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Discussion Starter #1
Hey everyone! Been a lurker here for a long time and have learned a lot from all the experienced members. But now, I have a question/problem. I have a 2014 Accord LX 6MT and while coming down a pretty steep hill, I accidentally slotted it into 2nd instead of 4th... I was going around 70 at the time and the tach immediately jumped up to 8K. This isn't my first manual transmission by a long shot but alas, I guess everyone makes mistakes! Anyway, I pulled over ASAP. No clunking noise in the engine, CEL was not on. Nothing looked like it was leaking as well. I read up on what happens if you miss a down shift that badly and it looks like I could be in for some hefty repairs :crying Any of you guys have any experience with this before? I checked the search and the only relevant post is of a guy who did the same, but heard a knocking noise immediately afterwards, which hasn't happened to me.

Any help is appreciated, thanks guys!
 

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I did that once but I was only doing around 40. Geez I imagine that's pretty nerve wracking but not much more you can do about it now. If the car drives normally and doesn't feel or sound weird then you probably dodged one. I'd take it easy over the next few drives and listen real good for any differences in how the engine sounds or if it feels any different, but I think you might be ok.
 

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about tree fiddy
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Had this happen to a friend of mine. His engine still ran fine, but all 16 valves were bent when he took apart the head.


You should have a compression test done to check for bent valves.
 

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Car so nice, bought twice
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A Honda engineer mentioned in the Si forum that the K24 engine can handle something like 11k RPM for a fraction of a second. I redline to 7500 RPM every day so I doubt 8 grand is going to insta-kill something.

FYI the engine overrev condition will be stored in the ECU, so unless you have an HDS to reset it, don't roll into the dealership all like "no idea how it happened" should you actually have suffered engine damage.
 

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Happened to me in my first Corvette. Downshifting from 5th, pulled stick a bit too far left and was in 2nd. Boy did the tach jump. Just over the redline, for a second at most. Mentioned it to the dealer's mechanic and he said it's fairly common, especially with people just getting used to driving a stick. Granted, I was rolling a 5.7 V8 so there was more room for error, but as long as you don't make it a habit, should be ok. Mechanically, no idea if you did any damage. Just don't deny it to the dealer.
 
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Discussion Starter #6
Wow! Thanks for the speedy responses guys. To answer your questions/comments, yeah it was pretty nerve-wracking. The noise the engine made along with the sudden deceleration really shook me up haha. Luckily, the tires didn't spin otherwise, things may have ended much more badly...

I plan on taking the car to the shop tomorrow and ask them to run the compression test. As for resetting the over-rev flag, can only Honda dealerships do it? Or is there someway for the technician at a local auto shop to reset it?
 

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Drive it tomorrow before you take it to the dealer.

Manuals have rev limiters that cut fuel/power at Max RPM in gear.The motor stutters/misfires for a split second.Feels weird when you hit it the first time.

Hopefully you got lucky,I hit the limiter in 3rd once, passing a bunch of slow moving cars( I don't drive like this normally).First time in this car but not 1st time in a computer controlled manual trans car.

I believe it's recommended
30 in first
60 in second
90 in third
I hit limiter at 95 or so,knew what it was right away.Car runs fine after this,wouldn't make a habit of this but think positive.

Pete
 

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Car so nice, bought twice
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I plan on taking the car to the shop tomorrow and ask them to run the compression test. As for resetting the over-rev flag, can only Honda dealerships do it? Or is there someway for the technician at a local auto shop to reset it?
Don't worry about resetting it. I don't remember off the top of my head if its timestamped, but it's basically there for taking a snapshot of what the engine was doing when the "fault" was triggered. (probably for warranty claims) It captures what the engine temp was, what the speed was, what the rpm was, etc. Basically all the parameters of the engine get stored for that instant.

My car gets it set all the time because it seems with the rev limiter set to 7500 rpm, the engine revs faster than the ecu can stop it so it sometimes revs to 7600 and that triggers it.

Average mechanic shop isn't going to be able to reset it. It's usually a dealership or high end mechanic thing to have the tool + software to do it.
 

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If damage happens from over revving, you usually know it immediately. If the car is running fine it probably is fine. No need to worry.

There are few concepts at play here. At high rpm the valves start to float. Float describes a condition in which the valves springs can’t close the valves fast enough anymore and they remain open too long. Open means they still stick down into the cylinder. When the piston comes up at the top of it's compression stroke it makes contact with the valves and they bend. (Typically the valve stem bends or the valve deforms and is no longer round.) If a valve bends – even a tiny bit- that valve won’t seat properly anymore and allow pressure to leak through. A common symptom is a backfire. If taken to an EXTREMELY high rpm sometimes the connecting rods stretch (steel is a tiny bit elastic) and the piston can also kiss the valves, even if the valves are not floating.


Interference Engines - The Complete List - Your Car Angel

EDIT: According to this list above, published (July 16, 2014), Honda’s 2.4-liter engine appears to be an interference engine. That means the piston and valves can touch.
 

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Drive it tomorrow before you take it to the dealer.

Manuals have rev limiters that cut fuel/power at Max RPM in gear.The motor stutters/misfires for a split second.Feels weird when you hit it the first time.

Hopefully you got lucky,I hit the limiter in 3rd once, passing a bunch of slow moving cars( I don't drive like this normally).First time in this car but not 1st time in a computer controlled manual trans car.

I believe it's recommended
30 in first
60 in second
90 in third
I hit limiter at 95 or so,knew what it was right away.Car runs fine after this,wouldn't make a habit of this but think positive.

Pete
The rev limiter is a safety feature. Hitting it won't damage your engine. It is specifically designed to prevent over revving.

This is completely different from downshifting and forcing the engine past redline. It is impossible (usually) to mash down on the throttle and over rev the engine. It is very possible to be going too fast and downshift forcing the engine to over rev. If you are in second, you can't accelerate past ~60. You could go past 60 in third gear and if you downshifted you'd force the engine past redline.

Also op: if there are no noises and you were only above redline for a few seconds you're probably good. You clutched in as soon as you realized something was wrong, right? Like others have said, consider a compression test. My gut feeling is that you're ok though.
 

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Excellent well-written posts here. Sooner or later, everyone misses a shift or stalls out when the light turns green. Usually, your buddies are in the car to "time stamp it" for eternity and start laughing at you.
 

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Given the fact that he simply downshifted, the car probably knew enough to cut power, as was mentioned. If it shifts normally now, I'd actually skip the compression test. Why bother. If damage was done, which I doubt, it's done. No cryin' over it now. Compression test won't be under warranty.
 

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if you want to do a real quick d.i.y ghetto compression test, take out the spark plugs and keep you hand over the "socket" if you will and crank it, if you're used to the feeling you can tell if you have good compression or not by feeling the force of the air coming out. Learned this track from my dad but i can't get anywhere near the accuracy of how he manages to do it, I'm usually always off XD
 

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I did a similar thing in my '12 Si. Freaked me out and I clutched in as soon as I realized what I had done. No issues after that. Not sure if it actually over-revved or not, but I didn't watch it to find out LOL. Missed the shift, siad "oh $h!t!" and clutched in, all in about a half a second :D
 

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2015 Accord Touring I4
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I will share my experience. This was on a 2002 Civic EX Coupe D17 motor. I was at about redline when I shifted from 3rd into 2nd instead of 4th. It happened for about a second before I realized what was going on and put the clutch in.

I had no immediate issues other than a noticeable vibration at idle... weeks went by and only in certain temps I would get a CEL indicating I had a piston misfire. The dealer reset the CEL many times before they finally sent the motor out... the valves were bent but only slightly... just enough to cause the occasional misfire.

They replaced the head, brand new valves and everything was resolved.

Good luck... I went through months of dealer visits before they were willing to replace as a good will.
 

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You're likely fine--as long as you clutched in quick 8K for a split second isn't going to wreak havoc on a K24.

My only recommendation is to to run through the gears with the clutch in during every downshift to prevent this (and also prevent synchronizer wear). Clutch in, 6-5-4, clutch out.
 

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You're likely fine--as long as you clutched in quick 8K for a split second isn't going to wreak havoc on a K24.

My only recommendation is to to run through the gears with the clutch in during every downshift to prevent this (and also prevent synchronizer wear). Clutch in, 6-5-4, clutch out.
I got the impression it was a 5-4 shift but he accidentally went into second
 

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Given the fact that he simply downshifted, the car probably knew enough to cut power, as was mentioned. If it shifts normally now, I'd actually skip the compression test. Why bother. If damage was done, which I doubt, it's done. No cryin' over it now. Compression test won't be under warranty.

It doesn't matter if the car cut power once you get to a certain point above the redline. What mechanism does the limiter use? Is it just fuel cutoff? If so, manual overspeeding might be less of an issue. Still, stuff is only designed to spin so fast whether or not the engine has cut power.
 

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Yeah mechanical overrevs have nothing to do with power or fuel or rev limiters. You have wheels and an engine that are mechanically linked via a clutch and gearbox.

A missed downshift will rev to whatever the wheel speed dictates relative to the gear ratio. If you want you can rev to 10K! 80mph in second will do that for you. For about 1 second before you drop a valve.
 

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I'm curious... if I rely on the centering springs, what are the chances of missing a shift? When I missed my shift from 5th to 4th, I accidentally put it into second because I consciously applied left pressure to the stick and overshot 4th, luckily I was already slowing down so I was at around 40 to 50. (The Accord is my first stick car). Now I just pull straight down from 5th with no side pressure and the centering springs always put it into the proper gate all the time. Is that good practice?
 
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