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Q: Crank shaft wobbly

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Hi my Subaru recently made a noise I checked under the hood and realized that the pulley was wobbly the next day my battery was drained and car would t start I took the battery out and charged it again and it worked but will stall randomly as soon as I come to a stop or idle goes anywhere below 1000 rpms could this be caused by a loose cranckshaft and what should I do in this situation ?

My car has 345000 miles.
My car has a manual transmission.

A: Hi there. On the "front" end of t...

Hi there. On the "front" end of the crankshaft is a harmonic balancer held on by one large bolt that is torqued to 132.8 ft. lbs that is pretty tight. It’s not too likely that the bolt is "loose". The "balancer" though has two integral pulleys bonded to it that accommodate serpentine belts. If the rubber bond between the pulleys and the rest of the balancer has broken, the pulleys may appear wobbly or loose. The balancer performs a very essential function in dampening torsional forces applied to the crankshaft so if you suspect an issue with the balancer, it is best to get it repaired quickly because a faulty balancer can cause damage to the crankshaft.

Be careful who you select for the work. Using an air gun to remove that tight nut is fine but it is completely improper to use an air gun AT ALL to tighten the nut because such will damage the crankshaft, bolt and balancer. Consequently, there is a very specific procedure to install the new balancer which involves using a torque wrench to torque the bolt initially to 32.5 ft-lbs. Then after torquing the nut to a finished value of 132.8 ft-lbs., the mechanic needs to confirm that at least 65 degrees of arc was passed through in reaching that value of 132.8 ft-lbs. If not, the bolt is no good and a new bolt should be used. To avoid going through this kind of measurement, it is possible to just simply use a new bolt which might be cost be fairly cheap as a dealer item (the bolt is OEM only).

At any rate, if you want it done right, make sure the mechanic has a proper high capacity torque wrench. If you would like to have this taken care of, a certified professional from YourMechanic can come to your car’s location to inspect the noise and stalling issue to make the proper adjustments or repairs.

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