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92 745 Turbo - 'thud', loss of power, now crank doesn't turn- 'is it dead Jim'? 700

posted by  NoVa Dad on  Mon Dec 10 12:12 CST 2018
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last visit: Wed Feb 5 06:42 CST 2014
[RELATED]

Hi All,

Its been while, but I've got a doozy for the group.

My son was driving our 92 745 Turbo (~200K miles) on the highway. The car was at normal operating temperatures when he accelerated to pass a car. The car surged as expected but as he passed he heard a "thud" followed by a loss of power, but no warning lights-that he recalls. He pulled to the shoulder and killed the car.

After a quick visual inspect of fluids etc, he tried to restart the car but only got the usual start sequence lights. There was also the audible sound of the starter "thunking" as it made contact with the flywheel- but no start.

After additional road side diagnosis, we towed the car home.

We've removed and tested the starter- it was fine.
Removed and inspected under the valve cover- nothing out of the norm.
Upon attempting to turn the crank via the retention bolt we discovered that it wouldn't budge.
Removed cover and inspected the timing belt- it was intact and well within mileage as it had been changed along with water pump etc less than 30k miles before.
Removed the timing belt and discovered the cam would turn just fine with no noticeable issues, but also discovered the crank could now be turned just a bit more than before.

I'm afraid the grand old lady has passed her last beemer but I'm not ready to call her out just yet and am open to any suggestions.

Anyone else ever dealt with these symptoms before? Is this a bottom end rebuild? or am I missing something simple?

Thanks!

NoVA Dad







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    posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

    Hi all,

    Thanks again for the feedback and input.

    I've pulled the plugs and the crank still only rotates about 30-40 degrees before stopping. The same is true if rotated in the opposite (from where it stops). So total free movement is 30-40 degrees. Anyone know how many times a cylinder fires before the crank makes a full 360?

    Visual inspection of the plugs shows they should be cleaned/replaced, but only because of carbon buildup. Nothing else looks out of the norm- none have oil on them or missing pieces nor terrible discoloration.

    All fluids are full and no (more than usual) leaks/seeps can be found.

    Under the valve cover- everything looks normal for a car with near 200k miles. All of the lobes and discs are in place and free of defect or out of spec movement. I haven't pulled the cam-yet.

    If the weather holds out, I'll get under the car to remove the bell housing and inspect for a loose/backed out bolt.

    More to come.

    Thanks again!



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      posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

      Can't offer any help from experience except to answer your question about the four stroke design; each of the four cylinders fires once every two revs, meaning two of them fire every rev.

      You can get a lighted USB inspection camera for under $10 these days good enough to poke through a plug hole. I've not used it on a cylinder, just through an oxygen sensor bung to see the catalyst. Not sure what you might see with one anyway.

      On an AW-7X (240 trans) there are two removable screens at the bell housing from which you can see the tone ring at least; not sure what sort of transmissions 700 cars may have. Too cold to be under the car now, and you might even have caught some of that last snowstorm.

      --
      Art Benstein near Baltimore

      I was going to wear my camouflage shirt today, but I couldn't find it.



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        posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

        Art wrote--"You can get a lighted USB inspection camera for under $10 these days good enough to poke through a plug hole. I've not used it on a cylinder, just through an oxygen sensor bung to see the catalyst. Not sure what you might see with one anyway."
        Through the spark plug hole you'd be able to see if the cylinders that work together (1&4- 2&3) have the pistons at the same height. If they're not---broken rod or wrist pin. A thin screwdriver could accomplish the same test. -- Dave



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          posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

          "Through the spark plug hole you'd be able to see if the cylinders that work together (1&4- 2&3) have the pistons at the same height."

          Excellent idea. Obviously some experience speaking!
          --
          Art Benstein near Baltimore

          If tomatoes are technically a fruit, is ketchup a smoothie?



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            posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

            Funny story to go with my knowledge of this aspect. Maybe about 1973 or so - bought a 1968 Toyota Corona 2 door HT - cute car - for $35 - needed an auto trans (BW35) and what I thought would be a valve job - ran but had a miss. Used trans went in and head came off. I'm looking at 2 pistons at the same height and 2 at different heights. Tapped one with a screwdriver and it dropped to the level of the other. The piston top had broken all around a ring land. Bought a used piston and a gasket set and we had a car to drive for under $200. Sold later for $600. Volvos were still 2 years off (1965 544). -- Dave



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              posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

              "...You can get a lighted USB inspection camera for under $10 these days good enough to poke through a plug hole....."

              Can you not borescope up through the oil drain and get a look at the lower rod connections?
              --
              Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (getting ever closer to road worthiness)



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                posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

                "Can you not borescope up through the oil drain and get a look at the lower rod connections?"

                I didn't give that much thought given my memory of what the oil pan baffle looks like and where the pump pickup lives. Pretty sure that thing I have isn't able to be manipulated around corners like a sewer inspector. Then again, what is there to lose?



                (More pics like this at http://cleanflametrap.com/oilpan/ )
                --
                Art Benstein near Baltimore

                No matter how much you push the envelope, it'll still be stationery.



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    posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

    Does having a "flywheel" mean your 745T has three pedals? What do the plugs look like?

    Every story I've heard of bottom end trauma included a picture of a hole in the block and an oil mess. Encouraging that you don't have that to report.
    --
    Art Benstein near Baltimore

    Change is inevitable, except from a vending machine.



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      posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

      Hi Art,

      My apologies- I should have written - flex plate- the car is an automatic.

      I'll update once i get a chance to pull of the plugs and do a visual on them as well as the cylinders.

      Thanks!



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        posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

        "Upon attempting to turn the crank via the retention bolt we discovered that it wouldn't budge. "

        Try this again when the plugs are out.

        Dan



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