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6.5 Diesel with 21 inch fan in a stock 1987 fan shroud. Need more clearance

Barrman

Barrman

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1987 V20 Suburban that came with a 6.2. I put in a GEP 6500 with a serpentine belt drive and the Heath hi flow water pump and 21 inch plastic cooling fan. Energy Suspension polyurethane motor and transmission mounts. Aluminum 2 core thick radiator but that shouldn’t matter.

I ran the 21 inch fan in a 21-5/8” fan shroud opening for over 20,000 miles and 4 years with no issues. While overlanding in the Buena Vista area of Colorado in 2022 I started to hear the fan hit the shroud when the truck was twisting. Then it got to any time the right front tire got pushed up any. I stopped and checked several times and couldn’t see anything broken. Once back on the highway headed 1000 miles to home there were a few vibrations that I didn’t remember around 70 mph but things always feel and sound different after off roading in my experience.

The fan hitting the shroud continued the next 15,000 miles. Going in and out of parking lots would cause it. I couldn’t see anything broken damage still. I had noticed a repeatable harmonic around 69 mph too. Just the last few days I was under the truck looking to make new cooler hoses for my 4L80E and I realized my transmission mount to transmission bolts were gone! The transmission/NP241 were shifter to the drivers side a little more than an inch. The ears of the mount were mangled up and jammed into the hollow spaces of the pedestal. Basically locking the assembly into its offset.

I really think the bolts came out on the trail in Colorado since that is when the fan noise started. Along with the 69 mph slight harmonic that I noticed but didn’t register.

Everything is straight again. I checked the engine mounts as well. They were good. Once everything was correct again I figured my fan hitting the shroud was a thing of the past. It isn’t. The harmonic at 69 mph is gone but getting one of the front wheels more than a foot above the other gets the fan to hitting still. Researching fan to shroud clearance shows that there should be an inch all around. I am running a 21 inch fan in a 21-5/8 hole. Stock fans were 19 inches. I would like to trim the plastic fan shroud to make a bigger opening. Any suggestions or should I just start from scratch with aluminum?

Thanks.
 
Hitting at the top, sides, all the way around?
 
The only spot I can see any evidence of contact is half way up on the drivers side.

I actually haven’t even thought of checking the core support bushings. I will do that tomorrow.

I pulled a 16 foot box trailer around 70 miles today with it. Getting into and out of some parking lots confirmed the hitting only happens when the right front tire is up. Left front tire up does nothing.

This is a very light tic tic tic. I have never felt it but it is there and needs to be fixed. At least in my mind it does.
 
I checked the core support bushing and bolts yesterday. All there, tight and looking almost 40 years old. But solid. I think I put the best looking bushings I had sitting around in there when I put it together 8 years ago.

Then I drove the truck 200 miles. Mostly all pavement and the non pavement was pretty level. No noises. I haven’t tried flexing it in the past few days either. I do have a 2 piece GMT-400 shroud that might be easier to cut up and I wouldn’t care if it had to be thrown away in the end either. I will report my findings.
 
I thought I hit the “New Post” button and instead got threads started by me and this thread was on top. I figured I should post the resolution to the problem.

Soon after my last post more than a year ago I got underneath again and found the driver side motor mount to cross member bolts very loose. Putting the Energy Suspension mounts in 40,000 miles ago it was very, very difficult to get the motor mount sandwich to fit back together. I did and I did tighten the bolts. But, the mounts must have settled and the bolts worked loose. Along with my already written about above Energy Suspension transmission mounts coming loose. That is why my fan was hitting. Loose bolts!

My take away is that polyurethane mounts need to have all of the bolts on both sides of the mounts checked with a wrench every 6 months or so.
 
Barrman said:
I thought I hit the “New Post” button and instead got threads started by me and this thread was on top. I figured I should post the resolution to the problem.

Soon after my last post more than a year ago I got underneath again and found the driver side motor mount to cross member bolts very loose. Putting the Energy Suspension mounts in 40,000 miles ago it was very, very difficult to get the motor mount sandwich to fit back together. I did and I did tighten the bolts. But, the mounts must have settled and the bolts worked loose. Along with my already written about above Energy Suspension transmission mounts coming loose. That is why my fan was hitting. Loose bolts!

My take away is that polyurethane mounts need to have all of the bolts on both sides of the mounts checked with a wrench every 6 months or so.
Click to expand...
Or tack welded
 
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