Weld or replace case? 2002 yz250

HardTaco
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2/12/2017 9:08pm
When the bottom end was done 45 hours ago the left case was apparently damaged. It's hard to tell from the picture but the bottom 1/3 of the oval around the crank seal is cracked and leaking. The crank is still tight as a tick, piston was even in very good shape. I can't find a good used left side case on ebay and my cost on new is 350.

Call me crazy but I thought about just removing the left side case, getting it welded by a bud who is experienced in welding aluminum, then popping in a new bearing and seal and calling it good. Anyone ever done this before? Any tips?


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FGR01
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Fantasy
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2/12/2017 9:14pm
I would trust it welded if it was done by a decent welder and sealed properly. Looks as if it would be stronger welded than original.

I wonder if having the extra flywheel weight hanging out there on the end of the crank could contribute to this ?
HardTaco
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2/12/2017 9:18pm
FGR01 wrote:
I would trust it welded if it was done by a decent welder and sealed properly. Looks as if it would be stronger welded than original...
I would trust it welded if it was done by a decent welder and sealed properly. Looks as if it would be stronger welded than original.

I wonder if having the extra flywheel weight hanging out there on the end of the crank could contribute to this ?
Improper bearing installation is the culprit here. But I did send my flywheel weight back to have lightened...lol.
BobPA
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2/12/2017 10:33pm
Welding it is an option for sure. I would split the cases, remove the crank and transmission. Then I would bolt the two crank halves back together and have your buddy weld it. The reason being is welding can cause objects to warp and deform.
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David934
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2/13/2017 1:51am
Since weld will be so long, im bit worried about the shape of the case.

The Shop

HardTaco
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2/13/2017 5:25am
BobPA wrote:
Welding it is an option for sure. I would split the cases, remove the crank and transmission. Then I would bolt the two crank halves back...
Welding it is an option for sure. I would split the cases, remove the crank and transmission. Then I would bolt the two crank halves back together and have your buddy weld it. The reason being is welding can cause objects to warp and deform.
Yeah I was thinking bolt the cases back together and leave the old bearing in to keep it from warping. I like it!
HardTaco
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2/13/2017 5:29am
David934 wrote:
Since weld will be so long, im bit worried about the shape of the case.
You think it will warp? I found this last night, so it seems to have been done. I guess it's only one way to find out...

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notme
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2/13/2017 10:22am
Id say go for it. Its been done before but you need to research it a bit more, its been a while but I recall someone telling me they preheat the cases before welding to help prevent distorting. Also a slow cool down after
bronwynrayne
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2/13/2017 10:56am Edited Date/Time 2/13/2017 10:58am
If you can get someone to weld it, make sure that they are proficient. Better to pay someone a little extra to have them prevent distortion, than have to replace the case.

If it is a relatively small crack (I assume it is because we can barely see it) then you shouldn't have much of an issue because it will be a single pass with a small bead. TIG will be able to fill it with a small piece of filler rod, and a stepped welding sequence will prevent any warping. It is a larger piece of metal so it shouldn't be noticeable unless your welder is careless with heat and rushes the cooling process. Patience is key.

Let us know how it goes!
HardTaco
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2/13/2017 12:52pm
Just spoke with my friend about it. He's the head fab guy at a 4wd/differential shop and has welded cases for me before on my 14 250F when the chain knocked a hole in it. He said it shouldnt be a problem and to leave the bearing in to be on the safe side. He then went on to explain how it would be fine without the bearing, because if you weld cast aluminum slow (apparently, deathly slow) and preheat like you are supposed to, it wouldn't warp in the first place. Im gonna get it torn down sometime this weekend and drop it off to him next week. Ill post pics when he gets it knocked out. Definitely gonna save me a pile of money!
sandman768
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2/13/2017 6:22pm
Same exact crack developed on my 2008 YZ 250. Mine was not from main bearing replacement,as bike had never been apart. We knew it had a wicked air leak, soon as you touched the throttle it would rev to the moon! We could not believe our eyes when we saw the crack! Around the whole circumference of the bearing pocket. Split cases, had it welded by a REALLY good welder, no issues at all, likely better than original....
HardTaco
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2/13/2017 6:35pm
sandman768 wrote:
Same exact crack developed on my 2008 YZ 250. Mine was not from main bearing replacement,as bike had never been apart. We knew it had a...
Same exact crack developed on my 2008 YZ 250. Mine was not from main bearing replacement,as bike had never been apart. We knew it had a wicked air leak, soon as you touched the throttle it would rev to the moon! We could not believe our eyes when we saw the crack! Around the whole circumference of the bearing pocket. Split cases, had it welded by a REALLY good welder, no issues at all, likely better than original....
Just for curiosity sake.... What crank and bearings were you running when yours developed the crack???
David934
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2/14/2017 12:19am
sandman768 wrote:
Same exact crack developed on my 2008 YZ 250. Mine was not from main bearing replacement,as bike had never been apart. We knew it had a...
Same exact crack developed on my 2008 YZ 250. Mine was not from main bearing replacement,as bike had never been apart. We knew it had a wicked air leak, soon as you touched the throttle it would rev to the moon! We could not believe our eyes when we saw the crack! Around the whole circumference of the bearing pocket. Split cases, had it welded by a REALLY good welder, no issues at all, likely better than original....
HardTaco wrote:
Just for curiosity sake.... What crank and bearings were you running when yours developed the crack???
i think no bearings issue
HardTaco
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2/14/2017 6:56am
sandman768 wrote:
Same exact crack developed on my 2008 YZ 250. Mine was not from main bearing replacement,as bike had never been apart. We knew it had a...
Same exact crack developed on my 2008 YZ 250. Mine was not from main bearing replacement,as bike had never been apart. We knew it had a wicked air leak, soon as you touched the throttle it would rev to the moon! We could not believe our eyes when we saw the crack! Around the whole circumference of the bearing pocket. Split cases, had it welded by a REALLY good welder, no issues at all, likely better than original....
HardTaco wrote:
Just for curiosity sake.... What crank and bearings were you running when yours developed the crack???
David934 wrote:
i think no bearings issue
huh?
sandman768
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2/14/2017 5:37pm
My engine was stock, never been apart until the case cracked. so.....my crank & bearings were stock, original, Yamaha parts. Yamaha makes really good cranks, no reason to use aftermarket cranks...
HardTaco
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2/14/2017 5:42pm
sandman768 wrote:
My engine was stock, never been apart until the case cracked. so.....my crank & bearings were stock, original, Yamaha parts. Yamaha makes really good cranks, no...
My engine was stock, never been apart until the case cracked. so.....my crank & bearings were stock, original, Yamaha parts. Yamaha makes really good cranks, no reason to use aftermarket cranks...
No shit. Wonder what causes it? Crazy failure for sure
sandman768
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2/14/2017 6:00pm
My bike had a good amount of hrs on it, but I have never seen a case crack like that. If I had to guess, I woukd say case needs more material around bearing pocket....I don't remember my crank bearings being excessively worn either.
2/15/2017 12:29am
Unbeknownst to me, my 02 YZ250 had a full circle weld repair on the left crankcase as pictured above when I purchased it a some years back. I did a full top end immediately after purchase, but did not pull the flywheel or split the cases as there was no play in the rod or crank... assumed I was good to go. Engine was tight after topend confirmed by my leakdown test. Within just a few hours of shaking the bike down I begin to chase jetting all day. Went home to do another leak down test.... failure.

Pulled the flywheel and saw the full circle weld, and it had failed. I have no idea how many hours were on that weld before I purchased it. But it failed in short order for me. Couple hundred hours on a used ebay case since then with fresh bearings and no problems. No idea what caused it for the previous owner or why the weld job failed. But fail it did for me at least.

I have since collected a few cases halves off ebay and craigslist. Nearly have all the parts for a second spare motor I hope to build to X specs. They do show up, but most good ones seem to go for $150-200+ these days. 99-01 will also work and seem to come up priced a little more reasonably (You just need to bore the swing arm bushing out slightly to accept the larger swing arm bolt. Plenty of material there to do it). I have a 99 left case on the motor currently installed. Personally, I'd be tempted to go new if you can get it for $350 over a $200 used one.

Good luck!
notme
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2/15/2017 11:27pm
Sounds like this is not a rare occurrence, i saw a circle weld like described above in a local shop. But i dont recall if it was a 125 or 250.
HardTaco
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2/16/2017 5:23am
Hopefully mine isn't totally compromised because I caught it before it became a complete failure. Waiting on new case splitter to come in the mail then I'm taking it to my guy and seeing what he can do.

Josh
2/5/2023 6:38am

You can see where it split in the case, might be a bad casting lodged piece of dirt 💩 or something else, that looks harder than the surrounding material. I wonder if they have pictures that they can match, the study of cracks Oh my God it's one of those cracks!! $$$$ it's going to cost you. 

I forget what we had in the material some stainless steel and we couldn't do anything like drilling and stuff, like what the heck is going on? And it was a bad run off the mill, had crap mixed in the there real hard stuff the drill bit just shattered against it, and the plasma cutter couldn't cut it, it was through the entire batch of it, all of it was garbage, it was suppose to be certified as well.

 

2/6/2023 4:27am Edited Date/Time 2/6/2023 10:18am
HardTaco wrote:
Hopefully mine isn't totally compromised because I caught it before it became a complete failure. Waiting on new case splitter to come in the mail then...
Hopefully mine isn't totally compromised because I caught it before it became a complete failure. Waiting on new case splitter to come in the mail then I'm taking it to my guy and seeing what he can do.

Josh

For sure weld it, have the guy make a small v to fill it in, that way you are getting a little deeper into the material instead of up on top of it.

Lastly, when you go to service the bearings, heat up the cases in an oven @ 350 degrees until the case is smoking pretty good, (20 min+), and remove the cases and smack them down on a piece of pine board so it's soft and the bearings will fall out.  Then place the replacement bearing in that was sitting in the freezer over night and it will fall in.  If it doesn't fall right out, you could give the bearing a few taps with a bearing driver.

99.9% of the time, no hammers, they fall right out and drop right in.

Let cool down naturally and then you can assemble.

Good luck! J

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