vibration

046mag · 11-26-2007, 09:43 PM

I have a 1976 chevy short box, recently built a 350 for it. bored .030 over,.050 lift cam flat top pistons, swirl ported 2.02 heads. Runs well, But has a vibration from about 2200 RPM to 2800 RPM. Vibration goes compleatly away with higher or lower RPMS.

Any Ideas to what is causeing this would be grartly appriciated.

Thanks

75K30 · 11-26-2007, 10:00 PM

2200 to 2400 rpm huh? So this is rpm related, so the vibration is in the engine. What is the condition of the balancer?
Have seen the rubber in a harmanic balancer deteriorate and allow the balancer to slip causing all sorts of vibrations.
May also verify that you do not have an externally balanced flexplate on this thing.
Internally balance components only.
That would be my best guess.

046mag · 11-26-2007, 10:14 PM

harmonic balancer looks good is tight canot wiggle or move it rubber seems to be holding tight. This truck has a four speed and the flywheel that is on it is correct not sure what is causeing it but very strange, you would thing if it was the harmonic balancer the vibration would grow exponentionaly as the RPMS increased

75K30 · 11-26-2007, 10:36 PM

Balancers can be funny, andnot always vibrate all of the time, well let ne re-phrase that, some vibrations that actually occur may not be felt, even though they are present.
So the balancer appears to be alright, and no problems. Are any of the pulleys bent?
What type of fan are you running? Could there be a problem there? Maybe a bent blade or something like that?

046mag · 11-26-2007, 10:48 PM

as far as i know the pullys are alright, running a flex fan "noisy" will be comeing off soon. will check the pullys out tommorrow when i pull it in the shop. This vibration rattels the truck pretty good can feel it in the shifter hard to tell if it does it when driveing but can definatley feel when parked in neutral.

75K30 · 11-26-2007, 11:03 PM

I hope you find it. If it vibrates enough to rattle the truck a little, it can't be good on the crank, or bearings.
Gotta be in the rotating assembly.
You know, I was just thinking, I had a similar problem after a DYNO pull, and it turned out to be a crack in the water pump pulley. Could not see it very well, but it was there, and would allow the pulley to flex some causing a vibration.

11-26-2007, 09:43 PM	#1
046mag Full Member Join Date: Oct 2007 Location: La Grande, Oregon Posts: 18	vibration I have a 1976 chevy short box, recently built a 350 for it. bored .030 over,.050 lift cam flat top pistons, swirl ported 2.02 heads. Runs well, But has a vibration from about 2200 RPM to 2800 RPM. Vibration goes compleatly away with higher or lower RPMS. Any Ideas to what is causeing this would be grartly appriciated. Thanks

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11-26-2007, 10:00 PM	#2
75K30 Senior Member Join Date: Jul 2006 Posts: 2,518	2200 to 2400 rpm huh? So this is rpm related, so the vibration is in the engine. What is the condition of the balancer? Have seen the rubber in a harmanic balancer deteriorate and allow the balancer to slip causing all sorts of vibrations. May also verify that you do not have an externally balanced flexplate on this thing. Internally balance components only. That would be my best guess.

11-26-2007, 10:14 PM	#3
046mag Full Member Join Date: Oct 2007 Location: La Grande, Oregon Posts: 18	harmonic balancer looks good is tight canot wiggle or move it rubber seems to be holding tight. This truck has a four speed and the flywheel that is on it is correct not sure what is causeing it but very strange, you would thing if it was the harmonic balancer the vibration would grow exponentionaly as the RPMS increased

11-26-2007, 10:36 PM	#4
75K30 Senior Member Join Date: Jul 2006 Posts: 2,518	Balancers can be funny, andnot always vibrate all of the time, well let ne re-phrase that, some vibrations that actually occur may not be felt, even though they are present. So the balancer appears to be alright, and no problems. Are any of the pulleys bent? What type of fan are you running? Could there be a problem there? Maybe a bent blade or something like that?

11-26-2007, 10:48 PM	#5
046mag Full Member Join Date: Oct 2007 Location: La Grande, Oregon Posts: 18	as far as i know the pullys are alright, running a flex fan "noisy" will be comeing off soon. will check the pullys out tommorrow when i pull it in the shop. This vibration rattels the truck pretty good can feel it in the shifter hard to tell if it does it when driveing but can definatley feel when parked in neutral.

11-26-2007, 11:03 PM	#6
75K30 Senior Member Join Date: Jul 2006 Posts: 2,518	I hope you find it. If it vibrates enough to rattle the truck a little, it can't be good on the crank, or bearings. Gotta be in the rotating assembly. You know, I was just thinking, I had a similar problem after a DYNO pull, and it turned out to be a crack in the water pump pulley. Could not see it very well, but it was there, and would allow the pulley to flex some causing a vibration.