More duff info?

[Hugo]

Just setting my valve clearances & I thought I'd double-check the gaps. Google took me to the Jag-lovers page, which gives the clearance as .012"-.014" for both cams on the later engines (mine is a '71). It says the later camshafts can be identified by having four tapped holes and no oil holes in the lobes.
Well, mine have the four holes in the flange, but they also have oil holes in the lobes. They also have a groove round the flange, which I believe is significant, but I can't remember why?
What does this all mean?

Surprisingly, despite new valves all round & re-cut seats on some (which had worn eccentric), the inlet clearances were mostly spot on (or near enough), with the .100" shims re-fitted that were previously in there. Not so much luck with the exhaust cams, though; again all the shims were within a few thou of .100", but the gaps are all too small (though not by a great deal) and one had -.005" negative gap. (I measured this by slacking off the bearing caps till I could get a .015" feeler between the bearing halves, which left me with .010" valve clearance).
I'm only setting them roughly for now so I can run it - I'll do it properly after a hundred or two miles when everything has settled down.
I thought I'd be able to buy a box of shims but I have to buy them individually, which is a nuisance.

[mgcjag]

I posted this once befor for you......it might be usefull... http://www.georgiajag.com/Documents/Camshafts.html

[Hugo]

Useful if you want to give me a migraine perhaps ;) This article lists three cams; an early one with a two-bolt flange and an oil hole on the back of the lobe; and intermediate one with a two-bolt flange & a groove around the flange.
Then it says this; "Shortly after these cams were introduced, Jaguar changed to a 4 bolt design and dropped the groove around the front flange.  The lobe design remained the same and continued until the end of the Series 3 XJ6’s in 1987.  The oil holes on the lobes were dropped when the cams were changed to 4 bolt."

My cams contradict all of this info; they have a four-bolt flange; they have a groove round the flange; and they have oil holes.

I can't even remember why I asked the question! Now, where did I put those aspirin ;)

[mgcjag]

To identify your camshafts the Jaguar number will begin with a C followed by 5 digits, and will be engraved on a ground flat area on each camshaft.......you can then look this up in the parts catalogue

[Hugo]

Aha - now we're getting somewhere - thank you. I found the numbers on the camshafts - they're very tiny & I'd never have seen them if you hadn't told me.
But that's where the good news ends; My exhaust cam says C 3818; and my inlet cam says just 618 - that is all. Could be 613, but there's no 'C' or anything else on there.
Just to confuse things further, if that were possible, the parts book in the 'knowledge base' gives the following intriguing information;

Series 1 3.8; Inlet cam is C14985 from engine no 1001 to 1216; C17138 from 1217 to 5000; then it reverts to C14985 from engine no 5000 on. Exhaust; C13081

Series I 4.2; Inlet C14985; exhaust C13081.

Series II; Inlet C14985; exhaust C13081.

So ALL E Types had the same exhaust cam, and all except engine numbers 1217 - 5000 shared the same inlet cam.
All E Types but mine that is, which has its own unique camshafts.

Frankly I don't believe a word of this - what is going on?

[mark10337]

Is it conceivable that the camshafts are not original Jaguar items?

[Hugo]

Buggered if I know - I wouldn't have thought so, as it has the numbers stamped on a flat ground off the cast area between the front cams, which is where I'm told Jaguar put it. I double-checked those numbers and the shorter one is definitely correct - 618, or maybe 819 if I'm reading it upside down.
It is a US import, if that makes any difference. The engine looks entirely un-molested - just normal wear on a high-mileage engine - I don't know if that means anything, but it doesn't look like a modified motor at all.

[mgcjag]

Have another look for the numbers they are very small on a tiny smothed out surface.....also use SNG site they show all the different part numbers for the cams/ model......whats your engine number.....is it original to your car

[Hugo]

The numbers are correct. At least the inlet one is (618 or 819). The exhaust I have double-checked but will take another look in daylight tomorrow.
The info on Barratt's website contradicts the info in the knowledge base here, & my numbers don't appear anywhere - not on Google; not on eBay.com.
Also the fact that my cams have a four-bolt flange AND a groove AND oil holes on the back of the lobes - this combination doesn't exist according to the literature I've found.

[mark10337]

OK. On the Series 2 which you have there were 3 camshaft pairings. As you were reading 618 or 819 if it was upside down, you have the second pairing.

C.14985 Inlet Camshaft; Engine Nos. 7R.1001 to 7R.8687, 7R.35001 to 7R.38854
C.13081 Exhaust Camshaft; Engine Nos. 7R.1001 to 7R.8687, 7R.35001 to 7R.38854

C.31819 Inlet Camshaft; Engine Nos. 7R.8688 to 7R.14074, 7R.38855 to END
C.31818 Exhaust Camshaft; Engine Nos. 7R.8688 to 7R.14074, 7R.38855 to END

C.35556 Inlet Camshaft; Engine Nos. 7R.14069, 7R.14075 to END
C.35555 Exhaust Camshaft; Engine Nos. 7R.14069, 7R.14075 to END

This change happened in Nov 1969 and is covered in Service Bulletins B.78 & B.81.
Camshafts changed to give quieter valve operation and longer periods between valve adjustments; tappet clearance decal fitted to camshaft cover quoting .012in to .014in inlet and exhaust, valve timing now 17/59/59/17 degrees; camshafts identified by groove cut in perimeter of end flange.

The correct information is out there, you shouldn't just look at the differences between 3.8 and 4.2 / Series 1 and Series 2 engines, but also within the revisions of the 4.2

[Hugo]

Well, that makes sense of it - sort of. But where did you find those numbers? There is nothing in the knowledge base parts list (which seems to be entirely wrong), nor on SNGB's list, nor on the site McJag posted, nor could I find them on Google or eBay.com (although to be fair, I was only looking up the abbreviated numbers I have on mine).
There is no question that my numbers are as I stated - presumably just partial numbers. I've had both camshafts out, & inked in the numbers & looked under a strong lamp, but those are the only numbers stamped on there (apart from casting numbers).
I still find it odd that the printed sources say mine shouldn't have oil holes or grooves though.
My engine no. is 7R13569-9 by the way.
All I was trying to do was make sure I had the correct clearances though, so the rest is fairly academic (although I was never able to establish why they increased the clearances so dramatically on the later camshafts - that is a puzzle I would still like to solve.).

[christopher storey]

(although I was never able to establish why they increased the clearances so dramatically on the later camshafts - that is a puzzle I would still like to solve.).

Hugo - I think there are other threads which have gone over this ground, but the gist of the answer AFAIK is that the object of the parabolic cams ( which are fatter than the straight sided cams ) was to quieten the valve gear. To do this necessitated using a different - fatter - profile of the ramp of the cam so that valve acceleration was lowered. It is axiomatic that to achieve this, the cam would need to be in contact with the tappet for a longer period before achieving full lift . Having decided on this, so as to preserve the timing and duration of the valve opening, it is necessary to alter the clearance so that the metal to metal events occur at the appropriate moment

PS Incidentally, whether the later cams really are parabolic, or whether they would be more accurately described as Uniform Acceleration/Deceleration design is something I have often wondered . The mathematics of it is beyond me I'm afraid

[mark10337]

The 2 references I used for that complete info was Clausiger and xkebooks, and in turn referenced the Jaguar Service Bulletins.

I will freely admit, a good, indexed library of the complete set of Service Bulletins would be a very useful resource. As far as I am aware, there isn't a complete set available online. Terrysjag web site has a large number of them, but it is not complete. I would also be grateful if anyone could point to a resource where they are available.

xkebooks have an excellent manual for the Series 2. I'd definitely recommend investing in it if you are restoring a Series 2.

[mgcjag]

Hugo...the cam numbers for your engine number are clearly shown on the SNG web site as..
C31818 & C31819.....you cant just enter the numbers and search you just need to look up the relevant section for your model.... Steve

[Hugo]

Hugo...the cam numbers for your engine number are clearly shown on the SNG web site as..
C31818 & C31819.....you cant just enter the numbers and search you just need to look up the relevant section for your model.... Steve

Yes, but those are not the numbers I have! My inlet cam just has 819 (or 618, take your pick). I did find a gap on my exhaust cam just big enough for a figure 1, so that chimes with Barratt's list, but there is absolutely nothing more than 819 on the inlet cam. Obviously I am making a working assumption that this is an abbreviation for C31819.
And the numbers on Barratt's site are contradicted by both those in the Knowledge Base on here, and by those on the Georgia site you sent me earlier, so it's not as simple as "just enter the numbers and search", with so much contradictory info out there! Whom do I believe?
Pus the fact according that each of these sources, my cam doesn't exist (four-bolt flange with a groove round the flange and oil holes on back of lobes).

[Hugo]

[Christopher Storey] ".. the object of the parabolic cams [...] was to quieten the valve gear. To do this necessitated using a different - fatter - profile of the ramp of the cam so that valve acceleration was lowered. It is axiomatic that to achieve this, the cam would need to be in contact with the tappet for a longer period before achieving full lift . Having decided on this, so as to preserve the timing and duration of the valve opening, it is necessary to alter the clearance so that the metal to metal events occur at the appropriate moment"[end quote]

Yes I've heard this, but I don't find it convincing. It just seems to be a cack-handed way of doing things. I would have thought that if they were going to re-profile the cams, they could have done so in a way that would give the correct timing without having to resort to such an amateur-ish method of getting the timing back to where it should be.

By the way, I've been thinking - (cue for everybody to hit 'delete') - I wonder if the oil holes on the back of the cam lobes contribute to the oil consumption of the engine? Maybe that's why they did away with them? Too much oil sloshing around up there? Just a thought.

Incidentally, I'm told the way to visualise a parabolic curve is to imagine a wire rope being wound onto a spool; picture the trajectory of the rope from the perspective of the spool and you have your parabolic curve. At least I think that's a parabolic curve - it's the shape to which gear teeth are profiled, I believe.

[Hugo]

Sorry I should have said 'viewed from the perspective of a fixed point on the spool'. Otherwise you get a straight line ;)

[Series1 Stu]

Hugo

Gears these days have an involute profile. Previously, in the early days of clock making (circa 17th century onward), they used a cycloidal profile.

If I remember correctly a parabola is the perfect aero/hydro-dynamic profile. I don't recall it being used for gear teeth, although I could be wrong.

Regards

[Hugo]

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.

[PeterCrespin]

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.

That sounds like an appropriately realistic and honest self-assessment. But it does rather grate to read statements like "cack-handed.." tossed around to critique the work of professionals who DID know what they were doing.

As for "...though I was never able to establish why they increased the clearances so dramatically on the later camshafts - that is a puzzle I would still like to solve..."
I 'm not sure if you are serious or not. The answer was established multiple times by many forum members - you just weren't prepared to accept it. Back when you raised the subject, the rationale and method were explained multiple times by a slew of respondents but you just didn't accept anything put to you. Instead you threw up repeated objections and non-sequiturs and carried on 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. An inability on our part to grasp the basic principles of a concept overview, does not constitute an imperative for others to cover the same ground repeatedly until we do.

I remember as a kid my dad dissecting my hamster that had died. As he pinned it out on a waxed board he showed me the rib cage, lungs and heart. I saw the intestine and the fact that towards the end of the long wiggly tube there were what appeared to be pellets inside. I was probably about four or five and, thinking I'd discovered something I asked "Is that poo Dad?" He confirmed that it was and gave me a couple of sentences about how food changed as it moved down from the mouth, through the stomach and long wiggly tube until the goodness had been taken out to nourish the hamster, the same as happened to the food people ate.

A full-on lecture about digestive enzymes and peristaltic movement would have been inappropriate. Sometimes, Hugo, you just need to accept which end the poo comes out, then move on.