Belt Tensioner wobble

[Jeff Lewis]

I recently purchased an Albin with twin 270hp Cummins 6BTA´s. When I replaced the belts, I noticed that the port engine´s belt was shreddedd. Both engines had significant belt dust present. I cleaned and checked all pulleys and replaced belts. When started, I noticed the starboard engine´s belt tensioner and belt movement was “rock solid”, but the port engine´s belt was “wobbling” and the belt tensioner was”bouncing” rapidly 1/4″. All pulleys look rock solid. Pushing mid span on the belt, It felt significantly looser than the starboard engine. I assumed the belt tensioner was bad and replaced it. After I put the new tensioner on I had the same problem. All pulleys look clean, appear to be aligned, have no noise, and appear to spin free with no wobble. The engine seems to idle a little low, and at higher rpms the shake lessens, but it´s still not nearly as smooth as the starboard engine. Any ideas?

Topic

[Jeff Lewis]

I’m out of town, but I’ll look next week. It looks the same in pictures (ie the tensioner pulley relation to the alternator and idler pulley seem the same). This wobble is either the cause of or the result of the belt “jumping” or “slapping” between the crank and water pump. As I said before, both of those pulleys run smooth. I tried adding additional tension to the tensioner while the engine was running with mixed results (smoothed out some, but still not rock solid like other engine). I have included pictures from both engines so you can see relation.
Jeff

[Rob Schepis]

Are the alternators and brackets 100% identical between the two engines? Could something have been changed out over time effecting the belt wrap?

[Jeff Lewis]

Identical. All solid. It looks almost like the belt is too long or the tensioner is not providing enough tension (but it’s new). I’ll look into the idler pulley upgrade, although I don’t think it is responsible for my current problem.
Jeff

[Rob Schepis]

Good that it is a twin setup so you can compare the two. With belts off any difference in the sound or feel when you spin the alternators?

I would start with upgrading your idler to a grade-8 bolt setup and replace the bearings with new. That should be done regardless of whether or not it is creating your current problem because it will eventually bite you in the a** if left OEM. That metal cover on your idler pulley indicates that this is still factory setup. Here’s some parts options and a read. I am working to update this artice to include swapping the bearings on existing pulleys as an option to not go all new or just to renew the bearings on installs that are already upgraded to the grade-8 bolt.

https://www.sbmar.com/product/complete-idler-pulley-upgrade-kit/

https://www.sbmar.com/product-category/engine-components/idler-pulley-kits/

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