Turbo bolts keep breaking

I said so long as it meets spec. A Grade 5 would not meet spec. It must be the correct fastener, but the name stamped on it does not matter.

 

Yes, I prefer the cat bolts. They are very similar to some of the ARP header bolts. And in the right dimensions with the correct high temperature rated interference fit nuts they would probably be adequate. I buy a fair amount of Fastenal stuff but not for something like that. Fastenal bargain fasteners are mostly import and seem to vary in quality quite a bit. While I appreciate your attention to detail when torquing things up ( and for the most part you make valid points) I don't think that Caterpillar intended it to be quite that complicated. To those who say "well just use Cat bolts-problem solved" I did 3 of 4 times. I have a fair amount of industrial machine shop experience and a copy of the Machinists Handbook that I reference when torquing certain things. Honestly, I seriously doubt that most people go to the trouble of using a torque adapter to make sure they get all bolts torqued even. I did. I spent around 300bucks on the proper Cat bolts and nuts. Granted, that engine had plenty of vibration. It also was making a round 40psi boost. I pulled it to 900 occasionally but usually around 850. So maybe Cat bolts will cure his problem, but it went deeper than that for me. After doing as instructed by someone that works on hot rod Cats daily and has for the 25 years I have known him, I finally quit having the problem. Sometimes it isn't what u know, but who you know. I am pretty picky about checking things for squareness and proper torque. I usually toque things in 3 steps of 5 Ft lb increments. Sometimes 4. So this whole fiasco was making me feel pretty dumb.

 

I believe I was told that Cat high temperature bolts are made from alloy of one of grades of Inconel. Has high nickel and chromium content. Used to be used in exhaust valves. Pretty hard, so PITA to drill. Mack used same style in ASET exhaust manifold studs. Only way to remove broken ones successfully for me was welding a nut to them. Mack came up with a fixture to hold nuts in place and special rod from Cronaweld to weld the dissimilar metals. Mig with ER70S always worked for me. So I guess what I am getting @ is just buy the Caterpillar bolts. They are the correct bolts for sure. Cat states to use anti-seize, so it works as the lubricant for helping achieving proper bolt stretch.

 

I'm not a mechanic and certainly not as smart as most of you here, especially when it comes to wrenching, and that is why it makes sense to me to just use what the manufacturer provides for a specific application such as turbo bolts.

Also, having done service work and minor repair work on Cat heavy equipment for a long time, I can tell you that problems with bolts most generally seem to occur when someone had used a run of the mill hardware store grade 8 bolt instead of a Cat bolt.

 

Speaking of Fastenal, our local store has closed for public walk-in business and just serves their larger corporate customers now it seems. Anyone else see them doing that?

 

Very disappointed few times I stepped in one, my four year old seemed more knowledgeable than the counter people I bothered.

 

A thought, given how impossible that location is to get your wrenches in depending on engine compartment, how bad of an idea would it be to simply prestretch the bolts on the bench? Get peice of metal, drill holes, snug nut onto bolt, tighten as you say, hit with torch, let cool, remove, install on turbo...

??

 

All these replies have good information; thank you all. The OP asked why did the bolts fail; my guess is inadequate preload aka bolt stretch.

I had already written a short novel there so I didn't want to elaborate on the alternative to OEM fastener issue. I almost deleted that; hindsight is so much better than late night thoughts. Also, thanks for not smashing me with insults. Despite knowing better, here I go again.

I didn't say go to Fastenal to get a box of bolts you think meet spec. I also didn't say to ask the kid behind the counter for a bolt that looks like this one. So I should qualify my thoughts. It's unwise to attempt to use any fasteners on or in your engine other than OEM supplied parts unless you fully understand fasteners and materials. The OEM part will always be the correct material and it will fit. I also agree there's not much money to save here. For me, I've worked to identify certain frequently used and/or challenging to acquire fasteners to source a quantity of correct replacements. It's no simple task but over time it made my work much more efficient. And Fastenal rarely had what I needed in-stock, but they have been able to source almost everything I needed. I really had to as most engines I build do not have an OEM.

That being said, CAT does not have an exclusive on bolts that will hold a turbo flange in place. They do not have an exclusive on the alloy material used to make the bolts. And the alloy they use is not the only alloy suitable for this purpose.

A Grade 8 bolt will not work in this application. Hardness is not the most important quality needed. In fact, it'll work against you. The first issue is that 41fllbs of torque will not stretch the harder bolt sufficiently to preload it. And it's too brittle. And it'll corrode. There's no chance it'll survive.

Steel bolts are much harder than any version of Stainless or Inconel. Nickel and Chromium rich alloys are less hard but resist oxidation (corrosion) much better. Inconel is a trade marked alloy that was developed about 90 years ago, so the patent expired about 70 years ago. There is no secret regarding their alloy. The same alloy with any other name will perform exactly the same. Like Stainless Steel, there are many varieties of Inconel for use in various applications, the recently developed alloys are still patent protected. The trade mark prohibits other from saying things like "just like Inconel" or such. Inconel doesn't even list turbo flange as one of the applications. Turbo flange bolts are widely used and mass produced so pricing is really low which keeps them out of that market.

Inconel is probably perfect for this application. It resist oxidation even where the temperature swings quickly from below freezing to well over turbo flange temp, and retains its tensile strength very well at high temps and through many heat cycles. I don't recall specifically but I think it retains tensile almost to its melting point around 1300C. While that's awesome, there are other alloys which will do this job even better.

Turbo flange mounting fasteners are nothing new or rare. CAT bolts are not magic, but they are handy and cost effective.

So there I went again rambling on without actually fully covering the subject. One day I'll learn.

 

The bolt will return to its original length when the pressure is released. The tension on the bolt stretches it out, like a spring with a weight hanging on it. If you remove the weight, the spring will return to its original length.

If you heat the bolt with a torch to red and let it cool slowly it would anneal the metal thus reducing the hardness.

The result would be a longer but softer bolt which would not provide the required preload tension when stretched to spec.

 

Those bolts have always been known to break. Not as often as yours. Just saying. My Cat had a broken one. I was told to always look for broken bolts. Pretty common.