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Jun 23, 2020 15:16:47 GMT
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My additional thoughts: Lubrication - a common error is to lubricate threads, threaded joints only stay done up because of friction lubricate the tread and you change the friction, I've seen wheels come off commercial vehicles because of this mistake basic rule is unless the manufacturer says lubricate the thread leave it dry, if you want to avoid it sticking in the hole you can lubricate the shank. As mentioned above it's the clamping and friction between the two parts which holds them together not shear load on the bolt so you should also not add anything to the mounting face of the wheel either for the same reason. I do not fully agree with you on the lubrication issue. I do not use copper slip on my wheel bolts but apply it to all other bolts on my cars and motorbikes and they never come loose. You could look at it from another way. If you torque up a bolts, as you mention the tension, clamps the parts together and the friction keeps these in position. The issue s that you do not know which parts of the torque is used for the friction component and which part of the torque is used to create tension in the bolts. There are rough guidelines in the bolt calculations for the friction componetn when lubricating the bolts or not. When you apply lubricant to the bolts, more of the specified torque is used for the clamping so the construction should me more save and there is still enough friction to avoid a bolt coming loose. I have worked for a manufacturer of large hydraulic cylinders (up to 30m) for industrial, civil and off shore applications and have dealed with managing a waranty claim on a cylinder which was used in a paperpulp plant Underneath as picture of the cylinder which had a diameter of approx 1m and the cover was held with M40 bolts And this is waht happened All bolts broke so an investigation started for the root cause. One of the suspects were the bolts and the torqing sequence and the lubrication used. The plant had 4 lines so i made a mark on the bolts head and the cover, loosened the bolt, lubricated it and retorqued and found out the mark on the bolt was not matching with the housing anymore So a few bolts were equiped with a tension sensor and we soon found out that the assembling people in the factory did not always lubricate the bolts enough and then too much of the torque was needed for the friction component which left not enough for the tension component. We also found out that different brand of greases showed a lot of difference in the friction. The moral of the storey is that with lubrication, you can be more certain that the tension in the bolt is closer to the theoretic tension. In the end, the drawing of the cylinder was copied to a CAD program which easily calculated all stesses and it showed the cover was a bit thin, so it bellowed a bit which caused fatique on the bolts. Another experience i would like to share on the SS aloy combo Underneath a picture of a SS bolt A2-70 in the alu casing of my Ducati 860. Its there for approx 10 years now and fitted with cupper slip. There is absolute no corrosion visible although because of the SS and Alu, it should be there but maybe the cupper slib is helping to avoid it It is an interesting discussion for sure Peter
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Jun 23, 2020 15:57:13 GMT
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Hi, I understood that electrolytic action can be mitigated if there's a barrier between them, a coat of paint or a sealant is enough but it's not always practical. Re. the Copper slip, is it the Copper particles or the oil it's suspended in that's providing the protection?
Colin
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Jun 23, 2020 17:32:10 GMT
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Without wanting to derail the thread, what's the issue with powder coating? HI, The problem for me is when the surface gets damaged it lets water in and the corrosion creeps along under the coating bulging up the coating and they look scruffy quite quickly. They're not easy to repair and usually involves removing the whole lot. As well as that, once the water is behind the coating, it doesn't dry out as quickly leading to corrosion problems, in much the same way that old underseal would trap moisture behind it and do pretty much the opposite of what it should.
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Jun 23, 2020 17:46:32 GMT
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I think we are in agreement on lubricating bolts, if it is specified by the engineering spec as in the cylinder you showed lube should be used (this will have been factored into the specified torque), if it's not specified assume a dry joint.
As you point out lubing the thread increases the tension for a given torque, if you apply lube and the torque for a dry joint you risk necking the bolt.
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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: 11,715
Club RR Member Number: 34
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Jun 23, 2020 17:52:52 GMT
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HI, The problem for me is when the surface gets damaged it lets water in and the corrosion creeps along under the coating bulging up the coating and they look scruffy quite quickly. They're not easy to repair and usually involves removing the whole lot. As well as that, once the water is behind the coating, it doesn't dry out as quickly leading to corrosion problems, in much the same way that old underseal would trap moisture behind it and do pretty much the opposite of what it should. This is is really. Powdercoat is a ‘shell’ coating. It is hard coating, but it doesn’t adhere to whatever it’s applied to, It only makes a protective layer when it is baked and melts to itself. So as soon as that layer is compromised in any way, moisture gets in and runs rampant under it, usually making any corrosion much worse as the water is trapped against the surface of the metal, Making it permanently wet. then Eventually It comes off in sheets. Paint is better for literally every single automotive application there is, as it actually sticks to the base material, and can deal with stone chips and the like. For most underbody stuff a Non-catalyst paint that doesn’t set as hard as a 2k is preferred for its impact absorbing properties. A lot of specific underbody products will fit this description. The reason people use powder coat are twofold. One it’s cheap, especially in terms of labour and wasted materials as it’s applied electrostatically, and two it requires a much lesser skillset than paint. You just huff it on and it all levels out in the bake, there’s no real skill to it’s application, not compared to paint anyway. That means more or less anyone can do it and it’s pretty hard to get a poor finish. What it does not make it is the correct product for the application.
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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: 11,715
Club RR Member Number: 34
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Jun 23, 2020 18:10:42 GMT
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The problem is most people are magpies, and uneducated ones at that. I’ve spent the best part of 20 years telling people to never use stainless into aluminium alloy castings, but ‘they look pretty’ always overrides ‘you won’t be able to undo that in a year’. Que knackered casings and lots of helicoils. Same with stainless exhaust studs and nuts. But, they’re generally the same people that think powder coating is an acceptable coating for automotive applications. They don’t even learn the hard way. I have positive experience with powder coating on my own car. My MGB V8 is on the road for 12 years now and all suspension parts and also brake calipers have been powder coated and it still looks like new, even the brake calipers. The car is not used in the winter but has made a fair bit of rainy kms. Back then powder coating was not so common so i used a compagny about 150 km from where i live and threw the years, i have used 2 compagnys more close but returned to the first compagny. They shotblasted every component, then gave it a layer of primer and then 2 coats of powder coating. On one of my Rovers, which lives outside and is also driven in the winter, i also got the calipers powder coated and after 7 years, they still look as good as the day these were done. Have seen poor powder coated parts so understand what you mean but in combo with primer applied and the double coat, i believe it gives a lasting result. Peter
I would say there’s one of two things happening there, depends on what product the primer is. The primer has potentially melted into the powdercoat when it’s baked, making an amalgous coating that actually has adhesion properties. Either that or it’s actually the primer doing the work with the powder as a finish over the top.
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andyborris
Posted a lot
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Freedom is just another word for nothing left to lose.
Posts: 2,173
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Jun 23, 2020 18:12:29 GMT
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Very interesting.
Not an expert, but here's my 2p's worth, when replacing a nut on a bolt or a bolt in a component, on any of the heaps of rust I've owned through the years, my rule of thumb is, if the old one was rusty, the new one goes on/in with Copperslip.
Please critique.
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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: 11,715
Club RR Member Number: 34
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Jun 23, 2020 18:19:16 GMT
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never use stainless into aluminium alloy castings Guilty as charged. Let me explain the situation, so you (or someone else) can offer a better alternative. My Saabs with Ford Cologne V4 engines have a cast aluminium thermostat housing that is held onto a cast aluminium intake manifold with steel bolts from the factory; this is the case on many other engines too. These bolts will snap at some point, I suppose due to galvanic corrosion, either when you're undoing them, or completely voluntarily. The alternative I've found works best, is loctiting 316 threaded rod in the holes, and using 316 nuts to hold everything together. I do the same to hold carbs in place. I admit to using brass washers under the nuts to pretty things up on occasion. It's worked for me for over a decade, but I'd be interested to hear if there are better solutions, as what the factory did is not perfect either. Same with stainless exhaust studs and nuts. [...] They don’t even learn the hard way. Similar issue here, but steel studs in cast iron exhaust manifolds. I have quite a few Cologne V4s go through my hands each year, and the majority of studs snap or have snapped. Admittedly, most will come out first time when I weld a nut onto the stub, they seem to rot on the boundary of cast iron and air. I replace them with 316 threaded rod and I have used standard 316 nuts and brass and copper exhaust nuts on different engines. I know stainless is less than ideal, and I'm not sure how well 316 is supposed to handle heat, but I wanted to test in practice what would happen (call it "the hard way"). Again, worked for me for some time now, but always happy to hear about alternatives. Mild steel into ally is better than stainless, as they're closer together on the galvanic series, so you’re *theoretically* sacrificing less aluminium if it does corrode. Using zinc plated fasteners is also good as it acts as a further barrier. You’ll probably find that the Loctite you’re using is acting as a barrier to mitigate any corrosion though. Brass or copper washers are also good for this as you’ve already said. For exhaust studs I always use high tensile steel studs with brass or copper nuts. What you have to remember is that by replacing the mild steel sud with stainless, you are choosing to sacrifice another component instead.
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Jun 23, 2020 18:51:13 GMT
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I have positive experience with powder coating on my own car. My MGB V8 is on the road for 12 years now and all suspension parts and also brake calipers have been powder coated and it still looks like new, even the brake calipers. The car is not used in the winter but has made a fair bit of rainy kms. Back then powder coating was not so common so i used a compagny about 150 km from where i live and threw the years, i have used 2 compagnys more close but returned to the first compagny. They shotblasted every component, then gave it a layer of primer and then 2 coats of powder coating. On one of my Rovers, which lives outside and is also driven in the winter, i also got the calipers powder coated and after 7 years, they still look as good as the day these were done. Have seen poor powder coated parts so understand what you mean but in combo with primer applied and the double coat, i believe it gives a lasting result. Peter
I would say there’s one of two things happening there, depends on what product the primer is. The primer has potentially melted into the powdercoat when it’s baked, making an amalgous coating that actually has adhesion properties. Either that or it’s actually the primer doing the work with the powder as a finish over the top. I always make coverplates from steel to protect surface which i do not want to get powdercoated and i have tried a few times to get the powdercoating off but i had to grind it of. It is possible that it connects to the primer like you said. You are right about the cost and the skills and the even coatings without runs. The compagny i use does only powdercoating for ages
Peter
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Last Edit: Jun 23, 2020 21:56:53 GMT by petervdv
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Jun 23, 2020 18:56:40 GMT
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Hi, I understood that electrolytic action can be mitigated if there's a barrier between them, a coat of paint or a sealant is enough but it's not always practical. Re. the Copper slip, is it the Copper particles or the oil it's suspended in that's providing the protection? Colin I cannot explain it. When you torque a SS bolt into an alloy housing, there are contact areas in threads. My best quess is that the copper slib seals the spots where there is contact between the SS and the alloy from moisture and i believe some moisture is needed for creating corrosion.
Peter
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jonomisfit
Club Retro Rides Member
Posts: 1,762
Club RR Member Number: 49
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Jun 23, 2020 19:30:36 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.
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melle
South West
It'll come out in the wash.
Posts: 1,987
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Jun 23, 2020 20:00:17 GMT
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Mild steel into ally is better than stainless, as they're closer together on the galvanic series, so you’re *theoretically* sacrificing less aluminium if it does corrode. Using zinc plated fasteners is also good as it acts as a further barrier. Ford used steel fasteners, but after half a century it's impossible to tell if/ how they were originally coated. I tried to remove some steel bolts from an '80s Ford inlet manifold the other day, and they had all rotted away and snapped. I hope I'll live long enough to see if my 316 replacements will fair any better, and if the manifold survives! For exhaust studs I always use high tensile steel studs with brass or copper nuts. What you have to remember is that by replacing the mild steel sud with stainless, you are choosing to sacrifice another component instead. What I have found is that stainless nuts (even if copper coated) on stainless studs is not the best good idea if they go through heat cycles, that's why I use (softer) brass or copper nuts now.
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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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jonomisfit
Club Retro Rides Member
Posts: 1,762
Club RR Member Number: 49
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Jun 23, 2020 20:06:08 GMT
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Hi, I understood that electrolytic action can be mitigated if there's a barrier between them, a coat of paint or a sealant is enough but it's not always practical. Re. the Copper slip, is it the Copper particles or the oil it's suspended in that's providing the protection? Colin If an insulator of suitable size is set in between the two materials you cannot get an electric current setting up between them and galvanic corrossion cannot occur. It gets a bit more complicated if the items are submerged in an electrolyte fluid (like seawater) as you can them get "throw" from the current/ voltage which means corrossion can start further out than you may expect. It has lots to do with the relative surface areas of the materials and things, but I cant see it being a substantial issue on cars. Hi, I understood that electrolytic action can be mitigated if there's a barrier between them, a coat of paint or a sealant is enough but it's not always practical. Re. the Copper slip, is it the Copper particles or the oil it's suspended in that's providing the protection? Colin I cannot explain it. When you torque a SS bolt into an alloy housing, there are contact areas in threads. My best quess is that the copper slib seals the spots where there is contact between the SS and the alloy from moisture and i believe some moisture is needed for creating corrosion. Peter
Despite containing copper, copper slip / ease isnt really conductive. So using it may providing an insulating barrier at the key point (last thread out of the hole). If the copper slip is effectively filling the remaining space between threads then it will also act as a barrier preventing air and moisture working its way down the thread and corroding. With both these bits if you cant get salty water touching both parts you cant get galvanic corrossion. In terms of tightening threads up any compound applied will have extruded out from under the threads that are in full mated contact. The pressure at the mate points of the leading threads is immense when a bolt is tightened and will be far beyond the force needed to extrude any grease / oil / copper slip into the root or the space onthe unloaded flank. This is why in my first post i've said I find topical compounds to be usually more miss than hit for galling prevention. What i've had great success with is plated surface coatings. I.e. nickle PTFE coatings. The form a microns thick layer over the metal and are chemically bound into it. The aim here to plate to above the worst height of asperities (rough peaks in the surface finish of the material) meaning the similar stainless materials cannot get in direct contact and start the galling process. Its also why care has to be taken if making and braking the joint repeatedly as the coating can be abraded. Abrade enough and asperities may start contacting again. To me retention of a nut / bolt comes from the amount of tension developed within the bolt when fully tightened. Lubrication doesnt have a substantial impact on the break out torque for releasing the joint as this is driven by the bolt tension not the friction in the threads being rotated. Its a static system and the coefficient of friction in a static condition is higher than dynamic friction. What slip compounds do in a bolted join is to reduce the friction from the surfaces sliding on each other, and from the friction the develops under the bolt / nut head. This means you can get the required tension on the bolt without over stressing the material trying to force it to rotate. Its why I also like nuts onto studs v's bolt into a blind hole. I think of it as with a nut you are directly tightening a thread on thread. With a bolt in a blind hole you a using a torsion spring to wind a thread into a thread. The friction effects mean you loose torque to twist on the bolt shank and the effect gets worse as the thread goes in and the bolr tension increases as the friction in the threads increase, and so the twist on the bolt increases. You can really feel this on big slender bolts into blind holes.
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jonomisfit
Club Retro Rides Member
Posts: 1,762
Club RR Member Number: 49
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Jun 23, 2020 20:07:53 GMT
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And this is waht happened spot where the first thread on the bolt was v's the threaded mating part :-) In high pressure things, when one bolt goes it does tend to like sharing the pain round its friends.
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Last Edit: Jun 23, 2020 20:11:04 GMT by jonomisfit
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Jun 23, 2020 20:45:56 GMT
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Just came across this thread, great reading.
I have a question that hopefully somebody will be able to answer.
What about using stainless steel nyloc nuts on steel bolts (suspension, mounts etc) where the nut is only acting to retain the bolt in place while the bolt takes all the strain? No, aluminium casings involved. Hope the question makes sense.
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Last Edit: Jun 23, 2020 20:49:47 GMT by Woofwoof
Still learning...still spending...still breaking things!
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ferny
Club Retro Rides Member
Posts: 985
Club RR Member Number: 13
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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.
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Proton Jumbuck-deceased :-( 2005 Kia Sorento the parts hauling heap V8 Humber Hawk 1948 Standard12 pickup SOLD 1953 Pop build (wifey's BIVA build).
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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. I have one of those kits, though I'm not sure the process I go through to plate and passivate is the same as a plating company would do. The process is basically - acid pickle, nickel plate, dangle in clear passivate, dangle in yellow passivate for longer, leave to dry for 48 hours. The effect looks good, but I'm not sure that a professional plater does the same thing. I should have asked. I think having it done as a job lot isn't terribly expensive, but it helps if you have several companies around that do it to keep the prices competitive. I don't, so when I sent a batch away it was dearer than I expected, but I know others who have had more done for less money. I like being able to do stuff myself, though I'm limited on the size of item. 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. Mk1 Audi TT is an example of this - the engine mounting bolts are stretch bolts, and they have to be removed and replaced when the cam belt is done, or anything down that side of the engine such as the water pump. I had mine done once, the bolts weren't replaced (but were torqued up to spec, so doing the "stretch" part a second time) and a few months later they snapped, leaving the engine resting on the front subframe. On that car, the rear suspension bolts are also marked as "renew every time". But they don't have the "plus x degrees" that I associate with stretch bolts. So, why do they need to be renewed each time? These allow the (limited) adjustment of toe on the rear suspension, so in theory any time you have that adjusted, new bolts are required. Or am I just wrong about the "plus x degrees" being the indication that they're stretch bolts?
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Jun 24, 2020 10:18:28 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?
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slater
Club Retro Rides Member
Posts: 6,390
Club RR Member Number: 78
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Jun 24, 2020 12:32:34 GMT
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TI gauls badly so should be lubricated. It doesnt suffer from the corrosion issue in normal environments tho really. It has fatigue issues and although it has high temperature stability it will oxide at very high temperatures too. I'd does depend a bit in the specific alloy but for most automotive stuff the gaulling is the worst issue.
At least theres a point to TI fasteners!
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