massive vibrations at 2500 - 2900rpm

[alaska60]

I have a 1985 60 with a 383 stroker motor. I have new motor mounts and this thing vibrates so bad at 2500 rpms. slight vibrations at idle but massive at 2500 then it gets better as the rpms raise Vibrations are found when in nutural and reving to 2500. I can also feel the vibes as I travel. I am truly stumped on locating the vibration. Any ideas or experience with this ???

 

[PhilC64]

Motor mounts and trans mounts could be the issue. Get friendly with the underside and look for any cracks in the mounts.

 

[alaska60]

thanks .... I'll get to the tranny as i know the motor mounts are new.

 

[vipergrhd]

belt

if this runs on a multi-belt system i would remove 1 belt at a time,and if serpentine belt just remove it temporarilyto see if it goes away,it's possible that it could be 1 of your acc. i.e water pump,power steering pump.before i forget check the harmonic balancer if the ruber is starting to slip or signs of spinning.

john

 

[FJ40Jim]

The stroker 400/383 crank is factory imbalanced and must be used w/ the matching factory imbalanced flywheel and harmonic damper assembly. If any one of the components is wrong, the system will be out of balance, resulting in nasty vibe.

Had this once w/ AMC 390 engine w/ 304 flywheel. It ran, but tried to disassemble itself at certain resonant RPM's.