Alot of people dont understand why I used grade 5 and I was thinking that they would bend ,But not shear ,When the alternator is in the car it hangs low in the front a hair below the centerlink bar ,And if it sheared it would be thrown under the car and could cause damage or injure some one ,That was my thinking on the grade 5 ,I never sheared a grade 8 bolt ,I hear stainless does ,But I wanted to get more info on grade 5 .
Grade 8 is nearly 50 percent stronger in shear than grade 5. And anything over 1 1/2 the diameter of the bolt is more than enough thread depth.
In a cast block, I would go as deep as possible, without shanking the bolt, presuming the manufactuerer had a purpose in that regard.
I used to be a firm believer in grade 8, for everything. I few years ago I developed a problem with a truck that I had built up, that kept breaking alternator mount bolts. I couldn't figure out the problem, so I asked an older guy at a shop down the street if he had any thoughts. He said yeah, get rid of the grade 8 bolts and use grade 5's. I though "yeah, what does this guy know" but I'll try anything. Changed to grade 5's and drove the truck for several years before selling it. Never broke another bolt! Three years ago, bought a new Cat skid steer loader with air conditioning, that broke the air conditioner compressor mount bolt, about every 3-4 hours of use. Dealer kept repairing it. Finally looked at it myself, and found it was a grade 8 bolt. Changed it to a grade 5, and it now has approx. 3500 hours on the same bolt. If you need grade 8, or grade 5, full threaded, longer studs, both grades are available in ready rod/all thread. Purty long winded huh??
This is probably the best synopsis of the grade 5-8 debate. Grade 5 has some give to it, grade 8 while stronger can fail in the wrong application. Just think of how much stuff you slapped together with bolts out of the 5-gallon hardware bucket that most of us have and it still runs. Bob
This my be a little late for you,but.......... First there is no need for lock washers if you are using elastic lock nuts as pictured. And I would not use them more than twice before replacing them. Since you need a long fastener, two studs might work better. Thread a short stud into the block. Instead of welding the front and rear bracket together, just keep the pieces seperate. Now slide on the rear bracket. THREAD on the "round bar spacer" that you have welded.Thread on another stud and slide on the front bracket. Now you have two shorter, stronger, studs joined by a larger spacer in the middle. You can take the whole thing apart to remove.
That sure looks like allthread rod from the hardware store to me. Allthread rod is about the cheapest and weakest threaded fastener out there. It is not grade 5. It is made to be easy not strong. Hacksaw the head off of a grade 5 bolt with the 3 check marks on the bolt head and then hack saw a piece of allthread. You will notice a big difference. I used to get it for free (we used it for pipe hangers) but I won't use it anymore. No one can tell you how long it will last but I'd bet a hundred that you wont be in your drive when it snaps off.
Flex and stretch are not the same thing. Flex has advantages, but stretch is bad. When the bilt stretches/yields, clamping forces is reduced and the capacity of the joint is compromised. Vibration is just loading. A given load will deflect a #5 or #8 bolt a certian amount. Because it takes more load to deflect #8 bolt the same as a #5 bolt, bending them back and forth in a vice is not an apples to apples comparison. Level ground would be loading the #5 and #8 to the same load, without exceeding the elastic limit of the #5 bolt, over and over(vibration). Under the same load the softer/weaker #5 will deflect more than the #8. Deflecting the #8 the same amount as the #5 would require more load. A couple possibilities; the clamping strength of the #8 was crushing/yielding something in the attachment. Or, the weaker #5 allows some a little slippage at the the joint. I have seen both of these scenarios. Normally movement at the joint is bad, but sometimes it isn't. I am not disputing the good results you got from substituting a #5 bolt, but here is another perspective on it. For several reasons Caterpillar uses #8 bolts for everything on their engines. Brackets, flywheel housing, oil pan, valve covers, belt guard, heat shields ....everything. In spite of that, stuff normally doesn't fall off of their engines. If there is a problem, the problem is diagnosed and addressed rather than substituting weaker bolts.
Hey John, Power master makes a bracket for what you are doing, they have a couple of different types of kits for moving brackets around, see if you can get a peak at one of their catalogs, do a bit of visual on the part you are making if you need to.
Engineers often know less that they assume, but I wouldn't want to see the average backyard mechanic take over the design of bridges and airplanes. I am normally not an asshole, but there are those who will tell you I can be. I took the time to post what I thought would be some useful information. Feel free to continue playing with each other, I'm gone.
Don't be all pissed off Al, I read every one of your posts, I have the difficult decision of whether or not to replace the front suspension bolts on my truck, G5 to G8. I don't really want to spend 150 bucks on bolts if they are going to be of less integrity so I read your posts with great interest. Any time you post anything on a forum there is going to be debate don't just assume that you are being dismissed by everyone just because you get a few negative posts towards yours. I personally appreciate you sharing your knowledge with us.
Harder grades of steel are not stiffer, they just can deflect more before they yield (bend permanently). The trade off is that just a bit more stress makes them break, while softer steels will deform a lot more before they break The problem with the alternator bracket design is that it has a large cantilevered load supported by a relatively narrow, single attaching point (single if you look down from the top). Look at OEM bracket setups, they have another brace somewhere to support most of the load from the belt.
Squirrel, If I read the original post correctly I think he is NOT saying the modulus is different - I think he is suggesting that when torqued - (each to their different max value) in that situation one deflects differently than the other. I understand your example is of 2 similar samples (unloaded perhaps)- they deflect similarily until yield occurs... -OR- I misread the origional post - it's happened (to me) numerous times before
A lot of good info here, but I was curious about adjustment for belt length: it looks like it might be pretty limited.
The info on the grades of bolts is good, the debate about deflection and breakage is good too, but did you all read he bought the bolts from Lowes? They are cheap China crap, whatever grade they say they are is in question. Being used as he intends, I expect we will hear about a bolt failing at some point in the not so distant future, regardless of what grade he thinks he bought from Lowes. I wish him luck and hope I'm wrong. Gene
Hey, the Granville Bros. were untrained in engineering and aeronautics and they built the Gee Bee!! Doc.
I'm an engineer and get to look at high-end hardware all the time. We have to be fastidious about what torques we use for assembly on aircraft grade hardware and hydraulic assemblies. Torques go by the tensile strength class of the fastener. The design engineers select the fastener based on the application and tensile strengths are the basis of yay-or-nay over almost any other property. Of course a lot also depends on the cross-sectional properties of the fastener as well. The links below may be a tad deep for some here, but it gives you an idea regarding modulus of elasticity, bolt stretch and fastener properties. The Rock Crawler link is probably the most useful for most of us. What those guys DON'T know about breaking hardware would fill a thimble. Bob http://www.engineeringtoolbox.com/young-modulus-d_773.html http://www.engineeringtoolbox.com/bolt-stretching-d_1164.html http://www.k-tbolt.com/bolt_chart.html http://www.rockcrawler.com/techreports/fasteners/index.asp
TB33ANDA3RD - To answer YOUR question, grade 8 (REAL grade 8) doesn't corrode as fast...due to the alloys used. As for graded bolts...I was fortunate enough to score a tremendous stock of all different sizes/lengths of Supertanium bolts about 30 years ago. These bolts will bend a LOT without breaking, and are way overkill for anything that I'll ever need. If you preload (tighten) a fastener beyond any working load it will encounter in service you should have no problems whether you are at the full capabilities of the fastener or not. I would rather have overkill than be 10% or more under whats required...
Unless you have a good supply store close by all we can buy now are cheap china junk, Ace hardware is all china as is lows HD and the rest, I still get myne from Lawson products and there stuff last order I got was still made in USA, there are only 2 or 3 fastner manufactures left in this country, very seldom use Gr 8 other than frame and suspension. Most flat and locks are cheap garbage also, if you can cut them with a pair of side cutters they are trash, I've had lock washers unwind when tightening the nut, threw them out.
The BEST info on fasteners I ever got was found in the late Carrol Smith's book on Fasteners & fittings. It was a sequel to his "Prepare to Win," "Engineer to Win," & "Drive to Win" series. He wanted to title it "Screw to Win" but the publisher chickened out. His books are available from Steve Smith Motorsbooks & others. I've used excerpts in engineering courses I occasionally teach because Mr. Smith really cuts through the BS. The entire Grade 5/Grade 8/AN fastener argument is covered in detail along with double shear/single shear. Chuck Schultz Winfield, Illinois BTW, I agree that Gr.5 is sufficient for an alternator bracket.
Nope. Grade 5 will bend alright where a grade 8 will snap off. Grade 8 delivers more tenstile strengh but is more brittle (less shear strength).. Plenty of people think that a "higher Grade" denotes a "better" bolt. They usually figure it out after having to drill out a few, broken, case-hardened grade 8 bolts they've installed.
This is the most accurate response. Grade 5 will be fine. There are hundreds of fastener manufacturers in this county, I run one of them, mostly aerospace and make to print items. here's a link www.twisttite.com. Oh and don't be fooled, there can be a huge difference between those products identified as "aerospace quality" fasteners and those products that ARE aerospace products.
That's the guy equivalent of an old wives' tale. There's a reason why OEMs use bolts that are the equivalent (since everything is now metric) to Grade 8 or higher on suspension components; you won't find a Grade 5 or equivalent in such applications. The OEMs design the mounts to reduce/eliminate the affects of vibration. They do this through multiple mounting points, triangulation of mounting points, and making the brackets themselves rigid enough to prevent vibration. Often times home-made mounts lack such design. Grade 5 (or equivelent) bolts would be used because the design didn't dictate anything stronger. Doing so would also help to keep costs down, as the stronger the fastener, the greater the cost. OEMs are all about keeping costs down when possible, you know. See the above. If the Grade 8 fastener was snapping in an application where the Grade 5 is bending, but not failing, then I'd suspect the fastener wasn't actually to spec or the fastener wasn't pre-loaded properly (which affects the strength of the joint). The former is possible due to the increase in counterfeit fasterners, while the latter is an issue of human error.
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