The part came back ...

Because it cracked on the weld when the guy tried to drive a ball bearing
back into it's recess . It's obvious that the weld material mixed with the
base metal , when it broke it took part of the base metal with it , leaving
a crystalline-looking surface . Weld is very brittle , not at all like
aluminum should be . I used 5356 the first time , but I also have 4043 on
hand . I've considered buying some of that low-temp aluminum brazing rod to
redo this ... this part is apparently difficult to replace , I've been
looking around on the web and get conflicting data - some say it's the same
, some differ .
This is the outer right side crankcase cover on a 1987 CBR125R dirt bike .
Reply to
Snag
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The casting alloy is usually pretty high in silicon. I have had crankcase successfully TIG welded (by pros, not me!). I will try to find out what filler they used. For the record, the CR125 is a tuned 2 stroke single cyl motocrosser. Parts are still pretty common for even older models like that, certainly in Europe. The CBR125 (4 stroke single) is a modern 12bhp road bike. Bad luck on the return. It would probably have held up ok if he had preheated the casting and put the bearing in the freezer before pressing it in. JB
Reply to
JB
Not a total loss for me , I found him another case . I'm not going to make much on this , but I'll have a satisfied customer . The money will come later ... it's a small town . Found out his wife works where mine does , just a different department . Point being that he'll say Good Things , and it gets around - it IS a small town !
Reply to
Snag
One problem with welding something like that is it might distort the casting and make the bearing recess inaccurate and require subsequent machining. Some years back I repaired a stone saw that had a weld repair which had done that and led to the saw binding at the extremes of travel. The saw had cast aluminium end plates which supported 3 50mm chromed ground bars and the saw head had 6 recirculating linear ball units, 2 for each bar, head travel was 2.5m IIRC. The users had abused the saw resulting in the castings cracking and they had it welded but that pulled the bores from their correct location resulting in it binding near the end of travel. In the end I ditched the castings and machined new bar supports out of aluminium and made new supports for the bar supports in steel, the original was all one casting. Worked great except the owner didn't want to pay for new 50mm bars and so the seals running on the old bars wore rapidly and knackered the new expensive linear bearings.
Reply to
David Billington
Ive had clients do the exact same thing. They paid more in return service calls than if they had spent a few bucks up front.
Thank the God$ for stupid customer$!!
Reply to
Gunner Asch
Great philosophy. This is what will give you a good rep as you say.
JB
Reply to
JB
4043 is far better than 5356 for castings, but 4047 is even better than 4043, if you can find it.
Reply to
Ernie Leimkuhler
I was hoping you'd chime in on this . Is the brittleness caused by the rod selection I made ? Lesson learned , and all it cost me was a bit of profit but I still have the customer's good will . Profits are a-comin' down the road , I can smell 'em , yes I can !
Reply to
Snag's Shop
The rules of welding castings.
1. Clean clean clean.
2. Grind out the crack to a V-groove so you don't have to melt a lot of the base metal. Use carbide die grinders to prevent contaminating the groove with grinding wheel grit.
3. Pre-heat to prevent an uneven heating of the casting. A minimum of 500 degF, but you can go up to 800 deF. Heating can be done a in a kitchen oven, using propane weed burners or over large propane stove burners. I often use the burners for commercial Woks.
4. Weld with the minimal amount of heat possible to flow the filler metal onto the surface of the base metal, while melting as little as possible of the base metal.
5. Slow cool by burying in an insulating material such as vermiculite, powdered lime or ash. Alternatively you can wrap it up in welding blankets of place in an oven and slowly reduce the heat.
These rules apply to cast iron, aluminum and bronze.
Addenda: For cast iron you can gas weld using cast iron filler rods, or TIG weld with a Nickel rod.
Aluminum castings are porous so you may have to grind out and reweld until contamination stops boiling out of the aluminum. This mostly applies to engine parts.
For bronze you have to keep your heat down or you will cook the alloying metals out of the mix and will have weld areas that are mostly copper and therefore a redder color.
Reply to
Ernie Leimkuhler

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