Bearing noise on front of the motor

When I crank my truck it sounds like a bearing going bad. Kinda like a scraping sound that increases with the rpm. I have replaced the tensioner, alternator, idler pulley, power steering pump and took the belt off the ac. The water pump does not leak but it is the only part on the front of the motor I have not replaced. 2006 172K

You did not specifically mention the belt tensioner in your description of the parts you had changed.

Maybe you just didn't list it.

I usually replace the idler pulley when I replace the belt tensioner, just for good measure.

I would think you could take the main belt off and crank the engine for a moment and that would tell you if the noise is external, or not.

If nothing is spinning externally and the noise is still there, then the noise is most likely internal.

It shouldn't take but a very short bit to tell.

Others should be along shortly to give you some other ideas.

I have a very similar noise coming from underneath the engine that I couldn't pin point at first. So the first thing I did was removed both belts and the noise was still present, so that ruled out those parts. Judging from where the noise was coming from it had to be either in the bottom end or the rear main. Using a stethoscope, it was obviously coming from the oil pan area. So my guess is a bad crank bearing. Luckily she still runs strong and has good oil pressure.

stewartr said:

When I crank my truck it sounds like a bearing going bad. Kinda like a scraping sound that increases with the rpm. I have replaced the tensioner, alternator, idler pulley, power steering pump and took the belt off the ac. The water pump does not leak but it is the only part on the front of the motor I have not replaced. 2006 172K

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Did you try it without the main belt? If not just take if off and start it, if the noise is gone then its the water pump..

lt1jerome said:

I have a very similar noise coming from underneath the engine that I couldn't pin point at first. So the first thing I did was removed both belts and the noise was still present, so that ruled out those parts. Judging from where the noise was coming from it had to be either in the bottom end or the rear main. Using a stethoscope, it was obviously coming from the oil pan area. So my guess is a bad crank bearing. Luckily she still runs strong and has good oil pressure.

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Take a look at the starter gear. Sometimes the spring that retracts it breaks and they bounce off the flex plate. Still starts and runs normal but makes a strange sound when running that comes from the bottom of the motor at the rear. If you had a bad main bearing you would almost certainly have a loss in oil pressure and a rod bearing you would usually hear a knock.