear from the length of tubing.The only time this part would be stressed is when I'm starting it.  I do realize that there is centrifugal force on this gear when the engine is running, but it's probably a much smaller for than what it experiences when starting the engine.  If I try to braze it and it fails, the gear will probably just slip off the flywheel.  The whole flywheel assembly is in a shroud, so I'm not too worried about shrapnel.HH187Harris O/AInfrared thermometerHalf a dozen angle grinders
Reply:Originally Posted by paulinkansasI looked for a replacement part at various online sites (including Jackssmallengines and Ebay).  They are around $154 plus shipping.  This is for a new flywheel and ring gear.  The individual ring gear is not available by itself, I'd have to buy the flywheel too.  It's a Kohler 22hp v-twin.  It was manufactured in May of 2007 with a 2 year warranty.  I've contacted Kohler and am waiting on their reply.4sfed, I can see how this gear would have come from a tube.  First they would cut out the gaps for all the teeth, then cut off each individual gear from the length of tubing.The only time this part would be stressed is when I'm starting it.  I do realize that there is centrifugal force on this gear when the engine is running, but it's probably a much smaller for than what it experiences when starting the engine.  If I try to braze it and it fails, the gear will probably just slip off the flywheel.  The whole flywheel assembly is in a shroud, so I'm not too worried about shrapnel.
Reply:Im with jman id braze er up too. Once you have wagered the possibility of it piling up on you. As far as the actual repair your method sounds fairly good. If it is infact cast iron. Use a 1/3 2/3 rule if you can get to both sides when repairing grey cast. And lots of preheat. Pean about every 2-3" to control the cooling rate of the weld. You should be able to tell what kind of cast it is by doing a simple grind test. If the sparks burst close to the wheel and are a orange colour as opposed to yellow, chances are its grey cast. Also when done with the braze you can put it in the oven for a bit and slow cool it, once you pull it out I would wrap it in some pink insulation and keep it in a warm area for a day. If you have access to a welder then 7018 is the best rod to use for high carbon stuff but keep the part HOT, like a dull red.
Reply:Well, I've emailed Kohler from their website last week.  Haven't heard back from them yet.  Now I've mailed them a letter via the post office with several pictures of the broken part.  I'll let you know what they say.HH187Harris O/AInfrared thermometerHalf a dozen angle grinders
Reply:A month has gone by since I sent the lettor off to Kohler.  Haven't heard a thing from them.  So after a week I tried brazing (my first attempt at something like this).  I grinded out a U shaped portion, with the crack in the middle of the U.  Then I heated up the whole gear and brazed it.  Then I grinded away the excess and tried to put it back on the flywheel.  It no fitty.  So I heated up the gear again, and it dropped right on.  I've put about 10 hours on the mower since fixing it.  No problems yet.HH187Harris O/AInfrared thermometerHalf a dozen angle grinders
Reply:The ring gear broke again last week.  The repair lasted about a year.  It broke into 3 pieces.  One break was where I brazed it.  I have found that Kohler does not sell the ring gear as an individual unit, but only as a complete assembled flywheel.I have found a source of just the ring gear for about $25.  It's from websites where people competitively race riding lawnmowers.HH187Harris O/AInfrared thermometerHalf a dozen angle grinders
Reply:Originally Posted by paulinkansasThe ring gear broke again last week.  The repair lasted about a year.  It broke into 3 pieces.  One break was where I brazed it.  I have found that Kohler does not sell the ring gear as an individual unit, but only as a complete assembled flywheel.I have found a source of just the ring gear for about $25.  It's from websites where people competitively race riding lawnmowers.
Reply:Originally Posted by Scott Youngdo you have the address?
Reply:thanks
Reply:Here is what you don't want on a flywheel. I know this isn't part of the orig posters question but good to keep in your mind of what could happen...Bobhttp://gardentractorpullingtips.com/...e/flybreak.htmBob WrightSalem, Ohio  Birthplace of the Silver & Deming Drillhttp://groups.yahoo.com/group/southbend10k/http://groups.yahoo.com/group/sawking/1999 Miller MM185 w/ Miller 185 Spoolmate spoolgun
Reply:We have welded up old cast iron motorcycle heads be preheating and welding on top of a gas stove and a/o welding with cast rods or piston rings when we couldn't get rod. For cool down we would put it in a warm bucket of vermiculite and cover with some more and let it cool real slow.