Who's the expert on pistons? Pistons with holes!

"The piston will hole without much fanfare and you will be riding on 3 cylinders "...

Well damn, that's scary to think that's the only clue to this severe melt down. As I'm assuming (I hate assuming), this can occur rather quickly then, meaning without notice... :ohmy:

NOTE To thyself: Study & Learn 100% how your bike is running on all 4 cylinders. Check spark plugs regulary for discolorations...

Thanks for the exlanation WG.

OMR

Yeah I'm gonna have a wide band O2 on my bike the spring, putting it on while I do the bore out etc. That way I'll be able to tune and then monitor. It'll also come way in handy later on in other projects.

Thanks guys! I took more (close up) pics...

s179.photobucket.com/albums/w310/IA_Cuban/Technical/



steell wrote:

Here I go, disagreeing again

I don't believe that was caused by detonation, I believe that was caused by the cylinder overheating and the rings seizing to the cylinder walls, thus ripping the ring lands off the piston. Look at the sharp edges of that piston, that hole was made by fracture, not melting.

A lean mixture may very well be the ultimate cause of the overheating condition, but detonation didn't do that to the piston.

Hey Steell. I think I agree with you. Wonder what could have caused the temps to go up in that #2 cylinder? Air? We were riding at highway speed, through the mountains, in the rain. Lance told me he had no warning. The power fell off, and he saw blue smoke. Before that all was well... :huh:


timebomb33 wrote:

look for a very bad air leak or a completly plugged main jet. something was causing it to run insanely lean on that cylinder.

Don't know about an air leak yet, but I did pull the main jet. It's the stock size (#92) and clear...


Old Man Rock wrote:

Holly Crap!

Ok, I've got to ask the stupid question here....

To accomplish the severity in those images (holes/melt down) to that level, am I wrong in thinking there would be some tell tale sign that things weren't right?

I mean hollyshit, extreme pinging, grinding noises, running like crap, smoke, loss of compression something.... :blink:

OMR

There are no stupid questions. See above. Lance told me it was sudden. Funny thing is, since he is a rookie, I kept him ahead of me so I could keep my eye on him, for the whole trip. EXCEPT for when this happened. We were on a toll section, and I had the change in my tank bag, so I took the lead. Maybe I got 'on it' a bit, and he was chasing me when it let go. Otherwise, I would have witnessed the sudden (or not) appearance of oil smoke.


wiredgeorge wrote:

What did I say? AIR LEAK... CARB HOLDER cracked or leaking air because of a bad seal. You WILL NOT have major noises or banging. The piston will hole without much fanfare and you will be riding on 3 cylinders and an inexperienced rider might not even know the difference.

That falls right in line with what Lance told me after I stopped to wait for him. One minute, all good, next minute, no power and all that smoke. I haven't been able to find evidence of a major air leak yet, but I'll keep looking. Check out the new pics. I have a concern (question) with the end gaps on the oil control rings...

They're all lined up right under the point of destruction. Relevant?


Cheers!

I dont think that would cause that catastrophic a failure. If anything, they'd cause more oil to be in that area, not less. It really looks like a melt situation, see the aluminum stuck to the bottom of the top compression ring? I dont think you'll ever 100% know the cause, unless you find a problem somewhere. Just rebuild it if thats the plan, use new carb holders, and make sure the mixture is good on all cylinders.

wiredgeorge wrote:

What did I say? AIR LEAK... CARB HOLDER cracked or leaking air because of a bad seal. You WILL NOT have major noises or banging. The piston will hole without much fanfare and you will be riding on 3 cylinders and an inexperienced rider might not even know the difference.

i guess i am just amazed that can happen that quick.......

That is some scary stuff. Makes me want to run out in the garage and take the head off just to check mine. Be sure to post if you find the reason.

Here are my arguments supporting my earlier statement:

If you have pulled apart many motors, you have found that half or more have scored pistons, and the scored part of that piston is what got ripped apart. That's caused by heat and is usually worse on #2 and #3.

I have seen pistons holed by detonation, and they've all been melted, and there's a reason for that.

The temp reached during combustion is above the melting point of the pistons, but a thin boundary layer of air insulates the piston crown from a small portion of this heat. But it's enough to keep the piston from melting.

The shockwave of detonation scours the boundry layer from the piston crown and the piston melts.



Look at the top and bottom lands of the top ring, the surfaces have angles, where the pieces broke off, not melted.


I'd bet money the rings seized to the cylinder walls and pulled the lands off, taking the top piece of the piston with them


I am "NOT" saying it wasn't caused by an air leak, because it probably was

Pondering some random stuff ---

When were valve clearances last checked before the damage?
What are valve clearances now (perhaps none)?
Condition of valve faces, valve seats, and valve springs?
Was headgasket blown?
Condition of exhaust gasket; had the clamp come loose or fallen away?

Any indication of air intake pod element disintegration (such as possibly running cheap paper elements in heavy rain)?

Possible failure of any mod to air injection system?

Possible slip of ignition backplate or incorrect timing? Wonder what a static timing check would show right now?

Any gasoline odor in remaining crankcase oil?

Just mulling things over.

Good Luck!

Very typical of an over lean condition. Temps go up very rapidly, Torches the top out of the piston. Cast pistons are much more vulnerable that forged.

Years ago, with old school nitrous kits, one would hit the button and the fuel solenoid would fail and only nitrous would go in the motor. It would hole all four pistons before you could get your finger off the button.:woohoo:

By the way, todays nitrous kits are wired so that if one solenoid doesn't fire, the other one won't either.

Jay