Over-reved the engine

Discussion in 'Old's Cool' started by homerj, Mar 20, 2007.

  1. homerj

    homerj 742 Evergreen Terrace

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    So I finally got my bike back together and starting under its own power. On my first ride I missed a shift while merging onto the freeway and over-reved the engine (8K +/-) and the engine starting running poorly (no power, no accelleration). I got the bike off the freeway and stopped.
    After getting the bike home and letting it cool down, I pulled the valve cover and noticed about that the valves needed adjusting but looked straight.

    I also drained the gas in the tank left over from August and refilled with fresh fuel thinking that bad fuel could have be detonating and caused the valve to move out of adjustment (I know, probably wishful thinking) and the rough running.

    After adjusting the valves the bike seems to be running OK but I can't get rid of the feeling that I've fatally wounded the engine.

    Can these engines tolerate 8K for very brief durations without needing a total overhaul?
    If the engine won't tolerate 8K where should I look for damage?

    TIA
    I'm so bummed :cry
    #1
  2. Stagehand

    Stagehand Imperfectionist

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    I have to believe that they can take very brief intervals of over-revving, like on a missed shift. (lord knows I miss shifts all the time)

    but I cant explain why you are experiencing those other problems. maybe they are not related to the over-rev, but are related to the rebuild? You say it was on the first time out.. and just getting onto the highway indicates maybe the first time over 1/2 or 3/4 throttle? Maybe the probems were there already, just not noticed till you got up to a good speed. You may have just had shit gas in it, like you said.

    did it run like crap the whole way home?
    #2
  3. RocketJ

    RocketJ Been here awhile

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    Unless you heard some really ugly noises. Most likely the valve adjustment and poor running had nothing to do with it.
    With stock pistons and valve train I don't beleive you could hurt it.
    #3
  4. Lurking Luddite

    Lurking Luddite Been here awhile

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    give it a compression test
    #4
  5. datchew

    datchew Don't buy from Brad

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    when was the last time you re-torqued the heads and tuned the valves?
    #5
  6. jdiaz

    jdiaz .

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    I've heard that the rotor windings are the limiting factor to max rpm in an Airhead. :dunno
    #6
  7. Rubber Cow

    Rubber Cow GS Dork

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    Do a leak down test and compression test.
    I've over revved and done nothing and I've over revved and bent valves.
    #7
  8. nick_rhinocycles

    nick_rhinocycles Been here awhile

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    I agree. You should not worry, do the general maintenance for the sake of sanity, then go out and over-rev it again! I mean Run it! =-)
    --N
    #8
  9. AntonLargiader

    AntonLargiader Long timer

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    I'm going to go against the tide here and suggest that you have a problem. It doesn't mean that the engine needs a total overhaul but you may have bent valves. Did the clearances open up? That indicates a bent valve that isn't closing fully. If performance dropped off then you probably were losing compression. The only way to get loss of compression through the valves WITH increased clearances is if you bent some valves.

    If the clearances closed up, then maybe nothing bad happened. But either way, you aren't going to see the bent part just by opening the valve cover.

    Just for grins, look inside the valve cover and see if there are rub marks from the rocker arms.

    So, which way were the clearances off?
    #9
  10. BMWRich

    BMWRich Long timer

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    I'd think you'd have a "valve float" condition.
    Motor spinning so fast that the valves don't close all the way,no combustion so no power.

    Definition: A high-rpm engine condition in which the valve lifters lose contact with the cam lobes because the valve springs are not strong enough to overcome the momentum of the various valve train components. The onset of valve float prevents higher-rpm operation. Extended periods of valve float will damage the valve train.

    Did it a few times on an old airhead GS100. Never any damage just loss of power.

    Compression check will tell if valve/s are bent.
    #10
  11. Dolly Sod

    Dolly Sod Red Clay Halo

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    I've done similar on my R90/6, was cruising along using the "cruise control" knob mounted on the the throttle. I went to down shift for passing, pull in the clutch and just let go of the throttle, forgetting I'd locked it in place.. ZOOM.. Well over 8 grand, but thousands of miles later, no sign of bent valves..
    #11
  12. opposedcyljunkie

    opposedcyljunkie Heavyweight Boxer

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    solution there would be stiffer springs but your top end's life is halved...
    #12
  13. homerj

    homerj 742 Evergreen Terrace

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    They were tight, but i forgot to measure how much they'd moved.

    I checked the valve cover and there aren't any rub marks. I also took a look at the pushrod ends by rotating the engine past TDC and they looked OK (not mashed or scarred in any visually detectable way).

    It looks like a leakdown compression is the test for bent valves?

    Also, I plan on just finishing out this tank of gas (300 mi +/-) and rechecking the valves.

    It's been so long since i rode it I'm just having an issue knowing what noises are normal and what noises mean trouble.

    Thanks for the help.
    #13
  14. Poolside

    Poolside Syndicated

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    <BR>Asked of the Airhead experienced . . . Could he have twanged a pushrod?

    - Jim

    EDIT: Apparently I had this thread open in another window for a long while, and responded without hitting refresh. And so did not see Homer's response. I see that bending a pushrod would open the valve lash.<BR><BR>
    #14
  15. AntonLargiader

    AntonLargiader Long timer

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    Valves float and the oil pump cavitates (about 8200 RPM I think).

    Maybe I misunderstood what you wrote. Did you indicate that you had a persistent loss in performance until you got home and adjusted the valves, or just that power was off while you were over 8000 RPM?

    If you just had top end work done, some tightening of the valves would be expected on the first ride. Otherwise, well, dunno. I guess I'm not sure of exactly what you experienced.
    #15
  16. jdiaz

    jdiaz .

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    Whoa! 8200 is way up there for an old bike.

    I'll be interested to see if a charging problem develops this year. The guy who passed the info to me is normally spot-on.
    #16
  17. AntonLargiader

    AntonLargiader Long timer

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    I'm not saying your guy is wrong; I'm just adding these restrictions in also. But I think plenty of Airhead racers are running stock charging systems close to 8k.

    I wish I had a tach with a telltale so I knew what RPM I hit when I knocked the shifter into first when I was redlined in second at BeaveRun. That one cost me a valve, and knocked the guide right out of the head.
    #17
  18. jdiaz

    jdiaz .

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    Really? I would think the first thing you would do on a dedicated Airhead racebike is to yank the rotor and stator and run total loss just to minimize rotating mass from the crank. Does anyone do that?
    #18
  19. AntonLargiader

    AntonLargiader Long timer

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    Oh yeah. Mine is total loss, and so are a number of others. But I don't think all of them are.
    #19
  20. jdiaz

    jdiaz .

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    Does it pick up revs a lot more quickly? What else did you and Cutter do to your bike?
    #20