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Thread: Lost a water pump belt - some data & lessons learned

  1. #1
    '82 T3 FABombjoy's Avatar
    Join Date:  May 2011

    Location:  Lansing, MI

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    Lost a water pump belt - some data & lessons learned

    Had an exciting moment on the highway this weekend when the water pump / alternator belt snapped. Everything turned out OK, no engine damage, only spoiled plans. Belt was a Dayco top-cog, no more than 5 years old. I did recover the belt which was flung up into the engine compartment and it had clearly just plain wore out, rather surprising given the age and limited mileage. Has numerous cracks in the rubber along the top side.

    Megasquirt 3 is always recording to SD card which gives a glimpse of how quickly things go down (or up, rather). Figured a few people might find this interesting:

    Ambient temp: About 85F, sunny, humid, AC on full.

    From the moment of belt loss (battery suddenly drops 2v, the exact point is pretty obvious) there was no measured temp increase for 30 seconds at the Y-pipe.
    After 30s, temperature increase 1.5 degrees F per second. I'm guessing that it took a little time for coolant to circulate by convection which is why there was such a long delay.
    Dash gauge read 260 when I was finally safe to engine-off.
    I boiled away about 1.5gal of coolant/water in 80 seconds.
    I'm sure the charge light came on but I didn't notice it, being red and right about behind where my hand is on the wheel. I did notice the abnormal gauges (high temp, low volts) but the 2nd half of the game had already begun.

    I carry a tool kit & spare belt, but had never actually used those tools to change a belt. A magic "all in one" type wrench that seemed useful on paper could not fit between the engine bay wall and the bolts locking the AC belt tensioner. I cut the AC belt off so the water pump / alternator belt could be installed which was not ideal. A stock-style alternator tensioner is not an easy affair to work when you're on the shoulder, and the shoulder quickly transitions to a drainage ditch. Once cooler, was able to drive the car in surges to a weigh station 1 mile up the road and at least get off of the shoudler. Given more time I may have been able to work out a solution to release the AC belt but traffic passing at 80MPH only a few feet away, plus I had one of my kids with me, and the problem called for a more rapid solution.

    Lessons learned:
    -If you lose this belt you have at minimum 30 seconds to "find a landing spot"
    -250F+ is a scary number to see but absolutely no damage resulted
    -Water boiling stirs up crud, consider a full-flush if this happens (currently in progress)
    -If you carry spare parts, check that your tools are actually useful to install them
    -Consider a turnbuckle type alternator tensioner instead of stock

    A stranger stopped to help, assuming it was a fire given the cloud pouring from the engine bay and came running with a fire extinguisher. He also drove up to the nearest exit to bring back water. Good people are out there!
    Luke S :: 10270 :: 82 Grey 5-Speed :: Single Watercooled T3 .60/.48 :: Borla Exhaust :: MSD Ignition :: MS3X Fully SFI Odd-fire EFI :: DevilsOwn Methanol Injection

  2. #2
    Senior Member
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    One of the top reasons a belt will fail is if the pulleys are not lined up, ie, in the same plane. Use a string or straightedge and make sure the alternator is lined up. Other reasons for a belt to fail include;
    A bent pulley
    Stretching a belt to put it on (causes internal damage to the cords)
    Overtensioning or undertensioning the belt. There is not so much load on the belt that is should jump off unless the water pump bearings seize up or the fan on the alternator chews up the side of the belt.
    David Teitelbaum

  3. #3
    Senior Member Bitsyncmaster's Avatar
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    Location:  Leonardtown, MD

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    So what voltage did it instantly fall to. I set my electronic otterstat to beep below 12.5 volts to warn of a belt break.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  4. #4
    '82 T3 FABombjoy's Avatar
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    First 0.7s: 13.5 to 12.4
    Next 8s: drops to 11.92
    --From this point it slowly tapers down as battery slowly depletes
    At 80s: 11.68

    I have a CAN bus gauge with programmable warnings. I'll be setting it up to trigger a "Thrown Belt" alarm, something like RPM > 700 && BattV < 12.5
    Luke S :: 10270 :: 82 Grey 5-Speed :: Single Watercooled T3 .60/.48 :: Borla Exhaust :: MSD Ignition :: MS3X Fully SFI Odd-fire EFI :: DevilsOwn Methanol Injection

  5. #5
    '82 T3 FABombjoy's Avatar
    Join Date:  May 2011

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    Luke S :: 10270 :: 82 Grey 5-Speed :: Single Watercooled T3 .60/.48 :: Borla Exhaust :: MSD Ignition :: MS3X Fully SFI Odd-fire EFI :: DevilsOwn Methanol Injection

  6. #6
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by FABombjoy View Post
    First 0.7s: 13.5 to 12.4
    Next 8s: drops to 11.92
    --From this point it slowly tapers down as battery slowly depletes
    At 80s: 11.68

    I have a CAN bus gauge with programmable warnings. I'll be setting it up to trigger a "Thrown Belt" alarm, something like RPM > 700 && BattV < 12.5
    Sounds good. My otterstat is powered by the RPM relay so it only warns when the engine is running.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  7. #7
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    So did you have an extra AC belt too?

    I guess you know you can put a belt on with a screw driver. Not perticularly fun or safe. But I seen guys do it many times. I've done it on a VW, but it's much easier/safer on them because of the access.

  8. #8
    '82 T3 FABombjoy's Avatar
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    Quote Originally Posted by Helirich View Post
    So did you have an extra AC belt too?
    I do now, as of 1PM LOL

    Finding quality belts in-stock for a reasonable price was a challenge. O'Reillys wants something like $30 for each belt. The local NAPA had them and they're made by Gates, XL style. The cheap one is a non-XL and was only maybe $3 or 4? Cheap enough to keep around for an extra.

    I have some extra plumbing above the muffler for the turbo, as well as a non-stock config on the LH water pipe side which does make things a bit more challenging. The AC idler pulley tensioner bolt has been hacksawed off to make room for the turbo oil/water lines, but a tire wrench is enough to leverage that belt tension well enough. This is actually how all of the Island TT kits are set up.

    I've seen the screwdriver trick but have the parts to make a double-heim alternator tensioner on the way. Managed to pick up a surplus universal part for about $15 that should work. I probably could have levered the AC belt off using the screwdriver but would prefer to hone that technique under better circumstances.
    Luke S :: 10270 :: 82 Grey 5-Speed :: Single Watercooled T3 .60/.48 :: Borla Exhaust :: MSD Ignition :: MS3X Fully SFI Odd-fire EFI :: DevilsOwn Methanol Injection

  9. #9
    '82 T3 FABombjoy's Avatar
    Join Date:  May 2011

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    Plan "C" is ready for the next belt failure.

    Luke S :: 10270 :: 82 Grey 5-Speed :: Single Watercooled T3 .60/.48 :: Borla Exhaust :: MSD Ignition :: MS3X Fully SFI Odd-fire EFI :: DevilsOwn Methanol Injection

  10. #10
    Senior Member
    Join Date:  Dec 2018

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    That's a pretty cool rack. Does it go up with the louvers or do you have to remove the four knobs? If it stays will the struts hold it up? (Nothing on it) Do the pieces that the knobs screw into remove easy or do they stay when not useing it? Does the rack fit into the trunk?

    Nice bike also.

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