BENT VALVES in the head: tell me how that happens....

[Tamago]

Originally Posted by Loren

Barring extremely unusual circumstances, don't valves only get bent when they come into contact with pistons? There's really only one way that can happen... the valve timing has gone off in a major way. Typically, that means something broke (timing chain broke or stretched, VVT messed up, whatever) or the engine was severely over-revved to the point that the valve springs couldn't keep up and one or more valves stayed open when they should have been closed.

I'm going with the "3-2 shift". Winding up 3rd and missing 4th, dumping the clutch in 2nd gear with the car going 80 mph. Ponder that for a moment. If the engine turns about 6200 rpm at 60 mph, you can easily zing it past 8000 in this manner... instantly. And if you're not quick enough to realize it instantly (or quite possibly even if you are), you can do some damage in a hurry.

I did it once in my old Saturn, but I realized it before I even got the clutch fully engaged and no damage occurred. From what I'm seeing with my son as he's learning the finer points of driving a stick... if he did it, he'd more likely fully engage the clutch and leave it there and wonder "why don't I have any power" until valves started poking holes in the hood. And I don't think my son is all that unusual as far as young folks learning to drive stick go.

Remember, a rev-limiter can save you from over-reving under power. The engine will simply never rev ITSELF far enough to hurt itself, the ECU won't let it. But NOTHING can save you from a botched shift! The solution is to learn to trust your shifter. Don't FORCE your shifts, "guide" your shifts. The shifter is spring loaded and will go into the proper place if you let it.

hey, everyone, Loren's here! now you can believe what i said waaay back in post #2 lol

[Loren]

Originally Posted by Tamago

hey, everyone, Loren's here! now you can believe what i said waaay back in post #2 lol

Yeah. What you said!

(as is typical of me, I said the same thing, just used a helluva lot more words)

[FunctionSpec]

Originally Posted by Tamago

lol dude...

tight valves.. lifting too much... yet somehow coming in contact with the pistons??

the valve springs lift the valves, the cams push them down..

Literally you are right but technically valve "lift" is the distance the valve moves from full close to full open. So how far the cam pushes the valve "down" is valve "lift".

Mis-shift would also be another possibility but he never mentioned if it was auto or manual.

[YarisSedan]

Usually when this happens the computer records the live data. It will record engine rpm and vehicle speed in freeze frame. Dealer can see how fast you were going and what rpms. If you are above redline and shows you going 100mph and engine coolant temeprature shows the vehicle isnt even warmed up then dealer is going to say sorry bozo.

I mean usual way to bend valves is when you have the piston colliding with the valves due to incorrect timing or in most cases cars that run timing belts and the belt brakes. I have seen a mechanic install a timing chain wrong once engine ran for a few seconds and you hear this clack clack clack. removed the cylinder head and the piston snapped the valve off turned it upside down and it punctured a hole through the piston head.

[Loren]

Since this car is at a Toyota dealer... do the Toyota diagnostic tools have the ability to look at things like "max RPM" and such? I would think a missed shift situation would show up as a pretty serious RPM spike. Max speed might be in there, too... 70 mph?

[Loren]

Originally Posted by YarisSedan

Usually when this happens the computer records the live data.

Haha! We must have been telepathically linked.

[Tamago]

Originally Posted by Loren

Since this car is at a Toyota dealer... do the Toyota diagnostic tools have the ability to look at things like "max RPM" and such? I would think a missed shift situation would show up as a pretty serious RPM spike. Max speed might be in there, too... 70 mph?

i've done it :(

3-4-3 :( didn't take too much speed

[Loren]

Originally Posted by Tamago

i've done it :(

3-4-3 :( didn't take too much speed

3rd gear is good to about 80 mph, so you'd have to be going considerably faster than that in 4th to get into trouble by going back down to 3rd, wouldn't you? Dunno how sensitive this engine is, I guess if it's particularly fragile, maybe it doesn't take much.

Or is it the immediate acceleration of the engine to 6000 rpm rather than high rpm itself that's causing it to break?

[BLAZINBLUEVITZ]

FYI: its a manual TC.......

[Tamago]

Originally Posted by Loren

3rd gear is good to about 80 mph, so you'd have to be going considerably faster than that in 4th to get into trouble by going back down to 3rd, wouldn't you? Dunno how sensitive this engine is, I guess if it's particularly fragile, maybe it doesn't take much.

Or is it the immediate acceleration of the engine to 6000 rpm rather than high rpm itself that's causing it to break?

i'd imagine that the extreme acceleration to ANY rpm would cause a temporary flex of the valvetrain (cams, vvti setup, timing belt) enough to throw valves into a place they don't belong.

and yes, i was going considerably faster than i should have been.. it snapped the crankshaft pulley's rollpin (thankfully no harm was done to the crankshaft) and slightly bent at least one set of valves..