Fan Clutch adjustment...C2

[Larry S.]

I have 66 BB (427-425) coupe that is running hot 220 deg+. After much adjusting (timing, etc) I believe the fan is not turning fast enough when the engine has warmed up. I have taken the fan/clutch off and inspected it and found no oil leaks at all (perfectly clean). On the front (rad side) of the fan clutch there is a coiled spring that can be adjusted/moved a half turn at a time either clockwise or counter-clockwise. This moves the center pin also a half turn. Does this change the operating rpm or cut-in point of the fan clutch? If not, is there something else I can do to increase the rpm of the fan system without replacing this fan clutch as it looks to be near new. Numbers (ink stamped) on it are C19D1A on the spring side of the clutch. Also has CK ink stamped at 180 deg to the first number, which is also on the spring end of the clutch. Also stamped into the metal on the same side says " STORE THIS FACE DOWN".
Anyone with an idea or two?

[Joe R.]

Re: Fan Clutch adjustment...C2

Larry,

How did you get the temperature you called out? If it's from the dashboard gauge, I would recommend using an IR gun to verify it. Does it only run hot only when in stop and go traffic? If so, test the fan clutch or maybe temporarily swap in a new one to see if the problem is definitely in the fan clutch.

Joe

[Larry S.]

Re: Fan Clutch adjustment...C2

Yes, I guess I should borrow an IR gun and check the true temp. Thanks.

[Joe R.]

Re: Fan Clutch adjustment...C2

I have 66 BB (427-425) coupe that is running hot 220 deg+. After much adjusting (timing, etc) I believe the fan is not turning fast enough when the engine has warmed up. I have taken the fan/clutch off and inspected it and found no oil leaks at all (perfectly clean). On the front (rad side) of the fan clutch there is a coiled spring that can be adjusted/moved a half turn at a time either clockwise or counter-clockwise. This moves the center pin also a half turn. Does this change the operating rpm or cut-in point of the fan clutch? If not, is there something else I can do to increase the rpm of the fan system without replacing this fan clutch as it looks to be near new. Numbers (ink stamped) on it are C19D1A on the spring side of the clutch. Also has CK ink stamped at 180 deg to the first number, which is also on the spring end of the clutch. Also stamped into the metal on the same side says " STORE THIS FACE DOWN".
Anyone with an idea or two?

Hi Larry:

That "coil spring" is a bi-metallc coil that opens and closes a valve on the fan clutch based on the temperature of the air passing over it. In principle, you can change the setpoint by rotating the spring a few degrees, but I have never seen a good description of what would be an appropriate amount. I don't recommend fiddling with it without first doing some careful analysis.

I have thought about doing a little "science project" buy putting a fan clutch in the oven when my wife is not home, and monitoring the temperature response of the bi-metallic spring.

Keep in mind that all the valve does is to change the coupling between the fan and the water pump from "sort of tight" to "tighter." There is always slippage in any mode, but less slippage when the cluch tightens up. It's very hard to tell the difference visually.

If your IR gun measurements show a genuine overheating condition that occurs only at idle, first check to make sure you are getting plenty of vacuum advance at idle. That can make quite a difference. If the vacuum advance looks okay, the fan clutch would be a prime suspect. If so, you might just try putting on a new fan clutch to see if that cures the problem.

[Richard D.]

Re: Fan Clutch adjustment...C2

I have 66 BB (427-425) coupe that is running hot 220 deg+. After much adjusting (timing, etc) I believe the fan is not turning fast enough when the engine has warmed up. I have taken the fan/clutch off and inspected it and found no oil leaks at all (perfectly clean). On the front (rad side) of the fan clutch there is a coiled spring that can be adjusted/moved a half turn at a time either clockwise or counter-clockwise. This moves the center pin also a half turn. Does this change the operating rpm or cut-in point of the fan clutch? If not, is there something else I can do to increase the rpm of the fan system without replacing this fan clutch as it looks to be near new. Numbers (ink stamped) on it are C19D1A on the spring side of the clutch. Also has CK ink stamped at 180 deg to the first number, which is also on the spring end of the clutch. Also stamped into the metal on the same side says " STORE THIS FACE DOWN".
Anyone with an idea or two?

Larry, I have an old article from a corvette mag that I found some years back that describes adjusting the clutch. It's too big to attach (PDF file with some pics in it) but if you want it, email me at rwmnc@optonline.net and I would be glad to send it to you. Regards, Rich

[Michael F.]

Re: Fan Clutch adjustment...C2

Just turn the spring counter clockwise a half turn. So it can hang on the tab at that position. Works like a charm. No rocket science here.

[Wayne M.]

Re: Fan Clutch adjustment...C2

.....is there something else I can do to increase the rpm of the fan system without replacing this fan clutch as it looks to be near new. Numbers (ink stamped) on it are C19D1A on the spring side of the clutch. Also has CK ink stamped at 180 deg to the first number, which is also on the spring end of the clutch. Also stamped into the metal on the same side says " STORE THIS FACE DOWN"......

Sounds like you have a newer service fan clutch # 3916141, which is calibrated for '68-up emissions control (target 195 deg min. vs. 180 in prior C2 years). So it will run warmer than the original would have, in your '66.

[Larry S.]

Re: Fan Clutch adjustment...C2

Thanks fellas,
I think I will probably replace the fan clutch as everything else has been done and I believe is correct.

[Joel T.]

Re: Fan Clutch adjustment...C2

Sounds like you have a newer service fan clutch # 3916141, which is calibrated for '68-up emissions control (target 195 deg min. vs. 180 in prior C2 years). So it will run warmer than the original would have, in your '66.

Wayne;

Interesting piece of information... I started another thread on my 65 BB which runs hot as well... My fan clutch is a reproduction but I have no idea at what temperature it it tightens up... What I do see is a lack of spinning upon hot engine shut off which leads me to believe that it is tight.. but by that time, the engine is in the 210 range as well.

Do you have any idea how these reproductions are calibrated?

Thanks,

Joel

[Louis T.]

Re: Fan Clutch adjustment...C2

Hi Larry,



Good luck!

Louis

[Michael F.]

Re: Fan Clutch adjustment...C2

Wayne;

Interesting piece of information... I started another thread on my 65 BB which runs hot as well... My fan clutch is a reproduction but I have no idea at what temperature it it tightens up... What I do see is a lack of spinning upon hot engine shut off which leads me to believe that it is tight.. but by that time, the engine is in the 210 range as well.

Do you have any idea how these reproductions are calibrated?

Thanks,

Joel

It kicks in over 200 degrees. Hence the need to re-clock it.

[Larry S.]

Re: Fan Clutch adjustment...C2

Thanks to you all for your responses. My fan clutch is the newer type and in checking with Corvette Central, Ecklers, and Corvette America, they are selling this same clutch for 60 thru '70.

[Michael F.]

Re: Fan Clutch adjustment...C2

Which means you will need to re-clock for it to be at early 60s specs.