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2.5L 96 Legacy Outback Engine Vibration


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2 replies to this topic

#1 theeddie

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Posted 27 September 2004 - 06:22 AM

96 Outback Legacy has engine vibration at about 3k on the tach. Car sitting still, or at speed (about 70 mph). Vibration is felt in steering wheel when car is still. Car has about 91k on it. I saw this on a 99 also, though less obvious. Any ideas what this might be? :-\

Thanks,

PS:

While stopped making a left turn in her 98 Outback Wagon, my wife got rear ended by a dump truck going about 45 mph. Car totalled, wife not a scratch. Needless to say we are looking for another Outback!!:D

#2 Adnan

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Posted 27 September 2004 - 11:34 AM

Hi,

Engine vibration can be attributed to several causes, some external to the engine, some internal. Since it happens at only one RPM, it sounds like you're hitting a resonance mode of some kind. The vibration you feel in the steering wheel suggests an engine/chassis interaction of some kind.

My suspicions would first be directed to the engine (and tranny) mounts. They may be worn, and therefore not damping out the engine modes as well. If I recall correctly, a flat-4 engine is perfectly balanced, with all primary and secondary modes cancelling each other.

The next set of possibilities are internal problems, with something out of balance. That's unlikely unless the engine was worked on or the flywhel changed for an unbalanced one. An incorrectly aligned timing belt?

Glad to hear your wife's okay. My wife rolled her '96 on the freeway (hit & run, never found the guy) and walked away unscathed. We now have a 2002 OBW, naturally.

Regards,
Adnan

#3 Commuter

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Posted 27 September 2004 - 12:09 PM

If I recall correctly, a flat-4 engine is perfectly balanced, with all primary and secondary modes cancelling each other.

True to a point. The 180 degree "V" (flat, horizontal) does provide a cancellation of certain vibrations, since they oppose each other. (I couldn't tell you which mode or harmonic, since I'm not that up on it.) But, the 2 banks of cylinders are offset. The pistons are not directly across from each other. So there is still a vibration mode. (I believe it would be one that would want to 'twist' the engine about a vertical axis, as oppose to 'rocking' it.)

My guess would be engine mounts as well. They are probably worn / hardened / aged. When I had the engine work done on my 97 OB over 2 years ago, I had them put in the newer liquid filled mounts. It helped to dampen a slight vibration that I got after putting a lightweight crank pulley on.

There's another thought for you. Crank pulley. But I can't say I've ever heard of one going bad (in this sense).

Commuter




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