1992 Jaguar XJ40 SuperTurboDiesel

March 24th 2020

Been pottering about on various things without making a lot of progress (mainly cleaning my tip of a garage), but the sunny weather and time indoors due to the plague has promoted some activity

First step was to rearrange the area outside my garage. Can't fit the Jag inside at the moment so the majority of work will need to be done outside. It was on a bit of a precarious sloping footing so I've shifted it directly in front of the garage.



It's still a bit sloping which I'm not 100% happy about, but a belt and braces approach to jacking seems to help. Axle stands on wooden boards to spread the load, wheels underneath to catch it if it does fall, and an extra jack supporting it any time I'm underneath.

Next was to drop the rear suspension. It's quite a simple job really, and having done in 3-4 times now it all came back to me pretty well. As did the sheer heft of the thing when dragging it into the garage...




That allowed access to these guys:



Drained the fuel tank of what remaining fuel it had, and managed to work the fuel fittings loose. I'll need new ones anyway as the metal on the other end is well past its best. But it means I can get the old fuel tank out!



Last job I sorted was to strip the rear suspension unit down. It's all a bit crusty back there, and I've ordered various polybushes to fit once it's rebuilt and repainted. There's some other bits and pieces to stiffen it up, like the braced rear mount you can see at the back of this picture which replaces the two dogbone links on the XJ40:



Also, if you want to see the difference between a diff that struggles at 200bhp compared to one that will take pretty much anything you throw at it, just stick a Spitfire diff next to an XJ40 one

Thanks man yeah there's something about a really good old barge, but with today's fuel prices and my NHS wages it's not something I'd be able to sustain for long!

Of course, I've totted up how much the conversion has cost me so far and I'd have to drive nearly 100,000 miles to recoup my losses but that's not the point could have done it much cheaper, but decided to go all out

Thanks dude plenty more to come to bring it up to date

31st March 2020

The brief spell of good weather we had here gave me a chance to start tackling some of the rust at the back of the car. First off was this mangy set of plugs at the front of the boot.



Last time I'd replaced the diff I'd forgotten to fill it with oil before fitting, which then involved much contortion to get the oil into it while everything's in place. So I took the opportunity afforded by the rust to make a little access panel.

Choppy choppy...



...bendy bendy...



...painty painty.



I've welded the studs to the body so I don't have the other end spinning, and having them point into the boot means there's no exposed threads under the car.

I've also refurbed the rear coilovers a bit. From this...



...to this!




The shocks have only covered about 3000 miles since I fitted them so they stayed, as did the shockingly good condition original spring pan bushes and bumpstops. I don't know what environmentally toxic processes they used to use to make rubber but older stuff really does have so much more longevity than new rubber. Especially bumpstops seem to disintegrate in ~5 years.

I've also fitted a set of 35mm lower 25% stiffer springs I bought ages ago from Coilsprings.co.uk. The company's very good, but I ordered them when I had much less of a clue what I was doing generally with cars so we'll see how well they turn out! The XJ8 subframe brace has turned up as well, as modelled by one of the cats:



Lastly, I've found a solution to the low-ratio diff issue. Here's an outline of the problem.

I've worked out that with a 2.88 diff ratio and the Jag's slightly larger wheels, the gearing should be within a couple of mph of what it is in the 330d with its 2.47 diff. That should mean 2096rpm when cruising at 70, and a nicely overdrive 6th stretching to 183mph (vs 1941rpm and 198mph in the BMW).

There are plenty of 2.88 Jag diffs about, and the majority of them come from XJS' so are fitted with an LSD (and the better of the two varieties of Jag LSD to boot). Unfortunately, to fit the physically larger 2.88 gearset those diff casings are slightly different, being machined wider and having a ring gear mounting flange with more offset.

There are two types of Jag diff, early and late. Early ones are fitted to pre-XJ40 cars, so XJS and back. New types are fitted to XJ40s, X300s, X308s and 4.0/42 XK8s. There were 2.88 diffs made in the newer casing, but these are very rare indeed. As far as I can tell, they were only fitted to early 3.6 USA-bound cars. All of the Jag's rear suspension hangs off the diff, and the early and late types are significantly different enough to make fabrication a PITA. This left me in a bit of a pickle.

The next longest Jag diff ratio is 3.07, which would probably still be workable and has the regular offset. 2234rpm at 70, and 178mph top. However, I already have the 2.88 LSD and want to do this properly.

I was put onto SimplyPerformance in Dorking who are well rated in the Jag world. I emailed about making a hybrid and they said 'yeah sure, we've done a few of these already'. Result!

Diffs are with them now

Thanks man! Hopefully should be a hoot to drive when it's done. I've always wanted one of these old barges that could just curse word off into the distance, but could never justify the fuel costs that a twin-turbo AJ16 would accrue! Super-turbo-diesel sounded like the perfect compromise

Next update from the back catalogue

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2nd April 2020

Bit more progress did some rust-prevention on the underside and inside of the boot. The aim of the game here is more halting the progress, rather than completely excising. Get the swap/conversion done and the car driving, then I can potter about sorting the rust while I can use it.





I've also made a start on the new fuel tank. By and large it's in good condition, but there are a few rusty bits to clean up. Considering how annoying it is to remove I don't want any pinholes to develop after I fit it, so I used some old aircraft fuel tank sealant I've acquired to cover it up. At the very least, it'll mean that the rust will need to spread much much further to actually cause a leak, by which time the rest of the car will probably have disintegrated.




Lastly, I found an old pot of POR-15 that still had some left in it so I started the suspension repaint with the XJ8 frame I bought. Not looking too bad I think

Haha yeah that's part of the reason I'm splitting my mega-thread into ones for each car. It's trickier for people to spot the stuff they like when it's mixed up with other stuff.

Glad you're along for the ride

While we're here, I'll get the next bit up to date:

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6th April 2020

The weekend's been spent wire-wheeling, pickling and painting all the various bits of the Jag suspension. Started off as this mess:




...went through various stages of de-rusting...




...until finally they were painted and baked in front of our stove




There were some casualties unfortunately. These brackets that stop the subframe dropping off its bushes are a little worse for wear so some new ones will need to be sourced.



One of the wishbones put up a real fight as well. The rear coilovers on all but the very late XJ40s mount on a sodding great inch-diameter through bolt in the wishbones. One side came out easily, but the other was stuck solid. I'd tried soaking it in penetrating fluid for a couple of days, heating it with a blowtorch and then impacting it out, but no luck. Tried a breaker bar with a 3 metre scaffold pole on the end but to no avail. Then my mate suggested pressing it out.

Took a bit of fenangling to get it to press nicely. Added a spacer tube to bolt the nut to so the force is distributed to the main shaft and not just the threads, and chopped up a piece of box section so it would sit square to the press as the through-bolt is at an angle in the wishbone. Here's the contraption:



Nearly 10 tons of force and a lot of blowtorching later and it went! Had to press it out inch by inch as it would only slip about 5-10mm at a time, but eventually got it out.



I can see why it was so stuck now!

Still, slips in nicely now after a bit of a clean up, and will be going back in with plenty of aluminium grease to stop it seizing again

Thanks man! There's a fair bit to catch up on so plenty more to come

9th April 2020

So, in this strange environment work on the Jag is proceeding depending largely on which bits have turned up in the post soonest. Learnt a lot in the past couple of days and my brain's hurting, so figured I'd list it out before it all tumbles down the memory-hole.

First off, the excellent people at Simply Performance have sorted my diff and it's bloody lovely. Apparently there's more to be done to fit the 2.88 centre to the newer type casings. The later stub-shafts have an oil thrower which fouls on the early-type LSD cores. SP get round this by machining the cores to retain the oil throwers, rather than remove the oil throwers.



Anti-roll bar

Next, a simple brain teaser '94 final year XJ40s had the X300 suspension fitted, alongside an anti-roll bar. Differences are they used different shaped cast wishbones and a different shock/spring setup. The wishbones and ARB look something like this:



They're interchangeable with the earlier XJ40 wishbones so long as you bring the shocks and springs along for the ride too. That's the typical way of getting ARBs into most XJ40s, and improves the rear-end handling no end. However, despite them being plenty good enough for the 322bhp/378lb-ft XJR, I've never really liked the wishbone design. To my eyes, the more triangulated early wishbone design seems stronger. The issue is that they poke out behind the suspension unit and foul on the later ARB arrangement:



So, I decided to combine the two. Welded some captive nuts onto the a-frame so I can bolt the ARB underneath. It'll need some pretty short droplinks, but the overall suspension travel is pretty small on XJ40s so shouldn't be a major problem just awaiting adjustable droplinks in the post



So far so good

Fuel pumps

Next up was the fuel pump setup. Early cars use an external fuel pump mounted on the suspension subframe which would make the whole thing much easier. Later cars like mine have a little sump in the fuel tank and an in-tank pump. Pulled that out and took it apart and it looks like this:



It's got a little walbro sitting inside it. 'That looks near enough to a walbro 255' I thought.

It's got a 6mm outlet, but I bored out the little rubber seal it sits in and test-fitted an 8mm rod. Seemed to work fine so I ordered a pump. Turns out the 255 is a little larger than the stock pump, so there was a bit of experimentation to get it to fit.




Here's a rough outline of what I did to make it fit. It's very snug, but it does clip closed (although it could probably do with a strap of some variety to stop the top popping off). I'm hoping cutting the one-way valve out won't be an issue as there's a one-way valve fitted behind the brass outlet on the sump body.




The reason for all of this is that the Jags stock fuel pump flows about 162l/hr at 3 bar. Higher performance versions like the supercharged XJR and the V12 used two of these little pumps to provide enough flow, which seems like a decent solution back in the day but you can get a lot more flow out of just the one pump nowadays.

BMW 330ds have two feeder pumps, one low-pressure lift pump in the tank, and then a higher pressure pump under the car feeding the injection pump. The high pressure pump flows about 175l/hr at what I think is 3 bar. However, that pump runs at a constant 4 bar, so I need to drop the numbers across the board.

What's lucky is that it seems that as far as I can tell, the vast majority of automotive petrol pumps will work with diesel no problem. What I can't find for love nor money is a comparison of flow rates between petrol and diesel. I'm presuming diesel will flow less as it's more viscous and higher density, but nothing I can find publishes both so I can compare.

Closest I've found is a rough approximation that 1lb/hr of petrol is 9.95cc/min, and 1lb/hr of diesel is 9.05cc/min. Haven't got it straight in my head whether that comparison works, but that indicates a potential 10% lower flow rate (maybe).

So, that puts the Jag pump at about 146l/hr at 3 bar, minus whatever it loses for working at 4 bar pressure. Can't seem to find reliable info on what the BMW injectors flow, but that's starting to look a little marginal. Hence the over-specced walbro 255 to act as a single lift pump and make sure it will always get as much fuel as it needs.

That's if diesel is actually pumped at a lower rate than petrol by positive displacement pumps. Haven't come across anywhere that says that, just assuming. If anyone knows I'm all ears!

The quandry

Unfortunately, I can't seem to work out what would be the best option to go with. There are a few different setups I can think of:

Walbro->injection pump
Jag pump->injection pump
Jag pump at 1 bar->BMW pump->injection pump

Honestly can't work out what would be best...

10th April 2020

In my 3-day search for the vernier calipers I came across the old walbro from the Fiat. Lo and behold, it's ever so slightly different. The Fiat's pump is a genuine walbro, whereas the one I bought for the Jag is a TI Automotive pump. From what I gather one of TI Automotive and walbro owns the other, and yet the pumps are subtly different.



The bodies are the same, but the pins for the genuine walbro plug are deeper set, the non-return valve is held in by a metal sleeve, and the other bits on the top are generally a lower profile. These subtle changes add up to it being simpler to fit inside the Jag sump, and the lid clicks down without any issue. Here's the procedure:




I'm not even sure the cutting of the lower rubber bit is necessary with this one, will test that one later. I'm also not sure about the drilling of the seal that the pump fits into. It's a snug fit, but there are scores in the side of it. If I end up getting another sump I might just see if I can get the 8mm outlet to fit into the seal unadulterated.

So, the plan is now in-tank walbro directly to the BMW high pressure injection pump and see how it goes one more thing planned out!

Good work!

Haha next one incoming!

14th April 2020

Couple of steps forwards on the Jag

Adjustable droplinks arrived for the ARB so got to making some brackets. Tested it out through a range of motion on the wishbones it seemed to be alright. The lower balljoint does bind at full suspension droop, but the shocks should stop the wishbones before they hit the a-frame when it's all bolted up so it should be good.




Next up were the crusty compliance buffers on the wishbone tie at the back. They're little metal cones which in XJ40s and X300s have a rubber bush on the back and help locate the wishbones and the rear subframe mount. Unfortunately they're NLA and mine were a bit worse for wear. The X308s replaced them with solid mountings, and you can buy solid spacers as replacements which are both annoyingly pricey options. A bit of measuring showed the compressed rubber on mine was 1.6mm, so some 1.5mm steel shims to replace the rubber should work (with the extra difference being made up by the rubber wishbone bushes).






I'll check to make sure everything's still going to plan at the back after some driving, but seems good to me if anything does look funky, I had an idea to get some solid bushes machined that can be pressed into place. Have most of the measurements for that if anyone wants to test it out. Was thinking a stepped tube with these dimensions:

Overall length: 52mm
ID: 20.5mm
Inner step OD: 36.8mm
Outer step OD: 55mm (with one side cut off, a la the original buffers)
Outer step length: 11.5mm

On another note...



...aah what's that?! Turns out a little poke with a screwdriver at a bubbly bit of paint has exposed quite the rusty sill. 3/4 door shuts seem to have disintegrated a bit, but the rest seems in good nick. One done so far:








Also had to re-make the little channel that the door seal sits in, which involved beating a strip of metal over some conveniently sized screwdrivers spot-welded in place and sealed with seam sealant to hopefully prevent something similar happening again (I reckon water capillary-actions up behind the channel and rots it out from there).




Oh, and painted a fuel tank and put the fuel pump assembly together




Put two 90-degree low-profile terminals on as the standard wiring has one that's a bit bulky and another that's a small-sized terminal. Had to isolate them with some fuel-resistant heatshrink as they're a little close together, but went ok

Also added some hylomar blue into the rubber seal to take up the space where the drill had scored the rubber. Probably not necessary, but I was regretting drilling out the rubber. Still, all fits together neatly enough interested to see if it works!

It's been a productive week

The odd size nuts will be part of their poke yoke idiot proofing, each fastener with a given torque has a unique head and the tools on the line are the same therefore you can't over tighten or under tighten the fastener by using the wrong tool.