With apologies, I'll therefore start with the conclusion, for those that might fall asleep.
There is a new and potentially revolutionary crank seal now available.
Instead of fannying about with split oil-seals and buying a different rear-seal block, or modifying your original rope one, you can now buy an SKF Viton "flexi-seal" from Rob Beere in Coventry that will fit as a direct replacement for the rope-seal ; your crank will still need grinding, or has already been ground, to either 75mm or 3", but that's about it.
It's much more tolerant of deviations from standard of the main-bearing axis (as a result of any line-boring of the block) than the split lip-seals, and massively more so than the original rope-seal.
I have no connection with Beere other than as a customer.
They are the only retailer in the UK (that I have found in 16 years of E-Type ownership) where you can immediately get someone on the 'phone who knows anything about engineering, that answers emails, where they are using in their workshop the very same parts that they are selling to us, that only works on XK engines, and that can be bothered to supply comprehensive and accurate fitting instructions that make sense.
Oh, and and where you can, for example, buy a degree disc that has clever zones picked out to make setting up XK cam-timing idiot-proof.
Shame their web-site is dire, and littered with hyperbole and exclamation marks.
Their seal stretches over the flange that carries the flywheel, then quickly regains its original shape, after which the crank is lowered into the main-bearing shells, with the Viton seal into the upper rear-seal housing, and the lower half is then bolted into place along with the mains caps.
Basta. But it costs an eye-watering £180 + VAT .......
Beere has been using this approach for a while, with complete success, developing it originally on V12 automatics where they didn't want to get into making new swash-plates to fit the smaller PCD bolt pattern they use on their flywheel for the 6-cylinder cranks.
They've not made much of a fuss about it as they already had a perfect, if expensive, solution to rear crank sealing - in the form of a re-machined crank, with smaller PCD drillings, and a new flywheel.
(Note to the doubters - this "weaker" method has never, ever, given them the slightest problem, and the same principle and proportion has been used in millions of other engines for decades.)
For me this was revolutionary, and if you're just looking for a solution to your rear crank leaks then you don't need to look any further.
Here are the fitting instructions, note that they show a V12 crank but the principle is the same, followed by the pictures of doing this on my engine.
This shows the seal itself.
These are with the taped flange, and doing the oily-stretch.
These show the two versions of the (probably) XRN Engineering castings, which are incidental to the above, except that as I didn't have a rope-seal housing, my engine being earlier and having only the scroll to keep the oil in, I had to use the "rope-seal" version of these ; next to it is the version that is available with a much wider groove to cope with the lip-seal type that is discussed below.
If you're interested in the alternatives, or why the above is such good news, read on.
I was sold the lip-seal crank mod by Chesmans in Coventry a couple of years ago, when they were machining my crank.
I was still wet behind the ears as regards the XK engine, and had not yet discovered Rob Beere.
As I became increasingly disillusioned with Chesmans, and don't believe most of what I read on Forums, unless I know a lot about the author, and even less of what I read from retailers, unless I've met them and grilled them in person, this is a topic that I decided to do my own research for, rather than just cross my fingers, assemble my engine, and wait for leaks.
You may not believe what you read on Forums either, but what's written here might help you to make up your own mind.
For those who are new to this, here is the general context.
All the attempts at improving either the early crank "seal", which was no seal at all, but a reverse scroll running in a tight-fitting cast-iron block, or the later one which involved the famous asbestos rope-seal running in a cast-iron seal carrier, involve machining the crank sealing area down to either 3" or 75mm according to whoever is selling you the bits to do it.
This shows the rope-seal arrangement.
(There are versions that move the sealing surface onto the periphery of the actual flywheel-carrying flange, and use an un-modified lip-seal in a much bulkier rear-housing, but these don't seem to be as common, certainly not in the UK ?)
The above show some of the alternatives, both running on the flywheel flange and split-seal types.
One thing is for sure, nobody agrees on what the best way to do it is, which is a bad sign.
Within a split rear-housing block, you either use a completely-split conventional lipped oil-seal, which I believe is the US approach, or a partially split one, implausible though that may sound, which is retailed by SNGB, David Manners, Ken Jenkins etc
The latter have always had the lions' share of the market.
Both are carried in a different rear housing, which is either a re-machined original cast-iron rope-seal one (Ken Jenkins), or a completely new housing - some are machined from solid aluminium, others are rather elegant alloy castings (probably made by XRN Engineering then retailed by Guy Broad, Chesman and others), and the rest are chemically-blackened steel (SNGB, Manners).
The half-split seal kits we tend to use in the UK are almost all, as far as I can ascertain, made by the same colourful character in the Midlands, whom I was able to question at length, but as he does not have a public presence I shall maintain his anonymity.
Let's call him Joe Midlands.
He supplies the black steel version to the trade, alongside many other lines. Joe has made thousands of these, over 7.000 he claims, since 1994 ; and "only three failures". Current production running at about 40 a month ......
Below, available from Manners, SNGB etc - tho' the brown Viton seal shown is not the one supplied.
He began trying to stop race engines from bluing their cranks, claiming that the rope-seal consumed 5hp until it had bedded-in, which race engines didn't have time to do. A great example of the self-made, abrasive and opinionated characters that inhabit the darker corners of the old-car world, Joe seemed long on attitude and short on maths, physics, and materials science ......... but he has a wealth of experience tinkering with XK engines.
He says that at one point 1 in 30 new cars were suffering from rope-seal failure, and that the current equivalent for the original asbestos rope-seal might as well be made - I quote - of grass and dog-shit.
His lip-seals are retailed by all the usual suspects, and are spoken of in hushed tones as having been slit by "a 4-thou surgeon's bone-saw".
I initially fitted my own cast-aluminium Chesman seal-block with what indeed looked like a remarkably thin
and neatly split 95 x 75 x 10mm black oil-seal, see above, which was cut all the way through on one side, and just through the steel housing 180° away on the other, leaving about 3mm of lip intact.
(It is incidentally already physically impossible to manoeuvre a 75mm bore oil-seal, that has been split in this way, over a 75mm crank journal, without putting the tenuous 3mm "un-cut" portion under some considerable stress, and potentially beyond its elastic limit.)
You are meant to position your cuts at about 4 and 10 o'clock upon assembly, having first reassembled the un-screwed lip-spring over the crank, and then over the seal's lips, with the housing splits at 3 and 9 o'clock, and pray that when the two halves are clamped together (with some gasket cement on the seal-joins) you have got the wherewithal to keep all the oil in the engine.
Once my engine was together, but not yet in the car, it gnawed away at the back of my mind for months that this was a really crap engineering solution ; you cannot see or control the deformations of the oil seal, and its lips, as you are positioning the crank into the main bearing shells, and the seal into the upper-half of whichever housing you are using, and this is even more the case as you fit the lower-half and clamp it all together. Even if you assemble the rear-seal housing on the crank first, the exact behaviour of the clamped seal is out of sight.
It's also a lousy way to keep oil in the car ; the very fact of "partially" splitting the seal is actually just an admission that this is not engineering at all ; if one complete split is presumed to work, then so should two.
Our US friends admit this and split their seals properly.
So I took my engine to bits again, and vowed to look more closely at what was going on.
Removing the crank and the rear-seal housing destroys the rear seal, of course, so no judgement of the condition of the seal is possible, and you now need a new one.
So I ordered a new one from SNGB - £40 + VAT a pop.
As you can see from the above, this one (and there are pictures from other suppliers I asked to see pictures from before I bought) was light-years away from the neat splits that had been done on the Chesman one - they looked like they had been done on the fly by a schoolboy with either a junior hacksaw or a fret-saw ; the slits were neither at 180°, square, nor even thin, and everything was pretty raggy - see the pictures.
Joe Midlands had told me that my alloy seal carrier would "grow by 3mm when it got hot", and whilst I knew that was bollocks, I decided to stick to the order-of-service for the time being and ordered a complete new kit via David Manners, with Joe Midland's split steel seal block, and one of his seals, for £250-odd.
(I did the tests of Joe's steel seal-housing and my cast-aluminium one in boiling water, and found changes in the bores of just 0.11mm for the steel and just 0.15mm for the alloy, which is about what their respective coefficients of expansion would predict.)
Here are the fitting instructions you get :
Anyway, I digress - it was immediately apparent (see below) that my new Manners' seal (Taiwanese TTO brand in Nitrile) had been done by the same schoolboy, none other than our colourful friend Joe therefore.
He had claimed that his blade was now 11 thou, so the seal loses 22 thou on its diminished diameter, which ought to reduce the seal OD by about 0.5mm.
My measurements immediately showed that the true loss in diameter was double that ; the plastic exterior of a nominally 95mm TSS seal is about 95.55mm, but the Joe/Manners seal measured 94.45mm.
That's a 1.10 mm reduction, which makes the seal truly "oval" in my book.
So I resolved - who wouldn't ? - to try making my own split seals, at this point still believing in the 4-thou bone-saw legend.
I bought a selection of 95 x 75 x10 seals in both Viton (brown) and Nitrile (black), got the very thinnest silicon-carbide slitting saws I could find, 9 thou, and made myself a sliding saw-bench for the Dremel.
https://www.ebay.fr/itm/222144007028?ul_noapp=true
(roughly 1€ a pop, I consumed one per two cuts, ie one per seal)
(Incidentally, the max peripheral speed of the XK crank in this area works out at about 24 metres/sec. The data I could find about safe lip-speeds for Nitrile seals suggested 10 metres/sec was the limit ; Viton, on the other hand, is good to 45 metres/sec. The biggest diameter oil seal in a Ducati engine is always behind the clutch ; they're always in Viton.)
These shots will give an idea.
I discovered that it is pretty easy to slit these seals cleanly, neatly, and cheaply, with very little loss of material, so that the diameter remains plausibly intact. If you were doing these in quantities, with a screw feed, steel guides, and lashings of cutting fluid, which would be normal for 40 per month, rather than using a jig made of plywood and plumbing fittings like mine, it would be a doddle.
The above split, for example, is vastly better than any of the split seals I was able to buy.
I even sent all the pictures to Joe Midlands, before he stopped speaking to me or answering my emails, as I naïvely - what an idiot I am ! - though he would be interested in seeing how seals could be cut in less than 2 minutes, instead of the professed quarter-of-an hour he spends on cutting then dressing the edges of each one.
My Heath-Robinson lash-up gave me splits of 0.25mm on Nitrile, and 0.4mm on Viton, the differences could be down to the way the different plastics "grabbed" the very fragile slitting discs and encouraged them to abrade the sides of the cut during the process ; furthermore, my cutting-slide was not rigorously parallel with the cutting disc. So you could get much tighter splits if you did it properly.
At this point I was naïvely still intending to just use my own split seal in the Manners seal-carrier.
However, now I had decent split seals, I wanted to see what actually happened when I fitted them.
This is when the penny dropped.
Essentially, splitting a seal and clamping it with its cuts off-set to the mating faces of the housing is nothing less than a mechanical abortion.
I can well believe that you can get away with it, and that there are thousands of satisfied customers, but there are unquestionably an awful lot for whom this approach has not worked, and this will show you why.
Armed with a small pile of seals, I had the luxury of clamping them up without having observations rendered impossible by the crank, although I did have a hard plastic sleeve of exactly the correct dimensions to mimic the effect of the crank when required.
The seals suffered contortions, stretching, ripping, and distortion that no seal-manufacturer had ever designed them to cope with
The groove in the seal-housing was tight enough * for the seal's entry into it to require a quite inordinate effort, even when lubricated, and this meant that they systematically failed to centre themselves correctly within the housing.
(* groove width 9.85mm, TTO seal width 10.03mm - preposterously tight ; oil seals are not designed to be constrained laterally as there is no way of distributing the load across their periphery when fitting ; contrast that with the uniform effort available with a peripheral circular drift, which is how the seals are meant to be used.)
The edges of the groove ripped the seals' outer sheathing, so that when the halves came to clamp together there was a big burr ready to get trapped in the gap.
The un-split band of the seal was often stretched way beyond its elastic limit ; and once the clamping was finished you could - every time - even see daylight through the supposedly-closed gap, just waiting to give you the leak you were trying to avoid.
The pictures tell a better story.
The Viton fared no better :
My conclusion is that the split-seal approach is a nonsense.
It works most of the time, but by luck rather than by design.
It's a good money-earner for everyone involved in its production and its retailing.
Engineering it ain't, and you won't find one in my engine.
Steve