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Jun 24, 2020 17:05:58 GMT
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Lots of debate! Thanks for the contributions. Powdercoating - it'd be great to get an in depth thread going on that, especially as we haev people who work in the industry on here. gib Is this something you can start up? I am guilty of having some stainless fasteners on my cars, and I will have to have a look at where they are. I just got so fed up of fitting BZP and having it covered in white corrosion a year after it went on. But, I've been aware of the different stretch properties of stainless bolts and don't think I've got any in critical areas. The only ones I can think of off the top of my head are the thermostat housing, and they're nuts rather than bolts on mine. If you look at OEM manufactures there is a reason they go for passivated bolts v's raw BZP bolts in a number of places. The passivation process prevents the rapid oxidation of the zinc from the environment by forming a thick oxide layer on the zinc. The Zinc still retains its ability to sacrifice itself for the base material underneath but it lasts a lot longer. Its possible to do at home with care (see a recent Project Binky) and you can buy kits. I suspect, although i've never used privately, that getting a load of bolts plated at the platers isnt overly expensive. Torque to yield - in the first post I think it's mentioned you shouldn't go beyond the yield point (ie when the metal begins permanently stretch) This though is what many automotive joints deliberately do, typically this will be when you get a series of torques then an angle, the purpose is to take the bolt just into yield giving a very consistent clamp load I think its fair to say that stretch bolts are used in specific locations / conditions in modern cars (read last 30 years), and for specific purposes. Head bolts / studs can often be stretch bolts, and its also quite likely that they are used on things like crank damper bolts, cam bolts, etc. Unwary re-use is a recipe for disaster as it not un-heard off for them to come loose very quickly. A lot of bolts on cars are unlikely to be stretch bolts, especially if the item is something that is conceivably a regular maintenance / service item. Subframe bolts, suspension bolts, etc. Its not to say in some cases they arent, but to me it seems unlikely in the majority of cases. To me Torque angle is about being able to accurately set the load on the bolt. It can take a lot of variability out that you get with using a torque wrench. Actual Torque on a bolt can vary wildly based on how much and what type of lube is used, and where that lube is applied. For me torque angle is less susceptible to this and the angle of turn relates directly the advancing of the threads, and therefore relates directly to the change in length the bolt has over its free length. This strain equates clearly to the bolt tension in the elastic region of the material, and based on the material properties and a clear understanding of the given elongation to expect when you move into the plastic region you can then be clear on the tension retained in the bolt. Torque to yeild is being used quite widely on suspension and subframe bolts now, if they have torque plus angle I would always check. The reason all oems went away from plated bolts was enviromental legislation about 8 years ago that outlawed most electroplating, the ones they use now are basicaly a paint. I ran a vehicle program testing new fastners to make sure nothing came undone with the new coatings. |
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Last Edit: Jun 24, 2020 17:13:05 GMT by kevins
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jonomisfit
Club Retro Rides Member
Posts: 1,745
Club RR Member Number: 49
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Jun 24, 2020 18:24:52 GMT
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Thanks. Great input there.
Something to be wary of as they start filtering down into being "older" cars. Any insight as to why?
Interesting, is that environmental legislation specific to automotive industries?
I've not seen anything affecting the industries I've been involved with, other than the phasing out of cadmium etc. Under RoHS.
Zinc plating still seems to be the norm where I work.
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jonomisfit
Club Retro Rides Member
Posts: 1,745
Club RR Member Number: 49
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Jun 24, 2020 18:41:00 GMT
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Out of interest, what's the view with titanium bolts? Someone I know was replacing the brake disc bolts on their bike with titanium and my response was that they're no stronger in that application than stainless so I'd not use them myself. In fact, I'd only use them to replace stainless in very high heat applications to prevent corrosion. Just wondering if I'm completely wide of the mark as I have no formal training.
I was going to mention titanium bolts. I am no expert in bolt materials but in aerospace we use titianium bolts in the gas turbines, as you say, in high heat applications. We used to coat the threads in a never seize application, but now we seem to just coat bolts in oil prior to installation. We also do use them in non high heat which would see the same kind of temperatures as brake discs. when the engines come back into the repair and overhaul bases we never have an issue with them having corroded with the mating material. As you can imagine, the engine is subjcted to extreme weather variations - hot and cold, wet and dry, and the bolts to extreme stresses.
So for the experts here, I too was going to ask, is there anything I have not considered regarding titanium. I am guessing cost would be a big prohibiting factor?
Do you replace the bolts or re-use? Like stainless, to me, titanium grades are great in the right application. It is highly reactive, which is a bonus as it forms ti oxide layers which are very resistive to further oxidation in normal conditions. nalesutol may have some insights into practical use in a home setting As I think he was saying he's got them on his car. My experience is, like a number of very strong materials, it has to be used with care. As covered above it is another material that is suffers from galling for self on self. The biggest drawback to me are a number of grades are pretty notch sensitive. Meaning substantial care is needed in handling not to scratch it, as the scratches produce a surprisingly high stress raiser meaning under tension it can fail at much lower levels than expected. Oh and it's definitely not inexpensive. It's got a low coefficient of thermal expansion so can be quite a good partner with composites if bonding bits together. And it's light. Really light. We had some custom Ti bolts made for a job once and all the engineers needed a go feeling them as it was a mind bender such a large bolt weighing so little. If you are looking for high strength bolts NAS bolts are very good. There's a fair few places in the UK sell them, and they look a fairly common fit on high end race cars. |
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Last Edit: Jun 24, 2020 19:54:59 GMT by jonomisfit
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Jun 24, 2020 19:09:05 GMT
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Wow 3 pages on bolts, who knew. Thing is, is it not just a bit over zealous? I’ve rebuilt countless motorcycles over the years (always use stainless, coz ya just do) restored lots of cars. NEVER (to my knowledge anyhow) had a bolt come loose, snapped a bolt off rebuilding the things or had a problem removing one a few yrs after if required.
I mean F1 or the space shuttle I get it.
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Dez
Club Retro Rides Member
And I won't sit down. And I won't shut up. And most of all I will not grow up.
Posts: 11,712
Club RR Member Number: 34
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Jun 24, 2020 19:22:44 GMT
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Wow 3 pages on bolts, who knew. Thing is, is it not just a bit over zealous? I’ve rebuilt countless motorcycles over the years (always use stainless, coz ya just do) restored lots of cars. NEVER (to my knowledge anyhow) had a bolt come loose, snapped a bolt off rebuilding the things or had a problem removing one a few yrs after if required. I mean F1 or the space shuttle I get it. You’d be surprised. Doing what i do I have a reputation for being pretty old school, and being able to fix things everyone else says to throw away. I’ll end up with some tricky jobs no one else will touch because of it, but I don’t mind as i get to charge accordingly. Or double accordingly if they’ve already had a go 😉 A large proportion of those jobs that come my way are as a result of unsuitable fasteners being substituted for originals, in either a ‘that’ll do’ repair, or as a deliberate ‘upgrade’. |
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jonomisfit
Club Retro Rides Member
Posts: 1,745
Club RR Member Number: 49
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Jun 24, 2020 19:50:34 GMT
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An interesting philisophical point.
In some ways you will be correct. You can put anything in there and it will last for a period of time. It may be one stress cycle, it may be substantially more. You may face a problem, you may never face a problem from it.
The point of this thread is not to say you should only do this or that, but more to give food for thought so people consider is that the right choice for them.
In engineering even small and incoccious details can have signficant consequences.
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Jun 24, 2020 20:35:20 GMT
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Thanks. Great input there. Something to be wary of as they start filtering down into being "older" cars. Any insight as to why? Interesting, is that environmental legislation specific to automotive industries? I've not seen anything affecting the industries I've been involved with, other than the phasing out of cadmium etc. Under RoHS. Zinc plating still seems to be the norm where I work. There's loads of stuff specific to cars, high voc paint is another, and theres all the legislstion about end of life. The torque to yeild on suspension is to improve the joint robustness, basically its to get the max clamp load. If you design a non yeild joint you have to set the torque quite a way below the yeild poìnt to always avoid getting into yeild and therefore the clamp is lower. |
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Last Edit: Jun 24, 2020 20:35:47 GMT by kevins
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Jun 24, 2020 21:29:01 GMT
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An interesting ac point. In some ways you will be correct. You can put anything in there and it will last for a period of time. It may be one stress cycle, it may be substantially more. You may face a problem, you may never face a problem from it. The point of this thread is not to say you should only do this or that, but more to give food for thought so people consider is that the right choice for them. In engineering even small and incoccious details can have signficant consequences. I know exactly what you are saying, I’m 55 Ive been a mechanic (or whatever plums the latest dealership want to call their spanner monkeys) since I was 16. I’ve heard it, more than once, twice, 50 times, my point is, it’s all a bit ‘folks in white lab coats’ in the real world, it don’t happen. Go knock yourself out, buy the latest Teflon coated, pre-stressed, titanium stud or whatever you think will hold your alloy water pump onto its cast iron block in some witchcraft manner, that will be better than an ‘average’ bolt. |
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Jun 24, 2020 22:42:20 GMT
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I've got literally hundreds of stainless bolts on my car.
But not one in the suspension area. Stainless is (I have been told) more brittle than normal steel and liable to fracture.
I have ARP stainless bolts in my alumimium inlet manifold and ARP stainless bolts into the heads for the exhausts - no issues as far as I know even with corrosion - but then ARP bolts are very high quality (grade??) bolts.
All the stainless bolts everywhere else are non structural, many have nylon washers under the heads (fixing floor panels/dash panels/boot panels etc) and the others all have a dab of copperslip on the threads.
I'd be interested if anyone can answer whether it's ok to use a stainless nut on a 8.8 steel bolt - I'm fed up of the rusty nuts on the suspension bolts - I paint every one, but the spanner damages the paint so they rust.
Also whether stainless wheel nuts on std steel studs would be ok? Again, my chrome ones are suffering where the socket damages the chrome.
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Jun 24, 2020 23:46:01 GMT
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I'd be interested if anyone can answer whether it's ok to use a stainless nut on a 8.8 steel bolt +1. |
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Last Edit: Jun 24, 2020 23:49:38 GMT by Woofwoof
Still learning...still spending...still breaking things!
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Also whether stainless wheel nuts on std steel studs would be ok? Again, my chrome ones are suffering where the socket damages the chrome. I have done that. On my Ducati 860, i fitted some SS nuts to the intake manifold stuts which were plain steel. Also in other more critical places i did that. Again fitted with cupper slip and no corrosion to be found. From a strength point of view, when you speak about suspension bolts, my opinion is that you have to be a bit more carefull. If the bolt or nut needs to be tighthened with a high torque you may strip the thread of a SS nut. However i believe the bolt or the stud is a weaker part then the nut. Its like fitting head bolts or studs in aluminum engine casings. The alu is much weaker then the steel is and still, you give these a relatively high torque.
During my engineering education, we learned to calculate bolts, shafts and other mechanical constructions. My first job was at DAF engineering drive line components and you noticed that few things like bolts were calculated. It was often a best quess or experience from the past. In those days it was difficult to determine the loads on components. So prototypes were heavily road tested and checked and designs were altered. The moral is that there are loads of constructions in cars or mechanical structures that were build much stronger then needed but you will not always know. So your left to your common sense if a steel nut can be replaced by a SS. My best quess is that in most places it will not cause problems as lots of parts on older cars are overengineered but i would not do it in high risk constructions. In todays world, there are fancy CAD systems with stress calculations included which makes life easier but with dynamic loads, it still remains difficult to determine what loads a component is seeing. With the hydraulic cylinder manufacturer, i for the first time saw that every component was calculated. A cylinder came with a calculation book of about 70 pages of calculations. This was often required because of the use in civil constructions.
So my opinion is that it can be done in many constructions but i would be a bit carefull if it comes to risky parts. Most of you are spannering for quit a long time and you can see how modern cars often use smaller diameter bolts for certain applications
Peter
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Last Edit: Jun 25, 2020 5:42:10 GMT by petervdv
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I'd be interested if anyone can answer whether it's ok to use a stainless nut on a 8.8 steel bolt +1. You are in for a long wait before anybody with any relevant knowledge will have the balls to answer that.... |
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Last Edit: Jun 25, 2020 6:23:37 GMT by Deleted
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It's a grey area on reuse. certain bolts are strictly single use only, but there is no hard and fast rule on the re use everywhere else. when the engines are stripped if the bolts are slaved then they are visually inspected and reused. very often they get binned though. cost prohibits using all new every time I should imagine.
It still blows my mind how light they are. I forget the material now, but a different material bolt was trialled a few years ago which made Ti bolts feel heavy! they had an iridescent type finish to them. They worked just as well, but I think they were not adopted due to cost.
I will have a look at NAS thanks!
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bricol
Part of things
Posts: 281 
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Jun 25, 2020 11:17:28 GMT
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You are in for a long wait before anybody with any relevant knowledge will have the balls to answer that.... Hmmm. you can use it. You just can't torque it to the same level as may be required as stainless steel is weaker, has a lower fatigue limit etc - eg tightening torque for an M10 grade 8.8 non-plated mild steel bolt is 58Nm For an M10 A2 stainless bolt its 37Nm. Considerably lower. I would not use stainless in anything taking an important load or being vibrated as a direct swop for a mild steel fastener - your average car manufacturer doesn't tend to go oversize on fasteners as they cost more money, so to downsize their capabilities is playing with fire. As a design engineer, if I needed stainless, I'd look at the load and increase size to deal with it. |
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melle
South West
It'll come out in the wash.
Posts: 1,983
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Jun 25, 2020 11:22:27 GMT
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As a design engineer, if I needed stainless, I'd look at the load and increase size to deal with it. And look at the grade, maybe? |
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www.saabv4.com'70 Saab 96 V4 "The Devil's Own V4" '77 Saab 95 V4 van conversion project '88 Saab 900i 8V
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Jun 25, 2020 12:11:09 GMT
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Well all of my suspension bolts are 1/2" thick - so a little over engineered  They are all in double shear, so the nut is more to stop the bolt falling out than to keep it torqued up. I tighten them to urrrgggh....that'll do.... with 2 long 19mm/3/4" spanners normally. |
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Jun 25, 2020 12:16:38 GMT
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You are in for a long wait before anybody with any relevant knowledge will have the balls to answer that.... Hmmm. you can use it. You just can't torque it to the same level as may be required as stainless steel is weaker, has a lower fatigue limit etc - eg tightening torque for an M10 grade 8.8 non-plated mild steel bolt is 58Nm For an M10 A2 stainless bolt its 37Nm. Considerably lower. I would not use stainless in anything taking an important load or being vibrated as a direct swop for a mild steel fastener - your average car manufacturer doesn't tend to go oversize on fasteners as they cost more money, so to downsize their capabilities is playing with fire. As a design engineer, if I needed stainless, I'd look at the load and increase size to deal with it. Thanks for your comments. Does the same apply to using a S/S nylock nut on a steel bolt, say where the bolt shaft is under pressure while the nut is just a retainer? |
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Still learning...still spending...still breaking things!
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slater
Club Retro Rides Member
Posts: 6,390
Club RR Member Number: 78
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Jun 25, 2020 12:31:51 GMT
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Read the first post in this thread again. The nut is never just a retainer.
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Jun 25, 2020 13:23:23 GMT
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You are in for a long wait before anybody with any relevant knowledge will have the balls to answer that.... Hmmm. you can use it. You just can't torque it to the same level as may be required as stainless steel is weaker, has a lower fatigue limit etc - eg tightening torque for an M10 grade 8.8 non-plated mild steel bolt is 58Nm For an M10 A2 stainless bolt its 37Nm. Considerably lower. I would not use stainless in anything taking an important load or being vibrated as a direct swop for a mild steel fastener - your average car manufacturer doesn't tend to go oversize on fasteners as they cost more money, so to downsize their capabilities is playing with fire. As a design engineer, if I needed stainless, I'd look at the load and increase size to deal with it. The issue is using SS nuts on steel bolts, I believe the recommended torque of a bolt is based on the tension in the bolt and not so much in the nut but i can be wrong. How could you otherwise use high tensile bolts like cylinder bolts in an alu casing. I know the length of the thread is rather long but not all windings see load Peter |
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Jun 25, 2020 17:02:24 GMT
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For my bolts I don't have a specific torque - as I designed the bit's I just built them extra strong My shock absorbers all have 1/2" bolts as well, they again are all double shear so I's guess that 30Lbs/ft was a perfectly good torque rating on them. Suspension arms are a sleeved urethane bush, the bolt clamps the sleeve against the double shear mounts and the urethane revolves around the sleeve. So again I'd guess something like 40 to 50Lbs/ft would be about right. So for the clever helpful people who know about load ratings - what is the load rating fo a mild steel 1/2" UNF nut compered to a stainless 1/2" UNF nut? (both on 8.8 or 10.9 steel bolts). A bit of Google searching has found 1/2" x 20UNF nuts in both grade 2 and grade 4 stainless - grade 4 is more expensive so I assume that is the better grade but neither list torque loadings. The Grade 2 are DIN 985 std but the grade 4 are not standardised. |
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