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  #1  
Old 03-29-2005, 10:36 AM
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617 Over-Rev?

I accidentially knocked my car into neutral and the engine briefly hit 5000+ rpms. Very quick and I let off the fuel immediately. This is an 83 617 with the turbo. It still seems to run OK. Did I overspeed the engine or is 5K not past red-line.
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  #2  
Old 03-29-2005, 10:48 AM
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Yes, that probably was an overspeed. But from the sounds of it, must not have been bad enough to do any damage. Redline can be hit or even pushed when under load but freereving past red isn't good.
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Old 03-29-2005, 11:00 AM
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The car won't over-revv.. the injection pump prevents that.. your engine is fine.
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Old 03-29-2005, 11:26 AM
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I'd agree the IP would stop it from staying over redline but wouldn't the inertia of the motor accelerating there rapidly cause it to go over?
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Old 03-29-2005, 11:40 AM
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At lunch time I'll check the oil and take it for a ride and report back. I'm hoping nothing is wrong. For all I know, the inertia of the tach may have also been indicating a higher speed than the engine actually hit. It's not knocking (other than diesel knock) any different than before. Lunch-time run should tell.
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Old 03-29-2005, 01:01 PM
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Yes the inertia may let it spin another ~100rpm but it will keep cutting the fuel when it senses the car is near redline. Don't worry about a thing.
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Old 03-29-2005, 02:41 PM
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Took it out at lunch. Nothing strange, same old noisy box-a-rocks. No white smoke nor black. Nothing funny smelling under the hood. Hard to kill these damn things.
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Old 03-31-2005, 11:55 AM
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I forget if it was the 81 or 83 SD but once I was accelerating at the top of third and managed so put the shifter in second while reaching to put it in fourth. Tach went to 5500, maybe more before the revs dropped. Didn't seem to do a lick of damage.

In situations like this I'm way more concerned about the transmission than the engine.

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Old 03-31-2005, 01:49 PM
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I was trying to isolate a slight vibration I was feeling in the car. I think I was going about 60 or 70, slipped the car into neutral to see if the vibration changed. When I put it back in gear it just didn't engage right away and I was already pressing on the fuel to get my speed back up. Surprized me how quickly it revved up! Anyway, it really doesn't appear to have hurt anything as the old plugger ran nice and strong today.
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Old 03-31-2005, 02:05 PM
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Quote:
Originally Posted by turbodiesel
The car won't over-revv.. the injection pump prevents that.. your engine is fine.
How does the IP do that?What gets damaged first?
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  #11  
Old 03-31-2005, 03:09 PM
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On robust engines that don't break easily, throw rods and the like (I think the 617 qualifies) the next potential damage from over-reving can come from valve float where the valve springs don't close the valves fast enough before the piston comes up from below and hits them. Given the considerable stroke and compression of these engines it's probably pretty hard to do that unless you get the RPMs really up there. In any event, you'd know it if you've hit a valve. You should be fine.
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Old 03-31-2005, 04:04 PM
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I did the exact same thing, it was rather frightening having it hit 5K RPM all of a sudden when i tried to shift it back to "D." Engine still runs fine, and that was like 5-6 months ago.
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  #13  
Old 03-31-2005, 05:11 PM
VeeDubTDI
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Lightbulb high RPM and engine damage

The IP has a flyweight governor inside of it that is calibrated for approximately 5,050 RPM. You can experience it by flooring it and holding it in neutral. Don't worry about damage, the Finns calibrate their governors for somewhere around 6,000 RPM. You'll also notice that the tachometer has no indicated redline. This is because there is no point in the indicated RPM range at which engine damage will occur. So unless you pegged your tachometer, there is nothing to worry about.

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