November 27th, 2012, 02:28 PM | #1 |
wat
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blown crank journal bearing
here's what it looks like when you blow out a crank journal (big end of the rod) bearing:
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November 27th, 2012, 06:46 PM | #2 |
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" thats not good" ya that is definitly not good.
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November 27th, 2012, 06:53 PM | #3 |
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Hope the crankshaft is not damaged.
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November 27th, 2012, 08:32 PM | #4 |
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I bet the crank looks like a dogs chew toy
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November 28th, 2012, 09:57 AM | #5 |
wat
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i'm sure the crank looks like ****. i haven't bothered splitting the bottom yet. i've already written off the case crank and rods... i think i can reuse the pistons though... i think the transmission is fine so i'll reuse that too
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November 28th, 2012, 10:47 AM | #6 |
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Twin cylinder weed wacker? Looks like an engine, only smaller!
Sucks, what were the miles/hours on it. Lots of high RPMs I'm guessing (duh!)? Can you pinpoint a cause for the failure? Anyone done a stroker crank on a 250? |
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November 28th, 2012, 11:07 AM | #7 |
wat
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not exactly sure but i think it was a combination of over-revving downshifts, poor throttle control, not enough clutch between transitions, and a crappy cooling system. it happened during qualifying at CVMA last round and i didn't get to race
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November 28th, 2012, 11:24 AM | #8 |
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As long as there was that film of oil between the parts, nothing else would have mattered: it is a hydrostatically lubricated plain bearing.
Lubrication failure must have been: metal touched metal (around 200 times per second). http://en.wikipedia.org/wiki/Plain_b...id_lubrication
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November 28th, 2012, 11:25 AM | #9 |
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Damn. I am not familiar with the bottom ends and oil circuits on these yet (and hopefully don't ever need to!) but i'd be checking the oil pump and all the delivery ports/jets too. With enough scruitny you should be able to find the culprit.
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November 28th, 2012, 11:29 AM | #10 |
wat
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i'm wondering if the damage was done when i blew out my spark plug earlier... same cylinder. would the engine running with one cylinder having 0 compression (open hole up top) cause more wear on that journal bearing? instead of having a single direction of force (pushing up against compression/combustion), with no compression the crank is forced to pull on the piston much harder each revolution to bring it down.... so its possible that the added force caused damage to the journal bearing which then cascaded, burning up oil and then burning through the crank... just a thought... the plug blew out near redline
my mind must be stuck in 2 stroke mode. forgot about the intake stroke /facepalm. ignore this.
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November 28th, 2012, 11:37 AM | #11 |
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The severe imbalance could be a factor with that scenario. Are there any Ninja 250 engine specialists who build alot of them. I know a few great KTM guys who can determine the cause with just the remnants of an engine on the bench, or by pics sometimes!
When you tear it down be sure to take some detailed pics, especially of discolored parts. |
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November 28th, 2012, 11:42 AM | #12 |
wat
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i'll post up pics when i disassemble the bottom. it wont be for a couple weeks when i go pick up the replacement bottom
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November 28th, 2012, 12:21 PM | #13 |
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November 28th, 2012, 01:06 PM | #14 |
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hopefully that bearing didnt get down to bare steel, otherwise thats align boring the rod and machineing the crankshaft, and worse if it needs a new rod cause balancing a crank doesnt run cheap
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November 28th, 2012, 02:07 PM | #15 | |
wat
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Quote:
i'm just lucky the head cylinders and pistons are ok.
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November 28th, 2012, 03:45 PM | #16 |
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If the case is fine, Id just get a new crank, and measure clearances, then see where to go from there
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November 28th, 2012, 03:53 PM | #17 |
wat
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no, like seriously... the crank and case bearings need to be accurate to within a very small fraction of a MM. i would have to fully assemble the engine with plastigauge on the current crank, hope its extremely close already so that the plastigauge will actually measure correctly (it wont be) pull everything apart and buy new, correctly sized crank bearings (like 100$ minimum) then reassemble and check again with the new bearings. if its not perfect, you get to buy another set of bearings and you can't return the previous set. cranks+rods by themselves sell for around 250... the case sells for 150ish by itself... there is really no sense at all in trying to replace the crank without keeping its paired up case and bearings. when you can get a complete bottom for around 300... i mean... if you want to **** around with an engine for a few weeks, by all means... if you want it to simply work again so you can get back to riding.......
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November 28th, 2012, 06:59 PM | #19 |
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Knocking on wood!! Knocking on wood!!!
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November 28th, 2012, 08:05 PM | #20 | |
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Quote:
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November 29th, 2012, 08:46 AM | #21 |
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ouch, at least it didn't completely come apart while you were riding!
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November 29th, 2012, 08:49 AM | #22 |
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Rotten luck alex. I am jelly that you know how to do all this work yourself. Good luck sir.
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November 29th, 2012, 08:55 AM | #23 |
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November 29th, 2012, 10:18 PM | #24 |
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November 30th, 2012, 08:57 PM | #25 |
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how are the cam journals? they usually show oiling problems on the left cylinder cam journal first...
cranks are replaceable they make different size bearings to use them with proper clearances...but not sure if you have seen the price 13031-0120 CRANKSHAFT-COMP,B 1 $436.79 crank bearings are under $9ea for both sizes. If you're going to spend that kind of jack buy some pistons and rings, don't half a$$ it. you can find a low mileage motor complete for in the neighborhood of $750...
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November 30th, 2012, 09:04 PM | #26 | |
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Quote:
On a side note...I never use the clutch on an upshift... Done 4 hour endurance races in 110ºF...did not overheat even once. We run top 3 usually...One of my riders last year was the WERA GNC National Champ...so cooling system is solid with distilled water and water wetter.
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January 29th, 2013, 11:14 PM | #28 | |
RIP Alex
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Quote:
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January 30th, 2013, 09:38 AM | #29 |
wat
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it will last about 500 miles and then the bearing and crank will be shot again if you don't have clearances correct
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