Mechanical Over-rev / Money Shifted

tinyman392

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Hmm ya so if I saw the tach hit 8k rpm I for sure engaged into 2nd. Or possibly missed 4th (lol) and blipped throttle. Doubt that though.

Shit is eating me alive. Live and learn I guess.
Yeah, if your tach hit 8k, then you at least partially engaged 2nd, though it may not mean you blipped the throttle (but it would be far more violent if you didn't). Sorry to hear this happened :( Hope the car is all good, maybe a compression test to ease some unknowns?



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MstrSHAKE

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Yeah, if your tach hit 8k, then you at least partially engaged 2nd, though it may not mean you blipped the throttle (but it would be far more violent if you didn't). Sorry to hear this happened :( Hope the car is all good, maybe a compression test to ease some unknowns?

Haha yes well for sure it didn’t get throttle in 2nd gear. My hope was that I blipped throttle in neutral from missing 4th gear altogether.

Car runs and feels fine for now. May have to do a compression test to settle the anxiety.
 

CivilciviC

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Why are you compression testing the engine and assuming it's ok? Your piston rings won't be damaged on an over-rev. This doesn't make any sense to me.

What more likely happens is you have valve float occur and you burn your valves. This can also lead to valve and piston contact- valves stay open longer than they should and the pistons come into contact. It depends how fast the engine was actually spinning, and for how long it was spinning at that speed.

If the engine is still running after a misshift, there likely is no issue. The engine can still run if the valves are only mildly damaged- his could result in additional engine noise, less power, worse fuel economy. A totally destroyed valve would likely take the piston out also. You'd know if that happened.

Either way, a compression test won't tell you much.
 

MstrSHAKE

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Why are you compression testing the engine and assuming it's ok? Your piston rings won't be damaged on an over-rev. This doesn't make any sense to me.

What more likely happens is you have valve float occur and you burn your valves. This can also lead to valve and piston contact- valves stay open longer than they should and the pistons come into contact. It depends how fast the engine was actually spinning, and for how long it was spinning at that speed.

If the engine is still running after a misshift, there likely is no issue. The engine can still run if the valves are only mildly damaged- his could result in additional engine noise, less power, worse fuel economy. A totally destroyed valve would likely take the piston out also. You'd know if that happened.

Either way, a compression test won't tell you much.
Thanks for the reply. But I thought valve float can cause loss of compression. Either way, I think I would of felt it by now I think. I gotta go back to high rpm pulls to see if I feel loss of power. Don’t mine me and my paranoia
 

Si_chRis

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Why are you compression testing the engine and assuming it's ok? Your piston rings won't be damaged on an over-rev. This doesn't make any sense to me.

What more likely happens is you have valve float occur and you burn your valves. This can also lead to valve and piston contact- valves stay open longer than they should and the pistons come into contact. It depends how fast the engine was actually spinning, and for how long it was spinning at that speed.

If the engine is still running after a misshift, there likely is no issue. The engine can still run if the valves are only mildly damaged- his could result in additional engine noise, less power, worse fuel economy. A totally destroyed valve would likely take the piston out also. You'd know if that happened.

Either way, a compression test won't tell you much.
I doubt you would get burnt valves in the short duration of a mechnical over rev. Burnt valves tend to develop over time. If anything, the damage would be valve float and P2V contact. If this happens, your valve seats will not be sealing and a compression or leakdown test would tell you a lot and if something major took place in the engine during the mechanical over rev.
 

TheShadow

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I doubt you would get burnt valves in the short duration of a mechnical over rev. Burnt valves tend to develop over time. If anything, the damage would be valve float and P2V contact. If this happens, your valve seats will not be sealing and a compression or leakdown test would tell you a lot and if something major took place in the engine during the mechanical over rev.
I think his point was that if you did do damage from the over rev (piston to valve contact) you are probably going to notice it without a compression test. Ever tried to drive one of these 4 bangers when one cylinder isn't holding compression? They don't run to well on only 3. Yeah a compression test will tell you that you can't hold compression if you goobered up a valve, but you will feel the engine not running right long before that.
 

CivilciviC

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I doubt you would get burnt valves in the short duration of a mechnical over rev. Burnt valves tend to develop over time. If anything, the damage would be valve float and P2V contact. If this happens, your valve seats will not be sealing and a compression or leakdown test would tell you a lot and if something major took place in the engine during the mechanical over rev.
Yes, I agree. If anything, they might be a bit scorched, but I too would think there is no real damage. A second or two of extreme heat should be ok.

Hmm and now that you mention it, I was thinking the leak down only checks the piston rings for leaks- but you're right, if a valve was damaged, it would leak compression that way too. It's a lot less common for the valves to be damaged, unless of course, they're over revved, hence why I wasn't even thinking about it that way.

The few times I've done leak down tests was to see how the rings were. I've never over revved an engine myself, so it never dawned on me :p
 

CivilciviC

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I think his point was that if you did do damage from the over rev (piston to valve contact) you are probably going to notice it without a compression test. Ever tried to drive one of these 4 bangers when one cylinder isn't holding compression? They don't run to well on only 3. Yeah a compression test will tell you that you can't hold compression if you goobered up a valve, but you will feel the engine not running right long before that.
That, and if any bit of that valve breaks off, it'll be making a very nasty mess inside that cylinder. Noise and likely catastrophic failure. Not to mention, as you pointed out, the engine being unbalanced with one piston doing nothing, making everything very obvious.

Glad to hear OP isn't having those issues. He also guesstimated how high he over revved, which isn't entirely accurate. Truth be told, while Honda limits the rev range to only 7k on the CTR, our engines likely can handle more without much issue. Honda always over designs their engines and it shows- you can beat the life out of them and they continue chugging along. It also comes down to long life reliability and Honda knowing this engine was made to be beat on.

I haven't checked, but I would assume the stroke length is similar between the K20C and older K20s. If that is the case, the valve springs might end up being the limiting factor on being able to rev higher, but they can be swapped! :p
 

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Hey y’all. Looking for some input as to what I should do next after having a pretty bad mis-shift. I was in 3rd gear travelling approximately 75-80MPH (near red line). I missed 4th and accidentally went into 2nd. I did a rough calculation and the engine over revved to 9,000-9,500 RPM... rookie move I know. Has anyone else done something similar? Hopefully someone can advise on some next steps. The car drove home ok and seems to idle ok for now. I did notice a sputtering sound when the car decelerates from 2k-1k rpm. Not sure if the car did this before.
Hey y’all. Looking for some input as to what I should do next after having a pretty bad mis-shift. I was in 3rd gear travelling approximately 75-80MPH (near red line). I missed 4th and accidentally went into 2nd. I did a rough calculation and the engine over revved to 9,000-9,500 RPM... rookie move I know. Has anyone else done something similar? Hopefully someone can advise on some next steps. The car drove home ok and seems to idle ok for now. I did notice a sputtering sound when the car decelerates from 2k-1k rpm. Not sure if the car did this before.

I had the same thing happen a long time ago, in an MG, shifting out of 3rd at 7,000 rpm and accidentally hitting 2nd instead of 4th. I didn't see the tach, but mathematically the rpm's would have been north of 9,000 if the clutch fully engaged. That noise was something you never want to hear again. The engine seemed OK at first, but about a mile later it revved up, no longer connected to the rear wheels. The bolts between the flywheel and crankshaft had sheared. The valves were not bent, so it probably didn't get all the way up to 9,000. So, this type of damage from the torsional shock is something to consider, in addition to the bent valves and damaged pistons that others have suggested.
 
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I had the same thing happen a long time ago, in an MG, shifting out of 3rd at 7,000 rpm and accidentally hitting 2nd instead of 4th. I didn't see the tach, but mathematically the rpm's would have been north of 9,000 if the clutch fully engaged. That noise was something you never want to hear again. The engine seemed OK at first, but about a mile later it revved up, no longer connected to the rear wheels. The bolts between the flywheel and crankshaft had sheared. The valves were not bent, so it probably didn't get all the way up to 9,000. So, this type of damage from the torsional shock is something to consider, in addition to the bent valves and damaged pistons that others have suggested.
Holy necro post lol. Car was actually fine for the next 15k miles and saw hard track time. Ended up selling it for a '19 in CW
 

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