I prefer to use new fasteners in critical applications.


My M120 V12 will likely be getting all new bottom end fasteners after it comes apart for inspection. I do have length specifications for the bolts but would rather spend a few bucks for the peace of mind.

On a related note, it's interesting how far down the single use fastener road Mercedes has gone. All kinds of stuff has single use bolts now. Brake calipers, flywheels, heads, cam caps, main caps, rods, turbos (yellow metal alloy), and many other bits all require fastener replacement.

Yes they see $$$$$$$
Unknown bolts, replace, if you bought new and torqued them right from the start, don't see a plroblem. Like the guy said, they're just springs, how many cycles does a spring have if not over stretched? If you torque a bolt in steps normally one can feel when a bolt-nut is getting weak or not right. My 2cents

Rod bolts and stretch to yield bolts get replaced. Others, it depends on condition and application.
When I rebuilt and changed the gears in my Dana 60, I noticed someone was using mis-matched bolts on the diff bearing caps. I think one may have been a head bolt? I upgraded to studs.
On the ring bolts, I think I cleaned and re-used them with new thread locker on them.

They see lawyers and warranty claims. There are also many aluminum bolts being used to save weight on the cars. Those are definitely single use.






That's a rather uneducated thing to say.

Springs?

Seriously?

Please tell me the modulus of elasticity of various metals.
4130?
4140?
Inconel?
High strength steels?
Titanium?
Aluminum?
Bronze?

Not all metals are the same.

Just repeating what was said. Go jump in his sh!t. Aren't all metal elastic? And when tightened does it stretch? Does it return to its original state after released? I will replace my "bronze" rod and main bolts after each use.

Show me the Inconel bolts on a car. You are trying to confuse the point.
Then show me the titanium bolts on a production vehicle. Or the bronze bolts. Or the aluminum bolts. deliberate obfuscation!

Steel, from the lowest 1015HR to 4340 has a modulus of elasticity of 29 million, plus/minus one million, at 70 degrees F. Aluminum is about 13 million. Gray cast iron is about 20 million and nodular is quite close to steel. It's not rocket science, it IS knowledge that a decently educated mechanical engineer should have in his brain.

AndyF is completely right. The fasteners we call bolts or capscrews are, in most of the uses we care about, used as springs. They exert a clamping force proportional to how much they are stretched, the cross sectional area and the modulus of elasticity. Very rarely do we see a modern fastener loaded in shear.

Another common misunderstanding is the number of cycles a bolt experiences. This will be hard to swallow for some of you. IF the bolt is properly designed and properly torqued (stretched), as long as the bolt does not see a stress greater than the stress from the torqueing, the bolt doesn't see any cycles. For heating, as long as the bolt isn't heated into the stress-relieving band of temperatures, that doesn't have an effect either.

Regarding Mercedes-Benz and the torque to yield bolt, my 1975 M110 engine has torque to yield rod bolts. The factory service manual has a simple procedure to determine if they can be reused. Use a caliper and measure the minimum diameter of the necked down portion. If it is above the specified diameter, the bolt is reused. I admit I was just a little bit uneasy the first time I took my self rebuilt engine and buzzed it to 6500 rpm, but the principle held, as did the rod bolts. The concept of torque to yield bolts is that when they have yielded they are exerting as much clamping force as they can. So no pussyfooting about deciding whether 80 percent of yield or 90 percent of yield is a good value, just torque'em until they stretch. Why do we replace so many now? Maybe on a $35,000 car or a $75,000 pickup the bolts are a minor expenditure.

Regarding throwing away bolts that have not failed in service - I believe it increases your risk. The reason is that the bolt served the purpose well. If they had failed you'd know about it. Now put in new bolts and they are back to being unknown quantities. I guess if they torque up properly they are probably good. But, don't fool yourself that you have lessened the risk. If the FSM says replace them then of course do it. But I have never replaced a main bearing bolt, and very few rod bolts. I have replaced a lot of exhaust manifold bolts and studs due to damage.

So I want to see some aluminum bolts from a passenger car. Maybe Feets knows where they are. I guess I'm still in the iron age.

R.

I'll leave the "uneducated" for others to ponder, but their use is indeed just a "robust spring", with it's strength dependent on design, temper, and material, which to the uneducated, may seem incorrect.

It's time to go meet friends for dinner but if you really want I can send you some pics of the bronze bolts Mercedes uses. Plenty of aluminum bolts too.


As for the rest of your rant, well, rant on.

I know what I know.

You know what you know.

Apparently, the two differ.


Here. I slid a pic in on my way to the car.

Very rarely do we see a modern fastener loaded in shear.

Wouldn't a flywheel,pressure plate,or ring gear be a "loaded in shear" application? Some flywheel bolts have a shoulder built in to keep it from shearing off. Most import pressure plates have pins to help locate the plate and provide additional shear protection from what Toyota engineers have told me.
Gus

.

i used to work on a lot of the olds diesels,they had all kinds of problems but mostly head gaskets from broken head bolts,the gm ones were really hard and were torqued to 130#,ive seen several with the heads popped off,i got to using grade 8 bolts from Caterpillar with a hardened washer under the head,torqued to 125# in 4 steps,never had a problem, with them,once in a while one would stretch when installing but it didn't break just got skinny between the threads and the head

I'm not educated, but IMO the clamping pressure keeps those parts from moving, unless, the bolts loosened up. Like that alignment pin in a camshaft, it won't hold the gear from turning the bolt does by clamping. I was told a six penny nail has a 2000 pound shear capacity. What supprized me is the lift plate that's bolted to an intake that will support a 500 pound engine with four little 5/16 bolts and nuts.

Those bolts will hold like 5000 lbs each !!!!

How many do you want to see? These are in the drawer behind me.

Here's a video I made comparing the strength of thread inserts. I did torque tests as well as pull out tests.

Things go *BANG* when they let go with nearly 10,000 lbs of load.

Did you expect an 8mm (close to 5/16") bolt to hold the full capacity of my Horror Freight 20 ton press?



If you want to skip the intro and go straight to the good stuff...
The torque tests start at 5:20.
The pull out tests start at 13:02.

Ain't that something.

This is better than watching TV.

ob·fus·ca·tion
ˌäbfəˈskāSH(ə)n/
noun
the action of making something obscure, unclear, or unintelligible.
"when confronted with sharp questions they resort to obfuscation"