I have a 1987 XJSC which has recently blown a head gasket, and I'm told one of the heads has gone soft.
I have found a 1990 Daimler double six that I can purchase the motor from.
I believe these are the same motor.
Can anyone confirm this, and/or mention any reasons it won't fit easily into my XJSC?

Thanks in advance
Vic

 

Same basic motor but you will need to swap over some fittings and ignition components and engine loom from your dead motor as there were changes between the two years.

 

Ignition systems will be the same so there's no problem there. Your XJS will have Lucas ignition and so will the 1990 DD6---as the Series III V12s never got Marelli ignition as the later XJSs did.

But, yeah, a few bits might be different.....so don't throw anything away !

Will you have an opportunity to hear the replacement motor run before buying? That would be a plus.

Cheers
DD

 

Thanks for the replies.
Turns out the donor car is a 1993 XJ40 Daimler, so it won't be an option.

 

Bit more work but will work and makes for very nice package when done.

 

Also, if you do not want to transplant the entire ECU, gearbox loom, etc etc from the donor, the XJ40 6 litre motor will run quite Ok on your Lucas ignition, but might need slightly different fuelling from your current ECU - which can probably be achieved by upping the fuel pressure a bit, or using slightly bigger injectors maybe.
Greg

 

Any advice on how or where to get details of what is required to fit the 93 XJ40 motor to the 87 XJSC?

 

I have a 6 litre/4L80E from sedan in my '89 XJS. Love it.
Not sure where to start with advice but can answer any specific questions you might have.

 

In outline, the actual motor will drop straight in and all the ancils will bolt on, and if you use the Lucas ignition and loom in its entirety, that will bolt straight in/connect straight up. I am pretty sure that the jackshaft that runs the dizzy will there in the motor too, even though it was dizzy-less.

The gearbox, propshaft and final drive is completely different on the saloon donor, and will not swap. The differential on the saloon is not just a different ratio, but a different design and will not bolt up. The easiest thing is the fit the original gearbox to the new motor. The 6 litre engine has a different bolt pattern to the 5.3. So the new engine will need some new dowels and bolt pattern fitting to it. The engine casting is the same, so the places for the holes and dowels to be drilled will be there. If you use the engine and gearbox from the saloon, then a diff or entire rear end from an outboard facelift XJS 6 litre will be the easiest way to go. Then as long as you keep the gearbox ECU, you can still (I believe) use the Lucas ignition and injection. But Baxtor can clearly sort you out on how to do that once you have decided upon the strategy!

I have never done this, but I believe that these are the simplest ways to do it. There are people on this forum who have (for instance) fitted manual gearboxes to the V12 and they have had to deal with bolt pattern differences, so there is expertise out there about that aspect.


Greg

 

If it's XJ40 the '93 motor will be marelli ignition so the swap of distributors will be straightforward. (The later motors that were distributorless were NOT fitted with jackshafts)
Water pump on the donor will be serpentine drive verses V belt on the 5.3 original, easily fixed.
The bell housing dowells are the same as the 5.3, bolt pattern different but as Greg says the casting has the bosses, they just need drilling and tapping.
I think this is a backward step though and a better idea is to go with the 4L80E gearbox and run an aftermarket TCU, 6 litre rear engine mount and propshaft.
Everything will fit with not too much work and the overdrive and lock up is a huge step up from the T400.
I did actually drill and tap my 6 litre block to take the T400 so I have the future choice of either gearbox.

 

Just curious:


1. Head gone soft? What is that? A real term or merely figurative? seems a lot easier fix than an engine swap. Unless it is like for like, then mebbe. but when the adaptation comes in....


2. Were it I, I'd keep the 4l60E. So much better. And a prop shaft make up
seems easier than drill and tapping of an engine block. Drive line shops rather common around here.


Carl

 

I agree about the propshaft, the trouble is the diff ratio, it would need changing for a 6 litre XJS diff, or an entire rear end.


Greg

 

Vic
Does your XJSC have Lucas or Marelli ignition?
Greg

 

I suppose diff ratio is a personal choice sort of thing but l have found 2.88 is no problem with the torque of the 6 litre and is great at cruising speed. Pickup from the 3.54 might be wasted here anyway cars can get impounded for loss of traction.
'87 would be lucas ignition.

 

The later cars use a 4L80E, not 60. Both need an ECU and all the wiring that goes with it, while the TH400 just needs a vacuum line. It's all doable, but it isn't just a straightforward swap.

 

Aftermarket tcu is easy enough. I used a TCI EZY TCU which needed less than ten wires connected. Might not work with lucas ignition though.
OEM TCU would be a bit too involved l think due to it's integration with other in car systems.

 

I'm not a mechanic, but those I hired sent the head in for testing, and they reported back that the (one) head was 'soft', and therefore unusable and unsuitable for ongoing use or refurbishment.
I am looking for a replacement head (hard to find without an engine attached), and was only considering the engine purchase as a 'last resort' (cheaper option), so throwing in a gearbox, prop shaft & diff is getting further & further away from the goal... which is to get the car operational again with minimal detraction from its original glory at minimal cost.

 

Lucas ignition

 

New or decent second hand heads are available on UK ebay. Would the transport cost to NZ be prohibitive? if not, this would be your easiest bet. USA heads have a lower compression ratio, so not suitable unless your motor is US spec.
Greg

 

Thanks Greg

I did find heads on UK Ebay, but only from a USA supplier.
How would I tell/what should I ask to determine what compression ratio they are?