cr 250 CRACKED case HELP

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steveotimmy

Member
Sep 22, 2009
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I was rebuilding my motor and saw cracks in the bottom of the case where the crank sits. need help i dont know what to do. the cracks are only a inch big
 

Ol'89r

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Jan 27, 2000
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You need a good tig welder. Someone experienced in tig welding of aluminum should be able to repair your cases. Where are you located?
 
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Porkchop

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Apr 27, 2001
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Please show pictures, inside & outside, before any commentary will be offered.
Did the lower rod bearing let go?
 
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plynn41

Member
Jun 8, 2009
107
1
Worst case, you're going to need to replace the case. I had the same thing in my '97 cr250r. My crack extended into the main bearing journal, making the cost to weld it and re-machine the journal not worth the fix. You might get out cheaper if the main journal is not compromised. I bought a beautiful, clean set of used cases for $155. Good luck!
 
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steveotimmy

Member
Sep 22, 2009
20
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posted pictures in the gallery only way i could figure out how to post pics, there under keyword- cracked case, title- cracked engine case.
 

whenfoxforks-ruled

Old MX Racer
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Oct 19, 2006
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Merrillville,Indiana
Thats no casting mark. I have a pair of 82 480 cases worse than yours. Can you find an experienced Japanese aluminum welder near you? And a machinist to make it flat again? Vintage Bob
 

Ol'89r

LIFETIME SPONSOR
Jan 27, 2000
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That's really not a big deal. A good tig welder can fix that. Make sure he is experienced in welding aluminum castings.

Probably caused by a piece of your piston getting in between the crank and the case. If you can't find a welder in your area, PM me.
 

MikeT

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Jan 17, 2001
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Ol'89r said:
That's really not a big deal. A good tig welder can fix that.
Click to expand...
What if.....

89'er tell me what you think of this. What if he drilled a hole at the end of the crack to help stop if from progressing. Then took a grinder and opened up the crack a little, cleaned it and used JBWeld on it?

I cracked a clutch cover on an old street bike I had in the past and fixed it in this manner. It held up and never failed.
 

ellandoh

dismount art student
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Mi. Trail Riders
Aug 29, 2004
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i did the same thing on an old clutch cover but i used a gutter product called seamer-mate. itwas in non stressed area and was just needed to stop a leak and did so for 4 seasons, was still good when sold
 

whenfoxforks-ruled

Old MX Racer
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Oct 19, 2006
8,129
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Merrillville,Indiana
Them posted jb jobs was not done in an area of the cases that has fluctuating pressures/vacuum and vaporized fuel? They are in a vented trans? Its apart, fix it as good as possible, imo. Even my horrible cases, if I can get a guy to weld them, I can make it look back to normal, and flat. Its aluminum, easy to work with. Vintage Bob
 

MikeT

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Jan 17, 2001
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I used it in a clutch cover. Since he does have it apart, it probably is better to have it welded but I bet the JB could do the job.
 

whenfoxforks-ruled

Old MX Racer
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Oct 19, 2006
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Merrillville,Indiana
I have used it when a good part of the case around the sprocket area was damaged Mike, no leaks. But never on the compression part of the engine. His is below the crank. Bottom end pressure? Just like 89er said more than likely, a piece of piston got wedged down by the crank and cracked the seam of the cases on 1 side. Mine got both rather evenly, and a lot further. The old "let her cool off and try push starting it" comes to mind? Vintage Bob
 
J

_JOE_

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May 10, 2007
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What were the pieces that caused the damage from?
 

Ol'89r

LIFETIME SPONSOR
Jan 27, 2000
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MikeT said:
What if.....

89'er tell me what you think of this. What if he drilled a hole at the end of the crack to help stop if from progressing. Then took a grinder and opened up the crack a little, cleaned it and used JBWeld on it?
.
Click to expand...

Mike.

I prefer welding over JB Weld. Simply because, as vintage Bob pointed out, when you have a case with internal pressures, oil, gas and constant heat cycles, the JB Weld can loosen and fail over time. And when it does fail, according to Murphys law, you will be at least 30 miles from your truck. :yikes:

Also, with an engine case damaged the way that one is, the welder will probably have to clamp the cases to bring the crack back together before he welds it. JB Weld won't hold the crack together like tig welding will.

JB Weld is good stuff and has it's place, but I have repaired many cases that people have used JB weld on only to have it fall out at the most inopportune time.

Plus, when you consider the time it takes to tear your engine down to the bare cases, why not fix it right the first time?

JOE.

I remember reading a post that a piece of his piston broke off and got into the lower end. That is what normally causes cracks like that.
 
J

_JOE_

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May 10, 2007
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Ahh, yes! I see that old thread.

Steveotimmy, got pics of the shrapnel?
 

MikeT

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Jan 17, 2001
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Ol'89r said:
Plus, when you consider the time it takes to tear your engine down to the bare cases, why not fix it right the first time?
Click to expand...
Agreed.
 
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Porkchop

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Apr 27, 2001
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Hello Steveotimmy & Mike T, Hello TIG welder, Grind out & clean things up then Get it welded. I would turn up an aluminum disc to support the roundness of the case, place it inside where your crank lives, temporarily, & weld it from the out side first, then grind & weld the inside next.
Then starts the fun part? Filing ,Grinding, & using a wet stone & what ever final finishing you want, to seal up & look how you want it to. I like to use zink chromate primer, topped with Rustoleum hammer finish silver rattle canodize spray.
you will need to lap the mating surfaces with wet-or-dry silicone carbide sand paper, placed on a flat surface like a piece of glass or a granite stone. Check & test the fit-up near the repair zone with a thin feeler gage. Where are you located? Good luck.
 
Last edited:
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steveotimmy

Member
Sep 22, 2009
20
0
Found a welder and he did a great job on fixing the cracks and he made sure the gasket surface was smooth
 
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