350 vibration
 

I have a 84 Chevy 4x4 with a 350 auto. At idle it vibrates and when revved up you can feel it vibrate. I thought it was missing but you can put it in gear and give it gas and hold the brake and it does not miss. I replaced the plug wires and the plugs looked good. Could it be the harmonic balancer? I need it smooth because I am trying to sell the truck.

Re: 350 vibration
 

Could be the H.B., but I'd check 1 more thing before I replaced it... Run a compression test across all the cylinders and make sure they are even. It could be all 8 are firing, but 1 cylinder is way weaker than the others. For example all are 120 and one is 80, or some stuff like that. A burnt valve can act like this.

Re: 350 vibration
 

check for bent/cracked/broken fan blades
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Re: 350 vibration
 

Thanks for the replies Compression was good. I slowed the timing down a little and it seemed to help at idle. The engine runs very well so it shouldn't be much.

Re: 350 vibration
 

Just tell 'em it has a mean cam in it ;)