MikeM
Novice Class
Posts: 49
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posted October 13, 2002 07:04 AM
Crack in crank case: advice please?
Have found a small crack (10mm long) probably caused by very low speed spill in the following location; lower crankcase half, in the "pocket" area that the alternator rotor runs in, runs from behind the tapped lug for the alternator cover bolt imediately below the crankcase horizontal face at the front of the engine and runs vertically up to the split face, it is all outboard of the bearing journal and weeps a little oil. It has gone completely through the material and there has been slight displacement between the material either side of the crack (one side stands about .5mm proud of the other). Do you think it is posible to have it welded? Does the fact that there is not a gasket but sealant between the two crankcase halves mean that the mating faces are machines to tight tolerances? Or because is sealant used for its' gap filling properties meaning that any minor distortion caused by welding up the crack will have minimal impact?
If the crack can be welded, if I were to turn the engine upside down (with the top end intact) and remove the lower crankcase half would everything (crank, gearbox etc?) stay in place and make re-assembly easier?
I suppose that if welding is not possible then new crankcases are only sold as matched pairs?
  
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ra12r
Zone Head
Posts: 919
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posted October 13, 2002 07:29 AM
I would leave the motor together and weld the crack from the outside. Unless, you feel the crack is from something gone wrong internally.
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ZHooligan
Moderator
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Posts: 3829
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posted October 13, 2002 10:30 AM
I would check around for some experienced guys in your area. It is sinful in some peoples books to weld the case. But I have seen some amazing results. When we crash the RC51 at Daytona this year there was a little traveling machine shop in the pits. They welded up the damage (even the magnesium parts) and we were able to go back out for more practice. So it is worth checking into.
the trick is finding Magiver (sp?) in your area.
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krexken
Zone Head
Posts: 732
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posted October 13, 2002 02:09 PM
I doubt many welders would want to weld on it unless the cases were empty so they could get everything as clean as possible. ALuminum welding is very picky when it comes to being clean. I might would have to go with some black silicone smeared on the outside of the crack and live with it.
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ZHooligan
Moderator
Post Whore Extraordinaire!
Posts: 3829
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posted October 13, 2002 06:10 PM
Yeah the truth is I have had pretty good luck on my stuff in a pinch using JB weld and silicone. It might weep some but could work. Aloy has to do with what is happening in the engine on the other side of that spot. If use JB weld or something make certain you clean the heck out of it. One of the best cleaners I have found to remove everybit of the solvents etc. Even after carb or contact cleaner is starting fluid. It is cheap, evaporates right now and does not leave a residue. Stinks the hell out of the garage. Good luck.
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To those who do not count their life in years, but in how life
has touched them in the past and how much it can hold in the
future; -- Youth is forever.
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TedG
Moderator
Posts: 8222
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posted October 13, 2002 06:31 PM
It would be easy to weld, but the thing about being clean is correct. But you can remove the engine and remove the bottom case without doing anything to the top end. I would try the JB weld trick.
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VincentHill
Needs a life
Posts: 6520
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posted October 13, 2002 08:32 PM
Ecco Bond with Catalyst 11! The same expansion as aluminum and a serious rockwell hardness! Used it in the 2 stroke cases to reshape that bottom ends! A place in Mass sells it! If you weld it, it "MUST" Be assembled because you will never get it back in shape!
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OZZY
Needs a job
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Posts: 3172
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posted October 14, 2002 05:38 AM
Grind the crack out on a 45 degree bevel, just to the depth of the crack, and glue it with either Vincent's or Zh's suggested product.
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VincentHill
Needs a life
Posts: 6520
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posted October 14, 2002 06:37 AM
quote:
Grind the crack out on a 45 degree bevel, just to the depth of the crack, and glue it with either Vincent's or Zh's suggested product.
At lease 50% of the depth of the material and remove all paint and surface for about 1/2 inch around it! make the product you apply at least 1/8 to 3/16 inch thick (Under 1/4" thick or 6 MM! and 3/8 inch past the area everywhere! Follow the mixing and waiting (Curing) procedures)
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