Yellow or Green Belt for 6BTA5.9?

[Charles Burton]

I need some additional help to identify which belt I need for my 6BTA5.9-M3 CPL 1975 S/N 46160878 and 46160385 engines.
I have Delco Remy alternators P/N 3934778 which appear like the “Large Frame Alternator” in the Seaboard picture.
I have the idler pulley.
My alternator frame mounts in-between the mounting bracket arms like the green belt picture but unlike the “Large Frame Alternator” which mounts forward of the mounting bracket arm in the yellow belt picture.
My alternator has a lower swing arm P/N 3934941 similar to but shorter than the “Large Frame Alternator” lower swing arm in the yellow belt picture.
Which belt do I need?

Topic

[Charles Burton]

Many thanks.

[Tony Athens]

You have a Delco type 19SI alternator—-Standard factory option for that motor–Your picture shows that 100%–Look at the top mount

GREEN BELT

[Rob Schepis]

Green belt.

Idler pulley upgrade should be considered. Notice the sheetmetal cap on yours but not on mine.
https://www.sbmar.com/product/complete-idler-pulley-upgrade-kit/

[firehoser75]

Charles,
To me, it looks just like the belt set up on my engine, and I use the “green” belt (most common on these engines). Just replaced mine a few weeks ago.
Good luck,
Tom

[Author]

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