ac mounting bracket bolts sheared off??

CK. to be sure the new next bolts that are put on have 5 marks on head, this will have a grade above the ones that snaped off witch most/like had none on them and were junk, but CK. the head too be sure? F/liner had same deal years ago selling black bolts with no marks on head of bolt an were made of close to pot steel and not able to take the vib. for long?

 

Detroit 60 engines had this problem from day 1. I've read if it has under 500K miles Detroit will fix it for free. They had a sleeve repair kit and later they come out with 2 "L" brackets. There is also a kit where you drill and tap the holes to 7/16". Someone else posted 3/8" grade 9 bolts will work. Some had the whole gear case replaced to the tune of $2500.

Here's a page of possible solutions.
http://cartaste.com/transport-equipment/article-2-03116.html


Poor video quality but it might help.

[video=youtube_share;Yb-M-zXfT14]http://youtu.be/Yb-M-zXfT14[/video]


This is some good info.

http://www.thedieselgarage.com/forums/showthread.php?t=102210

 

Grade 9 bolts do not have the shear strength and will break. Grade 8 is what the OP needs.

But to the OP, if you are driving the engine, are you also the mechanic?

If not I would leave it to the people who work on these things for as living because this is a "mission critical" truck. There may be an issue with the engine itself if the bolts are breaking, a torsional vibration that is causing the bracket to move enough to break bolts. The idle may be too low or that it has a missing cylinder or even the vibration damper has gone bad.

 

I just quoted that article. Besides that grade 9 and 10 bolts are mainly used in aviation. They are a high grade alloy steel and still a stout bolt or planes would be crashing. You won't find them down at your local hardware store. I know grade 8 classes are the strongest because we used them in the nuclear plant I worked at. I worked with some of the QC guys that tested them. Like baha said those were probably grade 5. The mechanic that worked on it probably extracted the broken bolts, chased the threads and threw some bolts in he had laying around the shop, not paying attention to the grade. The bolt will have an 8 on the head or two consecutive slash marks on adjoining sides of the hex.

This problem has to do with a misalignment of the bracket design and the bolt has to force it into place against the gear housing. With the vibration, off they break. I agree grade 8 is best. I would drill and tap to a 7/16" bolt. But if Detroit will pay for the fix I would make them do it.

 

Is it the DT466 engine? International had lots of problems with those bolts breaking. Last one I worked on we even tried to build a fancy bracket with extra bracing. It held for awhile. I expect that it will be the piston type AC compressor that is giving you the problem. There are kits out there to convert from the piston compressor to the rotary style compressor. Once you change to the rotary style compressor the problem will go away most likely. It seems to have something to do with the vibration set up by the piston style compressor.

 

The bolts could have been over-torqued. Some guys love using 3/8 impact guns on bolts like this for some reason. Those guns are good for 250 ftlbs or more. Also need to watch the mounting pads are not worn so the compressor isn't sitting un-even. Also make sure the main drive belt and routing is correct and not too tight.

As for compressors breaking off, never hear of it on these engines. (Detroits, yes)

 

Quite a few folks have overcome any of these issues by changing the crankshaft damper (often overlooked) and adding a crankshaft balancer when they did the damper.

 

Good point. This engine probably has a dead hole and they don't know it.