1971 Jaguar XJ Series 1 AJ6 - This update blows...

I had some time around the holidays, so I decided to make the step to evolve the new engine from decorative (it’s a pretty thing after all) to functional. To do so I needed to finish off all the remaining jobs under the car: fuel system, rear ARB, and exhaust.


Fuel system

I wanted to run the AJ6 on petrol first before adapting it to LPG, but as my car had never run on petrol with the original engine in all the years I had it I knew this would be a challenge.
Removing the original fuel feed line showed that it was completely gummed up and holed in a few places. At this point I decided to redo the entire fuel system.




Here's a little schematic I made based on someone else's picture (not the exact same boot floor but you get the idea). I used the external pump and filter (brown in the picture) from the donor in the boot, right where the original ones would have been.

I routed the feed line (orange in the picture) across the boot to the left hand side of the car, and the return (green in the picture) on the RHS. I made sure to run both lines along the cold side of the transmission tunnel to avoid exhaust heat.

I chose to run only the right fuel tank (pink in the picture), as my LPG filler blocks the left filler opening anyway. I chose to use an early Series 3 tank, which has connections for the fuel return, but still uses an external pump. This tank came out of a scrap car, and whilst leak free turned out to not be in great shape internally. As a new tank costs 400€ I decided to renovate what I had.

I removed all the tarred up gummy deposits from the bottom of the tank with a scraper and a few liters of isopropyl alcohol. After which I filled the tank with 50% phosphoric acid, which removed any rust and created a nice protective layer to prevent flash rusting afterwards. I repeated this process until the entire tank was clean and no more residue would come out. No pictures of this I’m afraid as it was a pretty messy process that took a few days.




I then got busy with the pipe bender to make new feed and return hardlines out of 3/8” copper nickel tubing, which I made some nice flares to keep the hoses in place. I joined the hardlines with some ethanol proof high pressure fuel hose.


Rear anti-roll bar



Remember I said this? I was under the car anyway so decided to tackle this. There’s no factory mounts on any of the Series XJs, but quite a few others have converted their cars to run a rear ARB.






People typically fold a thick bracket which is bolted to the underseat area. This didn’t look very structurally sound to me, so I decided to make my own mounts out of box section.






I used large washers to spread the load from the bolts and then welded everything up, measuring carefully to keep the angles of the ARB correct. A splash of paint finishes it all off nicely.




My XJS rear ARB matches the front one, so to prepare it I put new rubbers in the body mountings and the dogbone drop links. I then welded my brackets to the body (upside-down welding whilst laying on your back is always a joy) and mounted the bar.




I’d already mounted the correct radius arms that have the mounting for an ARB, so everything just bolted up.




Here it is all mounted up, you can also see my shiny new fuel lines. The driveshaft is just my original Series 1 example, it fits perfectly lengthwise with the new drivetrain and bolts right up to the ZF 4HP22.


Exhaust

My original Series 1 exhaust had two downpipes coming into an X-pipe and then moving out to a full dual system.




As the AJ6 downpipe is a single pipe I switched to a later S2/S3 Y-pipe, which I shortened and welded to the stub of the AJ6 downpipe. I made sure to route it properly so it doesn’t hit the tunnel and gives a good gap around the transmission sump.




I made it out of a used pipe just to make sure it all works, as the rest of my exhaust is stainless (I’m keeping the original mufflers as they’re in great condition and nice and silent) I can always have a stainless version of the Y pipe made up in the future.


The moment of truth

All of this meant that I could start putting fuel, oil, ATF, and coolant in their appropriate places. I started the car without the ignition lead on first to build oil pressure. It also built fuel pressure just fine and didn’t leak anywhere, so all that was left to do is to start it up!




It works! Plenty of things to sort through, including tidying up the mess of original wiring which I didn’t touch until I was certain the new engine ran. It’s also hunting a bit at idle still which needs a good looking at, plus the AJ6 seems to greatly confuse my Series 1 tach (it reads about double what it should). Minor things of course - hearing the new engine run well put a big smile on my face!

You’ve built a very nice car here, you should be bl00dy proud!

good to see it up and running, shame about the wiring issues but at least you know its all OK now. Steering reservoir looks like MX5 to me.

Winner winner chicken dinner! It's an MX5 reservoir indeed, my friend whom I share my workshop space with has an NB and the reservoir looked perfect to replace the manky plastic one that came ziptied to the engine (shown here with a green cap, next to the distributor).



I rewelded the outlets of the NB reservoir to point the right way and made a mounting bracket for the inner wing. Looks a bit more factory now I feel.

The cockpit is a big part of the appeal of this kind of car to me. Mine was fine, but if you looked closer it let the car down. Especially the wood on the dash looked bad, as this picture without gauges shows:




The wood had been refinished poorly by a previous owner, plus the veneer was sanded through in a few points. So last winter I bought a second dash to redo.

Because the dashboard is all simple flat wood, redoing it was relatively simple but laborious. For all three separate pieces I took the following steps:

1. Remove old veneer
2. Flatten new walnut veneer, by wettening it and clamping it between two boards to take the waves out that naturally occur in the material
3. Glue to the original dashboard
4. Sand flat and fill any cracks with colourmatched paint
5. 4 coats of UV resistant yacht lacquer
6. Sand flat with a mirror
7. Polish to a mirror shine

The mirror finish on the lacquer gives the burls in the walnut a really nice depth that looks beautiful when it's in the sun





They layed on the shelf for a while until I recently exchanging the old pieces for the new ones






The result looks pretty good I feel! It's obviously not as good as a professionally refinished dash but it feels good knowing I did it all myself.




Gauges

Because I fitted the AJ6 I needed to adapt a few gauges to work correctly with the new engine. This is what had to be adapted:

Fuel - No change needed
Volts - No change needed
Clock - No change needed (they're always broken anyway)
Coolant - Remove the AJ6 sensor and thread in the original Series 1 XK sender into the AJ6 head, a simple like-for-like replacement
Oil Pressure - I just connected the AJ6 sensor and it appears to works just fine with my gauge

Rev counter - My original rev counter was an RVI type and as such didn't work well with the signal from the AJ6 coil. The current that feeds the coil actually passes through the rev counter, so some handywork was needed. I gave the coil its own switched live, and took my rev counter apart to change it from RVI to RVC with a set from Spiyda, this one to be exact.

The Spiyda set is nicely made with a simple module that replaces the old rev counter innards, and a cable to calibrate it to suit your needs.



My original 4.2 rev counter had the redline at 5000 rpm, and the scale ended at 5500. As the AJ6 can rev much more I got a 2.8 rev counter (redline 6000, scale goes to 6500) and resprayed the redline area to the correct 5700 rpm for a factory look.




The only big thing left in the dash is the speedo - there's no cable drive in the ZF gearbox so I aim to adapt it to use a GPS signal.

Hey, great build. My XJ6 is awaiting the same treatment. I know someone who casts and machines special tailpieces for the ZF gearboxes with a mount for the speedo cable. But you can only buy it iff he mounts them himself... Let me know if you want to come in contact with him. He's Dutch and lives just across the border in Germany

Thanks for the offer! I already got myself a Speedhut Speedbox to drive my original speedometer, so that should keep things a bit more simple. I'm happy to help of course when you get your engine conversion started!

That's another way that works, the speedometer. Though personally I like the elegance of the custom tailpiece...

I have already read the thread twice, and you have covered many details I was thinking about. Years ago I already bought a 3.6 XJ40, just for the tires. But then the idea of an engine transplant came up, especially since I saw it done on a visit to a classic car garage in New Zealand. 

This week I started with getting the XJ out of storage and giving it a wash... the original motor is already removed. The 3.6 too is ready, but I am am keeping the ZF autobox, although my XJ6 was a 4 speed manual with o/d. It just fits the character of the Jag ride imo. Also I ordered the engine mounts of an XJ-S 3.6...

Are you still running your XJ 3.6 on LPG? (G3?)

I get the impression the 3.6 is the engine to have really. Revvier, and pretty much the same power as the 4.0. Plenty torquey enough as you say!

Though I gather people don't quite compare apples to apples with the 3.6 and 4.0. Most 3.6s were uncatalysed, whereas most 4.0s were catalysed. Comparing those two gives you two engines at ~220hp. However, the non-cat 4.0s were 240hp-ish so did make a fair chunk more power in a like-for-like configuration.