Curved fan teeth?

[Ronald L.]

Re: Curved fan teeth?

Dave,
The blue print will tell us how, if at all. Many are pretty low tech and I doubt balanced at all.

[Lyndon S.]

Re: Curved fan teeth?

In Bills photo with the hood off is that the correct fan clutch for a 72 ? Are is that a after market replacement one?

[Bill C.]

Re: Curved fan teeth?

it is a GM replacment.

I still have the fully functional SC fan clutch.
I used to put it on the car before I had it judged.


BTW --- know anyone who could use it. let me know .....

[Kenn S.]

Re: Curved fan teeth?

Dave,
The blue print will tell us how, if at all. Many are pretty low tech and I doubt balanced at all.

Could be. But that's an undamaged original part. Once these are straightened, I'm sure whatever car it goes on, that owner will want to know it's 100% good to go. I'm hearing stories that these fans are famous for eating shrouds and extensions.

[Kenn S.]

Re: Curved fan teeth?

BTW --- know anyone who could use it. let me know .....

If it were me, when I "got back to Vettes," watch I'd wind up with another '72 LS-5 that just happened to need a fan clutch. You know it's true.

[Bill C.]

Re: Curved fan teeth?

na - np more 1972 BB Vettes....

I am looking to get into a 66 427 coupe. I have my eyes on a real nice 390 hp car with factory AC..... lots of good documented options....

guy is not in a hurry to sell, but I should have him wore down and ready in a years time.

Thats how I got the Challenger - 2 years of corresponding.. LOL

[Terry M.]

Re: Curved fan teeth?

Could be. But that's an undamaged original part. Once these are straightened, I'm sure whatever car it goes on, that owner will want to know it's 100% good to go. I'm hearing stories that these fans are famous for eating shrouds and extensions.

The are because of the low clearance between the fan blades and said shroud & extension. You absolutely must have a straight frame and good engine mounts -- oh and don't forget the shims at the engine mounts as well. As these 1970 > BB with C60 Corvettes get old and worn all the chassis flex and play in the parts causes contact between the rotating fan and the stationary shroud & extension when acceleration is requested.

[Duke W.]

Re: Curved fan teeth?

Kenn,

My understanding is that a clutch fan assembly is not engaged at speeds above 30 or 35 MPH (or some speed in that range). The fan does spin at high speeds but it is the wind created by the car going fast that spins the fan but much slower then the engine speed. I don't think that a clutch fan would ever come anywhere near 7000 RPM's.

I have always wondered how an automotive cooling fan was balanced. Are they balanced statically or dynamically?

Dave

That's not how it works. The viscous clutch thermostat works off radiator exit air temperature. If it is below clutch engagement temperature the fan will only turn about 1500 regardless of engine speed.

As radiator exit air temperature increases, the fan clutch gradually tightens for greater fan speed at any given engine speed, but full clutch engagement will only result in a maximum fan speed of about 3500, even at peak revs.

Above about 30-35 MPH steady state speed there should be enough dynamic air flow to keep radiator exit temperature below clutch engagement temperature unless it is very hot outside. The fan is there primarily for idling and stop-and-go low speed driving.

My data and calculations indicate that a fully engaged fan can eat up to about 15 lb-ft torque at 3500, which is 10 HP from 3500 on up. At 1500 or less, fan power absorption is no more than 1-2 HP. (Fan power absorption increases with the cube of fan speed!) The clutch allows the use of a large fan that moves a lot of air at low engine speed, but doesn't result in excessive noise or parasitic power loss at high engine speed.

It's a costly, but elegant design. GM knew that Corvette cooling would be a challenge given big engines in small bodies, so the engineers used the best technology of the day and kept the bean-counters at bay.

Duke

[Joe L.]

Re: Curved fan teeth?

That's not how it works. The viscous clutch thermostat works off radiator exit air temperature. If it is below clutch engagement temperature the fan will only turn about 1500 regardless of engine speed.

As radiator exit air temperature increases, the fan clutch gradually tightens for greater fan speed at any given engine speed, but full clutch engagement will only result in a maximum fan speed of about 3500, even at peak revs.

Above about 30-35 MPH steady state speed there should be enough dynamic air flow to keep radiator exit temperature below clutch engagement temperature unless it is very hot outside. The fan is there primarily for idling and low speed driving.

My data and calculations indicate that a fully engaged fan can eat up about 10 lb-ft torque, which can be up to 15 HP at very high engine revs. The clutch allows the use of a large fan that moves a lot of air at low engine speed, but doesn't result in excessive noise or parasitic power loss at high engine speed.

It's a costly, but elegant design. GM knew that Corvette cooling would be a challenge given big engines in small bodies, so the engineers used the best technology of the day and kept the bean-counters at bay.

Duke

Duke------


I agree with your description of the functionality of the Corvette fan clutches. I think that Dave must have been thinking of the NON-THERMAL type fan clutches. However, these were never originally used on any Corvette and, as far as I know, never used on any other Chevrolet application, either. The non-thermal units are aftermarket-only and are often used by "budget-conscious" folks in need of a fan clutch but not wanting/able to pay as much as a thermal type unit costs. I realize that it may seem strange to make this sort of functionality sacrifice for the 20 bucks, or so, difference in price between aftermarket thermal and non-thermal fan clutches but, I guess for some folks, it does.

[Kenn S.]

Re: Curved fan teeth?

I took the fan to a local tool and die. This isn't your typical small tool shop...it's quite a large operation, and I chose it because I gambled I'd have a large population of old heads to discuss this with. The more guys who'd seen it all, the better.

And, once I got past the moat dragon, I did collect a small crowd. More than a couple had Corvettes back in the day and appreciated why I'd care to restore this fan.

Long story short, they understood the machining I was describing. What they didn't/don't have is a machine tooled to the proper curvature of the blade. While anything can be built, the cost to build a custom machine for this task is far more expensive than the fan itself. If we were restoring many fans, that's one thing, but for one fan, it's cost-prohibitive.

They did leave me with a couple of suggestions:

1) Use a bandsaw and cut a 4X4 oak board to the same curvature as the blade. Secure the blade to the convexly-curved oak piece and use that as a surface to tap the teeth back into place, using a maple mallet. Tap slowly, lighly, and at any sign of fatigue, stop (heck the fan is as worthless then as it is now, frankly).

2) Find an old bodyshop guy, someone used to working with the old metal bodies. They're skilled in peening metal, and have tools to do the job (a leather bag filled with shot that conforms to the curvature, for example).

Of course I discounted the usual "cut the teeth off' suggestions, which came early on before some understood what this fan was for.

I've nothing to lose, everything to gain, so I'll try to get that oak block cut and see how it turns out. Maybe, just maybe it'll turn out well, and we'll save this one from the recycle bin.

[Joe L.]

Re: Curved fan teeth?

I took the fan to a local tool and die. This isn't your typical small tool shop...it's quite a large operation, and I chose it because I gambled I'd have a large population of old heads to discuss this with. The more guys who'd seen it all, the better.

And, once I got past the moat dragon, I did collect a small crowd. More than a couple had Corvettes back in the day and appreciated why I'd care to restore this fan.

Long story short, they understood the machining I was describing. What they didn't/don't have is a machine tooled to the proper curvature of the blade. While anything can be built, the cost to build a custom machine for this task is far more expensive than the fan itself. If we were restoring many fans, that's one thing, but for one fan, it's cost-prohibitive.

They did leave me with a couple of suggestions:

1) Use a bandsaw and cut a 4X4 oak board to the same curvature as the blade. Secure the blade to the convexly-curved oak piece and use that as a surface to tap the teeth back into place, using a maple mallet. Tap slowly, lighly, and at any sign of fatigue, stop (heck the fan is as worthless then as it is now, frankly).

2) Find an old bodyshop guy, someone used to working with the old metal bodies. They're skilled in peening metal, and have tools to do the job (a leather bag filled with shot that conforms to the curvature, for example).

Of course I discounted the usual "cut the teeth off' suggestions, which came early on before some understood what this fan was for.

I've nothing to lose, everything to gain, so I'll try to get that oak block cut and see how it turns out. Maybe, just maybe it'll turn out well, and we'll save this one from the recycle bin.

Kenn-----


The fact that the machine shop couldn't do the job is exactly what I figured you were going to encounter.

I think your best bet is something like your option (2). However, I would look for a guy that does custom bodywork FABRICATING AND REPAIRING body parts for hot rods and really old cars. These are the guys that are expert at the kind of metal-working that needs to be done to repair the fan blades. If a guy has an English wheel in his shop, that's the kind of guy you're looking for.

[Terry M.]

Re: Curved fan teeth?

Kenn-----

I think your best bet is something like your option (2). However, I would look for a guy that does custom bodywork FABRICATING AND REPAIRING body parts for hot rods and really old cars. These are the guys that are expert at the kind of metal-working that needs to be done to repair the fan blades. If a guy has an English wheel in his shop, that's the kind of guy you're looking for.

If there are any street rod shops in your vicinity, they might be a place to check out. Some of them still work in metal, and do a bang up job of it.

[Kenn S.]

Re: Curved fan teeth?

On page 43 of the new in-color DriveLine (Sep-Oct 2011) there is an ad for a 1970 fan blade. I talked to Alex, the seller, and it's a 3993889 fan (didn't get the date code). I was fortunate enough to find a 3993889 fan (am still looking for a 3969926 fan), so I can't use his. Anyone out there needing a 1970 BB w/C60 fan blade? They be hard to find...

Still waiting to hear about straightening the curved teeth of the other fan. When I hear, I'll let everyone know if it worked out or not.

[Grant W.]

Re: Curved fan teeth?

On page 43 of the new in-color DriveLine (Sep-Oct 2011) there is an ad for a 1970 fan blade. I talked to Alex, the seller, and it's a 3993889 fan (didn't get the date code). I was fortunate enough to find a 3993889 fan (am still looking for a 3969926 fan), so I can't use his. Anyone out there needing a 1970 BB w/C60 fan blade? They be hard to find...

Still waiting to hear about straightening the curved teeth of the other fan. When I hear, I'll let everyone know if it worked out or not.

Hi Ken
The tip is not quite curved to the same curvature of the fan blade. It is somewhat flattish at the tip end.

Use one of those horse shoe things. Best 100.00 investment ever in a tool. It has paid back 100 fold. This one weighs like 200 lbs. The round tapered end works perfectly in forming the curvature of the fan blade. I used a rubber mallet for fixing my bent fan blades. In your case I would heat slightly with a propane torch and take your time tapping it straight.
I have one of those fans at home but dated D81 and I can bend the tips with my fingers. Again the very last portion of the tip is somewhat flat. Not curved the same degree as the fan blade itself.

.....Did someone bend those tips for Halloween???? Fangs for the car.

Hope this helps you out.
Grant

[Grant W.]

Re: Curved fan teeth?

Hi Ken
The tip is not quite curved to the same curvature of the fan blade. It is somewhat flattish at the tip end.

Use one of those horse shoe things. Best 100.00 investment ever in a tool. It has paid back 100 fold. This one weighs like 200 lbs. The round tapered end works perfectly in forming the curvature of the fan blade. I used a rubber mallet for fixing my bent fan blades. In your case I would heat slightly with a propane torch and take your time tapping it straight.
I have one of those fans at home but dated D81 and I can bend the tips with my fingers. Again the very last portion of the tip is somewhat flat. Not curved the same degree as the fan blade itself.

.....Did someone bend those tips for Halloween???? Fangs for the car.

Hope this helps you out.
Grant

I forgot to post the pic but here is that horse shoe thing a ma-jig.