View Poll Results: Have you mis-shifted?
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Have you ever mis-shifted?
Joined: Sep 2011
Posts: 1,893
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From: Fremont, CA
The bottom end can survive the momentary ride to 10,800RPM. The valves contacting the pistons is the potential issue at that RPM. A compression and leakdown test should give some insight.
Be kinda smart for car manufacturers to include a clutch disengage solenoid for mechanical over-revs on H pattern manual cars. That's the only type of "rev limiter" that would work in that situation.
Be kinda smart for car manufacturers to include a clutch disengage solenoid for mechanical over-revs on H pattern manual cars. That's the only type of "rev limiter" that would work in that situation.
How is it possible for the valves to contact the pistons at high RPM? Don't the valves open when the piston is near the lowest point? As long as the crankshaft is running in harmony with the valves via the timing chain how does it happen?
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Joined: May 2015
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That happens if the valvetrain components cant keep up with the speed needed to open and close correctly in time with the piston/bottom end.
When you go past the mechanical limit of the springs and retainers, the valve can still be open when the piston is coming up. Valetrain component also usually have a safe RPM limit known, or listed in some applications. Mechanical overrev is the common way for this to happen.
When you go past the mechanical limit of the springs and retainers, the valve can still be open when the piston is coming up. Valetrain component also usually have a safe RPM limit known, or listed in some applications. Mechanical overrev is the common way for this to happen.
Joined: Sep 2011
Posts: 1,893
Likes: 160
From: Fremont, CA
That happens if the valvetrain components cant keep up with the speed needed to open and close correctly in time with the piston/bottom end.
When you go past the mechanical limit of the springs and retainers, the valve can still be open when the piston is coming up. Valetrain component also usually have a safe RPM limit known, or listed in some applications. Mechanical overrev is the common way for this to happen.
When you go past the mechanical limit of the springs and retainers, the valve can still be open when the piston is coming up. Valetrain component also usually have a safe RPM limit known, or listed in some applications. Mechanical overrev is the common way for this to happen.
Joined: Nov 2007
Posts: 8,841
Likes: 1,705
From: Illnoise. WAY downtown, jerky.
Originally Posted by B serious' timestamp='1446120045' post='23789196
The bottom end can survive the momentary ride to 10,800RPM. The valves contacting the pistons is the potential issue at that RPM. A compression and leakdown test should give some insight.
Be kinda smart for car manufacturers to include a clutch disengage solenoid for mechanical over-revs on H pattern manual cars. That's the only type of "rev limiter" that would work in that situation.
Be kinda smart for car manufacturers to include a clutch disengage solenoid for mechanical over-revs on H pattern manual cars. That's the only type of "rev limiter" that would work in that situation.
How is it possible for the valves to contact the pistons at high RPM? Don't the valves open when the piston is near the lowest point? As long as the crankshaft is running in harmony with the valves via the timing chain how does it happen?
On the intake stroke, the intake valves are opening close to when the piston is leaving TDC. The valves are chasing the piston.
On the exhaust stroke, the exhaust valves are closing as the piston gets to TDC. Piston is chasing the valves. This is when the piston is most likely to hit valves.
Valve float happens when the valve train is moving so fast that the springs lose contact with their opening mechanism. The valve is left open slightly, and the piston touches it.
Imagine your wheel or tire skipping over bumps because they are happening with too much frequency. Same basic concept. The "bumps" from the cam are happening so fast that the valve springs can't follow them.
For S2000's, this happens around 11k RPM. The valve train is moving at ~92 revs per second. The bottom end is going in circles at 183 times/second. At that speed, it only takes a touch to create an enormous amount of damage. Lots of force behind those little bastards.
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