Engine Rattle

[RV Guy]

I have a rattle that is coming from the front of the engine. It starts when the AC clutch engages and stops when it releases. It is getting worse (louder). The belt appears to have plenty of tension, it moves less than its width, but there is a lot of vibration coming from the tensioner arm when the AC clutch is engaged. The complete AC system including compressor and clutch were replaced about two years ago. The shop that did it is now out of business. Is it the tensioner, the AC clutch, the AC compressor, or something else? How do I tell?

If it is the AC clutch, which is my guess, how hard is it to replace?

Thanks

 

[MBDiagMan]

It is most likely the compressor. With the engine off, turn the forward most portion of the compressor by hand. If it is smooth with the only resistance being compression pulses then the trouble is the clutch. Most likely, though the compressor will feel like it is full of rocks. If it does it must be replaced.

Is the a/c cooling? If it is not AND the compressor feels like it's full of rocks then you not only need to replace the compressor, but you also need to THOROUGHLY and COMPLETELY flush the ENTIRE air conditioning system. If you do not flush, the new compressor will fail in short order due to ingestion of the debris that was strewn throughout the system from the failed compressor.

My guess is that when your shop changed the compressor they converted the system to 134 or one of the many junk refrigerants that are out there. For converted systems the average life is two years.

The original refrigerant, R12, has come down radically in price and using it along with the correct mineral oil or a synthetic replacement oil will let your compressor live a very long life. To go BACK to R12, you must flush the entire system, so at the time of replacing a failed compressor it would be ideal timing to go back to R12.

Good luck,

 

[RV Guy]

Thanks for the information. Yes, the entire AC system was replaced about two years ago and it was converted to the 134 refrigerant. It is still cooling though. Interesting that R12 is available, I thought it had been removed from the market thanks to our environmental buddies.

 

[RV Guy]

There is not much on the front of the compressor to get a hold of and I can't turn it over. It is like it is up on compreesion and I can't get it started. Any ideas to try to turn it?

Thanks

 

[86PACER]

Theres a long torx head bolt that helps fasten the AC compresor to the cylinder head. It's hidden below the AC pulley. I left mine out cause it was a major PITA to remove and install to pull the head off. Ever since, I get the same vibration that you are describing. When I set my hand on the AC Compressor, the vibration and noise goes away. It's because I left out that bolt. Perhaps the shop who did the work decided to leave it out too.

 

[Mart]

I had a very similar rattle and it was coming from the AC pump, turned out to be the belt tensioner. Not enough tension caused the AC to rattle.

Not enough tension, I would check the tensioner to see if you are at or past the wear indicator. This solved more than one problem for me.

Mart

 

[RV Guy]

I had a very similar rattle and it was coming from the AC pump, turned out to be the belt tensioner. Not enough tension caused the AC to rattle.

Not enough tension, I would check the tensioner to see if you are at or past the wear indicator. This solved more than one problem for me.

Mart

I have looked on the tensioner and I cannot see any wear indicators even though I know they are suppose to be there. I also thought that it would be a good idea to change it and the belt anyway just out of general principal. The car is 19 years old and I'm betting the tensioner is original. Who knows when the belt was replaced. I called two auto parts stores and neither list the tensioner? Maybe I need to go to GM for it?

 

[Mart]

I had to get mine from GM.

There is a small line on one half and a cutout on the other half the line should within the cutout area when installed, mine was on the edge but after I replaced it the AC noise went away.

I forget exactly how the tension affected the AC. but it worked

 

[Jeb]

Auto parts stores sell a stethoscope for engine diagnostics. I've found it to be invaluable for determining the source of noises such as you are experiencing. Not expensive at all. If I recall, it was less than $20.

From what you've described, I wouldn't be surprised if you have a bearing failure and with the stethoscope, you can easily determine which bearing it is.

My guess would be that it's either the bearing in the tensioner or the A/C compressor.

 

[Mart]

I replaced the whole tensioner mainly because it might have been the bearing but the tensioner was at the limit (end of life) anyway so just replaced the whole thing.

Mine is an 86 as well.

 

[RV Guy]

Thanks for the inormation. I'll check with the local Chevy dealer for the tensioner.

 

[G Winter]

If it turns out to be the bearing in the tensioner, you can buy just the pulley and bearing for under $25. Most parts houses have them. Very common GM part.If the tensioner is at it's limits it just means the belt is stretched.

Glenn

 

[RV Guy]

Thanks everyone. The information is great but I have hit another snag. According to the owner's manual there are two belts for my '86 depending on the alternator. It lists one with the 108 amp alternator and another for the 120 amp alternator. The difference is 10mm in length. It also states that the alternator is marked 108A or 120A. My alternator has been replaced and all it says is Delco Reamy. I could find no other markings on it. Any idea how to tell which alternator and therefore which belt?

Thanks again!

 

[G Winter]

The amperage is usually stamped into it. You have to look closely to find it , might even be out of site so that you have to remove it to find it.

Glenn

 

[Mart]

I understand where you are going with the belt length, but if the tensioner is weak it's not going to keep the tension on the belt and cause a variety of problems.

Mart

 

[lagasvd]

I had the exact same problem with the rattle when the AC kicked on that you are describing in my 86. Ended up being the bearing in the tensioner. Cost me $8 for a new bearing at NAPA (took the old one to them, they are just pressed in and out, and they matched numbers. Replaced the belt at the same time and walah, noise went away. (Found my old belt significantly streched over the new one). Only about an hours work and rated easy to let the old lady do it while you drink a beer.

 

[Mart]

Well Said

 

[RV Guy]

Thanks to everyone for their input. Today I changed the belt and the belt tensioner and it solved the loud chirping noise. I did it in stages. First I changed the belt and it took care of the problem. However, since I had the new tensioner and it was a special order I changed it also. I did it just for peace of mind since the spring in the old tensioner is 20 years old I thought it should be retired.

It was interesting to see where the wear indicators are on the tensioner since before I couldn't find them. Well, that was because it was way past the end point. Now the indicator is about in the middle and I can see the range.

Thanks again to everyone.