Wobbly crankshaft pulley

[stevemedcroft]

Hi guys.

I recently inherited an 82 GMC 6.2 that was in pretty bad shape. It ran but I had to do a few engine repairs to clean up the previous owner's left-behind mistakes. Repair one was to replace the coolant crossover pipe (thanks Robyn). Repair two was to purchase and install the bracket that supports the alternator pivot bolt (the long bolt at the bottom of the alternator had snapped at the block too so there was some removing and tapping in there as well).

Anyway, I just finished putting it all back together. Since I have no practical experience with the way this truck should run (I have not yet lived with whatever its quirky little noises and movements are), I have a question about the way the crankshaft pulley is moving and its effect on the alternator belt.

When running (mind you, the first time its run in 45 days with whatever fuel and fuel filter conditions were there when I got it), the crankshaft pulley has a slight wobble to it - maybe 1/16 to 1/8 of an inch in when spinning. The wobble creates a whipping see-saw in the lower part of the alternator belt which in turn is making a low whoop-whoop-whoop sound.

Is this pretty normal? Is it something I need to address at the cranksahft pulley or alternator adjustment. Is this (gulp) signs of the lower pulley problems I have been hearing about?

Thanks in advance,

Steve M.

[john8662]

Could just be a bad or loose pulley.

The important part to observe is the harmonic balancer behind the pulley, if it's wabbling that is where it can get scary.

The pulley bolts to the harmonic balancer via four 15-mm headed bolts, it's also possible that it's just not centered well either.

J

[stevemedcroft]

Could just be a bad or loose pulley.

Thanks for the ideas.

Got under the truck. All five bolts on the crankshaft pulley were tight. There was about 1/2 inch thick of crud all piled up on one side that may cause (or be evidence of) a balance issue but I ran the batteries down firing up the motor too many times so I have to wait for them to charge overnight to get another look at the pulley as the engine runs. I'll keep you posted.

[stevemedcroft]

After taking a second look at the wobbling, the harmonic balancer does appear to be moving back and forth. Just from eyeballing it, the movement is 1 or 2 mm. :(

What now? Run the truck as is because it's within normal range? Replace the harmonic balancer? Don't drive because running it will cause more damage? Possibility of a problem further back in the engine?

Thanks again.

[daustin]

Replace the balancer soon, a broken crankshaft may follow if you don't. The 6.5's are known for that problem. Mine wobbled a little then moved back and damaged the front cover so i had to replace both. Lots of fun. lol
Don