6BTA Belt Tensioner

[Ken Hudson]

My STBD belt started screeching when the alternator was was under load.
Pt. one is OK. I'm going to replace belts over the winter but wondered if the tensioner was getting weak. What has been the experience with them?

My 6BTA 270's were mfd. in 11/2001. They only have about 1,050 hrs. I wonder if it is time rather than hrs. that might cause them to lose tension.

Thanks.
Ken

[In Memory of Vicroy]

Ken - I've never heard of the tensioner spring getting weak - the only issue I've seen with them is the bearing going out and there is a retrofit to fix that you can find on the Cummins B forum on boatdiesel.com.

My 6BTA 250s were made in 1989, now with over 2,500 hours and the tensioners have never been touched....in fact, I changed the belts for the first time at about 2,000 hours, so its a pretty fool proof system.

Your alternator bearings may be going out - I've had several alternators on mine go out over the years and the bearings will "screech" badly when you first fire the motors up. I've shot the bearings with CX and kept one going now for 8 or 9 years. Up until very recently they used Delco alternators and starters and a lot of us have converted to the "one wire" system and use the cheap Delcos from the auto parts store vs. buying the hi-dollar replacements from Cummins.

You can easily check the tension by just putting a half inch socket handle into the 1/2" square hole in the tensioner arm and levering it to loosen the belt - compare the two motors and see if the tension on the spring seems the same.....but I'll bet its the alternator bearings.

UV

[Harry Babb]

Is it possible that the belt has stretched and is allowing the tensioner to be operating near the end of its "Stroke"......therby not applying the proper tension

I have had the same situation on my old Chevy trucks....single "Vee Belt".....the belt would wear so that it bottomed out in the pulley on the alternator.....no matter how tight you pulled it, it still squealed.

Question: Are you making a lot of "Belt Dust"???

hb

[In Memory Walter K]

There IS an updated tensionizer that Cummins came out with for the 6B series.

[Ken Hudson]

Vic-
I do have the original 140 Amp Delco's. It sure sounds like a belt rather than a bearing, but I am always on the bridge when it does it and can't say for sure.

Harry-
Both engines have always made belt dust. I figured that it was the nature of the beast and just kept cleaning it up.

Walter-
There is a Cummins dealer not too far from my shop. I'll stop in and see what they have any info. They are a truck place, but I suppose it is the same.

Ken

[Harry Babb]

Ken, belt dust is the nature of the beast. But if you are getting excessive dust on the "Squealing Engine" then it may be possible that the belt is wearing from Rust on a pulley.

I have always had problems like that with single groove pulleys on my Merc engines......until I replaced them with Aumuinum Pulleys.

I am real curious what you find....keep us posted

hb

[Mikey]

Ken,
What Vic said. Fishing one of the first UVI's with Vic his alternator started squeaking. He raised the engine cover and gave it a shot of CX and we fished all day. Then every morning before leaving the dock the alternator would squeak, same routine. We'd run for hours and troll for hours and never look at it again. He got back to the camp a week later before replacing the offending beast. CX - great stuff.

[Ken Hudson]

Here's what I have found:

The alternator and idler pulley bearings seem fine. I can't really get a feel for the compararative tension of the idlers (PT vs. STBD) due clearance on the sttbd side.

My engines are so close to the bulkhead that I am considering cutting access holes in the bulkhead to access to the 'square' in the idler pulliey hole.

I have spoken with my Cummins guy. He is around the corner from my shop (Medford,MA) and is a friend. He deals with trucks but researched the idler pulley thing through all his Cummins sources.

He could find no history of idler pulley problems. In the last five yrs.......as far as his 'sales history' goes back, he has sold one. He is a pretty busy dealer north of Boston. He said that if i needed replacement that they cost around $125 from Cummins. He also said that Dayco makes them for Cummins and that he could do better buying direct.

His suggestion was to change the belts. I think that really makes sense. I have a lot of belt dust, but in careful inspection, I see no cracks, but the rubber feels dry. I have owned this boat for five years but it hasn't had many hrs. due to my renovations, etc. I have never changed the belts. They may be original from the re-power in 2001 for all I know.

Sometimes 'time' is the factor rather than hrs. of operation.

Ken