gm sp383 vibration
Thread Starter
Instructor
Joined: Sep 2014
Posts: 160
Likes: 2
From: Annapolis Maryland
gm sp383 vibration
replaced my 350 m21 3.73 with a sp383 autogear m20 3.08. getting noticeable vibration starts at 1300R to 1700R no change in/out of gear, clutch in or out. put in recommended flywheel for ext balanced gm SP383. any suggestions? 
Melting Slicks
Joined: Jun 2011
Posts: 3,116
Likes: 598
my ZZ383 vibration was 2000-2500. I ended up replacing the (flywheel / Clutch) problem much better / reduced but never really gone. These externally balanced motors are difficult to get a perfect balance. I also tried to rotate / remount the clutch 180 degrees this worked sort of / reduced but also never went away completely.
Race Director
Joined: Jul 2015
Posts: 13,082
Likes: 3,399
From: SW Florida.
GM and everybody else has been building external balanced motors for a long time. They don't custom balance any of them. I put a 400 sbc in a boat. Guy sold me a 454 flywheel thinking it was 400 sbc. Boat shook like my old 650 Triumph at and just above idle. If you assemble it with the correct parts it will not vibrate.
Thread Starter
Instructor
Joined: Sep 2014
Posts: 160
Likes: 2
From: Annapolis Maryland
my ZZ383 vibration was 2000-2500. I ended up replacing the (flywheel / Clutch) problem much better / reduced but never really gone. These externally balanced motors are difficult to get a perfect balance. I also tried to rotate / remount the clutch 180 degrees this worked sort of / reduced but also never went away completely.
Melting Slicks
Joined: Jun 2011
Posts: 3,116
Likes: 598
thanks for that, sounds very similar. wish GM sold these w/ the flywheel supplied (you get a flex plate instead), they would get better feedback if there was some kind of mismatch apparent, i think. the vibe is livable but i worry that something's gonna break eventually.
But I guess it depends how a person measures the vibration.
I used how much the mirror shakes . Or the feel in the steering wheel.
Most people I asked what they think, didn't notice or think there is a vibration change from 900-4500 rpm
Melting Slicks
Joined: Dec 2009
Posts: 3,233
Likes: 657
From: Thunder Bay
thanks for that, sounds very similar. wish GM sold these w/ the flywheel supplied (you get a flex plate instead), they would get better feedback if there was some kind of mismatch apparent, i think. the vibe is livable but i worry that something's gonna break eventually.
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Team Owner
Joined: Oct 2004
Posts: 81,241
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From: altered state
St. Jude Donor '05
^^^^I always take a new clutch assy and FW in and have them balanced no matter what the sales ad claims.
This engine doesnt "smooth out" til about 3k but doesnt move even a hair. Good balancing jobs are worth it your bearings will thank you
This engine doesnt "smooth out" til about 3k but doesnt move even a hair. Good balancing jobs are worth it your bearings will thank you