SC fan clutches--why the difference

[R N.]

Re: SC fan clutches--why the difference

Scott-----


Check out the fan clutch seen in the first link of your original post in this thread. As I mentioned previously, this is is a GM #3937771 as used for many 1968-70 C-60 Corvette applications as well as some non C-60 applications. Note that it uses bolts for fan attachment as I would expect for a 3937771. Also note the date of 11/69 on this clutch which means it could have been used for a very late 1969 or early 1970 Corvette.

Your second link shows a GM #3916139. This clutch uses studs for fan attachment and that's exactly what I would expect for a 3916139 (or, a 3916140 or 3916141).

Why the difference between a 3937771 and the others as far as fan mounting? I have no idea.

Hi Joe,

To confirm, 3937771 is correct for my E 1970 NON C60 BBC?

[R N.]

Re: SC fan clutches--why the difference

Kurt,

The fan-clutch has to be removed to see the "FRONT" and "66" stampings on the fan. To measure the fan just CAREFULLY measure the distance from the CENTER of the fan-clutch to the tip of any blade. If the measurement is 8 3/4" then it's a 17 1/2" fan, simple math C = 2R.
The 66-67 Corvette 427 and 68-70 Corvette fan measures 17 1/2" in dia., 3.00" BC, 2 3/8" hub hole, about 2 1/4" blade pitch (34.5 degrees), and is stamped "FRONT" and "66".

Your probably have the correct fan but only the stampings will tell you for sure.

Dave

Hi Dave,

I pulled my fan/clutch this evening..... It's stamped "FRONT" and also has the letter "H" stamped by itself.

[David L.]

Re: SC fan clutches--why the difference

Hi Dave,

I pulled my fan/clutch this evening..... It's stamped "FRONT" and also has the letter "H" stamped by itself.

Kurt,

Is the measurement from the center of the 2 3/8" hub hole to the tip of any blade 8 3/4"? Does the pitch measure about 2 1/4"? I assume that the BC measures 3.00".

Dave

[R N.]

Re: SC fan clutches--why the difference

Kurt,

Is the measurement from the center of the 2 3/8" hub hole to the tip of any blade 8 3/4"? Does the pitch measure about 2 1/4"? I assume that the BC measures 3.00".

Dave

Hi Dave,

YES, the hub hole measured 2-3/8", 3" measured diagonally for the bolt hole centers and a quick measure from fan clutch center to fan blade tip approx. 8-3/4" or a smidge more. If I recall correctly, my '66 L72 fan has the same markings

[D S.]

Re: SC fan clutches--why the difference

Jim,
My March built 1970 has the same as yours. I went to eBay and looked at C-2 and C-3 fan clutches and the many of them have studs. In the NCRS TDB archives I see references to studs and photos of fan clutches with studs being used through at least 1972. I guess it doesn't matter much as long as the fan is attached firmly. The JG makes no reference.

Since the JG is silent I figured that all that matters is that the fan is secured to the whatever by whatever. I believe that the fan clutch for my March 1970 LS-5 with AC is correct with studs and nuts but if someone wants to use bolts that's okay, too.

[Joe L.]

Re: SC fan clutches--why the difference

Joe, I thought the second link was the pie pan that required bolts and the first link was the fan clutch that required the studs.

Scott-----


No, the way it appears on my screen, the 3937771 is the first (upper) link and the 3916139 is the second (lower) link. In any event, the clutch that is being sold by John Meissinger is the 3937771.

[Terry M.]

Re: SC fan clutches--why the difference

Since the JG is silent I figured that all that matters is that the fan is secured to the whatever by whatever. I believe that the fan clutch for my March 1970 LS-5 with AC is correct with studs and nuts but if someone wants to use bolts that's okay, too.

You are reading far too much into the lack of information in the judging guide.

The lack of information simply means:
1) we didn't know
2) we didn't have enough data to make a decision
3) we couldn't agree on the details
You may chose any one of these.

[David L.]

Re: SC fan clutches--why the difference

Hi Dave,

YES, the hub hole measured 2-3/8", 3" measured diagonally for the bolt hole centers and a quick measure from fan clutch center to fan blade tip approx. 8-3/4" or a smidge more. If I recall correctly, my '66 L72 fan has the same markings

Kurt,
What about the pitch? Place the fan on a flat table and measure the vertical height of several blades. I suspect it will be 2 1/4".

Dave

[Joe L.]

Re: SC fan clutches--why the difference

Since the JG is silent I figured that all that matters is that the fan is secured to the whatever by whatever. I believe that the fan clutch for my March 1970 LS-5 with AC is correct with studs and nuts but if someone wants to use bolts that's okay, too.

Scott-----


Is the fan clutch of the "pie-pan" configuration (as seen in the eBay item of John Meissenger)?

[R N.]

Re: SC fan clutches--why the difference

As the saying goes.... "When all else fails, read the book"

Don't know why I didn't look earlier, but in the 1970 Factory Assembly Manual, UPC C60, Sheet C1, clearly shows this application as studs attaching the fan clutch hub to the water pump and BOLTS ATTACHING THE FAN TO THE FAN CLUTCH.

Furthermore, UPC LS5, sheet A8 shows the same attaching method for the 454 motor WITHOUT C60.

Clutch # 3937771 is called out for both of these applications.

Standard production cars, UPC 6, Sheet A3 show the application with studs for mounting the fan to the fan clutch and also at the fan clutch hub to the water pump. The fan clutch for the standard application is called out at 3916139.