70 454 Cooling Fan with A/C

**Jack H.** · November 23, 2005, 12:12 PM

Re: 70 454 Cooling Fan with A/C

Absent specific scoring directives on various parts stated in the applicable Judging Guide or in the standard deduction tables of the NCRS Judging Reference Manual, judges allocate originality points for given line items (see applicable Flight Score Sheet) across a five axis universe:

Finish, Date, Installation, Configuration and Completeness

So, if a given part was otherwise correct except for its date coding, you'd lose 20% of the available originality points. If it was incorrectly dated and a substitute part with different PN or obvious geometry difference, you'd lose 40% of the available originality points for violation of both the Date and Configuration axis.

**Joe L.** · November 23, 2005, 06:49 PM

Re: 70 454 Cooling Fan with A/C

Carr-----

First of all, the GM #3993889 fan blade assembly is not usually the correct unit for a 1970 with LS-5 and C-60. GM #3993889 is, essentially, a SERVICE-only fan blade assembly for your application. The original fan used for your application was GM #3969926. It is POSSIBLE that the GM #3883889 may have made it into PRODUCTION during the 1970 model year. However, if it did, at all, it was well after your car was built.

I am not sure of the configuration of the GM #3969926. I know that it is a 7 blade fan of 17-1/2" OD. However, I don't know, for sure, if it had the "pointed tips" (for noise reduction purposes) like the 3993889. I believe that it did, but it may not have. Also, I don't know if the part number was stamped on one of the fan blades, or not.

The 1969 with 427 and C-60 fan assembly was GM #3955182. This is a 7 blade fan assembly of 17-1/2" OD. It DOES NOT have the "pointed tips". However, it definitely DOES HAVE the part number stamped on one of the blades and they are usually dated, too.

I doubt that a GM #3955182 would have been used for your application, but I would not rule it out. On the other hand, are you sure that's what's on the car? Confirming it, one way or the other, should be quite easy as I have described above. If a date code is present, that would also provide a lot of information as to whether it could originally have been installed on the car.

Let us know what you find.

**Tom R.** · November 25, 2005, 04:18 PM

Re: 70 454 cooling fan with a/c

Carr, I had a similar situation last year. I found a 889 fan blade that was a service replacement from 1972. It was an NOS part. I payed $400. I'm still a couple of years away from getting my car judged, but after I found out how hard it was to try and find this fan blade I thought it would be better to take the hit for a wrong date. Tom

**Carr C.** · December 4, 2005, 01:26 PM

Re: 70 454 Cooling Fan with A/C

It took me a while to get the numbers off the current fan.

The fan is stamped with the following on the blades 1613282, and under that is 916617 D79.

What your take on this part number and the number before the date?

I assume the date is April 7, 1969, or maybe it's April 7, 1979?

Thanks for your input!

**Carr C.** · December 4, 2005, 02:09 PM

70 454 with A/C - water pump and fan clutch?

I have seen quite a few posts about the small water pump hub on 1970 big blocks vs. '71 and later big blocks.

What is the easiest way to identify the small vs large hub while on the car?

Is there a measurement you can make across the studs/nuts, or some other easy indentifier?

While looking for the correct 1970 BB with A/C fan, I noticed that the correct one has a distance of ~ 3" across the cooling fan bolts, while most have 3 1/4", which I assume is the same small vs. large comparison, except on the other end of the fan clutch.

Finally, what would be the correct part # for the clutch and visial identifers? Round vs flat thermal unit on the front?

What components would be judged and how?

Thank you.

**Joe L.** · December 4, 2005, 02:49 PM

Re: 70 454 Cooling Fan with A/C

Carr----

1613282 is a Cadillac part number. However, it's possible that it was also used for Chevrolets. I don't have any other information on it, though. It's also possible that it's not a GM part number, at all. Usually, the date on GM fans is a month and year. So, "D79" would decode to April, 1979.

**Joe L.** · December 4, 2005, 03:01 PM

Re: 70 454 with A/C - water pump and fan clutch?

Carr-----

1960-1970 fan blade assemblies for use with fan clutches have a 3" bolt circle; 1971-82 have a 3-1/4" bolt circle.

1960-1970 Corvette fan clutches have a 5/8" pilot hole; 1971-82 Corvette have a 3/4" pilot hole. Similarly, the pilot shaft on 1960-1970 waterpumps is 5/8" OD; the pilot shaft on 71-82 Corvette waterpumps is 3/4" OD.

1960-1970 measurement BETWEEN waterpump hub bolts/studs centers (NOT bolt circle) is 1-1/4". 1971-82 measurement BETWEEN bolts/studs centers is 1-1/2". This can easily be measured on the car.

Correct fan clutch for 1970 with 454 and C-60 was GM #3937771. A derivative of this number MIGHT be stamped on the side of the hub flange.

**Joe L.** · December 4, 2005, 04:49 PM

Addendum

By the way, the GM #3937771 fan clutch is Sweitzer-manufactured clutch and has a "rectangular bar, bi-metallic" thermostat. It has "straight" fins. It has a unique front configuration with a "pie-pan-like", smooth, dished perimeter surrounding the finned center section. The rear is finned all the way to the perimeter.

The 3937771 is a Corvette-only piece and was first used for the 1968 model year for 327 with C-60 as well as many 427 applications. It was also used for the 1969 and 1970 model years in similar applications. It was not used after 1970 since the flange and fan bolt patterns changed.

The GM #3937771 was discontinued from SERVICE in 1980 and replaced by the 3916141. The latter clutch is an Eaton-manufactured unit and is configured significantly differently

**Carr C.** · December 4, 2005, 11:02 PM

Re: Addendum

Joe,

Is this what it should look like?

http://cgi.ebay.com/ebaymotors/Corvette-Fan-Clutch-1969_W0QQitemZ4594493654QQcategoryZ34209QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Thank you.

**Craig S.** · December 4, 2005, 11:21 PM

Re: Addendum

Carr - that looks like an aftermarket supplied part....note the notches to allow both bolt circle patterns on the water pump. See the righthand most clutch in this photo on Fred Olivias site (link below) ....I THINK this may be the right appearance for your clutch but I bet Joe Lucia will verify.....Craig

GM Fan Clutches at Fred Olivia's site

**Craig S.** · December 4, 2005, 11:25 PM

Re: Addendum - CORRECTION

I wish we could edit posts.....the reference to the righthand clutch I posted is wrong......it is not a Sweitzer clutch with the rectangular bar. The LH clutch is.....but it is not the variety Joe mentions for the 70, it is the style I have for my 67. Sorry for any confusion my post caused......Craig

**Joe L.** · December 4, 2005, 11:29 PM

Re: Addendum

Carr-----

No, not at all. This seller is a "dreamer". This unit may have COME OFF the car he said that it did, but it didn't originally reside there. This is an aftermarket-type unit and it even looks like a cheap, non-thermal type one, at that. A used, aftermarket, non-thermal fan clutch? I'd say it's virtually worthless.

Among other things, note the "slots" for the clutch hub. These are a "one-size-fits-all" feature of many aftermarket fan clutches. That's so they can be used for BOTH common bolt patterns. OEM clutches use HOLES and not "slots". Some Delco replacement fan clutches do have the "slots", but they're NOT an OEM clutch----they're just an aftermarket-type unit in a Delco box.

**Joe L.** · December 4, 2005, 11:32 PM

Re: Addendum

Craig-----

None of the fan cluches pictured are the 3937771.

**Joe L.** · December 5, 2005, 12:11 AM

Re: 70 454 with A/C - water pump and fan clutch?

Carr-----

These pictures are not real good, but they'll give you the idea.

GM #3937771

70 454 Cooling Fan with A/C

70 454 Cooling Fan with A/C

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