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Old 05-03-2017, 07:50 AM
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Default JB Weld (or similar) for case repair??

     

I picked up a cheap Yamaha Blaster with a title (rare for our area), and I'm planning on flipping it. I got it cheap knowing it was locked up and began tear down yesterday. It seems the wrist pin bearing went out and allowed the piston skirt to contact the crank and broke the piston skirt. Got the head off (may need to be replaced as it does have some deep gouges) and the cylinder (it is surprisingly in decent shape). Once I pulled the bottom end/cases out from the frame I found that something seems to have jammed below the crank and pushed into the cases. There are two cracks below the crank, one on each case half.
So, I began a little research to see if JB welding is an acceptable fix. What do y'all think? Anyone repaired a case this way? Most of the info I'm finding is for fixing cases that have been damaged by the chain. The way I see it, this part of the cases does not bear much load and it's primary function is to seal in the gas and oil mix to keep the crank lubricated. I'd appreciate input from anyone with experience (good or bad) doing a JB weld (or similar) repair on cases.
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Old 05-08-2017, 02:00 AM
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Never had any experience with JB welding works but would like to know if they can do it.
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Old 05-08-2017, 12:40 PM
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Would never use JB weld on that point of the cases because there is some pressure difference at the crank case chamber while the piston operates up and down to "push" the mixture at high speeds into the combustion chamber.

Proper fix for this is aluminium welding.
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Old 05-08-2017, 06:07 PM
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I have seen it work before on a cracked case. I wouldn't try to patch a hole with it. I would look for a used case before using jb weld. If you do use it, I would do the patch from the inside. The pressure that is built in the crankcase is pretty low.
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Old 05-08-2017, 08:18 PM
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Thanks for chiming in! The cases have cracks, not holes. I agree that welding is more appropriate, but I'm trying to keep the cost as low as possible while doing a worthwhile repair. As of now I'm waiting for an impact driver since Yamaha thought it was a good idea to put cases together with screws instead of bolts. Once I tear down completely I'll have a better assessment of the damage. I also need to take the cylinder over to a machine shop to measure the bore.
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Old 05-12-2017, 08:08 PM
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No problem if done right. As said before, I patch from the inside and outside. Lots of carb cleaner to remove any oil residue, and I hit it lightly with a torch and a small bristle wire brush. Had an oil pump gear punch a rogue bolt head through the case. Patched no problem and was a bit of a hole, and split to the mating surface. Working great. Just make sure you disclose the patch to any potential buyer.

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Old 05-16-2017, 08:38 AM
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I will be having to purchase some cases or part the bike out. I split the cases Saturday night and there were chunks taken out of several areas all around the crank cavity
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