true! Dawn plus the lava bar for some scrubbing, and you'd never know I was elbow deep in used motor oil.
true! Dawn plus the lava bar for some scrubbing, and you'd never know I was elbow deep in used motor oil.
Can I ask a question about head bolts? The MB tech apparently knew exactly which particular head bolt would turn out to be the failure point. Well, what's special about that one? (Nobody spec's different bolts for different holes in the same head, right?) What's going on here? Insight would be welcome!
Stealthtercel wrote: Can I ask a question about head bolts? The MB tech apparently knew exactly which particular head bolt would turn out to be the failure point. Well, what's special about that one? (Nobody spec's different bolts for different holes in the same head, right?) What's going on here? Insight would be welcome!
I asked him the same question. He said the rear cylinders are the hottest (least efficient cooling due to the flow path) so they get slightly more expansion/contraction with every heat cycle. The head bolt failure is just a metal fatigue issue. Not enough material due to the torx design to stay outside the fatigue limits. The new design is a reverse torx and that little bit of extra metal is enough to solve the issue. This is why most of the failures happened between 40k and 60k miles (they say) because that's when the fatigue limit was met.
All of the head bolts are fatiguing the same way and I suspect that dye penetrant or something similar would reveal cracks forming on other ones. You only get one failure though and that releases clamping pressure enough to let the head lift. Word is that they heads don't warp so if you don't bend a rod you're good to go, which is nice I suppose.
In reply to mazdeuce:
As part of my job I size engine bolts (including head bolts), develop torque specs, and fatigue test those bolts. I can't imagine the shame of reading a thread like this on a bolted joint that I engineered. Also, that entire bolted joint must be marginal as berkeley if a hot spot in the head can induce a fatigue failure. Are there any grade markings on the new and old bolts?
mazdeuce wrote: I don't think you want to clean with WD-40 over and over through time. It will leave a varnish on things with repeated application over years. I generally only use it on parts that were last cleaned prior to installation in the factory and absurdly gross engines that have 1/2 inch of oil/dirt caked to them. I use a putty knife first on those. A quick spritz with water/Dawn dish soap gets most of the WD-40 off if you're worried.
Fun fact about cleaning with WD-40: don't use it on any surface that you'll be applying any sort of adhesives or sealants to. For example, if you wipe a surface clean with WD-40, then apply some Loctite 518 sealant, the stuff will never seal. WD works great for cleaning stuff up, but be sure to use some solvent cleaner or dawn on any surface you're going to paint, seal, etc.
Mezzanine wrote:mazdeuce wrote: I don't think you want to clean with WD-40 over and over through time. It will leave a varnish on things with repeated application over years. I generally only use it on parts that were last cleaned prior to installation in the factory and absurdly gross engines that have 1/2 inch of oil/dirt caked to them. I use a putty knife first on those. A quick spritz with water/Dawn dish soap gets most of the WD-40 off if you're worried.Fun fact about cleaning with WD-40: don't use it on any surface that you'll be applying any sort of adhesives or sealants to. For example, if you wipe a surface clean with WD-40, then apply some Loctite 518 sealant, the stuff will never seal. WD works great for cleaning stuff up, but be sure to use some solvent cleaner or dawn on any surface you're going to paint, seal, etc.
I like to use denatured alcohol to clean things I'm going to paint. Works like a charm at stripping dirt and other crud off.
maschinenbau wrote: In reply to mazdeuce: I can't imagine the shame of reading a thread like this on a bolted joint that I engineered.
Hell, I feel bad when customers find new and amazingly stupid ways to break products by using them in ways never intended. I feel it's my job to foresee that and plan for it, to a degree. How do you berkeley up a...bolt?
RedGT wrote:maschinenbau wrote: In reply to mazdeuce: I can't imagine the shame of reading a thread like this on a bolted joint that I engineered.Hell, I feel bad when customers find new and amazingly stupid ways to break products by using them in ways never intended. I feel it's my job to foresee that and plan for it, to a degree. How do you berkeley up a...bolt?
How do you think the Challenger's O-ring engineer felt?
Thanks, Mazdeuce, that makes sense. (Well, you know what I mean. It's a plausible explanation of a highly disreputable set of circumstances.)
In reply to Sky_Render:
That was an assembly issue IIRC.
maschinenbau wrote: In reply to mazdeuce: As part of my job I size engine bolts (including head bolts), develop torque specs, and fatigue test those bolts. I can't imagine the shame of reading a thread like this on a bolted joint that I engineered. Also, that entire bolted joint must be marginal as berkeley if a hot spot in the head can induce a fatigue failure. Are there any grade markings on the new and old bolts?
I'd be willing to bet these sort of failures are 90% attributable to bean counters.
AngryCorvair wrote: In reply to Sky_Render: That was an assembly issue IIRC.
The problem with the Challenger O-rings is that they were not designed to be used in sub-freezing temperatures. Rubber becomes a lot less flexible at those temperatures, and it couldn't seal properly. The engineers told NASA not to launch but NASA did it anyway because they'd done it before and never had any problems.
I'd love to be able to ask Mercedes about this particular failure. I'm sure they analyzed the crap out of the bolt, both shape and metallurgy, and they have a pretty solid idea what went wrong and how. They certainly figured out how to fix it as the failures have a hard stop at the engine number where they switched head design on the bolt.
codrus wrote:AngryCorvair wrote: In reply to Sky_Render: That was an assembly issue IIRC.The problem with the Challenger O-rings is that they were not designed to be used in sub-freezing temperatures. Rubber becomes a lot less flexible at those temperatures, and it couldn't seal properly. The engineers told NASA not to launch but NASA did it anyway because they'd done it before and never had any problems.
The launch went on even thought the engineers thought the cold weather would cause them to fail Roger Boisjol
codrus wrote:AngryCorvair wrote: In reply to Sky_Render: That was an assembly issue IIRC.The problem with the Challenger O-rings is that they were not designed to be used in sub-freezing temperatures. Rubber becomes a lot less flexible at those temperatures, and it couldn't seal properly. The engineers told NASA not to launch but NASA did it anyway because they'd done it before and never had any problems.
It was worse than that, the SRB joints never really worked right in the first place, they just happened to fail in a different and deadly way in the cold when the orings got hard. Though it probably wouldn't have been deadly if the shuttle, like every other space vehicle ever, had any realistic abort modes in the event of an explosion. The whole project was a middle finger to Murphy's Law.
In the case of the bolt, I wonder if it was some screwup at the hardware manufacturer, rather than MB underspecing a head bolt.
BrokenYugo wrote: The whole project was a middle finger to Murphy's Law.
Oh so it's like my projects.
"This there's 47 ways this WILL go wrong, but lets pretend it won't until it does."
In reply to Chadeux:
Pretty much, except this killed 7 people every time something went wrong, this article explains it pretty well, predicts everything that ended up going wrong.
http://www.iasa-intl.com/folders/shuttle/GoodbyeColumbia.html
Big, white, expensive, seats seven, many many ways to fail. Thank god the van doesn't fly. In fact, the clear quality of my judgement is probably why I'm banned from flying and limited to things that can largely roll safely to a stop.
Chadeux wrote:BrokenYugo wrote: The whole project was a middle finger to Murphy's Law.Oh so it's like my projects. "This there's 47 ways this WILL go wrong, but lets pretend it won't until it does."
If nobody minds, i just stole that quote for my signature sice it truly applies to most of my projects.
With all this talk about bad head bolts, I'd swear you were dealing with a 6.0L Powerstroke. 
mazdeuce, please check your emails. or, maybe I should just take a hint....
Funny how we're all seeing more articles interest in and about the R63 after Mazdeuce's made its public appearance.
Convenient timing? Or a lot of closet forum trollers?
No mention of the headbolts is an interesting omission.
"Active Ingredients: Chloroxylenol (0.30%)." It also has denatured alcohol listed as a Inactive ingredient
mazdeuce wrote: I'd love to be able to ask Mercedes about this particular failure. I'm sure they analyzed the crap out of the bolt, both shape and metallurgy, and they have a pretty solid idea what went wrong and how. They certainly figured out how to fix it as the failures have a hard stop at the engine number where they switched head design on the bolt.
Honestly, is looks like a spec defect with the torx indention going to close the shaft head mating area causing a fluctuation in the material property due to a thin wall state during tempering.
But without looking at the material closely I couldn't say for sure.
You'll need to log in to post.
