loud knocking constant with engine speed

[whatsmynameagain]

Eh, best case its covered. Ill eat it if I have too. Didnt buy an frs to drive miss daisy. I absolutely drive spiritedly. Just got lazy I guess. Like I said, it was slow traffic and when it finally spead up I got a little over zealous. But im definitely going to pay more attention now. Good advise though. I just want to know what I broke.

[whatsmynameagain]

On a good note. My wife is not tripping at all. Whats up with that?

[civdaddy]

Let's say your bill is "X" amount. The service advisor wants to make money off of your repair. The mechanic wants to make money off your repair. Your bill is somebwhat negotiable.

When they first give you the amount, tell them that is more than you were expecting and you will have to sleep on it and give it some thought. The next day they will call you back want to know your decision. I'd bet worse case scenario you will get 10% off if you express that you can only get the work completed for "Y" amount. Don't be afraid to ask to the service writer to ask his manger for a lower bill. And also don't be afraid to ask to talk to the manager. They want your business.

[BRZnut]

Isn't the rev limiter suppose to prevent events like this?

[civdaddy]

Originally Posted by BRZnut

Isn't the rev limiter suppose to prevent events like this?

Nope. The rev limiter won't peotect you from a mechanical over rev like this, at all.

[Ultramaroon]

Originally Posted by BRZnut

Isn't the rev limiter suppose to prevent events like this?

Ok, but in fairness that's a good question. Did civdaddy's answer click? If not, it's worth discussing. Otherwise I don't want to sound all condescending, you know, like I'm talking down to you.

[BRZnut]

Originally Posted by Ultramaroon

Ok, but in fairness that's a good question. Did civdaddy's answer click? If not, it's worth discussing. Otherwise I don't want to sound all condescending, you know, like I'm talking down to you.

More info would be great. I was always under the impression that with todays manual if you down shifted when you shouldn't the ECU would shut the car down to prevent damage

[JB86'd]

So the other day I was doing about 85 in 4th, went to upshift to 5th and went into 3rd, and released the clutch but before my revs could go past about 6500 I put the clutch in so the tach didn't overrev. Is this still considered an overrev and can it do damage even though the tach never went above 6500? Car seems to be running fine but my stomach just about fell out my a$$.

[Ultramaroon]

The rev limiter is there to prevent the engine from blowing itself up under its own power. "I'm going too fast! Cut the fuel/ignition now!"

In OPs unfortunate case, there isn't a mechanism to prevent an engine from being externally driven (overrevved) to the point of failure. Consider downshifting to engine brake down a slope. It's a very real danger to downshift too many gears and force the engine to rev too fast.

In the case of the valves, they are pushed open by a lever but a spring pulls them shut. If the engine is rotating faster than designed, the piston gets to the top of its stroke before the valve has time to shut on its own. This is called "valve float"

The piston smacks into the floating valve and - poof - catastrophic failure.

There are other reciprocating parts that will fail because of the extremely high forces generated from accelerating them. Valve float is just the first thing that comes to mind for most people

edit: technically, any time the camshaft turns fast enough to accelerate the valve/rocker arm assembly fast enough for it to lose contact with the camshaft (bounce) it's called valve float.

That's also why pushrod engines can't rev as fast as overhead cam engines. There's more mass to push back and forth.

[Ultramaroon]

Originally Posted by JB86'd

So the other day I was doing about 85 in 4th, went to upshift to 5th and went into 3rd, and released the clutch but before my revs could go past about 6500 I put the clutch in so the tach didn't overrev. Is this still considered an overrev and can it do damage even though the tach never went above 6500? Car seems to be running fine but my stomach just about fell out my a$$.

Nope. You saved it. Good reflexes!

[Kevinn]

Originally Posted by JB86'd

So the other day I was doing about 85 in 4th, went to upshift to 5th and went into 3rd, and released the clutch but before my revs could go past about 6500 I put the clutch in so the tach didn't overrev. Is this still considered an overrev and can it do damage even though the tach never went above 6500? Car seems to be running fine but my stomach just about fell out my a$$.

Should be fine, but it's still a strain on the engine/transmission if the RPMs fell to say 2k as you were shifting, and then force the engine RPMs up to 6.5k via the flywheel too fast.

[JB86'd]

Originally Posted by Kevinn

Should be fine, but it's still a strain on the engine/transmission if the RPMs fell to say 2k as you were shifting, and then force the engine RPMs up to 6.5k via the flywheel too fast.

Yeah luckily I didn't let the clutch out super fast so it wasn't TOO harsh but it definitely made me cringe. Thanks for the responses guys.

OP hope you get taken care of, best of luck. Bring your service guy some Krispy Kreme donuts and coffee lol.

[mav1178]

Originally Posted by BRZnut

More info would be great. I was always under the impression that with todays manual if you down shifted when you shouldn't the ECU would shut the car down to prevent damage

A mechanical overrev situation is when the vehicle speed mechanically forces the engine to rev beyond redline in a certain gear. It usually happens with a misshift.

Put it this way: If you had your engine off, you rolled the car down a hill to 80MPH, and put it into second, the same thing will happen. No electronics needed to spin an engine.

-alex

[BRZnut]

Originally Posted by mav1178

A mechanical overrev situation is when the vehicle speed mechanically forces the engine to rev beyond redline in a certain gear. It usually happens with a misshift.

Put it this way: If you had your engine off, you rolled the car down a hill to 80MPH, and put it into second, the same thing will happen. No electronics needed to spin an engine.

-alex

I see..thanks!