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Engine Suddenly Developed a Vibration

Tiny
JERRYLMO
  • MEMBER
  • 2001 CHEVROLET BLAZER
  • 227,629 MILES
A strange thing happened on the highway, heading to work, Tuesday morning. About halfway to work I had to accelerate pretty hard and afterward as I was cruising about 65, I noticed a vibration that'd never been there before. I immediately checked the oil pressure & it was normal. I have a AutoTap scanner on a Palm Pilot and it showed all cylinders were firing. There was no smoke coming out the exhaust. O2 readings looked normal and fuel injector pulses looked normal. Coolant temp was holding normal. I kept heading towards work and the longer it went the more it felt like a pulsation, not a vibration. At a stop light the idle would sag under 700 RPM then come back up. The engine never stalled and accelerated like normal. Under light acceleration the vibration seemed to fade away but holding a steady speed or idling the vibration is very noticeable. Ever since I owned it, when you shut down the engine, it made the infamous 4.3L V6 clunk-clunk. (GM issued service bulletins about it.) When I got it home, before I shut if off, I raised the hood to see if there was anything obviously wrong but didn't see anything. What I did notice was, when I shut the engine down, there wasn't any clunk-clunk. Is it possible that something happened to the balance shaft? Thanks for your time.
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Friday, March 16th, 2012 AT 1:14 AM

5 Replies

Tiny
CARADIODOC
  • MECHANIC
  • 33,874 POSTS
If you feel the vibration when standing still, you might suspect the harmonic balancer. The arrow in this photo from rockauto. Com points to the gel insert than can let go. If the outer cast ring rotates on the hub, and it has an extra offset weight, it will cause a vibration. Many engines are "externally balanced" and need that extra weight on the balancer and torque converter. Auto parts stores have large catalogs full of replacement balancers.
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Friday, March 16th, 2012 AT 4:16 AM
Tiny
JERRYLMO
  • MEMBER
  • 27 POSTS
The engine had also developed an oil leak on the back end of the intake manifold so I got it removed and noticed oil in the intake runners and the intake ports. The left side intake gasket fell off when I lifted the manifold off. The right side didn't take much to get it off either. Back to the balancer. I purchased a new one from the local parts store. I compared the two and noticed that, just like in your picture there's a timing mark, nearly in line with the keyway groove on the new one. On the old one, if the keyway is the 12 o'clock position, the timing mark is more like about 10 o'clock. To me that kind of points toward the balancer. Forgive my going on but after removing the intake manifold I verified that the balance shaft still turns. The crankshaft can be rotated back and forth about 1/4" or so before it moves. I'm guessing that's 227K miles of wear on the timing chain. If you have any thoughts or ideas, I'd be interested in hearing them. Thank you for your time.
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Friday, March 23rd, 2012 AT 2:38 AM
Tiny
CARADIODOC
  • MECHANIC
  • 33,874 POSTS
Don't read anything into the location of the key way. What you're looking for is evidence that the cast outer ring turned or is moving off the hub. If the timing marks are different between the two, that would appear to be the problem.
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Friday, March 23rd, 2012 AT 2:50 AM
Tiny
JERRYLMO
  • MEMBER
  • 27 POSTS
The more I see the more it looks like the balancer is the culprit. That being the case, since I'm going to remove the balancer can the oil seal for the balancer be replaced without a lot of grief? Thanks, Jerry
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Friday, March 23rd, 2012 AT 7:14 PM
Tiny
CARADIODOC
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Drill a small hole in the metal part of the seal, then run a long thin self-tapping screw into it. You might have to use two screws directly across from each other. Once they bottom out on the crankshaft journal, they will pull the seal out.

You can also reach into the hole with a cotter pin pick to pry the seal out. That's a fat pick with the end bent at a 90 degree angle.
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Friday, March 23rd, 2012 AT 7:51 PM

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