Dale Davies
Well-Known Member
Back to the bean counters again. If they can save 1/10,000th of a cent per bolt times millions of exhaust manifold bolts per year, the bean counter justifies his/her position.
2017 ram 2500 broken manifold bolts
- Thread starter diymirage
- Start date
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Swinger 340
Well-Known Member
Recalls don't save money. A five cents bolt may cost the manufactor hundreds of dollars for repairs, plus a customer in the future. Save me now, I'll pay later, attitude!!!! A bean counter can save a company money or close them down.
Dale Davies
Well-Known Member
Exactly so.
19DART66
Well-Known Member
So now a hypothetical scenario, The manufacturer decides to put the manifolds on with 3/8 grade 8 bolts now, to cure the problem of 5/16 low grade bolt snapping. The 3/8 bolt cost more but is much stronger, so now that bolt pulls the threads out of the aluminum head instead of breaking. How much is that going to cost in warrenty repairs?
It all come down to the almighty buck and which solution keeps the prophet margin the highest.
The engineers, bean counters, and management, I will bet will all vote to keep using the weaker 5/16 bolt.
It all come down to the almighty buck and which solution keeps the prophet margin the highest.
The engineers, bean counters, and management, I will bet will all vote to keep using the weaker 5/16 bolt.
Swinger 340
Well-Known Member
That is why you have torque specs. The threads on a larger bolt as you say, should also make the threads in the aluminum heads stronger to hold. Just follow the torque specs and no stripping out the head or breaking a weak bolt.
Dale Davies
Well-Known Member
Youse is overthinking da sityatun. Why do you introduce Gr 8 bolts? 9mm 8.8, 10mm 8.8 or 3/8 grade 5 bolts would be fine. IMHO the breakage is not from tension expansion of the manifold. Those bolts get plenty warm through heat convection from the bolt head in contact with the manifold. My belief is that the manifolds expand lengthwise putting a bending stress on the bolts. Hardened washers with antisieze between them and the manifold to aid slippage along with the larger diameter bolts that have the strength to resist the bending forces is the cure.
I really doubt that if the threads have the correct engagement they will not pull out of the Al heads.
I really doubt that if the threads have the correct engagement they will not pull out of the Al heads.
It goes all the way back to the slant 6 and possibly prior. They have special washers that basically act like a "spring" and allow the manifold some "wiggle room" if you will for expansion with heat.
What they should have done was put studs and nuts on instead of bolts.
19DART66
Well-Known Member
Now my question is which bolts have the higher shear strength, a gr-2, gr-5 or gr-8?
On the subject of studs and nuts, the GM LS engines and the Ford Mod engines both use studs and they are both having the same cast iron exhaust manifold attachment breakage problems as the new Hemi that uses bolts.
Guys, please do not interpret me as an overly educated man, I have alway been just a hard working blue collar stiff. I learned everything I know in my 70 years through practical experience, and from asking questions and listening to those with experience.
On the subject of studs and nuts, the GM LS engines and the Ford Mod engines both use studs and they are both having the same cast iron exhaust manifold attachment breakage problems as the new Hemi that uses bolts.
Guys, please do not interpret me as an overly educated man, I have alway been just a hard working blue collar stiff. I learned everything I know in my 70 years through practical experience, and from asking questions and listening to those with experience.
LS gm are horrible ford V8 are very close 2nd.
Hemis are distant 3rd .
I do about 10 broken stud/bolt repairs a week.
Last week I did a Ford 390 which all the bolts were broken lol, that was fun
Absolutely, 1 broken exhaust bolt means.... legally you must replace the logs with long tube headers lol.
Swinger 340
Well-Known Member
I say, the start of a broken bolt is when you insert them into "WHATEVER". I always add a little anti-siege when I install some as the water pumps and timing covers, wheel studs or any other locations that seems suitable. I no they make a high temp sealant for the exhaust, but not sure on an anti-siege.
diymirage
HP@idle > hondaHP@redline
i know for a fact there were at least 2 broken bolts (4 if you count the pieces) so im glad i put the headers on
I anti seize them too, dissimilar metals doing their thing always makes for a fun bolt removal
Dale Davies
Well-Known Member
Yes, the washers are like ththick Belleville washers and appeared to me to be of a hardened construction. The Chev 'liners had similar washers.
Everything engineered over the last 30 to 40 years has used metric measurements. Stepping up from the 5/16" or 8mm bolt or stud size to 9mm would be a vast increase in strength. Combine that with the conical washers and the bolt breakage would be pretty much elliminated.
Dale Davies
Well-Known Member
Two qualities to discuss; tensile and shear.
As the bolt grade increases the tensile strength increases through chemistry and heat treatment. This increased tensile strength provides higher clamping load, but at a cost, Shear strength. A gr 8 bolt will break in shear while a gr 5 or gr 2 bolt will tend to bend.
Hope that clears that up some.
Yeah but then they might have to spend a little money. God forbid.
19DART66
Well-Known Member
And the win goes to Dale Davies, Thank you!
You wouldn't believe how many people will argue that the gr-8 shear strength is greater because the bolt is stronger.
You wouldn't believe how many people will argue that the gr-8 shear strength is greater because the bolt is stronger.
gzig5
Well-Known Member
What is the source of shear load on the bolt in an exhaust manifold application? Considering the bolt is torqued to spec into a through hole with about .020" radial clearance, there should be nearly no shear or sideways force on the bolt, it's all in tension, no? Any force coming back from expansion of the pipe system that might cause shear would be absorbed by the mounting system and pipe deflection and anything else would be shared across all the bolts in the manifold. How significant could that force be?
Dale Davies
Well-Known Member
I the manifold is resting against the bolt when it is tightened, expansion and contraction of the cast manifold can cause the shear force. Another related to shear is the bending force as the bolt head sticks by friction and the clamp load. As the manifold expands and contracts, it slides against the head or the gasket. Of course the thread goes nowhere, so the bolt flexes at the exhaust surface of the head. This is really a fatigue failure, but related to the shear as it is not tension related.
Nothing in the rest of the exhaust piping has anything to do with manifold bolt failure, it is all in the manifold and the bolts.
Nothing in the rest of the exhaust piping has anything to do with manifold bolt failure, it is all in the manifold and the bolts.
gzig5
Well-Known Member
I agree that the failures are mechanical/thermal fatigue related, but I don't see any potential for a shear component. The major forces are acting on the z-axis of the bolt, not shear in the x-y axes. It's a moot point really. The fastening system isn't reliable enough and either didn't go through accelerated life testing, or the results were not properly acted upon. Just like all of us, these companies make their choices and take their chances.
Scamp Rhonda
Well-Known Member
Boy you guys are above my pay grade. I do have the 5.7 in my Ram so I'm very interested in all of this information being put out here. Thanks for taking the time to dumb it down for me 
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