Troubleshooting loud squeak on Cummins6BT

[Bob328]

I thought I'd share an interesting problem that came up on our Marine Trader 34DC. I kept hearing an increasing squeaking from the front of the Cummins 6BT. It sounded like bearing on the belt tensioner was bad. I replaced it and the squeak was still the same. Used stethoscope seemed it was from idler pulley. Replaced idler with no improvement! I had another mechanic verify. Decided to remove Balmar generator to have it tested. All good! Alternator shop owner that I've known many years recommended cleaning crank pulley with a steel brush. Still squealed, so he said try belt dressing! This was a serpentine belt with about 100 hours on it. Wouldn't you know the belt dressing cured it! It really sounded like bearing, not a squeal. After $600.00 and 3 days work we finally found success I have put 20 hrs run time since without any noise. Thought I'd share with the forum.













Two mechanics

 

[dhays]

What does the belt dressing actually do?

 

[Crux]

Serpentine belts can become 'case hardened' on the grooved side, causing them to lose their grip and slip. Use of dressing should be considered temporary. I would replace it now with Cummins oem or Gates Green Stripe.

 

[Bob328]

Replacement ordered. I have 2 spares, but not sure how old they are. I was surprised that the belt caused the issue with only 100 hours and only one year old.

 

[dhays]

I have one spare and it is old. I have wondered about getting another replacement just in case.

 

[Crux]

Replacement ordered. I have 2 spares, but not sure how old they are. I was surprised that the belt caused the issue with only 100 hours and only one year old.

Even tho only one year old to you, no telling how long seller had on his shelf; was he diligent in keeping his stock rotated ?....and same goes for distributor before that.

 

[Ken E.]

I have 2x6bt Cummins and experienced this problem after a repower with recon engines. As part of the repower, I upgraded to 160 amp alternators. According to the shop doing the work, the squawking belts needed to be tightened up, which they were and problem solved. I don't have the details of what they did. Send me a pm and I'll put you in touch with the shop and mechanic.

 

[Xlantic]

I had a similar experience with two rebuilt 6B 5.9 Cummins. One of the belts squeaked. I changed the belt and the squeak continued.

The rebuild-shop suggested tightening the belts by replacing the lower support for the alternators (see photo below) with a slightly longer one.

Although I had two fabricated I have not yet installed them as using belt dressing has eliminated the noise, at least for now.

 

[Crux]

I see you have some belt dust showing up...might want to verify alignments with a straightedge.
Also, one of the sheaves might've suffered a bump during repower handling? An easy thing to check with dial indicator and belt removed
As I read, the issue is with this engine and not the other?

 

[Xlantic]

Yes, only the starboard engine.

I will check the alignment. Thanks!