Can anyone tell me what the correct clearances should be for the exhaust and intake valves on a 1994 XJ40.
I am in the process of reassembling the cylinder head on one of my cars here and I need to double check the clearances before I get ready to lower the head back into the car.
Thanks

 

Also what is the torque spec for the bolts that hold the cam caps down to the cylinder head?
Thanks

 

Hi Steve,

You can purchase the official Jaguar Workshop Manual on DVD from the Jaguar Daimler Heritage Trust (jaguarheritage.com). You can also download a mostly-complete British edition of the Haynes manual at this link. It will have the torque and valve clearance specs you need. If I recall correctly, the valve clearances are to be measured with the head bolted to the block. The clearances are set by shims, which were still available from Jaguar the last time I checked.

Jaguar XJ40 Haynes Repair Manual

Cheers,

Don

 

The AJ6 and AJ16 engines are completely different in several ways to the earlier generation XK engines. In particular with the AJ6 and AJ16 engines, they have an unusual design "feature" where the cylinder head bolts pass THROUGH the cam caps. With the XK engine and the V12 engines this is not true. What this means is if you want to pull the cams to make any changes or adjustments to the valve clearances, it means the cylinder head bolts HAVE to be removed. And since Jaguar specifies that the cylinder head bolts are torque to yield single use bolts the parts and time expense of doing what should be a simple valve clearance adjustment becomes a MAJOR hassle.

I really like the AJ6 and AJ16 engines but this design feature is a royal pain in the ****.

 

Where did you read this?
I'm not absolutely positive about it, but as I remember, my spare 4-litre AJ6 cylinder head is sitting in storage with the cams and valves still attached ...so I don't see how that could be the case if the cylinder head bolts pass through the cam caps?

I could be off on this, but I can't see how I could have removed the head from the parts car as a complete unit like that? (it was a long time ago though, so I may be remembering the process wrongly)

Larry

 

Yes, it is possible to remove the head as a complete unit with cams and valves but what it completely not possible to do is to remove one or both cams and lifter buckets to get to the valve shims without FIRST removing the cylinder head bolts.
See the photo below of one of the cam caps. The smaller outer two holes are for bolts that hold the cap down to the cylinder head. The larger hole in the center is the hole for a cylinder head bolt that holds the cylinder head down to the block.

 

If I recall correctly, the head bolts pass through the cam caps, but the caps are also secured by one or two screws, so you can remove the head without the cams falling out. Jaguar had a procedure for removing the cams without affecting the head gasket seal by removing one cam cap at a time, installing spacers on the head bolt and reinstalling it to maintain the tension on the head, then doing the rest one at a time until the cams were free. The procedure is probably shown in the Haynes manual I linked to earlier.

Also, while Jaguar originally specified that the head bolts could not be re-used, they subsequently revised their position, allowing I think up to two re-uses of the bolts (though I suspect this was a cost-saving measure due to all of the premature head gasket failures XJ40s experienced due to the poor design of the original gaskets). The bolts were to be marked with a center punch each time they were re-used, so bolts with two punch marks were to be replaced the next time they were removed.

Cheers,

Don