A/C mounting bolt - PeachParts Mercedes-Benz Forum

Shern · #1 05-16-2018, 09:52 PM

Anyone know the dimensions of this missing bolt? Think the head of it takes a 13mm socket...

Finally traced a banging sound to the compressor housing knocking against the bracket.

BillGrissom · #2 05-17-2018, 12:38 AM

Pretty sure you are correct about the 13 mm socket for the head (been there several times). If I recall, that aluminum bracket attaches to the block w/ 3 bolts. I vaguely recall they differ in length. If you don't have a test bolt, push a stiff wire to the bottom of the tapped hole, subtract 1/4" so it doesn't bottom out and go to a hardware store and get a metric bolt with the correct length (from bottom of head). Kudos if you find a chromate plated one and grade 8. It also needs a steel washer so it doesn't dig into the aluminum. M-B used very thin washers, but any will suffice.

Worst-case, the old bolt snapped off in the block. Then you would probably have to remove the compressor and bracket, and hope enough is sticking out to grab w/ vise grips.

Shern · #3 05-17-2018, 01:08 AM

Quote:

Originally Posted by BillGrissom

Pretty sure you are correct about the 13 mm socket for the head (been there several times). If I recall, that aluminum bracket attaches to the block w/ 3 bolts. I vaguely recall they differ in length. If you don't have a test bolt, push a stiff wire to the bottom of the tapped hole, subtract 1/4" so it doesn't bottom out and go to a hardware store and get a metric bolt with the correct length (from bottom of head). Kudos if you find a chromate plated one and grade 8. It also needs a steel washer so it doesn't dig into the aluminum. M-B used very thin washers, but any will suffice.

Worst-case, the old bolt snapped off in the block. Then you would probably have to remove the compressor and bracket, and hope enough is sticking out to grab w/ vise grips.

Bill, that is an excellent idea... I'll do exactly that. Further research has confirmed the bolt size as m8. I hadn't even considered the possibility that the former bolt had broken off on the block... I once had a look under the hood during a refuel after hearing some light jingling and found one of the Ac bolts had nearly backed itself out. Kinda figured that's what had happened here. I just replaced another missing bolt from that assembly -the one that holds that upper AC line in place near the same region. Fingers crossed.

*** I imagine Antisieze paste is in order if the bolts aren't zinc plated? I know home depot has a pretty deep selection of metric bolts. Went fishing through them the other day for potential future broken thermostat housing bolts. Doing that job this weekend.

Shern · #4 05-17-2018, 02:22 AM

What a bummer... measured the depth and it seems the bolt did break off in the block.
Am I going through the trouble to remove the compressor and risk breaking off the other two bolts as well? Judging by the depth, I don't think there's anything sticking out to grab. Seems like a clean break = /

Mike D · #5 05-17-2018, 08:39 AM

One thing which might be in your favor is when the head of the bolt shears off, as in this case, the tension/torque is released and the bolt will usually spin out easily. Doesn't help the fact you will need to pull the compressor and brackets to get to it.

You wouldn't want to use an anti-seize compound but a thread lock compound such as the Loctite 242, the blue stuff not the red. The red requires heat to remove.

Don't use a stainless steel bolt. They are actually weaker than a grade 5 or metric 8.8.

https://www.boltdepot.com/fastener-information/Materials-and-Grades/Bolt-Grade-Chart.aspx

Bear in mind that you need to match the lock washer, if used, to the grade of the bolt.

I find that Ace Hardware, or the like, usually have a better selection of bolts than the big box stores.

dieselbenz1 · #6 05-17-2018, 09:56 AM

Not so certain stainless steel bolts are weaker but I do know of several people who changed out to stainless nuts and bolts to dress up their cars. They found out that wasn't a great idea as the bolts would fall out since lock washers don't work with stainless especially bad for steering and suspension. To top it off hey were fired from work once the boss found out where all the missing hardware went.

Shern · #7 05-17-2018, 11:53 AM

Quote:

Originally Posted by Mike D

One thing which might be in your favor is when the head of the bolt shears off, as in this case, the tension/torque is released and the bolt will usually spin out easily. Doesn't help the fact you will need to pull the compressor and brackets to get to it.

You wouldn't want to use an anti-seize compound but a thread lock compound such as the Loctite 242, the blue stuff not the red. The red requires heat to remove.

Don't use a stainless steel bolt. They are actually weaker than a grade 5 or metric 8.8.

https://www.boltdepot.com/fastener-information/Materials-and-Grades/Bolt-Grade-Chart.aspx

Bear in mind that you need to match the lock washer, if used, to the grade of the bolt.

I find that Ace Hardware, or the like, usually have a better selection of bolts than the big box stores.

How fragile are the other two bolts on the bracket housing? Are they known to be fragile (eg. thermostat housing bolts)? I thought perhaps if I backed the other two off I could slip a small piece of the leather or felt in there to absorb the vibrations.

Shern · #8 05-17-2018, 03:02 PM

Well, the other bolts were fine... good news. In fact, they were a little on the loose side and tightening them down stopped the vibration. One day, when I have the skills, I'll deal with the broken one. For now, a periodic check of the other two will have to suffice.

ROLLGUY · #9 05-17-2018, 07:32 PM

Since I have done MANY Sanden retrofits, I have a stock of aluminum R4 compressor mount castings. If yours is ruined from vibrating, I have a replacement. I also have plenty of the factory bolts.....Rich

Shern · #10 05-18-2018, 12:21 AM

Quote:

Originally Posted by ROLLGUY

Since I have done MANY Sanden retrofits, I have a stock of aluminum R4 compressor mount castings. If yours is ruined from vibrating, I have a replacement. I also have plenty of the factory bolts.....Rich

Thanks Rich -it just might come to that. Meanwhile, going to run on the two remaining bolts and hope it all holds together. So far so good.

ROLLGUY · #11 05-18-2018, 09:56 PM

I have not seen a broken compressor mount casting bolt before two days ago, nor with any of the 20+ Sanden retrofits I have done. However, just today I was removing all the R4 related pieces to do a retrofit, and what did I find? You guessed it- a broken bolt. It was not easy to remove though. After removing the compressor, I had to pry the casting away from the block so I could get pliers around the bolt. The forward one on the bottom broke. The other two were not that tight either. I found that one of the long compressor bolts was hand tight as well. The vibration from the loose compressor bolt is probably the cause of the bolt head breaking.

Shern · #12 05-19-2018, 02:47 AM

Quote:

Originally Posted by ROLLGUY

I have not seen a broken compressor mount casting bolt before two days ago, nor with any of the 20+ Sanden retrofits I have done. However, just today I was removing all the R4 related pieces to do a retrofit, and what did I find? You guessed it- a broken bolt. It was not easy to remove though. After removing the compressor, I had to pry the casting away from the block so I could get pliers around the bolt. The forward one on the bottom broke. The other two were not that tight either. I found that one of the long compressor bolts was hand tight as well. The vibration from the loose compressor bolt is probably the cause of the bolt head breaking.

wow, yep, that was the one. Of the remaining two, one was hand tight... glad I caught it when I did. I stuck a wire in there to measure the depth which is how I discovered the previous chunk of bolt still in the block. It's snapped clean off. Nothing to grab. When the time comes it's going to be an "easy out" that I've read about but haven't seen in practice, or some drilling.

ROLLGUY · #13 05-19-2018, 09:48 AM

Quote:

Originally Posted by Shern

wow, yep, that was the one. Of the remaining two, one was hand tight... glad I caught it when I did. I stuck a wire in there to measure the depth which is how I discovered the previous chunk of bolt still in the block. It's snapped clean off. Nothing to grab. When the time comes it's going to be an "easy out" that I've read about but haven't seen in practice, or some drilling.

Once the casting is out of the way, you should be able to work the broken bolt out without drilling or using an easy out. Even if it is flush with the block, they usually break at an angle, or at least in a way that leaves an edge to grab on to.