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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / August 2005Harmonic balancer on Mazda 626
Mazda 626 V6 2.5L ATX I just replaced the water pump and the timing belt. After this work, the car shakes badly when idle in "D". It does not shake in any other gear. Why is this happening, the harmonic balancer? Or a sensor? Where is this beast located and do I need to remove everything I just installed, like timing belt cover, alt/water pump belts, etc? >Mazda 626 V6 2.5L ATX >I just replaced the water pump and the timing belt. >After this work, the car shakes badly when idle in "D". It does not >shake in any other gear. Why is this happening, the harmonic balancer? How does it *run*? Runs like normal but just idles badly? Or runs like crap and idles comparably? Was the belt *broken* when you replaced it? If so, maybe you suffered some bent valves if your motor does not freewheel. If you installed the timing belt one tooth off it will idle very poorly if it even runs at all. Do a compression test to rule out the above. If you installed the timing belt extremely tight, there will be more drag on the engine making it want to die. If your motor is equipped with balance shaft(s), they may have gotten out of sync with the crankshaft while you were doing the other work. Did you remove a motor mount in order to access the timing belt? Maybe it is still loose. Did you check your ignition timing after replacing the belt? If it is too far retarded, the idle quality will be poor. Just some ideas to get you started. > Mazda 626 V6 2.5L ATX > [quoted text clipped - 6 lines] > Where is this beast located and do I need to remove everything I just > installed, like timing belt cover, alt/water pump belts, etc? 'Harmonic balancer' is just another description for the crank pulley. There is a rubber cushion sandwiched between the concentric hub and belt pulley sections of the crank pulley that absorbs minor, normal engine vibrations. You could have damaged it during removal, but I doubt this is the cause of your current dilema. You did *something* wrong or this vibration would not be occuring right after the repair. For purposes of diagnosis, it matters whether the engine currently has full power or not. IOW, is the engine misfiring due to bent valves or an improperly installed timing belt, OR is it running properly and the vibration cause lies elsewhere? If the engine is running properly, you may have damaged an engine mount during removal/replacement. Did you have to take a mount off or pry on it at any time? This would seem to be the most likely cause of vibration only in gear (unless your perception/description of the vibration isn't quite accurate). Or did you crank the engine with the timing belt not on correctly and nick valve(s), causing the engine to lose compression and run poorly (vibrate)? Did any of the cam sprockets spin out of control while you were trying to hold them in place during belt replacement? That alone could nick a valve. Finally, one piece of advice that another poster gave is wrong, so I will correct it --- "If you installed the timing belt extremely tight, there will be more drag on the engine making it want to die." I'm not trying to be an A-hole, but this is just simply not going to happen in the real world, so don't waste time thinking your belt --with automatic tensioner system!-- is "too tight". That's the least of your concerns right now. Toyota MDT in MO 'Harmonic balancer' is just another description for the crank pulley. There is a rubber cushion sandwiched between the concentric hub and belt pulley sections of the crank pulley that absorbs minor, normal engine vibrations. You could have damaged it during removal, but I doubt this is the cause of your current dilema. ================================= I found where it is.... I don't recall damaging it or doing anything to it. You did *something* wrong or this vibration would not be occuring right after the repair. For purposes of diagnosis, it matters whether the engine currently has full power or not. IOW, is the engine misfiring due to bent valves or an improperly installed timing belt, OR is it running properly and the vibration cause lies elsewhere? ======================================== The engine has full-power and is otherwise acting normally. No noises, no smoke, no vibration in drive, normal gas mileage, etc. If the engine is running properly, you may have damaged an engine mount during removal/replacement. Did you have to take a mount off or pry on it at any time? This would seem to be the most likely cause of vibration only in gear (unless your perception/description of the vibration isn't quite accurate). ===================================== Yes, I had to take one engine mount off. I put it back in place, and I thought I torqued it right. Maybe I damaged it somehow? Maybe I damaged the engine mount on the other side, by jacking up the engine? Or did you crank the engine with the timing belt not on correctly and nick valve(s), causing the engine to lose compression and run poorly (vibrate)? Did any of the cam sprockets spin out of control while you were trying to hold them in place during belt replacement? That alone could nick a valve. ============================= I did. The first time I put on the timing belt, it went on completely wrong and I tried to start the engine. It did not start. Is this Mazda 2.5L engine non-interference engine? I heard it was. >The engine has full-power and is otherwise acting normally. No noises, >no smoke, no vibration in drive, normal gas mileage, etc. I would do a compression test because it is easy to misjudge this. >Yes, I had to take one engine mount off. I put it back in place, and I >thought I torqued it right. Maybe I damaged it somehow? Maybe I damaged >the engine mount on the other side, by jacking up the engine? You could LOOK at the mount(s) and make sure the bushings look okay. Jack the motor up again (use a pine board under the oil pan) and see if anything looks amiss with the mounts as the motor moves up and down. >I did. The first time I put on the timing belt, it went on completely >wrong and I tried to start the engine. It did not start. Is this Mazda >2.5L engine non-interference engine? I heard it was. Whether or not it is, as long as you turned over the motor several times with the belt on to check for interference, you should have been okay. Does the engine use balance shafts? When you took off the crank damper did you notice if it had an offset weight inside? Most V6 engines don't use balance shafts, but I'm not explicitly familiar with this engine. If it does have balance shafts they will be driven by the timing belt. Also, if the timing belt was installed one tooth off, the resultant change in cam timing will have negative effects on engine performance. And if the ignition distributor is driven by the cam you'll have a double whammy.
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