AJ6 engine




XK engine


Cheers
DD

 

The AJ6 engine is a better engine, lighter than the XK engine as it's all-aluminium, and less prone to problems. The AJ16, the last of the AJ engines is even better. However, I suspect you like the lovely polished cam covers of the XK, the AJ6 doesn't look as good in this regard. Be aware that the later XK engines did not have polished cam covers, they were of the black ribbed type. In addition, they had covers over the exhaust manifolds which were left as unpainted cast iron. Of course these later manifolds can be shot-blasted and vitreous enamel painted like the old ones.

The final thing to be aware of is that spares and engineering support for the XK engine is most likely greater than for the AJ engines, especially in the US. The XK engine was probably the last of the easily repaired engines produced by Jaguar. The AJ engines lasted a lot longer without attention so rebuilds are uncommon, thus spares and engineering support is less.

 

It appears that a 1985-1987 XK6 engine would be the best choice for my project.
What is considered to be high mileage for a properly maintained XK engine?
Do the timing chains have to be replaced before the rest of the engine needs a rebuild?
Does the distributor use points or an electronic module?

Does anyone have the basic overall dimensions, length x height x width, for an XK 6?

 

Jay
With 1985 -1987 XJ6 S3 engine the previous maintenance and constant use is key vs Mileage or Age. The previous maintenance records are not usually kept up by casual owners. 75,000 to 100,000 1. you are going to have issues with wear and heat damaged ignition systems components . 2. Head Gasket and cylinder head studs that are bathed in the cooling system are very suspect. 3. Water pump seal and bearings. 4. Oil pan and cam cover gaskets. 5. Timing chain tensioners. 6. Once you have cylinder head off for gasket change, you can tell if repairs or a full Overhaul is needed.

Since you seem to be headed towards new carb set up, the intake/fuel injection system issues are not addressed.

The S3 ignition system once repaired, is a good GM based HEI system. If the distributor bearings are bad, there is an distributor overhaul shop in New England region, that will bring it back to new spec., and with better ign. curves to match fuel Octane numbers that are available today. Usually the advance unit diaphragm will be shot and the advance mechanism will be corroded.

Here are a few links that will give you some background.
https://www.jaguarforums.com/forum/x...epairs-210475/

https://www.jaguarforums.com/forum/x...gasket-244014/

https://www.jaguarforums.com/forum/x...needed-242876/

If the PO has good records and a diligent owner/operator/maintainer many of these items many have been done and he just ran out of money with the rusted body and aged interior. If you are patient in your searching, you can find an over maintained engine in a ratty car. I ran across a nice XJ6 S2 that a student was driving and after he got a quote to replace the blown head gasket from the Jaguar dealer, he let it go for $600... I thought about it over night, but when I went back the next day, it was gone.

I have done three head gaskets replacements and one cylinder head overhaul myself, on three owned Jaguars. Much easier if engine is out of car when these are done.

Rgds
David

 

David,
Thanks for the information about engine condition and what to look for.
Hopefully I'll be able to locate a usable engine in my area, they don't come up very often maybe I'll get lucky.

Jay

 

I found a 1985 Jaguar XJS HE V12 that's in running and driving condition. The engine is supposed to have had a basic rebuild, rings, bearings, timing chain, etc.
Is a V12 from 1985 a good engine in general?

 

The Jag V12 is almost indestructible.....until or unless you neglect the cooling system.

The V12s have fans, like me, and detractors as well. I think they're great. There are things a first-timer would need to learn and certain must-do repairs/services. It takes more patience to work on one. For V12 lovers it's a matter of more challenge, more reward.

Cheers
DD

 

I prefer the V12, the 6 would fit better under the hood, the V12 will require a lot of modifications but it would be worth it!

Is the distributor an HEI type or is the spark controlled by the ECU?

 

HEI. It's the same module as the 6 cylinder cars. All of the HE engines were EFI, but it's simple stuff. There is a shielded wire that sends the ignition signal to the ECU and it won't fire the injectors without this. Ideally, if you have access to the whole car take the wiring harness in it's entirety back to the ECU in the trunk and then it's pretty much apply power and ground and you have a running engine.

 

Can the HE V12 be converted to carbs? I've seen the dual 4 barrel intakes, would prefer Webers.

 

I'm sure it could, you would need the carb manifolds and a set of carbs and throttle linkage. Carbs were only used from 1971-74, so manifolds are not that common. The SU carbs are the best, but that kit is very expensive. To be honest, EFI is much simpler and will give better performance. If you have the engine/harness/ECU from an EFI car, you have almost all you need already.

 

The EFI makes the engine too wide, especially with the air filter cans.
I would like to attempt to fabricate my own intake, it may not be the most efficient or produce the best HP but it would be another unique part on my hand built car.

 

It is a big engine across the air filters, no question. I would see throttle synchronization as the biggest challenge for a custom built induction system.

 

I found a complete 1959 3.8 engine and standard transmission and the owner also has a complete 4.2 engine for sale. The 3.8 would most likely need a complete rebuild, the 4.2 was supposed to have been removed in good running condition. The 4.2 is not locked up and does turn over easily and it still has oil in it with no signs of water.
The plan is to purchase both engines, are any of the parts compatible between the two engines?
Can the transmission and starter from the 3.8 be used with the 4.2?

 

Heads, exhaust manifolds ( intake is different). The head with intake manifold can be swapped, cams, distributor, crankshaft, rods will all interchange. Many of the small parts will interchange too. The major difference between 3.8 and 4.2 is the bore, so the block and pistons are different. The pattern of the intake ports on the heads are different, the 3.8 has a B type head and the 4.2 has a straight port. because of this, the intake manifolds will not swap between the head types. You can see the position of the spark plug is different between the 2 types.

You need to keep flywheel, starter, clutch, release bearing and transmission all together. Use all 3.8 or all 4.2, you can't mix and match between them. Be aware the 3.8 transmission is likely what's called a Moss box and it won't have syncromesh on first and a weak syncro in second. It originally called for a SAE 30 engine oil, if you use Redline MTL the shifting will be improved considerably.

 

I appreciate the information.
Thanks

 

If you switch to a negative ground on a 3.8 starter will it still rotate in the correct direction?

 

Yes.

 

The 3.8 and 4.2 timing covers will physically interchange, but the water pump passages are slightly different. Use a 3.8 cover on a 4.2 and the coolant goes straight into the oil sump.

4.2 water pumps varied over the years with different impeller sizes, so make sure that the pump fits the cover properly before swapping. A small impeller on a big cover won't move any coolant. The cover is bolted to the block and then both are decked together to create a smooth seal for the headgasket, so care has to be taken when swapping covers to a different block.