Hello all-

I have an extra (good) 5.3 V12 engine from an 86 XJS (with Lucas ignition) and a friend has a 90 XJS with a bad engine. He'd like to use my engine in his car.

Is it possible to "upgrade" my earlier Lucas V12 to use the Marelli ignition pieces from the 90 and make it all work?? All of his ignition pieces are fresh and good- hence we want to use them....

Thanks and let me know

XJSC-Guy

 

Oh boy, you are pushing the memory cells real hard.

The engine basics are the same,

BUT

You will need to establish the front crank sensor/bracket, and pulley.
The rear crank sensor and associated bracket.

Using all his Marelli stuff on the Lucas engine is simple enough, FROM MEMORY.

Being USA and full of emission junk, versus my one, with near zero emissions junk, you will write that scribe for the archives, I am sure.

The 87 will be 11.5:1 comp ratio, and I have NO idea what the Marelli engine is, maybe the same????, hope so, coz that will mean the ECU will have the correct fuel mapping range. Some very dim, and I mean DIM light is saying that 1990ish was a drop in comp ratio, but please dont quote me, it was waaaaay too long ago.

There may be a sensor or 2 or 3 that will need changing, but simple enough also.

I will keep thinking and respond if anything else smacks me.

 

OK, Aussie assumption strikes again, or is it simply old age???

Thanks to Greg in France, and the wonders of the telephone.

You will be changing the distributor, obviously.

I suggest getting BOTH engines on TDC 1A Comp Stroke.
Note where the rotor is pointing on the Marelli dizzy, PRIOR to removal, mark the casing if need be. Ensure the rotor is pointing at said mark when installed in the "new" engine, simple??

Removing the Lucas Amp from the B Bank Manifold on the Donor engine i just taken as known.

 

Grant, according to Bywater, the 11.5 compression became standard issue for all markets when Marelli ignition was introduced.

Anyhow.....

Thinking from the other direction how about using the earlier Lucas engine as-is? In other words, converting a Marelli car into a Lucas car? It should be doable.

Just at thought

Cheers
DD

 

The front crank senor attachment is incorporated into timing cover...so the front cover mut be swapped. You can see the difference is these illlustrations

https://parts.jaguarlandroverclassic.../brand/jaguar/

https://parts.jaguarlandroverclassic.../brand/jaguar/

Not sure about the rear crank sensor. More coffee and time required for that.

Cheers
DD

 

And, you would need the crank pully with firing disc..item 16

https://parts.jaguarlandroverclassic.../brand/jaguar/

Rob

 

So it seems that the answer is yes- the Lucas engine can be made to work in the Marelli car, using the following Marelli pieces from the old engine:

1) Crankshaft damper/pulley assembly with firing disc
2) Front cover with crank position sensor
3) Marelli distributor and coils
4) Rear lower flywheel cover and crank sensor
5) Marelli-type wiring harness on engine

Going this way the standard Marelli ECM and ICM in the car should do it.

Thanks for the info

 

FWIW and purely conjecture; swapping front engine covers *could* be dicey as the cylinder block was machined with the cover installed. Gasket mating surface alignment issues could result, primarily with the head gasket. Maybe someone with experience in this regard can chime in.

 

I have an 1988 ( I think ) HE V12 engine from a car with accident damage.
Only thing damaged on the engine was the front engine cover, it had a small crack.
It was a very neglected engine and took a lot of effort to clean up and rebuild.

V12 rebuild

I asked local Jag spares shop if they had a spare cover, and the photo shows what they sold to me.
You can see the oil gallery is blanked off with a brass plug, which I have not see before.
That suggests it is from an early V12 but it fitted perfectly.
The impeller recess is modified because the engine will have a remote electric pump.
Now it is fully rebuilt it is a spare for the convertible, but annoyingly the convertible V12 at 130,000km is still in good nick apart from a few oil leaks.