blown crank journal bearing

[alex.s]

here's what it looks like when you blow out a crank journal (big end of the rod) bearing:

Link to original page on YouTube.

[Racer x]

" thats not good" ya that is definitly not good.

[Motofool]

Hope the crankshaft is not damaged.

[Racer x]

I bet the crank looks like a dogs chew toy

[alex.s]

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

[old3]

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?

[alex.s]

Originally Posted by old3

Sucks, what were the miles/hours on it. Lots of high RPMs I'm guessing (duh!)? Can you pinpoint a cause for the failure?

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

[Motofool]

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

[old3]

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.

[alex.s]

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.

[old3]

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.

[alex.s]

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

[choneofakind]

Originally Posted by alex.s

the plug blew out near redline

well, if it's any consolation, mine did the same thing in May. I haven't had any lasting effects? I think they're not related.

[DennyV]

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

[alex.s]

Originally Posted by DennyV

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

the rod is garbage. the crankshaft is almost guaranteed to be ruined. if its not bent, the bearing surface is destroyed and if the crankshaft is destroyed, it's not a bad bet to say the case side is damaged. even if its not, the case bearings need to match the crank very precisely and that kind of precision doesn't translate between two cases so its almost not worth replacing the crank without replacing the case as a set (already matched) and you might as well get the rods with that crank since they are precision matched as well. basically when part of the crank goes, its cheaper to just replace the bottom end completely (you know minus transmission and accessories)

i'm just lucky the head cylinders and pistons are ok.

[DennyV]

If the case is fine, Id just get a new crank, and measure clearances, then see where to go from there

[alex.s]

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.......

[alex.s]

Originally Posted by choneofakind

well, if it's any consolation, mine did the same thing in May. I haven't had any lasting effects? I think they're not related.

... Yet!

[choneofakind]

Knocking on wood!! Knocking on wood!!!

[DennyV]

Originally Posted by alex.s

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.......

I guess bike engines are different than car engines, I took automotive engine repair and yes I understand clearances are really tight on bikes, but I was taught that rods and caps are matched and the main bearing caps, or in this case the case is matched to its specific location. I was told its okay to swap cranks as long as all clearances are proper, and this is why we take the time to measure everything. Now on a cost perspective in a Crank is $150 and you need to get new rods and bearings then have everything rebalanced then I would go for a new bottom end granted that it truly is a "new" bottom end and not a used one with too much clearances

[tehcarguy]

ouch, at least it didn't completely come apart while you were riding!

[csmith12]

Rotten luck alex. I am jelly that you know how to do all this work yourself. Good luck sir.

[choneofakind]

All it takes is a thrifty rider and a garage full of tools to learn how to do it!

[DennyV]

Originally Posted by choneofakind

All it takes is a thrifty rider and a garage full of tools to learn how to do it!

and someone with a basic knowledge of engine assembly...cuase without that, not lining up oil holes, not knowing pistons and rods have a front and rear, etc etc

[jasle]

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...

[jasle]

Originally Posted by alex.s

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

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.

[alex.s]

It's not stock cooling system. Thanks for your reassurance though

[cuong-nutz]

Originally Posted by alex.s

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.......

This is something I really do not want to do right now. I'm really tempted to just go ahead and install everything back together without checking the clearances on all the bearings on the rods and journals.

[alex.s]

Originally Posted by cuong-nutz

This is something I really do not want to do right now. I'm really tempted to just go ahead and install everything back together without checking the clearances on all the bearings on the rods and journals.

it will last about 500 miles and then the bearing and crank will be shot again if you don't have clearances correct