I'm trying to help a friend with something on his motorbike.
He has bought some second hand 'engine bars' but they didn't come with the two 'longer' engine bolts that would typically have come with the bars from new to accept the extra thickness of steel on the bar brackets plus some spacers on the other.
Now, would could be 'better' than bolts would be a length of plain steel bar with suitably threaded ends as then he could add / remove the bars without having to take the bolt right out and support the engine etc.
Now, I could easily fabricate such a thing with my lathe, a length of M10 bar and a suitable (M10 x 1.5mm) die but I'm unsure what steel to use and if cutting a thread would be as strong as what I imagine would have been a rolled one?
Are bolts typically the same steel as what is normally sold as 'free turning mild steel' and if not, what should I look for please?
IF you wish to make some tough bolts for engine mounts I would not use threaded bar , I would make them out of something like 1080 steel which you can work in the lathe (untreated) look it up, you can even heat treat it but it is tougher than mild steel even without hardening and tempering
Nor would I. We have used some studding and a Nylok nut to 'prove' the length of bolt needed but I wouldn't use that for the final purpose. [1]
Thanks for that, I'll check it out.
I found some long M10 bolts on eBay but they were SS and A2 at least appears to not be as 'strong' as 8.8 steel.
If I could find a suitable M10 8.8 hex headed bolt, it seems that the relevant ISO std suggests bolts over 250m long have a threaded section of 45mm. So if we needed the plain 'shank' to be ~230mm, we would need a bolt length of 275 (or slightly less) mm (and cut it down).
Or I go back to running some thread on the ends of some suitable bar stock. ;-)
I was also concerned not to go too 'stiff' as it could make it more brittle and therefore likely to snap off rather than bend ect.
Cheers, T i m
[1] (3 of my) My folding boat(s) have a nylon wheel in the skeg and on the oldest one the wheel was very loose. On inspection they had used a straight machine screw for the spindle and 'of course', it had chewed the inside of the wheel up. I replaced the machine screw with a suitable SS bolt (where the plain section was (nearly) as long as the width of the whole skeg), turned the wheel out back to clean material on the lathe and turned a nylon insert up to return the correct diameter and it runs fine again and likely to stay that way for a good while. ;-)
The devil is in the detail. I would say that normally you would not need particularly high strength steel here, but I'm thinking classic British bikes; it is possible that some high performance Japanese job might have been designed to use "high tensile" bolting.
I assume that these new bolts are connecting the engine casting either to lugs on the frame, or more traditional mounting plates. Originally a through bolt with a nut and washer at one end.
So there are two bolts? Are they the only two bolts holding the engine near that location? If there was a bit of redundancy I would (personally) be fairly relaxed about just using studding, unless as I say it is a high performance bike.
Agreed, I was just keen to get any replacement bolts to be 'as strong' as the originals.
Whist this one is a Kawasaki, it wouldn't be considered as a 'performance jobby' (ER5, 500c twin).
Yup.
Correct. There is no marking reported on the head of the bolt(s) but considering they are only pinching ally between steel, aren't likely to be anything super strong. Nor is the engine a 'stressed member' so they are just there to keep the engine in the frame. ;-)
I believe so yes. There may also be some attachment between engine and frame at the rocker cover.
Whilst I agree, I don't think it's a particularly elegant (engineering) solution and so I've ordered some M10 EN8 steel bar.
I asked him to remove one of the nuts and try it on the M10 studding I get him to use as temporary fastenings and as expected (from previous experience), the thread isn't the 'std' (for M10) 1.5mm pitch but something finer, probably 1mm. I've asked him to give me one of the nuts to make sure.
I had an idea to stop the 'stud' rotating when being tightened in the light of it not having a head. Because it needs spacers between the frame / engine mounting tang / lug and engine bar tang ... to get some M10 stud joining nuts and cut them down to the +16mm length needed for the spacers and boring the thread out to a plain M10 hole. If I then fix (braze / bond) one on the shaft at the right spacing from the end to form a 'nut', it can be held with a suitable (22mm?) spanner whilst the opposite end nut is torque correctly, including the other floating spacer and engine bar mount. The engine bar can be fitted to the 'head' end and also torqued up.
This means he can remove the engine bars without having to worry about supporting the engine or the spindle rotating when you are trying to torque / undo (the worse might be trying to centre it correctly whilst doing it up. As long as one nut comes off you can always pull it out like a bolt, should one side get bent / seized / damaged etc).
I may not bother with the extra head as the weight of the engine on the bolt (friction / shear forces) might be enough to hold it still, even when using Nylock nuts.
Yes except that this means having extra thread exposed at the end.
The other Tim is looking to do a "proper job" which I can only applaud. I like to do this too, especially if it is for someone else. I'm more likely to do "quick and dirty" for myself. The other option, since he mentions brazing, is to silver solder a nut on to the end of his machined bar. Then of course it will go rusty, so should he plate it? Although he could try an A2 nut. I've never tried to silver solder stainless.
Agreed, however, given there is little in the way of spare thread sticking though the end of nut(s), the only way you might be able to do that is to remove one nut and then replace it with two half nuts, lock them together and hope they would have enough holding force to allow you to do whatever you need with the nut on the other end.
Say you did that to get a Nylock nut in the right position to centre the stud, what is to stop it de-centring itself once you put the Nylock nut on the other end? ;-(
We might be able to get away with it if the unthreaded part is just a couple of turns of thread shorter than the total width as then the chances are one nut or the other will 'bottom' on the shaft and still keep the stud fairly central. Or use Loctite on plain nuts as then there would be little friction whilst you are tightening the whole thing up etc?
Another way would be to make a sliding 'spacer / nut' by applying a flat or notch along the shaft at one end so a spanner on the nut would stop the shaft rotating whilst the two end nuts are tightened up, but this would weaken the shaft slightly?
Maybe the combination of the right length central plain shaft and locking nuts to remove the opposite nut (in the event of needing to remove the bars (for engine work, without dropping the engine) and Loctite would do it. ;-)
Sods law though, when you want to remove the engine bar on just one side, removing that nut unscrews the stud out of the nut on the other side. ;-(
Maybe once the steel shaft has seized in the ally crankcase we won't have an issue (till we need to get the engine out that is). ;-)
(As I know Mr Lamb personally, I know he too likes to do things properly where it's relevant etc). ;-)
It's funny isn't it, even though it's 'just' an engine bolt and it's 'just' on a mates old motorbike and I'm sure there are a variety of solutions that would 'work', as you say I would 'typically' try to do the best job possible *irrespective* of those things, just because that's how I am. I know it will probably cost more money to do it 'well' and typically cost more of my time and effort but again, I don't rally have any option, if I'm going to do it in the first place.
The idea is that I would like to do it once and provide a solution that is the most flexible practical.
Seconded ... which is strange to some I'm sure. ;-) Whilst the owner of the motorbike is no engineer, I know he will appreciate the effort that may have gone into any solution and he would appreciate a 'neat' final solution that continues to work well in the future.
I have some of that 'Liquid metal' epoxy and I was thinking of knurling the shaft at the appropriate place and would make sure it was chemically clean, warm and then allowed to cure over a good time before fitting.
I had already thought of that. ;-)
If I use plated or even stainless stud joining nuts as the base for the spacers, they wouldn't corrode and the surface would remain undamaged if it was chemically bonded over soldered / brazed. The hope was that worse case it could maintain the stated nut torque from the opposite end before the other nut is torqued.
See above re the use of a new 'nut' as the spacer(s), and the retaining nuts on the ends would be new std plated nuts in any case etc.
Part of putting a bit more effort into doing such things is the idea that if someone 'else' takes it apart in the future, that they might consider it 'neat' or 'a good solution', rather than 'WhoTF bodged this up then?'.
Because I am someone who sees this sort of thing, if taking on say an old motorbike, I'm much happier to find it's just tired from use over it being f'ked about by someone who doesn't realise there is a minimum standard / right way of doing things (F'my'/'Our'POV anyway). ;-)
I theory, for any given level of skill / machinery / materials available, many people would come up with the same (good) solution?
Yes but I can see some restorer in the distant future taking the bars off to make it "original" and then having a grumble because they can't use your nicely engineered bolts without tapping a bit more thread on each end!
It's not just the 'strength', it's not good engineering practice to have a thread sitting inside certain parts (especially if there is some rotation involved, like an axle).
For any given major diameter, a threaded section will not be as strong as an unthreaded one (specifically in shear in this case).
And so that's why we have and use machine screws and bolts for different things. ;-)
You will generally find a bolt used where there is a need to locate (like a dowel) *and* retain something. Like where a bolt goes though something to hold it against something and hold it in position.
In this instance there isn't but I was answering your question more generally.
But the threaded part isn't in an area of shear.
Agreed.
And shear strength ... in the case of this engine mounting bolt, worst case of the bike coming to a rapid halt and the engine wanting to carry on going, in theory the nut on a plain bolt solution could be finger tight and the bolt would still be effective (as it's a clean
10mm diameter pin). Like for like, a threaded section would be smaller for the given outer diameter and so weaker (in shear). I agree the a bolt would only be as strong as the threaded portion in tension.
I'd rather not have to decide, as long as it's as least as good. ;-)
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