Hi I have 1986 vanden plas with a great body and à détective motor and à very good 4.2 liters. Is it possible to replace the V12 with a 4 2 liters straight 6? Is the trans, wiring and motor monts compatible? Thanks

 

Should be doable.

Wiring, not much will match, that would be the most time consuming.

Engine mounts, same position, just the 6 cyl are thicker than the 12.

Trans mount, basically the same.

The trans on the V12 would be a GM TH400, and I doubt it will bolt up to the 6, although I have never tried.

Radiator is different.

Gearlever selector gate thingy is different, TH400 versus BW66. P to R is longer on the TH trans.

Front sway bar would be thicker, so no big deal.

LOT of work, and I would NOT do it, and thats MY opinion only.

FORGOT, old age.

Welcome to the Forums.

We fitted a V12 into a MK2 back when we were younger and sillier, took some serious thinking that one.

 

I would just buy a new V12 from ebay and slot it straight in.
And what is wrong with the original V12?

 

I went the other way 'round, swapping a 4.2 for a V12.

What you're contemplating should be 100% doable but it's quite a large project. Actual installation of the engine is the least of it. Sorting the dozens of other differences is where the fun (that is, hours and hours of labor) begins.

I would not recommend it unless you had a complete donor car alongside for all the other parts you'll need.

When done you'll have a car with about 100 fewer horsepower and an even more elderly engine design.

I'd strongly urge you to look at other alternatives.

Cheers
DD

 

Thanks all for your comments. I will see what I can do with the V12 first. I do have a complete XJ6 car with a so so body which would cost too much to repair and fix, The car has been sitting for 20 years in a garage. My mins is not done yet on this. The past owner told me that the car was running welll but the engine suddenly stopped and he parked the car in his yard for 2 years. he said couple of guys tried to fix it with no avail. I doubt these guys were Jaguar men though. He said it is not the fuel system but something related with the coil or distributor. I have not started to wortk on it yet. Maybe tomorrow. If you have any suggestions on what to look for I would be much obliged. I have worked on several XJ6 and rebuild 6 4.2 liters but never on a V12 and I am a bit nervous as they look sooo complicated compared with the 4.2...

 

https://m.youtube.com/watch?v=OVH1mrLuneI

Not sure if you have seen this, but he is a good mechanic that runs through V12 diagnosis method.

 

OK,

They be simpler in many ways.

Find the problem:

Does it rotate on starter? Simple test done is seconds.

Is there fuel AT the fuel rail? Prime the system, 2 or 3 On/Off of the Ignition will do that. 2 spanners, CRACK the Inlet fuel connection at the rail. RH side, easy to see. CAREFUL, fuel will spray if you loosen too much, so some rags around that joint.

Is there spark AT the spark plug? Unplug any easy plug lead, attach any old spark plug, ground that plug casing (jam it on any close by metal item), crank the beast, look for a Blue CRACK of a spark.

Slip into the XJS Section, next one down. Read the Sticky I have in there, "NO start of a HE........."

Come back with the results, then we move on one step at a time, and fire that thing up.

Bear in mind, those fiddlers may have screwed some items, so just watch for odd connections.

 

The ignition system on the HE engine of your year (1986) is straightforward, it can be checked pretty easily if you work methodically. The main components are:

• distributor
• amplifier (the black box about the size of a large cigarette packet bolted to he B bank (LHS) inlet manifold)
• coils (two, if still in factory spec)

The distributor has two main parts: a normal top part consisting of cap and rotor; bottom part consisting of a 12 pointed wheel and a magnetic sensor. This is the switching mechanism (called the pickup module) that sends a signal to the amplifier via two wires that come up from the dizzy base and plug into the side of the amplifier. The amp sends a signal to trigger the coils to send the spark to the cap and rotor.

The amplifier can stop working, and is easy to change. New ones are available. You can renew the internal HEI unit on your old one too, but unreliable new modules now available often mean this is a poor substitute for a new one.

Coils can pack up and new ones are cheap enough; but MUST be low impedence, under 1 ohm in total, or a single replacement for the two is available.

The first thing I would do is test all the wires in the system for continuity, broken copper inside the insulation is common, as is broken copper inside the connector insulation. I would also change the spark plugs and HT leads. Test that there is 12 volts at the coil positive, ignition on.

Then check if there is a spark at the coil HT lead to the dizzy cap. If not then you have a coil or amp or dizzy pickup problem. Work from there. You could renew all the pieces (amp, pickup, coils, cap and rotor) for about 500 USD, so the costs are not unreasonable for a new setup.

Just seen Grant's post above, which crossed with mine. Follow his advice, he is the Guru!

 

Thanks. I don t have the Jaguar yet in my garage. probably tonight or tomorow. I will follow the steps and let you know the progress.
You are correct I fear that the feddlers may have butchered the timing and wiring. Weel w ll see.

 

Dont forget a few things.

1) Sense of humour.
2) Beer, LOTS of beer.

The rest is just plain common sense.

Do not fear the V12, it is so simple in reality.

 

Spoken like a true Wizard.
(';')

 

The V12's are really special, if there was no option , i would go with an LS vs a 6 cylinder.

 

Elinor,

I am/was still looking at a way to shoehorn a V12 into the X Type. That V6 is fairly giving me the shiiits.

SADLY there is no way, so I persist with the "pretend" Jaguar, with a half size engine, bugga.

I WILL WIN with this thing, that is a given. I just have to work out how to remove the Check Engine Light, then I will be all sorted. I keep "checking", lift the hood and look at the innards, and it still looks like an engine, so what am I missing, HAHA.

I need a drink.

 

Grant, it's a Forduar! That's your problem right there!

Get behind the dash and UNPLUG IT! Or, put some black tape over it.
Trucklet's check engine light came on within the first week of my ownership.
For 2 years I had a tape over it until the element burned out I guess, cuz it doesn't show anymore.
No more Check Engine!

 

Hi Grant,
I got my Vanden Plas in my garage yesterday and I started to work on it. did a wash and clean the interior. . I found something that could explain why the Jag stop working; the two wires inside the distributior were damaged and partially sectionned. Not sure what could have caused this.
Question for you: I found on line at the firing order but I am getting two differents message on where the A1 starts: in the side of the front of the motor or on the side of the back? thanks for your help mate. JP

Which side is the front of the motor o this pic? This picture is inacurate as both the vaccum advance and the coil and amplifier are on the back. on this pic it shows the advance vaccum on the front.


Bringing the Jag home.

Jag in the garage

Found that the two wires in the distributor were damaged.

 

Good find on the broken wires.

Your '86 will have the Lucas CEI ignition system. The illustration you posted is for the Lucas Opus system. That's why everything looks different.

Are you sure "1A" isn't stamped on the distributor cap itself?

Cheers
DD

 

These might help.

 

Hi Greg, thanks for the two documents. Just to clarify, My Vanden plas is a 1988 not a 1986.
Last night I conected the spark plugs wires on the distributor.
Question: On the distributor cap, there was a number "1" in front of a connection. I presume that the wire "1A" goes there right?
After checking all the wiring, I cranked the motor, but thee were no spark on the spark plug. Not surprised
Today I will do a series of test as per the documents you sent me and see what I can find.
I heard that the problem can also be the ECU unit. Is it frequent to have a defective ECU or should I not worry to much about it?

 

Hi Doug, yes I found a "1" on the distributor cap. I presume it means 1A.

 

It does.
ECU very unlikely to be the trouble.