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I have an '86 gixxer750 whose chain, at some point, flew off and cracked the crankcase slightly near the clutch pushrod/sprocket area. I had it welded, but there were still two little holes about the size of a pencil point leaking oil. I patched them with JB weld, and they stopped leaking. My question is: If it is not leaking now, can I trust the that it won't leak in the future?
 

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yes should be fine for a while Its hasrd to repair engine and trans cases that are aluminum, as the alloy loves to collect dirt, most of the time the problem is when heat is applied the crack keeps going in the other directionas the heat and you end up with a three inch weld on a one inch crack it keeps cracking< I found that if you v-groove the en of the crack a little and start back a 1/2 inch and weld up to the crack and then do the same on the other side and complete the welds they seem to work better. Remember I have been a metalurgist for 9 years now.
 

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Thank you for the reply, 777. It's leaking already. I'm going to get it tig-welded tomorrow.
 

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Another thing is to preheat the area and it makes it alot easier to weld. Not to mention the hard part of welding cast pig metal like that. With all the crap in the cast to begin with, once you start to weld it, all of it come to the service making it a crappy leaking weld ( which sound like you found out already ).
 

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maybe preheat ferrus metal but not alloy as aluminum has a low melting temp you'd just melt through it and it makes a mess if you don't know what your doing, as its the hardest alloy to get penetration, it just does'nt want to fuse
aluminum repair cracks just run away from you so to speak.
as for the now leaking holes if you want to seal them you'e have to clean the cover of oil and anyother dirt and drill a hole right where the leak is comeing from use brass or copper on the back side to prevent it from penetrating through any more than you want. its used as a backing peice. and a heat dissipation method copper also works well ,as it pulls the exess heat to the brass or copper aluminum does'nt take heat well and becomes hot quick this will prevent it form happening some what. this is where the crack runs from is the heat spreading quickly
 

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Had an old Monte Carlo once that sat so long the oil pan rotted through!! Haa....held the oil in with JBweld and drove it for years after. The edges of the repair would eventually lift so I'd grind it down a little and put on another coat........then I'd be set for another year!!


Glad the chain didn't take out your leg!!
 

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no problem if ya ever got anything that has to do with metals just ask. I'm a fountain of useful info when it comes to metal working
 

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maybe preheat ferrus metal but not alloy as aluminum
Maybe I should have been a little more explanitory of the heat. But being a welder for close to 15 years, we had to preheat all our aluminum heads and engine componets to keep the temp in them, since your correct that it dissapates heat quickly. You would ruin a head just trying to jump right into a cold head and try to repair it. You would be pushing so much heat into a small area, that it would destroy that area before you could repair it. By preheating the head, the heat was already there , leaving you with little heat you had to add to the head to repair that area.

Glad to see you here, I am sure down the road I might have a few questions for you.
 

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I love jb weld, I havent had the chance to use it on a bike yet, I'm not too sure that I would but for a quick temp fix the stuffs hard to beat. You gotta let it cure though. I used it to fix the carb on 69 Ford F100 stakebed we had on our farm while growing up and I had a freind who fixed a busted front tooth with it and it held for the better part of a year. It turned black though. I heard a rumor that the guy did his own root canal with a dremel once too!
 

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any heat applied to metal is going to cause distortion if its such a little area. air can be used to keep the piece cool cooler is better on any metal.
 

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I think I know where your coming from. I believe distortion in the small thin part. But something large like a cylinder head, trying to get enough heat into the head to weld it doesnt work well , as the head dissapates heat so fast, you can get enough heat into the head to fix it. By preheating the head at 350 degrees keeps the head from distorting and allows you to get quick burst of heat into it to weld the area needing to be fixed. Even with some water pump covers, I used to preheat those and get beautiful welds on pretty thin pieces ( we re not talking coke can thick ). I ve found that quick short burst on and off the pedal with my tig when welding aluminum doesnt distort the material as much as guys that keep a constant flow of even heat into the part. I am open to new suggestions to try, so if you have input for me to try , feel free to fire away.

Thanks
 
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