Fiberglass Fan Shroud

Rockets2000

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So it's been a while since I've had to fabricate something from scratch, and the time has come to finally do something about my fan shroud. The 350 has been known to run at 240* on a couple of occasions and with a trip to Big Bend National Park planned for this spring, I cannot afford to overheat in the middle of nowhere.

After struggling with sheet metal vs. modifying a stock shroud vs. making something out of whatever I have on hand, I decided to try to make one out of fiberglass thanks to this thread: https://forum.ih8mud.com/80-series-tech/597038-homemade-fan-shroud.html

My needs are a little differrent than the OP above, so I took his idea and made a few minor changes. I started with a cardboard and duct tape mockup just to visualize what I had to build.


Then I went on to make a small scale prototype to make sure I understood the materials and the concept. This is my first time messing with fiberglass, so I wanted to experiment a bit before I jumped into the project.


I got good results with the test piece so it was time to make the full-size form. Using the same basic procedure as the other thread (measure and cut out fan disc, design battens/hold down system, and stretch speaker cloth to make basic shape), I made a frame to include my attachment rails and a shelf on top for tools. More on that later...




 

Rockets2000

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Next was stretching the material over the frame to make the form. It has many complex curves, so I needed to make sure it fit properly and was held down in the corners and along the sides where I needed angles.


I used 1/4" dowels to make the 90* angles along the mounting rails (1" slotted angle stock) because I want to glass over the rails to integrate them into the structure.


The trickiest part of this is the bottom section where the curve is reversed due to my fan center being lower than the center of the radiator. I decided to try to wedge a 1" piece of plywood to use as a guide for this area to keep the material away from the lower hose while still providing a curved flow surface. The top and sides of the frame are inside the cloth to make the main "box", but the bottom guide is on the outside of the cloth to complete the box and start the concave contour. Kind of a simple solution to a complicated probelm, but it seems to work. I anticipate problems with this area after I pull the frame off. Hopefully nothing that another layer of glass won't fix.
 
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spotcruiser

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I made a fiberglass shroud for my vortec install and have been slow to post up the details. :frown: A friend came up with this type of form made out of particle board that is reversed from what you see on hot rod forums.. It really can produce a nice shroud. I need to do a thread on it to share the technique.
Shroud 54.jpg
Shroud 55.jpg
Radiator Shroud.jpg
 
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Rockets2000

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Looks like a nice piece of work! Mine won't be quite that stout. That thing looks like it could handle a pretty good bump in the front - like an oak tree.
 

spotcruiser

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Thanks. You can glass it to any thickness you want. I made it thicker than 1/4" all the way around and then sanded it down to even it out and smooth it all up. It's stout, but weighs nothing. This is just out of the form and after final installation.

Looks like a nice piece of work! Mine won't be quite that stout. That thing looks like it could handle a pretty good bump in the front - like an oak tree.
Shroud 56.jpg
Finished-Installed Shroud1.jpg
 
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You lose a lot of efficiency on the air-draw when the blades don't come fairly close to the edge of the shroud. The idea is to create a low pressure area inside the shroud to force fresh air to come through the radiator. When you have over an inch of clearance between the blades and the shroud, you lose much of the low pressure you are seeking, especially when the blades have a relatively flat pitch. Not being critical of your installation, just passing on some info.:cheers:
 

Rockets2000

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You lose a lot of efficiency on the air-draw when the blades don't come fairly close to the edge of the shroud. The idea is to create a low pressure area inside the shroud to force fresh air to come through the radiator. When you have over an inch of clearance between the blades and the shroud, you lose much of the low pressure you are seeking, especially when the blades have a relatively flat pitch. Not being critical of your installation, just passing on some info.:cheers:
I'm shooting for 1/2" clearance. Once I put a couple of layers of glass mat down I'll pull it off the mold to check the fit, and trim as necessary.
 
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That's some REALLY nice work on both of those fan shrouds! I'll have to file that tip away for the next custom shroud I need to do.

Nick
 

spotcruiser

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You lose even more efficiency when your fan strikes the shoud and breaks while flexing on the trail. ;)

I actually made two shrouds and I wasn't comfortable with the clearance on the first one. It was fine for the street, but I would have had clearance issues while wheeling. I purposely adjusted my form dimensions to allow for 1" all the way around between the fan and this second shroud. Stock with a 2F is between 1/2" and 3/4". It's a compromise in efficiency for the sake of trail reliability. The radiator and shroud cool the 5.7l right where it needs to be, balls-to-the-walls on the highway or crawling on the trail. :)

You lose a lot of efficiency on the air-draw when the blades don't come fairly close to the edge of the shroud. The idea is to create a low pressure area inside the shroud to force fresh air to come through the radiator. When you have over an inch of clearance between the blades and the shroud, you lose much of the low pressure you are seeking, especially when the blades have a relatively flat pitch. Not being critical of your installation, just passing on some info.:cheers:
 
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I made one using florist foam as a mold. Basically made a block of foam by glueing the blocks together and cutting and smoothing the edges. The final result was very functional and easy to form. If you need something for a release I used non-stick aluminum foil and it worked pretty good. The final product would not as smooth as the above examples without a lot of sanding and buildup.

I shot for 1/2" clearance and haven't scrubbed the fan blades as of yet.

Those shrouds look great.
 

Rockets2000

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Please post more pics of the Cruiser, nothing in your album?
Great job, ;)
Rick Smith
Thanks! The lower frame piece came off with some slight tearing around the hose flange. It was too cold today to lay down any fiberglass, but hopefully this weekend it might warm up enough to lay down the first layer. Here are a couple of pics of the cruiser.
DSCN3758.jpg
P1050912.jpg
P1050860.jpg
 

Rockets2000

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The weather has not been cooperating this week, but I managed to get the form finished and put on two sections of fiberglass mat. Those brownish streaks and smears are wax that I put down to help with releasing, but it was pretty useless since the speaker cloth stretched so much after I initially laid it down.

So far, so good....
DSCN3857.jpg
DSCN3858.jpg
DSCN3860.jpg
 

Rockets2000

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I did learn a little about fiberglass though. If you use too much hardener, you don't get a chance to work the material in like it needs to be. Since it was the very first time I have ever used this sticky stuff, I was unsure of how much I needed. I started with 12 oz and a couple of squirts of hardener. I had brushed a coat of resin on the top and sides (intending to cover all three surfaces) and put down the first piece. I put the plastic container with the rest of my resin aside so I could place and work the glass into the base coat to keep it in place. By the time I was finished glopping resin on the first piece it had already started getting thick (5 min). I put it down again and started fidgeting with the corners using a roller and putty knife. I went to grab the resin, and it had become a useless glob with a brush stuck in it. Anyway, this is the result after about 30 minutes of cure time. OOPS!
DSCN3862.jpg
 

spotcruiser

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I used a resin that called for 10-15 drops of catalyst per ounce of resin and found it best to use the lesser amount of hardener, as it allowed more time to work the air out of the glass. Getting the air out is something that I found to be very important. My first shroud had a lot of little voids (and some pretty good sized voids in sharp turns). I worked in smaller batches on the second shroud and spent more effort working the air out as I laid down the glass.
 

Rockets2000

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I used a resin that called for 10-15 drops of catalyst per ounce of resin and found it best to use the lesser amount of hardener, as it allowed more time to work the air out of the glass. Getting the air out is something that I found to be very important. My first shroud had a lot of little voids (and some pretty good sized voids in sharp turns). I worked in smaller batches on the second shroud and spent more effort working the air out as I laid down the glass.
Yea, I learned that rather quickly. The second piece (bottom part of the shroud) went on much better with less hardener. I don't know if I'm supposed to wait for each piece to cure before putting on the overlapping pieces, but so far, the resin I mix up (8oz) has not lasted long enough before it is unusable to do more than one piece at a time. It's a very tedious project with all the curves and angles, plus I'm trying not to make much of a mess.
 

spotcruiser

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I used polyester resin and it may differ somewhat from other types. As I understand it, the outside layer of resin (the layer exposed to oxygen) never fully hardens. That's not to say that it stays soft, but there is no action required to get good adherence to the next layer of glass and resin applied. So, you can just keep slapping more glass and resin on as long as you don't run into other issues like slumpping.

When you say "one piece at a time", how large a piece and of what material are you speaking?. After letting the resin set a bit in the spandex that was used as the main form, I used random, hand-sized pieces of glass matt (not cloth) and just applied them until I needed to mix up more resin. Then I'd mix more resin and keep on going until I got tired and needed a break. Then at another time, the next day even, I'd mix up more resin and continue on.

You can purchase a wax product that is a surface curing agent and it's supposed to coat the resin molecules so that they are not exposed to oxygen and then will harden fully. I bought some but didn't really need it. I ended up sanding all of the shroud surfaces anyway, which removed the top layers and exposed the fully-cured layers underneath. But, even before sanding, there was no part of it that felt soft or tacky.

Keep going, it's looking good. :)

I don't know if I'm supposed to wait for each piece to cure before putting on the overlapping pieces, but so far, the resin I mix up (8oz) has not lasted long enough before it is unusable to do more than one piece at a time.
 

Rockets2000

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I used polyester resin and it may differ somewhat from other types. As I understand it, the outside layer of resin (the layer exposed to oxygen) never fully hardens. That's not to say that it stays soft, but there is no action required to get good adherence to the next layer of glass and resin applied. So, you can just keep slapping more glass and resin on as long as you don't run into other issues like slumpping.

When you say "one piece at a time", how large a piece and of what material are you speaking?. After letting the resin set a bit in the spandex that was used as the main form, I used random, hand-sized pieces of glass matt (not cloth) and just applied them until I needed to mix up more resin. Then I'd mix more resin and keep on going until I got tired and needed a break. Then at another time, the next day even, I'd mix up more resin and continue on.

You can purchase a wax product that is a surface curing agent and it's supposed to coat the resin molecules so that they are not exposed to oxygen and then will harden fully. I bought some but didn't really need it. I ended up sanding all of the shroud surfaces anyway, which removed the top layers and exposed the fully-cured layers underneath. But, even before sanding, there was no part of it that felt soft or tacky.

Keep going, it's looking good. :)
I'm also using fiberglass mat (not cloth) with polyester resin. I think I have the hardener ratio down with that second piece. Each piece is 24" x 5" roughly, so one piece covers each of the 4 sides plus the curved fan opening. I only have the top and bottom pieces on because it is about 45deg in my garage and I don't want to run into problems with uncured goo all over the place. I'm only doing this once. As of now, I have removed the shroud from the radiator and it is finishing up the curing in the house at 75deg. :)

After it is nice and dry I'll sand it down with 60 grit to remove the bumps and dips. When it warms up this week I will lay down the first layer on each side to get it rigid enough to work with, then cut out and test fit the opening. After that I'll flip it over and put one or two layers on the inside, depending on clearance and fit. I was going for two layers on the inside and two on the outside of the "spandex" base layer, but we'll see how it shapes up. The first two pieces have made the shroud remarkably strong, so I might not need to do four layers.
 
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