Thanks, Jan. And, happy birthday!
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When to use Grade 8 bolts
- Thread starter Alpine 1789
- Start date
Can you give an example?
Dry threads will gall,which is essentially damaging the thread; the clamping force will be reduced because the fastener cannot advance as far it should; dry threads will rust in wet areas, which we all know means more torque to undo them and they usually break while being undone.
Using oil; grease; anti-seize and even Loctite, lubricates the thread and allows more advance than doing them up dry. Check ARP's website for an interesting video on what lubricant they use.
As for Grade 5 vs 8, I am in the camp about evidence. How many people here have found broken Grade 5 bolts on any of their cars? I have been working on cars since 1977 including suspension; brakes; engines; gearboxes; differentials and so on and I have never found a broken high-tensile bolt anywhere. Is that the sort of example that you want Bill Blue?
Use Grade 8 by all means, I can't see that it would hurt, but I see little advantage for general road use, unless fasteners are constantly failing in a particular application.
Cheers Charlie
Yes, Charlie, that's the kind of evidence I am looking for. The very best however, would be situation where a broken Grade 8 was replaced by a Grade 5, which did NOT break.
I have seen a few broken bolts, specifically, Alpine crown bolts. However, as we all know, that is an extreme example of unintended shear and don't know quite what to make of it.
I suppose there have been a couple of other examples.
As I type this, another one came to me. I bought one of the first Ford Fiestas. The clutch rockshaft used a through bolt on the clutch release bearing. The bolt sheared into three parts. Don't know what to make of it, other than it was a bitch to remove. Had to saw the rockshaft in two in order to remove it from the bell housing. I do know the replacement bolt lasted three times as long and was still fine when the car was sold. Was a hard bolt replaced by a soft bolt? Does not seem reasonable. More likely a soft bolt was replaced by a harder bolt.
Bill
I have seen a few broken bolts, specifically, Alpine crown bolts. However, as we all know, that is an extreme example of unintended shear and don't know quite what to make of it.
I suppose there have been a couple of other examples.
As I type this, another one came to me. I bought one of the first Ford Fiestas. The clutch rockshaft used a through bolt on the clutch release bearing. The bolt sheared into three parts. Don't know what to make of it, other than it was a bitch to remove. Had to saw the rockshaft in two in order to remove it from the bell housing. I do know the replacement bolt lasted three times as long and was still fine when the car was sold. Was a hard bolt replaced by a soft bolt? Does not seem reasonable. More likely a soft bolt was replaced by a harder bolt.
Bill
Ninety dollars for a book is well beyond my interest in this subject. And if it is his opinion, not actual facts, I really don't care what his input might be.
Interesting that all this seems to revolve around racing. Years ago (when the Alpine was still a "modern" car) I read an article stating that NO serious racer used any SAE bolts and nuts. They supposedly used aircraft fasteners.
All of this is reminds me of the old argument that a little exhaust back pressure is necessary for top engine performance. Yeah, I distinctly remember seeing racing stories of teams swapping headers, looking for the optimum back pressure. NOT
Bill
Interesting that all this seems to revolve around racing. Years ago (when the Alpine was still a "modern" car) I read an article stating that NO serious racer used any SAE bolts and nuts. They supposedly used aircraft fasteners.
All of this is reminds me of the old argument that a little exhaust back pressure is necessary for top engine performance. Yeah, I distinctly remember seeing racing stories of teams swapping headers, looking for the optimum back pressure. NOT
Bill
RootesRacer
Donation Time
Ok Bill, I'll bite.
Years ago I lived with my grandparents on a farm where I worked quite regularly on tractors. One such occasion I was helping my grandfather bail some hay.
Now this hay should have sat on the ground another day as it was still a bit heavy (the owner of the fields choice to bail it not ours) and the bailier was having a hell of a time taking in the hay. My grandfather said go easy on it and slow or else I was going to break the PTOs shear bolt.
Sure enough I did and I had to go back to the shop and get a new shear bolt.
Shear bolt in this case was a 3/8 bolt with about 2.5 inches of unthreaded section.
I grabbed the nearest bolt that looked right and put it back in and was back on track. About 1 minute later (maybe 100 feet of hay) it broke again.
Went and got another one and within a few minutes I was replacing it again.
After breaking the second one, I went to go ask the master what I was doing wrong and he picked up the bolt and said, "you used the wrong bolt".
"This one is a grade 8, its too hard and brittle". He could tell by looking at it, it was an oil hardened automotive engine bolt, very likley a grade 8.
He went into the shop and picked up a cheap zinc plated bolt that he had bought for these very purposes. I would rate this part as a grade 2 hardware store bolt, the kind that you tend to round the flats when you torque it down. Dead soft if you will.
We put that cheap grade 2 fastener in and I don't recall having to replace it for the rest of the season.
Granddad was no metallurgist nor a mechanical engineer, but someone taught him at some point in time that different materials are needed for different applications. I seem to recall that it had to do with what happens with the material when it is taken to its yield point repeatedly. The soft material will deform "plastic" while the hard material will fatigue and fracture via a propagated crack.
This is also the man that taught me to gauge steel material and hardness with a grinder by the color of the sparks, but that's another story.
I think grade 8 is awesome, I think some of the inconel based fasteners are nicer yet, but if one size fit all there would be no such thing as grade 2, 5 and 8.
Years ago I lived with my grandparents on a farm where I worked quite regularly on tractors. One such occasion I was helping my grandfather bail some hay.
Now this hay should have sat on the ground another day as it was still a bit heavy (the owner of the fields choice to bail it not ours) and the bailier was having a hell of a time taking in the hay. My grandfather said go easy on it and slow or else I was going to break the PTOs shear bolt.
Sure enough I did and I had to go back to the shop and get a new shear bolt.
Shear bolt in this case was a 3/8 bolt with about 2.5 inches of unthreaded section.
I grabbed the nearest bolt that looked right and put it back in and was back on track. About 1 minute later (maybe 100 feet of hay) it broke again.
Went and got another one and within a few minutes I was replacing it again.
After breaking the second one, I went to go ask the master what I was doing wrong and he picked up the bolt and said, "you used the wrong bolt".
"This one is a grade 8, its too hard and brittle". He could tell by looking at it, it was an oil hardened automotive engine bolt, very likley a grade 8.
He went into the shop and picked up a cheap zinc plated bolt that he had bought for these very purposes. I would rate this part as a grade 2 hardware store bolt, the kind that you tend to round the flats when you torque it down. Dead soft if you will.
We put that cheap grade 2 fastener in and I don't recall having to replace it for the rest of the season.
Granddad was no metallurgist nor a mechanical engineer, but someone taught him at some point in time that different materials are needed for different applications. I seem to recall that it had to do with what happens with the material when it is taken to its yield point repeatedly. The soft material will deform "plastic" while the hard material will fatigue and fracture via a propagated crack.
This is also the man that taught me to gauge steel material and hardness with a grinder by the color of the sparks, but that's another story.
I think grade 8 is awesome, I think some of the inconel based fasteners are nicer yet, but if one size fit all there would be no such thing as grade 2, 5 and 8.
RootesRacer
Donation Time
No I didnt say that.
The above was an example where the sheer stress was unacceptable for a very hard fastener. The application needed a fasteners ductility, not its harness.
RootesRacer
Donation Time
Joking about what bill?
Several things. The most obvious that your Grandfather could look at a used, unmarked bolt and tell it had been heat treated, oil quenched and was probably Grade 8. That goes way beyond the spark test!
The remark about "very hard fastener". Grade 8 is not not very hard. By that, I mean they not only are not hard, they are pretty soft, having a Rockwell hardness in the mid 30's on the "C" scale. They are soft enough they can be machined with HSS and cut with a hacksaw. For reference, a cold chisel is made of high carbon steel and has a Rockwell or 42-45 on the "C" scale. Still, they are ductile enough the point will deform as it dulls.
You say a Grade 8 bolt will shear due to lack of ductility when compared to a Grade 2 bolt. A Grade 2 bolt and a soft Woodruff key have the same hardness, about 9 on the "C" scale. A Grade 8 bolt has a hardness of 35 "C" whereas a hardened Woodruff key checks in at 45 "C", yet has more ductility than the Grade 8 bolt?
Lastly, Google "shear bolts". You will find first hand accounts of what happens when a higher grade bolt is used. Usually results in a busted drive train sporting a like new shear bolt.
Bill
Nickodell
Donation Time
In some engineering applications you find no lubricant specified (especially in high temperatures where it might become coked and jam the threads. Some auto manufacturers (example, Mercedes) specify not lubing wheel bolts. I use a tiny amount of anti-seize on wheel lugs as they are exposed to water. This is different from lubing the whole thread.
I suppose the difference between specifying lubed or non-lubed is similar to specifying setting valve lifter clearances hot on some (like 'pines) and cold on others.
Thank you for the examples Nicko.
For high-temperature applications, the anti-seize products such as Loctite make, solve the problem of the lubricant drying out because they don't, and at the same time they prevent corrosion.
I have used Loctite Anti-seize nickel on exhaust manifold studs since about 1999 and never had a problem with doing so, and it is an absolute joy to remove exhaust fasteners years later, which not only come off easily but can be re-used.
I too use anti-seize on wheel studs and I set the nuts with a torque-wrench; so far my Land Rover has travelled 260 000 km on and off-road, with no wheel problems at all.
The man who introduced me to anti-seize, is a mechanic in the mining industry and it is used on most fasteners, because of the salty water found in most mines in Western Australia. Those blokes know what works and what does not!Why Mercedes advocate having rusty wheel studs, which will eventually damage the thread I don't know, but they are not alone. I have met heaps of people who sneer at using a torque-wrench on wheels - including one mechanic - and become angry if anyone suggests using a lubricant on them.
The reality is that any fastener, which is not tightened enough will come loose and probably break, or be badly damaged.
Any fastener which is over-tightened will stretch too much and become permanently deformed and will probably break in service. If they are re-used they will break when re-torqued.
Any fastener which is assembled dry, may be tight enough but it runs the risk of being too loose and of corroding - even if it is plated or coated - and once it corrodes it has stress raisers in it and should be mistrusted, if not thrown away. This applies especially to the safety systems of: suspension; steering and brakes.
So getting back to the original poster's question - inspect them very closely; Grade 5 should be fine if that is what Rootes used; lubricate appropriately; torque to the correct value more than once; and check them at every service for correct tightness.
It is a fallacy that the lubricant will make a fastener come loose; it is the tension between the male and female thread, which keeps the two tight; hence the need for a torque-wrench.
Cheers Charlie
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This is one of the more intelligent answers I've seen on this subject. Most guys don't understand that there's a reason for Grade 2, Grade 5 and Grade 8.
Here's another reason to use Grade 5 in clamping applications - it has a greater range where it is operating in its elastic range. A Grade 8 bolt has a shorter elastic range. Even if you properly torque a Grade 8 bolt, if the parts get cold, they might shrink enough to cause the Grade 8 bolt to unclamp.
More; the fatigue life of a Grade 5 (and especially a Grade 2) bolt is much longer than a Grade 8 bolt.
More; because Grade 5 bolts will stretch farther, if you have several bolts holding an assembly, one stressed bolt will stretch and the load will get transferred to the other bolts. A Grade 8 bolt won't stretch, will get overloaded, and snap like a twig. Then the next bolt gets the load and the process repeats until the assembly comes apart. Hopefully not while you're in the air or at speed on the track.
In an application like bolting a transmission to a bellhousing, you want a Grade 2 bolt - something with a little 'give', something that stretches and will stay clamped, and not fatigue and break.
I've seen skinny (1/2"?) Grade 4 bolts on the head of an early Ford 223 engine. Ford must have been going for a very flexible clamping system. Later 223's had slightly larger (9/16"?) Grade 5 bolts.
I'm slightly obsessive about using factory fasteners where I can.
Paul