C2: More Research on Alt. Pulley

[Michael H.]

A few days ago, the 67 350 HP alternator pulley was discussed and it is thought that the 67 AIM and JG incorrectly listed the 3875968 as being the correct pulley/fan for 350 HP with power steering. While researching the topic, I noticed that the 66 AIM also incorrectly lists the same part number for that application. The 66 printing of the parts book lists the 3829387 as being correct for 350 HP w/power steering.

My question is, does the 66 JG show the one piece 3875968 pulley/fan or the 3829387 with separate fan? Is the 66JG the same for 66 and 67?

Michael

[Wayne M.]

Many inconsistencies w/'65 Alt. Pulleys info

Sorry, can't answer for '66, but the 1965 AIM seems to have it correct -- ie. shows the 3829387 [3.625" od. -- no integral fan] on L79 w/N40 (also used as the non-P/S alt. pulley on L78's). My July '65 GM parts book confirms the above 2 uses.

But as I dig deeper into all '65 pulleys and their application, I find several instances of disagreement with JG (at least the 3rd ed.) [ie. they list no integral fan/pulley; no 3.05" dia. pulley for hi-horse air]. I may start a thread on this for my enlightenment.

[Peter L.]

Re: C2: More Research on Alt. Pulley

Michael - The '66 TIM&JG, 4th Ed. does not have the same information as is in the "67 TIM&JG. Fact is there is no mention of any "special" alternator pulley applications for the 327/350hp w/ PS and w/o AC or the 327/350 w/o PS and w/o AC.

The ALTERNATOR PULLEY APPLICATION table lists

300hp 2-13/16" pulley dia. one piece fan/pulley
300hp w/ AC 2-5/8" pulley dia. one piece fan/pulley

L79 3-5/8" pulley dia. separate pulley/fan
L79 3-3/8" pulley dia. separate pulley/fan

So from the table it appears that the alternators on the base 327 motors use the one piece fan/pulley and the alternators on the L79 327 motors use the separate pulley/fan. Only the C60 AC option that makes a difference in the alternator pulley and that is in the pulley diameter not the fan/pulley configuration.

It's still curious why the '67 TIM&JG calls out P/N 3875968AW (an older part number) for the 327/350hp w/ PS when the 3909817AW which has the identical pulley diameter but a different configuation to the fan blade portion of the pulley/fan assembly is used on other '67 alternator application.

Pete

[Michael H.]

Re: C2: More Research on Alt. Pulley

It sounds like the 66 JG is different, and much more correct, than the 67. While it does correctly list the separate 3 5/8" pulley/fan for all 350 HP engines, it doesn't mention that there is a difference between 350 HP with power steering and 350 HP without power steering. The parts book liste the L79 without p/s as using the 3871242 and the L79 with p/s as using the 3829387. These two pulleys look similar but the 242 is about 1/2" thicker than the 387. Both have separate fans.

I think the pulleys listed in the 66 JG for all 300 HP engines are correct. All would have had attached fans and smaller diameter pulleys.

The most probable reason why the 67 AIM showed the 3875968 instead of the 3909817 is the fact that the number didn't officially change in the system until April of 1967. The AIM page was probably carry over from the 66 AIM with only the necessary part number changes which did not include the change of the 3875968. Many of the original AIM's in the plant didn't have all of the running changes listed while others did. The change may have appeared in some of the manuals that were used for the engine dress line but not others. I have a few originals and there are a lot of changes listed in these that are not shown in the reproduction/reprints. The actual dimensions of the two different pulleys appear to be exactly the same so the change was probably minor. I still believe the AIM is incorrect on the 67 L79 w/power steering. It should list the 3829387 with separate fan. The parts book shows the 3875968/3909817 as being used only with base engine and A/C or base engine with 62 amp alternator, if there is such a thing. I can scan and post the entire page from the parts book if there's interest. Also would be nice to hear from some owners of original 67's on this issue.

Michael

[Michael H.]

Re: Many inconsistencies w/'65 Alt. Pulleys info

Wayne,

While searching for info on the 66 and 67 pulleys, I found info for the 65 that you were looking for. The base engine appears to have a separate pulley/fan and the pulley is a 2 13/16", 3871241. The pulley for Sp.H/Per 65 with A/C was a 3 3/64", 3846180.

[Gary Bishop]

Re: C2: More Research on Alt. Pulley

Depending on the DATE of the AIM could that be why there are differences?

[Michael H.]

Re: C2: More Research on Alt. Pulley

Sorry Gary, I haven't forgotten you. It's just that I'm not home now and won't return until later Friday. All of my books and info are there. I'll scan and post a few pages from the 66 and 72 printing of the parts books so we can get to the bottom of this pulley problem.

Michael

[Rick S.]

Re: C2: More Research on Alt. Pulley

Mike,
I haven't commented lately because I'm trying to learn as much as I can but I am in a position to buy a correct alt with a 3875968 pulley for $30.00. What do you think, pull the trigger or forget it. In case you forgot I have a 3829387 pulley presently.
Regards,
Rick

[Michael H.]

Re: C2: More Research on Alt. Pulley

Rick,

Unfortunately, we never did get much input from original owners on this issue so at this point, we really have no way to make a decision. However, I'm convinced that the AIM is incorrect and because the JG uses this info, it too is incorrect. I believe all 66 and 67 L79 350 HP engines are supposed to have a separate fan and pulley and all 300 HP base engines for 66 and 67 would have had the one piece fan/pulley assembly. Every parts book I've now looked in clearly states this also. The parts book also lists the 3875968 as being used on 66-67 base engine cars with air conditioning but also lists it as being correct for 66-67 base engine with 62 amp alternator. However, there never was such a combination.

The 3875968 pulley assembly was changed to a 3909817 in April of 1967 but I believe there is no major visible change in the part.

At this point, I would use the separate fan and pulley on any 350 HP car and take my chances on the judging. As was previously stated by someone, most judges accept this combination, even though it does not agree with the JG.

In either case, I would definitely purchase the alternator that you found for $30. if it's dated correctly for your car. Then you would have BOTH of the pulley and fan combinations.

Michael