SimonPearse

A coil at the bottom of the spring has a greater diameter than a coil at the top. Therefore a coil at the bottom has a greater circumference. As the spring starts to compress the coils of greater circumference are displaced more than the coils of lesser circumference since the deflection is constant per unit length of wire. the largest diameter coil is the first to become coilbound. when it does so it reduces the bendable length of the spring by one (large) circumference. This increases the rate of the spring. The spring therefore behaves at a variable rate as it is compressed. This is surely basic mechanics?

but surely that equation only describes a conventional fixed-rate spring, whereas a beehive spring does not have a constant rate. I don't think it is true to say that a beehive spring does not have a fixed resonant frequency', I assume that the advantage of the beehive springs is that they have a lower q factor......not sure if that is the correct term (my degree is in electrical/electronic engineering rather than mech eng) so that their behaviour is less 'peaky' at the resonant frequency. If the resonant behaviour is altered then you can use less seat pressure, and a lighter spring assembly. The diameter at the top of the spring is reduced so you can use a smaller, lighter cap. The reduction in sprung mass means you can further reduce seat pressure and use a weaker cap.. a 'virtuous circle'. Now as to whether they are worth the cost......

did you tighten the sump bolts while you were at it? - my guess is that the noise is due to the crank touching the sump pan / hitting oil in the front of the sump pan. I had it myself-fixed by taking the sump off and addressing the sump with a large universal adjusting tool (ball-pein type) and a lead dolly.

don't think the surface area is significant at dc. AFAIR skin effect only starts to come in at a few kHz (though its a long time since I studied). ARGHHH.....just looked it up. I thought I had successfully removed all memory of Bessel Functions.

Perhaps I am missing something about the end point not being clear, but the way I have used to measure chamber involves covering the chamber with a bit of glass (with a small hole) oil the head surface to seal the glass then inject soapy water through the hole. A bit of detergent in the water reduces the meniscus. Position the hole so that it is at the edge of the chamber and tilt the head so that the hole is raised (to let air out as you put the water in. The only difficulty in detecting the end point is due to the minimal meniscus at the injection hole.

this smacks of a distasteful witch-hunt. GT makes his living by selling his skills: is it any wonder that he advertises? He can be rude and obtuse, but no-one is forced to read his posts. By taking away his forum access you take away his ability to work. I have only met him once, years ago, and I've never met Steve, so I am not qualified to comment on their dispute. I guess that applies to most of us.

That's kind of the point that I was making... I was considering the physical layout of the system to be an integral part of the switching device, not just the bimetal/thermistor/whatever. The 'switch' is the change in state from a powered element to an unpowered element. If an inaccurate bimetalic transducer was immersed in the water then the kettle would be unlikely to work properly. By placing the transducer in a steam duct the inaccurate transducer becomes part of an accurate switching system. THe sensor is not in the water, but the sensor is not the 'switch' I hope you don't fail your interviewees on the basis of the semantic differences between a transducer and a switch!

I think that expressing yourself is generally a good thing- so keep doing it!

how to service an old car radio: change the plugs and grind the valves in!

true, though that's not particularly significant in the UK where we (virtually) all live within 500m of sea-level. 500m makes roughly 2 degrees difference.

every kettle that I have dismantled to fix vents steam onto a bimetallic strip-based thermostatic switch. A cheaply made bimetallic switch is not accurate enough on it's own, but steam production won't start until water reaches 100 degrees using vented steam to heat the thermostat greatly increases the accuracy of switching. The switch needs to be accurate: if it fires at 99 degrees then the water will not be boiling, and the water cannot possibly reach over 100 degrees. (assuming standard pressure!)

From an economic point of view labour is a resource. If the UK had the chance of buying lots of cheap oil we would jump at the chance, Wage elasticity in the UK economy is minimal due to the fact that a high proportion of us have mortgages costing a large proportion of our income, and the social inhibitions about cutting wages. Before slagging off too much consider: In the UK in 2011 the chance of you or your children starving to death is nill. You will not be conscripted into a war and used as cannon fodder. You are almost certain never to be tortured. You are almost certain not to die prematurely from an easily treatable disease. If you hate it in the UK you are free to go and work/live in one of the other EU countries. Historically there have not been many generations of people in any place in the world who can claim those things. We are the lucky ones.

sure I've read somewhere that at medium-high revs most of the oil flow through the big ends is due to the crank self=pumping. Centrepetal reaction sucks the oil out of the sump.

unless the oil pick-up is blocked, surely cleaning the oil system will reduce pressure rather than increase it? (decrease resistance, increase flow, decrease back pressure) Is the oil pressure at idle actually low? if not then you could perhaps put a washer under the pressure relief valve spring. Other possibilities (depending on the layout) include a new oil filter (has it been clogged with ptfe?), molyslip(often works well), sound deadening mat on the chain cover, and slackening an exhaust joint so that it blows a bit (cover up the noise, dealer knows that exhaust is an easy fix, knock a bit of the price and he thinks he is getting a bargain!) Promise to use some of the money saved to buy a book on ethics?

It's unusual for me to take more than a day or two to read a book, but after owning it for 20-odd years I've never completely read Douglas Hofstadter's 'Godel-Escher-Bach': it's a fantastic book but I just can't make myself work through it in a linear way. (which may be quite appropriate). Haruki Murakami, Mordecai Richler, J M Coetzee, and John Lanchester are always worth a read.