Compressor groan after head swap?

[moondog1]

Hello everyone!
I'm back for more free handouts of excellent information! I have greatly appreciated everything this far!

95 burb k2500 5.7tbi, aluminum heads, 180k miles.

So a while back I swapped in some Chevy, non vortec, aluminum heads. Since then, my compressor makes a groan between 600-900rpm, goes away with higher rpm over 900. Also isn't present unless the AC button is engaged. My mechanic buddy thought for sure it was the compressor going out, so we swapped it. Put a new one or reman and it makes the EXACT same noise in the same rpm range.

We are thinking there's a vibration or something we can't see but can feel. Also, the mounting bracket for the compressor, only two of the 3 bolt holes lined up with the stupid aluminum heads I put on. Could the third bolt missing be causing this vibration ?

Thank you for any help and advice. I really do appreciate the experts on here who always take the time to give detailed excellent info for free.

 

[PlayingWithTBI]

Also, the mounting bracket for the compressor, only two of the 3 bolt holes lined up with the stupid aluminum heads I put on. Could the third bolt missing be causing this vibration ?

It could, I have intermittent groaning with my Summit Racing aluminum heads too, I just turn up the radio more.

I even have the brace bar installed. What I had to do was get a longer bolt and added some washers to make it work.

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[alignman88]

Hello everyone!
I'm back for more free handouts of excellent information! I have greatly appreciated everything this far!

95 burb k2500 5.7tbi, aluminum heads, 180k miles.

So a while back I swapped in some Chevy, non vortec, aluminum heads. Since then, my compressor makes a groan between 600-900rpm, goes away with higher rpm over 900. Also isn't present unless the AC button is engaged. My mechanic buddy thought for sure it was the compressor going out, so we swapped it. Put a new one or reman and it makes the EXACT same noise in the same rpm range.

We are thinking there's a vibration or something we can't see but can feel. Also, the mounting bracket for the compressor, only two of the 3 bolt holes lined up with the stupid aluminum heads I put on. Could the third bolt missing be causing this vibration ?

Thank you for any help and advice. I really do appreciate the experts on here who always take the time to give detailed excellent info for free.

Absolutely it could. Cylinder head material difference than original and one less brace changed two things that vibrations need. Natural frequency of the components and transfer path.

I’d be interested if while it’s making the noise if you could clamp something to each bracket leg like a vice grip, or try a vice grip over a piece of rubber on the bracket somewhere to attenuate the vibration just enough.

Maybe an idler pulley or another component bearing headed south?

 

[L31MaxExpress]

I have not been around a quiet R4 compressor. Every last one of them has some moaning and groaning, even when they were new.q

 

[Schurkey]

95 burb k2500 5.7tbi, aluminum heads, 180k miles.

So a while back I swapped in some Chevy, non vortec, aluminum heads.

WHICH heads? The "Corvette" or "ZZ-series" units? Something else? Do they have the goofy angles on the center two intake manifold bolt holes?

The aftermarket intake manifold on my '88 K1500 does not have a boss to secure the bottom of the compressor-to-manifold brace. This hasn't been a problem for me since the A/C is non-functional. I'll fix that someday. Which probably means fabricating a different compressor-to-manifold brace that attaches somewhere else.

We are thinking there's a vibration or something we can't see but can feel. Also, the mounting bracket for the compressor, only two of the 3 bolt holes lined up with the stupid aluminum heads I put on. Could the third bolt missing be causing this vibration ?

I really didn't expect that you'd have problems getting the third bolt in. I thought the accessory holes on the ends of the heads were pretty-much universal all the way back to...1969, perhaps.

The accessory holes on BBC heads have changed size--some are 3/8-16, some are 7/16-14; but they're in the same place.

Absolutely it could. Cylinder head material difference than original and one less brace changed two things that vibrations need. Natural frequency of the components and transfer path.

I’d be interested if while it’s making the noise if you could clamp something to each bracket leg like a vice grip, or try a vice grip over a piece of rubber on the bracket somewhere to attenuate the vibration just enough.

Agreed.

Maybe an idler pulley or another component bearing headed south?

Also valid. Tensioner would be my first guess--if the arm jiggles, it's shot.

 

[moondog1]

WHICH heads? The "Corvette" or "ZZ-series" units? Something else? Do they have the goofy angles on the center two intake manifold bolt holes?

The aftermarket intake manifold on my '88 K1500 does not have a boss to secure the bottom of the compressor-to-manifold brace. This hasn't been a problem for me since the A/C is non-functional. I'll fix that someday. Which probably means fabricating a different compressor-to-manifold brace that attaches somewhere else.


I really didn't expect that you'd have problems getting the third bolt in. I thought the accessory holes on the ends of the heads were pretty-much universal all the way back to...1969, perhaps.

The accessory holes on BBC heads have changed size--some are 3/8-16, some are 7/16-14; but they're in the same place.


Agreed.


Also valid. Tensioner would be my first guess--if the arm jiggles, it's shot.

I'm sorry I don't know which heads. I bought them used when a shop told me I had a bad head and needed to replace them. I believe I was told they are 604 heads. I wound up not using that mechanic, but a very trusted friend who determined I just had a bad head gasket between two cylenders, my heads were still good but I had already purchased the aluminum heads. We had to really grind on the TBI intake middle bolt holes to get them to align with the heads. It was a giant pain for me and my limited skillset.



So I might could look for an aftermarket compressor mount to get rid of my vibration? Tensioner is new, most everything you can bolt on the front is new. Definitely isolated to turning the compressor on and off. Thanks for yall help and time responding.

 

[Schurkey]

Find someone with a welder that can fabricate a new brace that runs from the back of the compressor to an intake manifold bolt, or some other convenient place.

Better to build one bracket than to buy a complete set of brackets.

SOMEONE needs to deal with the computer tune on that vehicle. The "604" heads have no exhaust crossover provisions, which means the EGR has been disabled.

 

[moondog1]

Find someone with a welder that can fabricate a new brace that runs from the back of the compressor to an intake manifold bolt, or some other convenient place.

Better to build one bracket than to buy a complete set of brackets.

SOMEONE needs to deal with the computer tune on that vehicle. The "604" heads have no exhaust crossover provisions, which means the EGR has been disabled.

That is excellent info on the heads as well as the bracket. Thank you!