SC fan clutches--why the difference

[Joe L.]

Re: SC fan clutches--why the difference

Hi David,

YES, 5-blades. The fan is mounted on the car so I assume I can't see the word Front and the number 66. Can you see these without the taking the fan/clutch assembly off?

Kurt------


If the car has C-60, it should have a 7 blade fan with "spiked" blade tips.

[R N.]

Re: SC fan clutches--why the difference

Kurt------


If the car has C-60, it should have a 7 blade fan with "spiked" blade tips.

Joe,

Thank you - Non-A/C car

[David L.]

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

[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

Dave, thank you. I'm going to pull it off this week to check

[R N.]

Re: SC fan clutches--why the difference

More help needed....

Now that I know my fan is correct, are there differences between the SBC and the BBC fan clutches for E1970? I know earlier (Mid-year) clutches had a different clutch shaft etc and some used studs vs. bolts for attaching to the fan.

For my application (1970 BBC) were studs used for attaching to the fan or bolts? Are the attached photo correct? (NOTE: The fan is not mine)

As always, than you in advance.

[Joe L.]

Re: SC fan clutches--why the difference

More help needed....

Now that I know my fan is correct, are there differences between the SBC and the BBC fan clutches for E1970? I know earlier (Mid-year) clutches had a different clutch shaft etc and some used studs vs. bolts for attaching to the fan.

For my application (1970 BBC) were studs used for attaching to the fan or bolts? Are the attached photo correct? (NOTE: The fan is not mine)

As always, than you in advance.

Kurt-----


The 3937771 fan clutch used BOLTS for attachment of the fan (just as you have pictured).

[R N.]

Re: SC fan clutches--why the difference

Kurt-----


The 3937771 fan clutch used BOLTS for attachment of the fan (just as you have pictured).

Hi Joe,

Is the 3937771 fan clutch correct for my E1970 BBC application?

[Joe L.]

Re: SC fan clutches--why the difference

Hi Joe,

Is the 3937771 fan clutch correct for my E1970 BBC application?

Kurt-----


Yes.

[R N.]

Re: SC fan clutches--why the difference

Kurt-----


Yes.

THANK YOU Joe!

[D S.]

Re: SC fan clutches--why the difference

Kurt-----


The 3937771 fan clutch used BOLTS for attachment of the fan (just as you have pictured).

I have seen many fan clutches from 1969 to 1972 Corvettes on small and big block engines (but certainly not seen every one of them) and the majority of those I have seen used studs with lock washers and nuts to attach the fan blade to the fan clutch. There seems to be some confusion regarding using studs versus bolts when attaching the early C-3 fan blades. ???

[Jim T.]

Re: SC fan clutches--why the difference

I have seen many fan clutches from 1969 to 1972 Corvettes on small and big block engines (but certainly not seen every one of them) and the majority of those I have seen used studs with lock washers and nuts to attach the fan blade to the fan clutch. There seems to be some confusion regarding using studs versus bolts when attaching the early C-3 fan blades. ???

Scott my July built original owner 1970 SB with factory air uses studs, lock washers, and nuts. I am the only one that has replaced the water pumps, still have in use original fan clutch and fan with 160K+ miles. It is a lot easier to line up the water pump pulleys with studs sticking out of the water pump flange. My 68 L79 uses bolts.

[Joe L.]

Re: SC fan clutches--why the difference

Scott my July built original owner 1970 SB with factory air uses studs, lock wahers, and nuts.

Jim------


Your application should have used the 3937771, too. Every example I have seen of this fan clutch has used bolts for fan attachment. The 3937771 is the clutch with the "pie-pan" configuration surrounding the front of the clutch.

The GM #3916139, 3916140, and 3916141 clutches used for non C-60 applications did use studs for fan attachment. These clutches do not have the "pie-pan" peripheral configuration.

[D S.]

Re: SC fan clutches--why the difference

Scott my July built original owner 1970 SB with factory air uses studs, lock washers, and nuts. I am the only one that has replaced the water pumps, still have in use original fan clutch and fan with 160K+ miles.

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.

[Joe L.]

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.

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.

[D S.]

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.

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.