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My second engine failure 2006

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  • My second engine failure 2006

    ...I am not very lucky this Year...

    February: I crashed my 240SX
    May: First engine Failure with my Z31turbo
    June: I crashed my Toyota supra MKII
    Yesterday: Engine Failure number two with my Z31turbo

    So if i were you i would think twice before letting me drive your car.

    I was again tuning my bins, this time focus was on the high-boost area.
    Due to Exhaust-temperature problems (should not go far over 900°C i was told) i advanced timing up to 24°above 5200RPM and 25° above 5600RPM. AF was already in the very rich high 9th or low 10th.
    The exhaust temperature really went down to around 900°C. Fine. When driving some minutes at around 120-140mph i finally hit the pedal down and accelerated @ 18psi. About 10 to 12 seconds later @6400RPM i stopped accelerating because of traffic. Suddenly i detected a well known, very typical noise from the engine: crank-bearing failure. Car was still driving fine except the noise. I returned to home verly slowly and not very happy.

    Hmm, if the reason is engine knock i wonder why i it is just the bearings that was damaged, why always the bearings and not the Valves/Pistons. When the z32 and sx-guys have engine failures due to knock they always kill their valves and pistons, but never their bearings.

    See my bins (0psi=40; 7psi=60; 15psi=80)


  • #2
    Do you have a reliable way to listen for detonation? I would be more concerned with detonation then egts. AFRS of 9 and 10 is way to rich. You shouldnt be hitting running the boost so high that it requires 10s to stop detonating.


    • #3
      900 degrees Celsius is HOT!
      It is not recommended to confirm proper installation by driving into walls or other barriers as this could cause personal injury or damage to the vehicle.


      • #4
        Anyone else feel free to provide your input, but a main bearing failure is usually only caused by:

        -oil starvation
        -extreme overloading
        -excessive wear

        In your case I really don't see the second two being an issue. This is very weird (and concerning) to me as you've now had it happen two times and I don't know many people stateside whom have ever had it happen on a VG.

        If you have a hoist and don't want to pop another engine in it right now, you can pull the front crossmember, remove the pan, drop the main girdle and replace the main bearings like that...


        • #5
          @stinky: no, i do not have a reliable way of detecting detonation. Thats my problem. Just my ears, and above a certain speed the car is so loud that i do not hear knocking any more. Even at lower speed my knock-ear is not reliable. I planned to test an electronic-knock-detection-item working with the stock knocking sensor next weekend. A friend has developped that for the z32. But now i first have to change my engine before doing further tests.
          My focus on exhaust-temp is only to do it right for my new turbo. People told me that those modern GT-Series-turbos do not like temps far above 900°C, 950°C should be the absolut max. I have never cared for that in the past, and my stock t3-turbo is still alive after 220.000km. And now after having installed my EXH-T-gauge i have seen values of 950 and more and i raised fuel up to AFs below 10. As this was not enough i advanced timing by about 4 degrees in the last three columns and wooom my engine failed. Maybe too much gauges do not always make things better. Fortunately i have a spare engine i will switch to together with the new power clutch i have ordered.

          I am just wondering why some of you drive so much timing without problems and i killed the engine at my first power-test. This is unfair.

          How do you set your timing stinky, how is your tuning procedure?

          edit: the bearings had been changed last year, i got about 5000km since then.
          edit: the failure was on one rod bearing, the bearing between the rod and the crankshaft


          • #6
            an idea: if pre-detonation is very extreme the explosion could expand far to early pushing on top of the still upwards-coming piston leading to an extreme force on the rod-bearing.

            another friend who owned a boost-up z31 years before until he changed to z32 had also the same problem.

            In all three cases it happened while going at spped close to top speed, this is a situation that you need a ´autobahn´ for.

            @Jason: After my first failure i also considered oil starvation but now i do not think that both engines had blockated oil channels.
            Attached Files


            • #7
              The detonation causing bearing failure thing is a possibility. As you mentioned though its more common to kill pistons. Done a compression test lately?

              The timing values you have seem high to me. At 15psi i need to be in the 18 btdc range with my current tune. That's not to say its correct.

              I do my timing by listening for detonation with my windows up. I have a quiet exhaust and I dont usually hit the highway so its not hard to hear. I do, however, feel I have a lot of room for improvement over the entire map. When its all tuned I may end up with higher timing numbers like some of the other people.

              In my opinion you best bet is to find a good loading dyno and go rent it for a couple hours. The best way to tune your timing is by doing steady state loading and consistent pulls to watch the power output. When you reach peak output you have found optimal timing. It also happens that the optimal timing is just before the engine detonates so you can get your engine tuned without encountering much detonation if you keep an eye on the power. I'll be able to tell you more about this method in a few weeks when we get our new dyno.

              Where is your egt probe?


              • #8
                have you done any recent changes to the engine that could cause the rotating assembly to go out of balance.. like a clutch change, flywheel change, crank pulley change.. etc.. ive seen that a few times now. where someone install a unbalanced aluminum flywheel on a engine and the bearings die shortly.. sadly enough this guy i know when through two engines before he relized what it was.

                Just a thought

                12.88 @ 114 mph.. in a 91 maxima at 14 psi


                • #9
                  @Jeremy: This is a good idea, i was also thinking about that, although the only changes i have made is the bigger turbo. Clutch will follow but has not installed yet.

                  @stinky: you are right, i was going quite aggressive timing, i should not have done that, i was too much focused on exh-temp. (But Jason should stop communicating his mega-aggresive time tables :-) )Going to a dynoshop would be a good idea, but i do not know anybody around having experience with that. But i think i should go that way and find a good tuner shop.
                  Compression was tested one week before and was perfect, i didn´t check it after the failure, but i will do before pulling the engine. My second engine is prepared for the swap next week.
                  let us know if you played around with your Dyno and gained experience with that stuff.


                  • #10
                    Dino wrote: (But Jason should stop communicating his mega-aggresive time tables :-) )
                    I don't understand why, but that 7.8:1 engine LOVED tons of timing. it could have been the various other aspects of the setup that allowed such advancement, I don't know. I never ran it on the autobahn though, and in hindsight I should have developed another tune for extended periods of high-boost.


                    • #11
                      Wouldn't running it so rich cause the higher EGTs? Too much fuel means not all of it burns in the combustion chamber, which means it'll be burning on its way out the exhaust inceasing temperatures in the manifold. That's how I always understood it.


                      • #12
                        MachZ wrote: Wouldn't running it so rich cause the higher EGTs? Too much fuel means not all of it burns in the combustion chamber, which means it'll be burning on its way out the exhaust inceasing temperatures in the manifold. That's how I always understood it.
                        yes but it can also starve the exhaust of oxygen quickly leading to black clouds of death without getting super hot, might plug the cat after running like that a while though.... 10:1 ugh


                        • #13
                 cat at the moment...


                          • #14

                            you remember my post concerning my second engine failure. Meanwhile we pulled and opened the engine and.......all the bearings look like brend new. Compression test was very good and looking into the combustion chamber with an endoskope also showed nothing negative....

                            Question: Where did this knocking noise come from? We will remount the engine an see if the noise is still there. Our last idee is hydro-lifter (right word for that?). We will know better tomorrow


                            • #15
                              it could be knocking and not have any damage yet.... I would yank your plugs and injectors, swap with known good ones?