More duff info?

[Barry]

Hugo, just buy a new pair of cams, and then you know exactly where you are......at least the valve clearances and other info given here has been excellent advise.

[Hugo]

Sometimes, Hugo, you just need to accept which end the poo comes out, then move on.

No Sir, that doesn't work for me, I'm afraid. To continue your childhood analogy, I was never satisfied when my father would answer "Because I say so" in response to an seemingly intelligent question from me beginning with the word "Why...?".
I must take you to task you on one thing however - you accuse me of "berating the work of people more qualified than either of us, whose job it was to make the cam changes to achieve successfully the desired improved refinement.".
I have done no such thing. What I was doing - am still doing - is to try to get inside their heads & figure out what they were up to. I fully accept that the designers knew more than I do, but that does not imply that their reasoning is so complex and esoteric that I am incapable of understanding it, or worse, as you seem to imply, that I shouldn't even be questioning it - that I should "just accept it and move on".

You say "The answer was established multiple times by many forum members - you just weren't prepared to accept it.". Yes and no - I have heard many theories, but none of them I find convincing. I find this last theory, as I said, far too cack-handed a solution for a competent designer to adopt.
Are you seriously telling me that the designers at Jaguar decided to improve the cam profile, in the light of knowledge that had been acquired in the years since the XK engine was introduced, and then, having eventually got the profile they desired, said "Whoops, we've now buggered up the duration - how are we going to solve that? Oh I know, we'll just open up the gap to compensate. What do you reckon? Ten thou? Ok, let's try that. No, the valves are still open too long. Crickey - we're going to need to triple the clearance to get the duration right. Oh well, that'll have to do." You seriously want me to believe that's how the final design was arrived at?
No, there has to be a better, more intelligent solution out there somewhere.

Would you not agree that a competent designer, upon discovering that the duration was now wrong as a result of re-profiling the cam, would simply re-profile it again to give a shorter duration? What's wrong with that theory? Does it not make sense? If you can explain to me why it doesn't make sense, I will gladly accept your explanation and remain silent on the subject for ever more; If it does make sense, however, we're back to the original question - why did they increase the valve clearance, and by such a vast amount at that?
And now a secondary question - did the increase in valve clearance co-incide with the removal of the oil hole in the lobe (assuming you can actually remove a hole, that is). And if they did co-incide, is it actually a co-incidence? Or an example of synchronicity perhaps? Ok, time for my medication now ;)

[Hugo]

Hugo, just buy a new pair of cams, and then you know exactly where you are......at least the valve clearances and other info given here has been excellent advise.

Haha I don't want to admit this, but I just found the (larger) clearances on a label on the cam covers. But given that my cams don't seem to exist according to the literature, I wouldn't want to take that as Gospel. Given that I'm just doing a rough set-up for now, I am going with the larger clearances anyway, and if it clatters I would know it's wrong I guess ;)

[mark10337]

Perhaps you need to look for your answer in a different place, where people who would have the knowledge specific to your question would be.

The people here have all been very willing and helpful in providing their thoughts, experiences and knowledge they might have acquired either in an amateur or professional capacity. Many items can be resolved here amongst the great wealth of knowledge that everyone freely provides here, but there are limitations. Advanced camshaft engineering appears to be one such case. So either you can accept the thoughts from people who have spent time and effort to share with you and form your own theories or consult someone who has the correct credentials to answer.

Sometimes, we don't even need an answer. Although it is nice to know, it isn't always required. I don't need to know how electricity works to use it, but it might be interesting to know.

[Hugo]

I am unfortunately cursed with an enquiring mind ;) I only recently figured out how silicon chips work - that had me foxed for a long time - all to do with Boolean Logic apparently.
The trouble is that we now live in an age where it is virtually impossible for a layman to comprehend the question - never mind understand the answer. The Higgs Boson for example. Quarks. String Theory. Schroedinger's Cat. That type of thing. Sometimes I think they're making all this stuff up just to keep us in our place!
But not camshafts. That I can understand. But I have yet to understand the reasoning behind what Jaguar did when they changed the gaps ;)

[christopher storey]

I regret that this complex question seems to have become a subject which causes dissension on this board . It seems to me that the choice of valve timing, valve clearances, valve and tappet acceleration/deceleration, are interrelated and complex engineering choices rivalled only by choice of conrod length in relation to stroke in their complexity . Each facet has a desirable set of parameters, varying with the objective to be achieved, not all of which parameters are necessarily in accord with one another. Thus, as with most engineering problems, there are compromises to be made. Now as I have pointed out before , in relation to a given camshaft profile, chosen for its mechanical properties , the exact timing, duration and overlap of which is chosen for its capacity for producing a torque curve of a given shape and for an area under the torque curve of maximum extent , ,there will be an optimum running clearance which produces both the desired running characteristics and the longevity of valve gear which is needed in a road application . This is not cack'handed as you put it, but a compromise which produces as near the optimum outcome of all facets as it is possible to achieve.

Funnily enough, at lunch today I was sat talking to Ken Lea, who for many years was Rolls Royce's Chief Engineer, and thus had at least some acquaintance with these matters, and his view, given on a completely different subject from this, was that the XK engine was the outstanding power unit of all time . He at least did not seem to think that there was anything cack-handed about it

[Hugo]

I agree - I don't believe there is anything cack-handed about the XK engine either. That is why I reject the notion that they just opened up the gap because they couldn't figure out any other way of getting the duration right. Monsieur Crespin earlier accused me of 'berating' the Jaguar engineers. In fact I was doing the opposite - I was giving them more credit than he did, by rejecting the notion that they would come up with such an amateurish fix as this - fiddling with the gaps in order to correct a fault in the cam profile. I am certain they were better than that.
Surely if you are designing a cam, the starting points would be lift and duration? The profile would be dictated by these parameters, not the other way round.
In the case of the change in cam design of the XK engine, all the other variables are irrelevant to this discussion, because none of them changed. The valve clearance, I would have thought, would be dictated by the need to keep valve noise to a minimum whilst ensuring that the valves can fully close under all operating conditions. That, I grant you, may involve some degree of compromise, but the essential point is that nothing here has changed. The valves are the same, the head is the same, the operating temperature is the same. So why did the clearance change? If they had changed the valve material or started making heads out of cast iron or titanium, then yes, I would accept that the clearances would need to change. But they didn't!
Anyway, dissent is good - that is the only way we learn anything. The worst thing you can have is consensus. Unless you like the North Korean model that is.

Allow me to share with you one of my favourite quotations. It is from an obscure film by Nicholas Roeg called 'Insignificance', consisting largely of a dialogue between 'The Actress' (who bears a remarkable resemblance to Marilyn Monroe) and 'The Professor' (who looks for all the world like Albert Einstein). Here is Einstein's response to Miss Monroe when she tries to explain the Theory of Relativity to him;

The Actress: I only said I knew, because you said you knew.

The Professor: I lied. Knowledge isn't truth. It's just mindless agreement. You agree with me, I agree with someone else - we all have knowledge. We haven't come any closer to the truth. You can never understand anything by agreeing, by making definitions. Only by turning over the possibilities. That's called thinking. If I say I know, I stop thinking. As long as I keep thinking, I come to understand. That way, I might approach some truth.

[timhum]

Hugo
Its only a made up quote from a film and on the basis of what it says we can't agree with it, a complete circular argument in my opinion.
To get closer to an answer you can accept why not ask one of the experts at an engine development company, i would start with someone like Cosworth or even Jaguar/Land Rover via the Heritage Centre.
Good luck in you search for the truth,
Tim

[Hugo]

That is a very good idea. This is not something that is at the forefront of my mind - it is lurking somewhere at the back with things like the Monty Hall problem for company (which I once managed to prove both ways!) - but I'll keep digging & I'm sure I'll get there eventually.
By the way, all quotes are 'made up', aren't they? I find this particular quote very significant, even if it does come from a movie titled 'Insignificance'. Which bit do you disagree with?

[Series1 Stu]

I was once told, by somebody quite knowledgeable, that the wire/spool analogy was how to visualise the contour of gear teeth. But that is the extent of my knowledge of this complex and intriguing subject.

I didn't dispute the analogy, I corrected your observation about parabolic gear teeth.

Maybe you should ask that quite knowledgeable person about it. After all, nobody here could possibly know anything about such matters, could they?

[Hugo]

Why the sarcasm? I was only stating what I had been told about the ideal shape of gear teeth, and as I said, that is the extent of my knowledge. I think I might have described them as parabolic, but that was probably a careless invention of mine for which I apologise. As I said, it's a complex and intriguing subject.

[Series1 Stu]

If you're interested then I can recommend some great books on the subject, including the works of Isaac Newton and Robert Hooke, who were pretty much bitter enemies with Newton greatly resenting Hooke's work, especially his derivation of Hooke's Law.

Try reading some antiquarian horology books too, they give a great insight into the clockmaking contemporaries of people like Newton and Hooke, such as Thomas Tompion. These guys were the innovators of their days, being the first to apply new technologies being developed (or discovered) by the likes of Hooke etc. All without the benefit of such things as electric light, sanitation and a hardware store they can pop into for a box of screws.

The reason for the sarcasm should be obvious. You simply fail to acknowledge that the very people you ask for advice, are the ones that you upset by your stubborn refusal to accept that they might actually know what they are talking about.

Regards

[Hugo]

And who was the guy who invented the maritime clock that enabled sailors to know their longitude? Harrison, was it?
As for your last comment, do you mean I fail to acknowledge that other people might know more than I do, or that I fail to acknowledge that I upset said people?
The former is certainly not true, and as for the latter, if I do it is certainly unintentional.
But I have noticed an unwelcome trend on this forum, whereby if I dare to disagree with anybody I get censured for it.
It is very simple - if somebody says something that doesn't make sense I challenge it. Doesn't matter who they are. As for the case in point, everybody seems to just swallow this orthodoxy unquestioningly (that the Jaguar designers opened up the valve gaps in order to get the duration right) and tell me I shouldn't question it. Well I do question it, and if some people get upset by that then I am sorry. If people didn't question commonly held views, we'd still be living on a flat Earth ;)

[mgcjag]

Ok guys...yet another thread thats getting out of hand.....the original question was about camshafts......please go back to this discussion or go to the pub chat are to carry on your disagreements or i will lock this thread....thanks Steve

[288gto]

With Steve's request in mind, this is an interesting article on camshaft design.

http://www.hotrod.com/articles/ctrp-070 ... n-science/

Simon

[Series1 Stu]

Or measure the lift on your cams. They may well be after market re-profiled cams that have been re-numbered with the supplier's type number.

I've never fitted any upgraded cams to an XK engine but this sort of thing was common practice when we used to play around with Ford Kent engines.

[Hugo]

Yes I plan to do that when I get everything hooked up. Also, out of curiosity, while I still have some variations in clearances (they vary from a small 12 to 15 at the mo) I might try to measure the difference in duration that makes, if I can measure accurately enough. I am beginning to doubt the latter, since I was puzzled by the fact that I could sometimes get a 0.12 feeler into gaps where a .010 + a .002 together wouldn't go through. I measured my feelers with a digital caliper & the .012 came out at .009, while the .004 came out as .007. I decided I didn't even want to go there.
I would be very surprised if the engine has been messed with however - it looked like an untouched original engine with about 100,000 miles on it at a guess.
Also, there aren't that many cams available for an XK, unlike Harleys, where you have a dozen different manufacturers turning out a dozen different cams each. You can even buy lobes separately which you can weld onto a blank yourself!

[Hugo]

With Steve's request in mind, this is an interesting article on camshaft design.
http://www.hotrod.com/articles/ctrp-070 ... n-science/
Simon

Very interesting - thanks. But I have to take issue with one statement; "Incidentally, a cam’s position is always measured relative to the crankshaft’s position because that tells you where the piston is..."
That is not quite correct. It is extremely difficult to work out where the piston will be at any given point on the rotation of the crank. You would think that when the crank is at 90 degrees the piston would be half-way up, but that is not the case (unless your conrod is infinitely long). I don't know enough maths to be able to calculate it, but it depends, inter alia, on the ratio of conrod length to stroke.
Like a lot of things in life, it seems very simple until you start studying it!

[Barry]

Words fail me......a simple question about camshafts, and lots of learned assistance from some good guys on this forum who know what they are taking about. What’s your problem Hugo. This really has got out of hand, and I think you need to get a life, because you are seriously pissing people off.....good luck with your restoration project. Just go out and buy a set of cams the engine was designed for, and set the clearances at the factory recommended setting, and stop stressing!!

[Hugo]

I'm not clear which of my posts you are responding to, but I'm not stressing about anything. I'm just intrigued by it all. As for my cams, I have no reason to suspect they are anything but original. The rest of the engine appears to be untouched by human hand since it was built, at any rate.
Thinking about it, I am rather surprised that no-one else is surprised by the fact that, according to the literature, my camshafts do not exist. I would have thought at least somebody might be interested enough to correct the obvious errors in the 'knowledge base' for example.
And I have no idea why anybody should be 'pissed off' just because I reject a theory on the grounds that it makes no sense. I don't get 'pissed off' if somebody disagrees with me, nor would I expect any rational person to get 'pissed off' if I happen to disagree with them. That would not be a very intelligent response. As I have said before, if no dissent is permitted we are never going to get anywhere. I am even more surprised that so many intelligent people should just swallow this implausible theory - that the only reason the Jaguar engineers opened up the valve gaps is because they were incapable of getting the cam profile right. Why does such an outrageous idea not sound odd to anybody but me? That question is as intriguing as the original question about the clearances themselves.
Maybe I'm wrong and that is indeed the reason they did it. I am as always open to being persuaded, but the only way you will do that is to show me some evidence - telling me to just accept it and don't argue won't do it I'm afraid.