So as my friend and I were riding in this morning coming to my work to change his extremely bald rear tire. I found an open stretch of road and opened the cbr up alittle (171mph to be exact). I slowed down to 70mph to wait for him and as he's passing me I hear ALOT of noise coming from the bike and all the sudden oil and white smoke are trailing his bike. Mind you this little turd only has around 14,000 miles on it so it has what I think is plenty of life left. As I peek under the engine here's what I see...... I'm alittle surprised at this but then again this bike stays at 10,000rpms while doing 75mph.

 

haha that's funny, the ninja died while trying to stay up with a honda. That's crazy how it blew like that. how many miles was on his bike?

tell him to buy a honda next time lol

 

bye bye con rod!


that's also happened to lots of R1's before they went cross plane crank.


i'm surprised it did that though - i didn't think they had enough compression and engine speed to brake the big end of a con rod.

 

Compression has nothing to do with connecting rods letting go, its all RPM. 14k miles at redline will blow almost anything up.

 

compression load - suction or discharge can and will cause bearing failure - which leads to rod failure

 

Brings up something interesting I read somewhere. Someone said engine life is measured in WOT. That the amount of time spent at WOT in any gear pretty much sets the life expectancy.

Thoughts?

 

but the piston is what pushes everything, and partial to that is compression ratio. the forces with those applied pressures are much higher with higher compression - i.e. less reliable. think about what is actually pushing on the crank journal - the rod. yes it's pushing and pulling much more at higher rpms, but it's pushing and pulling much harder at higher compression.


if this wasn't the case, then there would be absolutely NO benefit to a higher compression ratio - which we all know isn't the case. there IS benefit - with more torque and power. more suction, more squeeze = bigger "boom"


i'm curious though, what was his oil level like before the motor grenade? does he know? when was the last time he checked?

 

I learned the low oil level lesson many years ago... It was the piston that flew apart in my case.

 

Not sure the oil level but he had not checked it in al least 4k miles. And yes mind you this is a ninja 250 and he also owns a 09 cbr1000rr so he beats the crap out of this thing just out of the speed habit you get riding a liter bike. I literally watched this thing blow and i don't remember seeing much oil come out of it, but it only holds 2 quarts. My dad also mentioned when he was driving to pick him up that he didn't see any big spills on the highway. Well I can't say I'm surprised though I've seen some experience with kawasakis and catastrophic engine failures.

 

Your talking absolutes vs feasable. In the case of the ninja 250 with stock rpm levels you'd have to increase compression levels to deisel levels to approach the loads needed to break threw the oil film and start galling bearing surfaces and cause failure. And even then its the bearing failing and taking out other parts with it. RPM is what will cause the rod to break itself even if the bearing is holding up. 9 out of 10 times even with massive compression or hydro lock the rod will bend before snapping.

There is no more suction then with lower compression. Suction is based on volume, which is a set value based on components. You can alter suction seen in the intake via things like varible cams but the amount of suction available is still constant. Compression is how much that volume is forced together.