1972 Base Engine Alternator Pulley - What's Right?

[Don L.]

Hi all.

I've recently come to doubt the correctness of the pulley on my '72 base engine (no A.C.). I looked at figure M 12.4 the new edition judging guide and while the description says I need a stamped pulley, the pulley's face in the photo looks like it has machining marks in it. Am I looking for a stamped pulley or a machined piece?

Would someone please post a section view picture of a known original base engine alt pulley, showing how the V belt orientation sits in the fore/aft position? Specifically, is the V groove centered in the pulley or is it set fore or aft? Correct GM part number would be extremely useful too.

Thanks so much!

[Patrick H.]

Re: 1972 Base Engine Alternator Pulley - What's Right?

Don,

No photos in those of my car?

Patrick

[Jeffrey S.]

Re: 1972 Base Engine Alternator Pulley - What's Right?

Don,
Page 3 of Patrick's photos has some good pictures of the alt. pulley. It seems to show a symmetrical groove identical to the photo of the '72 base below (i of 3 that I neglected to attach to the email)
Jeff

[Patrick H.]

Re: 1972 Base Engine Alternator Pulley - What's Right?

More here:

https://flic.kr/s/aHsjYhVebu

[Don L.]

Re: 1972 Base Engine Alternator Pulley - What's Right?

Thanks guys!

Patrick, I did look at your linked photos and noted that photo #950 (yellow car) seems to show a machined pulley. Photo 785 on the green car also looks to be a machined part. Am I seeing right? I know the yellow car to be a benchmark car but I don't know the green one.

Jeff, the pulley in your photo looks to be a stamped part but it also looks smaller in diameter than others I've seen. Am I seeing that right?

The judging guide calls for the base engine to use a stamped pulley.

My situation is that I have a machined pulley AND the V groove is not centered, which has the alt belt riding forward, causing a "too close" to the back side of the power steering pulley condition. Something's not right and I'm doubting my alt pulley. I want it right but am confused on just what I need. Unless I'm seeing it wrong (I hope I am), photos here don't seem to match the jg description.

Thanks again

[Paul O.]

Re: 1972 Base Engine Alternator Pulley - What's Right?

Here are some photos of a 1972 6500 mile car no A/C of the alternator.

[Patrick H.]

Re: 1972 Base Engine Alternator Pulley - What's Right?

Here are some photos of a 1972 6500 mile car no A/C of the alternator.

Same car I linked to, Paul.

[Joe L.]

Re: 1972 Base Engine Alternator Pulley - What's Right?

Here are some photos of a 1972 6500 mile car no A/C of the alternator.

Paul------


This is actually the pulley I would expect. It's a GM #1970831 (which was discontinued many years ago and replaced by GM #3844100).

[Joe L.]

Re: 1972 Base Engine Alternator Pulley - What's Right?

More here:

https://flic.kr/s/aHsjYhVebu

Patrick-------


Is there a small, single digit stamped on the front of this pulley?

[Don L.]

Re: 1972 Base Engine Alternator Pulley - What's Right?

Thanks again guys. I appreciate all the help and inputs.

Joe, I had done an archive search and found that you had suggested 1970831 as the original part number. What I didn't have is your advice that suggests how a pulley as shown in Paul's and Patrick's help is 1970831. Don't the photos of this part look like a machined part? If stamped, as the '70-'72 judging guide details, I think I would expect to see a 2 piece pulley, joined together at the center of the V groove. How else would it be stamped?

I clearly have a wrong pulley on my alternator. As I stated above, my V groove is forward of center, unlike what's shown in this thread. For the life of me, I can't figure out what I need to be TFRP. Do I need a stamped pulley as detailed in the JG or do I need what looks to be a machined part, as shown in the photos here?

Feedback much appreciated...

[Paul O.]

Re: 1972 Base Engine Alternator Pulley - What's Right?

Same car I linked to, Paul.

Patrick I knew that but the one photo seemed to be at a better angle. Just trying to help out.

[Patrick H.]

Re: 1972 Base Engine Alternator Pulley - What's Right?

Patrick I knew that but the one photo seemed to be at a better angle. Just trying to help out.

Yup, no problem.
I looked at several of another car I have here, and none of those have the correct angle either.

[David L.]

Re: 1972 Base Engine Alternator Pulley - What's Right?

Enclosed is a photo of a NOS 3844100 pulley which measures 3.19" in diameter and 0.83" thick. The I.D. of the machined area measures 1.62".

The 1970831 pulley (also used on 70 Z28 models) measures 3.19" in diameter, 0.83" thick, and with an I.D. measurement of 1.41".

GM #3844100 replaced GM # 1970831 as per Chevrolet Parts History.

Dave

[Leonard M.]

Re: 1972 Base Engine Alternator Pulley - What's Right?

Don, I probably added to the confusion with my comment to your WTB on the CF. As you say, you have 2 issues; belt alignment and when you change your pulley you of course want the correct one.
As you already know, the JG says stamped steel for base and L46; machined steel for LT-1 and LS6 except for LT-1 w/AC, but a few have been seen with the machined pulley. And, Fig 12.4 shows a machined pulley Not a stamped one as described.
Richard Prince's Restoration Guide gives the same information as the JG; all LT-1s w/o AC and LS6s use a pulley machined from solid steel material, But what he adds is this. "While this high performance pulley is randomly seen on other engines, most other applications used a zinc-plated, stamped steel pulley."
Even Joe says it is a confusing subject back in 2007.
"Well, it turns out that the JG was more correct than other GM information that I referred to earlier. However, these alternator pullies are one of the more vexing subjects regarding old Corvettes. I've always considered the GM spec information "sketchy" and unreliable. This case just proves my point that much more."
Reproductions of the 3 3/16" deep grove high performance pulley are easily found. Originals are Very hard to find and if they were the commonly used pulley on most all applications they would be plentiful. Here is an original machined steel and a reproduction. There are slight differences with the most noticeable being the smooth face. I'd go with the stamped steel for your base 1972 and say the JG has an incorrect picture.

[Gary B.]

Re: 1972 Base Engine Alternator Pulley - What's Right?

When the manual was written, it was based on what we knew at that point of time. As time marches on, we learn more and people help along the way. Alternator pulleys are another item we are learning more about, at least for me anyways. As I learn more and people have told me about errors, I try to keep the manual updated.

Pictures are from a 24,000 mile, base motor, power steering 4-speed. car. Built L17. July 17th, pretty late car.

I wonder if power steering versus non-power has an effect on pulley?

The more I learn, the more I understand how much I don't know?

Gary Bosselman