Engine vibrations help

Guys, I have a small block Chevy 350 stroked to 383. It ran smooth without any problems for about 25,000 kms. about 6 weeks I noticed it was running rough and was down on power. It happened gradually, it wasn't overnight. Checked plugs. One looked bad (#8) with a buildup of deposits. Changed all the plugs. Problem was still there. Checked the plugs again and #8 Looked new. Checked plug cable and it was no good. Changed the rotor/cap/cables and set timing and tps. Power is back but I still get a vibration.
Engine will idle smooth from 600 - 900 then vibrated at about 1000, smooth from 1100 to 1400 then vibrate from 1500 - 1600 then smooth to 1900 and start to vibrate again from there. This stays the same whether in neutral, drive, accelerating/decelerating or under heavy load pulling a trailer.
Any ideas/suggestion as to what the problem and solution maybe?
Thanks,
Mike
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The rotating assembley was balanced I'm hoping?
Doc
<DIV><FONT face=Arial size=2>Guys, I have a small block Chevy 350&nbsp;stroked to 383. It ran smooth&nbsp;without any problems for about 25,000 kms. about&nbsp;6 weeks I noticed it was running rough and was down on power. It happened gradually, it wasn't overnight. Checked plugs. One looked bad (#8) with a buildup of deposits. Changed all the plugs. Problem was still there. Checked the plugs again and #8 Looked new. Checked plug cable and it was no good. Changed the rotor/cap/cables and set timing and tps. Power is back but I still get a vibration. </FONT></DIV> <DIV><FONT face=Arial size=2></FONT>&nbsp;</DIV> <DIV><FONT face=Arial size=2>Engine&nbsp; will idle smooth from 600 - 900 then vibrated at about 1000, smooth from 1100 to 1400 then vibrate from 1500 - 1600 then smooth to 1900 and start to vibrate again from there. This stays the same whether in neutral, drive, accelerating/decelerating or under heavy load pulling a trailer.</FONT></DIV> <DIV><FONT face=Arial size=2></FONT>&nbsp;</DIV> <DIV><FONT face=Arial size=2>Any ideas/suggestion as to what the problem and solution maybe?</FONT></DIV> <DIV><FONT face=Arial size=2></FONT>&nbsp;</DIV> <DIV><FONT face=Arial size=2>Thanks,</FONT></DIV> <DIV><FONT face=Arial size=2></FONT>&nbsp;</DIV> <DIV><FONT face=Arial size=2>Mike</FONT></DIV></BLOCKQUOTE></BODY></HTML>
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I would suspect so since it was good for the first 25,000 kms
Mike
<DIV><FONT face=Arial size=2>Guys, I have a small block Chevy 350&nbsp;stroked to 383. It ran smooth&nbsp;without any problems for about 25,000 kms. about&nbsp;6 weeks I noticed it was running rough and was down on power. It happened gradually, it wasn't overnight. Checked plugs. One looked bad (#8) with a buildup of deposits. Changed all the plugs. Problem was still there. Checked the plugs again and #8 Looked new. Checked plug cable and it was no good. Changed the rotor/cap/cables and set timing and tps. Power is back but I still get a vibration. </FONT></DIV> <DIV><FONT face=Arial size=2></FONT>&nbsp;</DIV> <DIV><FONT face=Arial size=2>Engine&nbsp; will idle smooth from 600 - 900 then vibrated at about 1000, smooth from 1100 to 1400 then vibrate from 1500 - 1600 then smooth to 1900 and start to vibrate again from there. This stays the same whether in neutral, drive, accelerating/decelerating or under heavy load pulling a trailer.</FONT></DIV> <DIV><FONT face=Arial size=2></FONT>&nbsp;</DIV> <DIV><FONT face=Arial size=2>Any ideas/suggestion as to what the problem and solution maybe?</FONT></DIV> <DIV><FONT face=Arial size=2></FONT>&nbsp;</DIV> <DIV><FONT face=Arial size=2>Thanks,</FONT></DIV> <DIV><FONT face=Arial size=2></FONT>&nbsp;</DIV> <DIV><FONT face=Arial size=2>Mike</FONT></DIV></BLOCKQUOTE></BLOCKQUOTE></BODY></HTML>
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<DIV><FONT face=Arial size=2>Guys, I have a small block Chevy 350&nbsp;stroked to 383. It ran smooth&nbsp;without any problems for about 25,000 kms. about&nbsp;6 weeks I noticed it was running rough and was down on power. It happened gradually, it wasn't overnight. Checked plugs. One looked bad (#8) with a buildup of deposits. Changed all the plugs. Problem was still there. Checked the plugs again and #8 Looked new. Checked plug cable and it was no good. Changed the rotor/cap/cables and set timing and tps. Power is back but I still get a vibration. </FONT></DIV> <DIV><FONT face=Arial size=2></FONT>&nbsp;</DIV> <DIV><FONT face=Arial size=2>Engine&nbsp; will idle smooth from 600 - 900 then vibrated at about 1000, smooth from 1100 to 1400 then vibrate from 1500 - 1600 then smooth to 1900 and start to vibrate again from there. This stays the same whether in neutral, drive, accelerating/decelerating or under heavy load pulling a trailer.</FONT></DIV> <DIV><FONT face=Arial size=2></FONT>&nbsp;</DIV> <DIV><FONT face=Arial size=2>Any ideas/suggestion as to what the problem and solution maybe?</FONT></DIV> <DIV><FONT face=Arial size=2></FONT>&nbsp;</DIV> <DIV><FONT face=Arial size=2>Thanks,</FONT></DIV> <DIV><FONT face=Arial size=2></FONT>&nbsp;</DIV> <DIV><FONT face=Arial size=2>Mike</FONT></DIV></BLOCKQUOTE></BLOCKQUOTE></BODY></HTML>
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The rotating assembley was balanced I'm hoping?
Doc,
Do you think it could be possible for the balancer to give out and cause this?
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Yeah it a possibility but I doubt that's it. The balancer being shot would have vibrations throughout the RPM range, with the vibrations getting worse as RPM's increased. He has the vibrations coming and going at different engine speeds.
First thing I'd do is run a compression test on all 8-cylinders, especially seeng as how #8 was all buggered up before.
Doc
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would
worse
especially
Right.
Good point.
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"especially seeng as how #8 was all buggered up before."
The plug cable was the culprit for # 8. If one or more of the cylinders was down in compression, wouldn't power be down also. Since addressing the dead cable, the power is still real good.
Mike
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was
dead
Whoops, forgot that you found a bad plug wire for #8. My Bad.
Doc

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