1969 350/350 Alternator Pulley 1970831
Purchased the 1970831 pulley on E Bay. Represented as GM Original ? Did not pay any more than a Repo so not out any real money. Dimensions match those from another poster for a 1970831 pulley. Question is this a GM Pulley or just another Repo ? All I have seen are zinc plated. Thanks for any thoughts.Pulley 1.jpgPulley 2.jpgPulley 3.jpg
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Re: 1969 350/350 Alternator Pulley 1970831
Steve-----
Whenever one purchases a part advertised as "NOS" that's not in a sealed GM box or package, there's always the question as to whether it actually is an NOS part. In this case, I believe it is. Here's why: this pulley is zinc plated with a chromate overplate. Orinal PRODUCTION and older SERVICE examples of this pulley lacked the chromate overplate and were simply zinc plated. Later GM SERVICE examples of this pulley had the chromate overplate. I don't think any of the reproductions are so-finished---they're all simply zinc plated, as-original.
The GM #1970831 pulley was last used for Corvettes for certain 1977 applications. It was discontinued in November, 1984 and replaced by GM #3844100, a pulley that had been around since the 1964 model year. There is a very slight difference between the 1970831 and 3844100. The 1970831 has an OD of 3-3/16" and shaft orifice of 11/16" whereas the 3844100 has an OD of 3-7/32" and shaft orifice of 43/64". These are close enough that the pulleys can be used interchangeably.
By the way, the 1970831 is a Delco-Remy part number and specification. The 3844100 is a Chevrolet part number and specification.In Appreciation of John Hinckley -
Re: 1969 350/350 Alternator Pulley 1970831
Joe,
As usual you had the details and history. Guess I can have zinc plated and have a GM pulley though not original. Thanks again for spending the time to reply. SteveComment
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Re: 1969 350/350 Alternator Pulley 1970831
Steve------
You don't need to have it zinc plated; it's ALREADY zinc plated. All you have to do is to immerse the pulley in a very dilute acid solution and the chromate overplate will be removed leaving the underlying zinc plating. You want to leave it in the solution for the smallest amount of time necessary to remove the chromate without also removing the zinc.
You might start by just using vinegar (acetic acid). Dip it in, leave for a few seconds and retract. Re-dip as necessary for 10-15 seconds at a time.In Appreciation of John HinckleyComment
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Re: 1969 350/350 Alternator Pulley 1970831
Steve,
I found that the only major difference between the 2 pulleys was the inside diameter measurement around the surrounds the large nut that holds the pulley on to the alternator.
GM # 1970831.....I.D. = 1.41" +/-
GM # 3844100.....I.D. = 1.62"+/-
The larger I.D. gives you more room for the socket when installing and removing the pulley.
DaveComment
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Re: 1969 350/350 Alternator Pulley 1970831
Joe, Thanks for the tip on removing chromate. And, David for addition info on dimensions.Comment
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