can i repair a hole in a crankcase?

1999 blaster

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Apr 19, 2011
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Parker, PA
there is a hole in my crankcase were the shift shaft goes in my chain hit it and knocked part of my case off with it i tried jb weld but i dont think its gonna work is there something easy i can do besides buy a new one because this case is BRAND NEW!!! and it was 200$ i really dont wannna go threw all that again!!
 
you can have it TIG welded back together, there's also another method of aluminum repair that has been outlined on the site by sicivicdude
 
jb weld will work if you layer it and let it cure completely..there are also other welding epoxies out there...msr racing makes a few,,one called quick steel and another called aluma-steel i believe..ive use both of those products during desert races and they worked very well..i once knocked a whole in my kfx440 case the size of my thumb and stuck a spare spark plug in it and used that quick steel to seal and glue it in ... let it dry and finished the race..good stuff
 
jb weld worked on my warrior when my chain broke and snapped a piece off. Then over the winter i broke it off and had it heily ark'ed bit pricy but on a brand new case it would be worth it.
 
Thanks guys for the kind words but I wouldn't describe it as "all the info".

Here is what I know... JB weld is a GREAT repair to get back out of the woods or to finish a race. You have to clean the cases very well but it can take to the aluminum and hold for a short period. It will eventually separate from the aluminum and begin to leak again. JB weld (or any of the other epoxy based "repairs") is only temporary.

Tig welding is an absolute repair method by melting the base metal and adding an alloy rod to build up over the crack and permanently repair it. Unfortuntely there are a few issues with this method... First, Tig welding requires argon sheath flow to keep the base aluminum from oxidizing as the plasma melts it into a weld pool. Aluminum is slightly porous and absorbs petro chemicals (particularly heavy oils such as 2 stroke oil and transmission fluid) and that oil must be baked out of the aluminum before a repair can be made. Second, the aluminum that yamaha used to cast the cases out of is particularly poor. It's an alloy blend which does not readily take the filler rod alloys without some coaxing. It can be made to take the tig weelding rod but only after some work. Third, the resulting weld is considerably harder than the base material. If the welder slips and catches the mating surfaces and hardens that area, lapping the cases may be inneffective in smoothing the case back for a good seal.

There is a third repair method which is equally as permanent as tig welding without some of the drawbacks of Tig welding (but with a few drawbacks of it's own of course). Aluminum "brazing" using an alloy rod and a moderate heat source (Mapp gas or oxy-fuel) to repair the base metal. The material is marketed under the names "alumiweld" and "duraweld" and many other marketing names. The material isn't aluminum but a proprietary alloy which will take to pretty much any non-ferrous metal.

It is extremely sensitive to heat and not cheap to use. It needs between 800°F and 1,000°F to bond properly with the aluminum. Anything under that temperature and it simply won't melt, anything above and the alloy oxidizes and balls up. The trick to the material is heat control. The final product is slightly harder than the case aluminum (marginally so) and slightly more brittle (again only slightly so) but it matches the color and strength well. Machining it is easy and it sands and burrs well once it's cooled down. It also responds well to sand paper.

The material is available at harbor freight under the name "alumiweld". The package contains 8 rods and costs $15. A similar material is also available at this website:

Aluminum Welding - Aluminum Repair - Aluminum Brazing - AluminumRepair.com

Of course they claim their product is better than the others... I will be able to quote about that this week (I ordered a pound of it for testing purposes) but I believe it probably works about the same as the other products...the only hiccup is that you have to order 1# (34 rods)at a time for $65 plus $15 shipping and handling. The alumiweld can be had for $15 (granted the price per rod is nearly the same but it doesn't require you purchase a huge pile you may never use)

Another trick with both materials is the "tinning" you have to do with it. There is no flux, you actually use the rod itself as "flux" by "rubbing" the rod with a wire brush to force it into the pores of the aluminum. Once some of the alloy has taken to the aluminum, the repair can be made by pooling some of the alloy up carefully heating the nearby metal so you don't burn the alloy.

I've had satisfactory results patching all but the largest of holes (king size sharpie marker sized hole between the crankcase and the balancer shaft area.
 
I would just be extremely leary of purchasing anything from you...

JB weld is a temporary solution to a serious problem if the leak/crack/hole is located in the transmission case or crankcase. I have JB welded a stator cover side case together before because the only thing that part of the case does it seal the flywheel and stator cover away from moisture. Other than that, epoxies don't have any business around blaster engines.
 
I would just be extremely leary of purchasing anything from you...

JB weld is a temporary solution to a serious problem if the leak/crack/hole is located in the transmission case or crankcase. I have JB welded a stator cover side case together before because the only thing that part of the case does it seal the flywheel and stator cover away from moisture. Other than that, epoxies don't have any business around blaster engines.

Not like he is trying to mend an axle back together. I agree that its not that great. But if he does not want to fix it the right way by replacing the case then he has two options welding the case or using JB weld. He has implied that he does not want to put any effort into fixing it so most likely he was going to JB weld it before he even asked us. It would work but probably not for long..
 
You wanna see how the aluminum brazing works? You're close enough to ride over while I'm using it and see how well it works.

Of course, the cases have to be split and all of the rubber pulled out before it can be done but it doesn't require a Tig welder and works well once you figure out how to use it. The brazing is a completely permanent solution versus something which is only going to continue to fail (and possibly take some more expensive out with it)
 
My package arrived from aluminumrepair.com last night. It was a tube with 38 1/2 (who in the heck knows how they figured up 1/2 stick length) sticks of shiny metal alloy, a stainless steel bristled wooden handled "toothbrush" and a DVD with the video off their website on it.

The instructions are simple and straightforward and should not be hard for most folks to follow (at least not the ones who can figure out how to mix fuel and oil at a specific ratio)

I'll be repairing a set of cracked cases I have sometime this weekend... it looks like a piece of a ring slid to a stop at the back of the crankcase (between the crank and transmission housing) and broke both sides out about 1/32" deep and each crack is about 1/2" long. I've already sanded the top layer of aluminum off, pushed the cracked pieces back together and burred a trough in the backside of the crack open so the material can pool inside of it.

I'll be tracking the progress with pictures again this time and posting in the other thread ("case repair"). wheresthericego, the offer still stands, if you'd like to come over and see how the brazing works you're more than welcome.
 
there is a hole in my crankcase were the shift shaft goes in my chain hit it and knocked part of my case off with it i tried jb weld but i dont think its gonna work is there something easy i can do besides buy a new one because this case is BRAND NEW!!! and it was 200$ i really dont wannna go threw all that again!!

Depending on the geometry of the hole there is also another option.
You can drill and tap for a cover plate.
Aluminum is soft and easy to thread.
Simply drill small holes using a tap drill and a drill stop to keep you from drilling into any internal parts.
Then thread the holes using a small tap. A 6-32 is perfect and cheap.
Shape a piece of aluminum sheet into a nice cover and drill corresponding holes through it.
Use screws that are just long enough to mount the cover but not too long to interfere with internal moving parts.
Cut a piece of soft silicone gasket material the same shape as your cover then simply use the screws to attach both pieces.
If you use a little artistic flair on your part it will look like an original part of the bike and not even be noticeable.