SBC Fan Blade tip-to-shroud clearance (1 Viewer)

[RWBeringer4x4]

Hey all,

I’ve been working on a shroud for my SBC. I have a rigid 18” fan, which is huge (almost bigger than the radiator).

Most manufacturers recommend 3/4” clearance between fan and shroud - this is what I was going for. Unfortunately, when all is said and done it looks like I’m going to be a bit tighter.

It’s hard to tell from the picture, but I have about 1/2” on the passenger side, and not quite 3/4.” (Call it ~5/8”) on the driver’s side.

I’m not sure how much I can expect the engine/chassis to move in the mounts. Is this too close for comfort, or am I worrying too much over that 1/8” -1/4”

Just wondering if anyone has run a shroud this tight, or if I’m begging for trouble.

If this is too tight, I’m guessing the easiest solution at this point is a new, smaller fan?

 

[bikersmurf]

Mine was closer. Once I had 1/2" I didn't have any more issues when twisted up.

 

[RWBeringer4x4]

Mine was closer. Once I had 1/2" I didn't have any more issues when twisted up.

"Once I had" and "Didn't have any more?" So did the fan just clearance itself?

I've seen everything from "no closer than 3/4" to "just enough to slip a belt around the blades" so I'm PROBABLY ok. Just wanted to collect some second opinions.

It's an 18" fan, so it wouldn't be too difficult to go to a 17" fan and gain another 1/2" clearance all the way around. I could also just run it, and see if I get conflicts, but depending on how bad of an impact there is, I could be creating a LOT of work for myself.

 

[melvinjo]

I run a 16" electric Summit fan mounted directly on the rad, with no shroud. No probs with cooling

 

[RWBeringer4x4]

I run a 16" electric Summit fan mounted directly on the rad, with no shroud. No probs with cooling

Already have everything set up to run the mechanical fan, so I won’t be going this route.

I never ran a shroud in the past, but my fan was only about 1” from the radiator. Now it’s a bit farther. Plus a shroud is the best way to ensure the 350 gets cooled. I just want to make sure when the motor starts “a’rockin” the shroud is not “a’knockin.”

 

[pb4ugo]

I think the best you can do is turn the wheels all the way one way, then go the other. The frame will flex slightly. You can also jack up each tire individually to flex the frame, and then maybe turn the wheels at the same time. I can't recall how much clearance I had when I made my shroud, maybe 1/2 to 3/4". Everything was fine. I took it on my trails and still all was good. Then I went trail riding in KY, and found on some extreme situations the fan hit in 1 spot, not bad, but when I got home I did some alterations to it where it scratched the paint.

 

[B y r o n]

When I built my shroud I cut the hole just larger than the fan blades, I don't remember the exact measurement but it was no where near 1/2" to 3/4". Initially it was fine then I started to hear contact between the fan blades and shroud under load. I then discovered that the engine was torquing toward the passenger side and that is when the contact would happen. Under idle or low load no issue. My fix was to run a chain between the engine and drivers side frame, problem solved. Years later I discovered that the reason the engine would move so far was because the upper engine mount plate had separated from the mount. The could only be seen once I removed the mount.

You've got more clearance than I have so I think you're going to be fine.

 

[RWBeringer4x4]

When I built my shroud I cut the hole just larger than the fan blades, I don't remember the exact measurement but it was no where near 1/2" to 3/4". Initially it was fine then I started to hear contact between the fan blades and shroud under load. I then discovered that the engine was torquing toward the passenger side and that is when the contact would happen. Under idle or low load no issue. My fix was to run a chain between the engine and drivers side frame, problem solved. Years later I discovered that the reason the engine would move so far was because the upper engine mount plate had separated from the mount. The could only be seen once I removed the mount.

You've got more clearance than I have so I think you're going to be fine.

Yeah, I'm leaning toward running it and seeing what happens. It seems like the engine may not move as much as I seem to think it might. I went out and pushed and flexed the sheet metal and got it a little closer to 5/8" all the way around. As long as I can hold it all in place while I weld up the shroud, I should (hopefully) be in OK shape.

I also thought about running a chain as a precaution...I'm running the stock, square late FJ40/FJ60 motor mounts - they're pretty soft/flexible, which is why I'm nerbous. I'm also talking about a bone stock, 200HP 350 - not some torque monster, so I may be ok.

Obviously, the safe-bet is stepping down to a 17" fan. This would give me about 1.125 - 1.25 inches all the way around. But maybe I'll run the 18 inch fan as I have it, and see if I run into trouble first.

 

[B y r o n]

The motor mount that was busted were the OLD original round mounts. I replaced them with the same ones you did I think.

 

[RWBeringer4x4]

I think the best you can do is turn the wheels all the way one way, then go the other. The frame will flex slightly. You can also jack up each tire individually to flex the frame, and then maybe turn the wheels at the same time. I can't recall how much clearance I had when I made my shroud, maybe 1/2 to 3/4". Everything was fine. I took it on my trails and still all was good. Then I went trail riding in KY, and found on some extreme situations the fan hit in 1 spot, not bad, but when I got home I did some alterations to it where it scratched the paint.

When I built my shroud I cut the hole just larger than the fan blades, I don't remember the exact measurement but it was no where near 1/2" to 3/4". Initially it was fine then I started to hear contact between the fan blades and shroud under load. I then discovered that the engine was torquing toward the passenger side and that is when the contact would happen. Under idle or low load no issue. My fix was to run a chain between the engine and drivers side frame, problem solved. Years later I discovered that the reason the engine would move so far was because the upper engine mount plate had separated from the mount. The could only be seen once I removed the mount.

You've got more clearance than I have so I think you're going to be fine.

Yeah - I keep going back and forth on it. $30 would get me a 1” smaller fan and the peace of mind of a gap slightly over an inch. That will also make the shroud less efficient and move less air (which probably won’t be an issue).

Or I can run the big fan and cross my fingers the mounts don’t let the engine move 5/8.”

Not sure what the lesser of two evils is. It certainly seems like there are plenty of folks runnin 1/2” or so - but at the same time it sounds like the fans have been finding the shroud at one time or another...

 

[pb4ugo]

I'd run it and see what happens. If it makes contact it shouldn't be too extreme. When the frame flexes, the engine and shroud move with it.

 

[FF LC FREAK]

I'm curious as to why you can't just open up the hole another 1/2"?

 

[reddingcruiser]

Why not change your motor mounts to a Thru - bolt style like AA sells, most of your flex related issues will go away and you won't need a chain. Similarly, you never have to worry about them coming apart.

 

[bikersmurf]

"Once I had" and "Didn't have any more?" So did the fan just clearance itself?

I've seen everything from "no closer than 3/4" to "just enough to slip a belt around the blades" so I'm PROBABLY ok. Just wanted to collect some second opinions.

It's an 18" fan, so it wouldn't be too difficult to go to a 17" fan and gain another 1/2" clearance all the way around. I could also just run it, and see if I get conflicts, but depending on how bad of an impact there is, I could be creating a LOT of work for myself.

It didn't clearance itself. Probably had 1/4" to 3/8" on the passenger when I first did the conversion. There wasn't enough clearance on full flex. I reshaped it so it wouldn't rub.

It didn't do any damage when it scuffed... just sounded terrible.

 

[RWBeringer4x4]

I'd run it and see what happens. If it makes contact it shouldn't be too extreme. When the frame flexes, the engine and shroud move with it.

Not so worried about the frame flexing as the motor moving in the mounts when loading up.I agree, with the radiator mounted to the frame, when the frame flexes, the radiator should mostly flex with it.

I'm curious as to why you can't just open up the hole another 1/2"?

Bottom line, design flaw on my part - I’m out of space. I’ve mounted the radiator about as low as I can without contacting my Saginaw steering (only have about 1/2” clearance at the steering shaft too). If I go wider I wind up with a gap at the lower radiator hose, plus I’m maxed out at the edge of the “box” on the passenger side.

The ring is also flanged - so I’d need to cut off or reflatten the quarter inch flange and push it out further.

Why not change your motor mounts to a Thru - bolt style like AA sells, most of your flex related issues will go away and you won't need a chain. Similarly, you never have to worry about them coming apart.

This may be in the future - when I originally researched this, everyone seemed to dislike the AA mounts in favor of the stock LC mounts. In hindsight - I think AA may have changed to a through-bolt mount at some point in recent history - it may have been their old mounts that tended to separate.

That said, I believe the AA mounts are also taller, which would shift the motor up in the shroud. Not catastrophic as I could certainly shim the radiator up by the same margin. The only other issue would be the mount brackets I got from Downey are designed for the smaller LC “stud.” Id need to open up the hole in the bracket.

 

[bikersmurf]

I've been running through bolt ones since 96. AA was selling the same donuts at the time... but I used a Downey kit.

 

[pb4ugo]

I didn't know AA had a kit that used actual motor mounts. I purchased my AA kit in the mid 80's, and it was a thru bolt design . I like them because it eliminates the possibility of a broken motor mount. They do loosen up periodically, so I have to keep an eye on them. The AA rubber donuts are long gone, I now use some left over 40 donuts. They seem more robust.