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!

 

[Mac2]

Side note: WD40 is said to be the same/similar as belt dressing. I can't verify.

 

[SIBERNUT]

Now might be time for a reminder if your belt is behind plumbing

 

[OldDan1943]

Emergency belt dressing = liquid soap

 

[woodsea]

I’ve had excessive belt dust and squeaking using non Cummins belts. Only Cummins belts for me. No problems!

 

[ABfish]

I had 6CTA's with similar problems (squeaking and dust). Never fully solved either issue, but the Cummins belts were an improvement.

And a couple of years apart, the harmonic balancers on both engines got loose as the crank bolts began to back out. The first sign, which I didn't recognize at the time, was belt dust. New bolts, Loctite and torque to factory specs.

 

[Refill]

There seems to be a difference between a automotive and a marine application for belts.
This is what ChatGPT came up with.

The specific V-angle for serpentine belts typically varies by application, but in general:

• Automotive Serpentine Belts: Commonly have a groove angle of 36° to 40°.
• Marine Serpentine Belts: Often use a slightly different angle, usually in the range of 38° to 42° or more, to accommodate the unique demands of marine environments.

The slightly wider angle in marine belts helps improve water expulsion and maintain grip under wet conditions, which is critical for consistent performance in a marine setting. However, the exact angle can vary between manufacturers and specific belt designs.

Key Differences in Pulleys:​

1. Material and Corrosion Resistance
   • Marine Pulleys: Made from corrosion-resistant materials like stainless steel, aluminum, or specially coated metals to withstand saltwater and humidity. This prevents rust and ensures longevity in the harsh marine environment.
   • Automotive Pulleys: Typically made from standard steel or cast iron with anti-corrosion coatings, but not specifically designed for heavy saltwater exposure. Over time, exposure to moisture and salt can cause these pulleys to corrode.
2. Pulley Design and Groove Angle
   • Marine Pulleys: Often designed with deeper or slightly different groove angles to match the unique profile of marine serpentine belts, which improves water shedding and grip. They may also have wider or more aggressive grooves to handle high RPMs and the potential for water contact.
   • Automotive Pulleys: Designed to match the standard automotive serpentine belt angle and depth. They generally lack additional water-shedding features since automotive engines are enclosed and protected from direct water exposure.
3. Load and Durability
   • Marine Pulleys: Built to handle higher continuous loads and the demands of long, sustained high RPMs, which are typical in marine engines.
   • Automotive Pulleys: Optimized for variable RPMs, stop-and-go conditions, and lighter loads compared to marine engines.

So while both types of pulleys serve similar functions, the marine versions are built tougher with a focus on durability and corrosion resistance to meet the needs of the marine environment.


The 6bt Cummins was originally a automotive application and I assume a the drive pulley is for an automotive belt and the Balmar pulley might be for a marine belt. Just a thought. It would be interesting to hear what Balmar thinks about this.

 

[OldDan1943]

When changing the belt, preventive maintenance, tag the belt and save it.
If you are putting the boat for the winter, perhaps loosening the belt will extend the life of the belt or is that one of false theories?