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7N4 bracket replacement
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Those of us with the Chevrolet 454 from the mid to late 1980s are cursed by the partial change over from legacy style V belts, to a serpentine system. Part of the curse involves the use of the Sanden AC compressor, and a bracket cast from aluminum that isn't up to the task. This is part of the option 7N4. I took this course of action.

I am glad I did it, but I also think that if I had to do it all over again, I would take one of the broken brackets to a foundry, and tell the people that I want a copy made from high nickel content iron.

Generally no one cares about these type of problem, because most of the other brands of RVs have been junked decades ago. I see concerns on the Airstream boards as well.

I made a bracket from steel. I learned much about welding, and was happy when a friend said, "I have a friend with a plasma cutter".

This is the look from the front on the finished bracket. I made the bracket with a narrower gap between the front plate and the rear plate, so that I can have freedom to shim the compressor fore/aft to get the right belt alignment. I saw alignment problems when reviewing the other pulleys on the engine.

Happy Motoring,
Matt


1987 Barth 27' P32 Chassis
Former State Police Command Post
Chevrolet 454
Weiand Manifold, Crane Cam, Gibson Exhaust


homemade bracket 1
 
Posts: 454 | Location: Massachusetts | Member Since: 07-28-2006Reply With QuoteReport This Post
Picture of BarthBluesmobile
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top view


1987 Barth 27' P32 Chassis
Former State Police Command Post
Chevrolet 454
Weiand Manifold, Crane Cam, Gibson Exhaust


 
Posts: 454 | Location: Massachusetts | Member Since: 07-28-2006Reply With QuoteReport This Post
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view showing the shimming of the rear plate. On the stock setup, the aluminum bracket is mounted between the head and AIR pump bracket. I put the steel plate ahead of that, to give me more freedom to position the compressor later.

Dorman exhaust manifold studs are hardened and are used to mount this to the cylinder head.


1987 Barth 27' P32 Chassis
Former State Police Command Post
Chevrolet 454
Weiand Manifold, Crane Cam, Gibson Exhaust


 
Posts: 454 | Location: Massachusetts | Member Since: 07-28-2006Reply With QuoteReport This Post
Picture of BarthBluesmobile
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this job was undertaken because of the failures of two previous versions of the 7N4 aluminum bracket from the factory.


1987 Barth 27' P32 Chassis
Former State Police Command Post
Chevrolet 454
Weiand Manifold, Crane Cam, Gibson Exhaust


 
Posts: 454 | Location: Massachusetts | Member Since: 07-28-2006Reply With QuoteReport This Post
Picture of BarthBluesmobile
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the breaks are most in the region of the mounting to the AIR pump bracket area. This oblique view also shows how there are two version of "altitude" for the mount to the water pump bolt position. One reason for the breaks of the bracket could be differences in the height of the water pump bolt position, if the installing mechanic is not obsessive about this detail.


1987 Barth 27' P32 Chassis
Former State Police Command Post
Chevrolet 454
Weiand Manifold, Crane Cam, Gibson Exhaust


 
Posts: 454 | Location: Massachusetts | Member Since: 07-28-2006Reply With QuoteReport This Post
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a starting point was a "gusset" found on ebay.


1987 Barth 27' P32 Chassis
Former State Police Command Post
Chevrolet 454
Weiand Manifold, Crane Cam, Gibson Exhaust


 
Posts: 454 | Location: Massachusetts | Member Since: 07-28-2006Reply With QuoteReport This Post
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roughly shaped steel plates.


1987 Barth 27' P32 Chassis
Former State Police Command Post
Chevrolet 454
Weiand Manifold, Crane Cam, Gibson Exhaust


 
Posts: 454 | Location: Massachusetts | Member Since: 07-28-2006Reply With QuoteReport This Post
Picture of BarthBluesmobile
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a scene from welding a first pass. I got done with the welding, and decided to give it the "drop test". The welds broke. So I rethought my design, and also preheated the steel with a torch, so that my little "Harbor Freight" welder could get sufficient penetration of the weld in to the steel.


1987 Barth 27' P32 Chassis
Former State Police Command Post
Chevrolet 454
Weiand Manifold, Crane Cam, Gibson Exhaust


 
Posts: 454 | Location: Massachusetts | Member Since: 07-28-2006Reply With QuoteReport This Post
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one of the "trial fittings". This bracket assembly had been on and off the engine roughly 50 times.


1987 Barth 27' P32 Chassis
Former State Police Command Post
Chevrolet 454
Weiand Manifold, Crane Cam, Gibson Exhaust


 
Posts: 454 | Location: Massachusetts | Member Since: 07-28-2006Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 8/19
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Thumbs Up Thumbs Up Patience, perseverance, and engineering skills equal a nice fix. Mechanic
 
Posts: 2518 | Location: Ohio | Member Since: 07-29-2012Reply With QuoteReport This Post
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My compressor is shot and the bracket is broken. First big problem is what new compressor and refrigerant to buy. Secondly think you could manufacture another?
 
Posts: 29 | Location: Prince William County, VA | Member Since: 10-25-2020Reply With QuoteReport This Post
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2Puppers! Let's talk about the bracket. The second one would be vastly easier than the first... Plus I am also curious to check the local foundry about making one out of iron, based on an old aluminum one.

I need a new compressor too. Mine has pulleys for half inch belts, it needs to be 3/8ths. The "new old stock" GM part is on ebay right now, and the seller confirms it is set up for half inch. I don't know if GM made a mistake at the time, or if a supplier "goofed". I have seen pictures of some compressors that are with 3/8ths, some with half inch.

What part numbers do you see on your compressor? I found a picture of my compressor, next to the original from 2009, and both have half inch. I "researched" the compressors, and 3/8ths belts faded out as the 1990s progressed. Thanks to how Sanden supplied compressors for many brands, there are new and rebuilt units available that are intended for Dodge, Volkswagen, and Jaguar vehicles (with the 3/8 pulley). The biggest quantity seems to be for the VWs that is available. I would be uncertain how the offset of the pulley would work with a stock bracket.

Another problem that seems common, is that there is supposed to be a lateral brace that goes from the bracket to the exhaust manifold area. It seems to be missing from many pictures I see of engines in RVs. It is missing from mine.

One factor to consider in the compressors, is the pulley diameter and displacement of the unit. The case sizes seem identical in all cases. With a choice of units available, I'd want the one that gives the most cooling.

Let's follow up on this!
Matt


1987 Barth 27' P32 Chassis
Former State Police Command Post
Chevrolet 454
Weiand Manifold, Crane Cam, Gibson Exhaust
 
Posts: 454 | Location: Massachusetts | Member Since: 07-28-2006Reply With QuoteReport This Post
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You can see one of the brackets just above the the 1st spark plug. I'll head back out once little man is tucked away in bed.

 
Posts: 29 | Location: Prince William County, VA | Member Since: 10-25-2020Reply With QuoteReport This Post
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OK, this part of the job is done. In the top left of the picture, you can see the AC bracket I fabricated and mounted.

Attached to that, there is a swedge rod, affixed by brackets, to Chevrolet bracket 3969912. That bracket is the yellow component in the picture, and is intended for 1970 big block applications. I tracked that down on ebay. The nice thing about the swedge rod is the ability to adjust like a turnbuckle and bridge the gap present. This, I think, isn't intended to bear much weight, but to minimize the effects of vibrations on the AC compressor bracket. Having a bracket like that missing is probably a contributing factor to the demise of two earlier aluminum factor brackets.

The header paint hasn't held up to the heat of the headers.

On the headers, I used ARP stainless steel bolts, hopefully if those ever have to be removed again, the heads haven't rusted away. Before mounting those, I put "never seize" on the threads, it is recommended when using stainless bolts in iron holes.

You can also see the new AIR tube I installed. That was also an ebay item. It had never sold, apparently, from a GM parts department and made it to ebay. It was apparently a manufacturing defect item, and the left most fitting was not properly placed. It was offset and at the wrong height, and unable to mate with the port on the header. This required me to heat up that tube with a torch, and to manipulate the tube with a light hammer and pliers, to move the port where I needed it. The metal was cherry red at the time. That is why the shine isn't as good there, as it is on the rest of the tube. While I was at it, I also add a "new to me" AIR valve, the black component on the top right. It was also an ebay item.

Happy Motoring,
Matt


1987 Barth 27' P32 Chassis
Former State Police Command Post
Chevrolet 454
Weiand Manifold, Crane Cam, Gibson Exhaust


Side of a 454 with 7N4
 
Posts: 454 | Location: Massachusetts | Member Since: 07-28-2006Reply With QuoteReport This Post
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    Forums    Tech Talk    7N4 bracket replacement

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