Hello fellow Jaguar lovers. My 1993, XJ40, 4.0 seems to develop rocker gasket leaks every summer. I find the rocker cover screws tend to loosen off with expansion and contraction. I just tightened them for the fourth season and it has stopped again for now. I have read that these rockers are notorious for leaks so my question is now that I know this, rather than replace the gaskets , should I just remove the rocker cover, clean up existing gaskets and mating surfaces and use a high tech gasket sealant like modern manufacturers now use? Has anybody done this successfully ? If so, what gasket sealant is most suitable for the task ? It must be something that permits removal of the rocker cover should maintenance be required. The gasket kit is not that expensive but I really do not wish to be repeatedly performing this task in the future or enduring the messy leaks when there are quality solutions. The rest of the engine stays very clean. Any suggestions from others who have similar issues ?
Regards from Rodoz

 

Hi Rodoz,

I owned a '93 XJ40 for 16 years and never had a problem with the screws loosening on their own. My first thought is that perhaps oil in the threaded holes in the cylinder head could be contributing to your problem. The next time you have the cover off, try cleaning the threaded holes with a spray solvent (e.g. brake cleaner), cotton buds / Q-tip swabs, and compressed air, and clean the oil from the screw threads as well.

Note that Jaguar calls for RTV silicone sealant to be used at the two half-moon seals that fit into the recesses at the rear of the cylinder head that are made when machining the camshaft journals. I typically use Permatex Ultra Black in this application. In the U.K. and perhaps Down Under, Hylomar probably supplies a similar flexible room-temperature vulcanizing silicone sealant that is oil- and heat-resistant.

Modern covers designed for sealant instead of a gasket have flat gasket mating surfaces instead of the gasket groove on your XJ40 cover. Modern sealants are so good that Mercedes doesn't even bother machining the gasket surfaces flat. But I think it would be difficult to achieve a good seal of your XJ40 cover with sealant alone.

We have also had reports that some aftermarket gaskets are not as good as others. Some of the brands I've had good success with include Fel-Pro, Mahle, and Victor Reinz. Our forum sponsors should be able to provide top-quality gasket sets.

Also, I replaced the regular flat washers for the cover screws with sealing washers, which have a rubber washer bonded to a stainless steel washer. I can't recall the size I used, but they were similar to the ones at this link:

Stainless Steel / Neoprene Sealing Washers No. 12 Screw Size 0.375" O.D.

One other tip: since the AJ6 engine is an overhead camshaft design, with no rocker arms, Jaguar calls them "camshaft covers" or "cam covers," though many parts suppliers still refer to them as "valve covers."

Cheers,

Don

 

Thank you once again Don, you are a wealth of helpful information.

Once I finish my electrical upgrades I will remove the cam cover and attend to the leaky seals. It seems ok ATM but I am not driving it as we are in COVID19 lock down once again but I am getting a lot done on the vehicle. Still waiting on parts which are slow to come due to delivery delays but there is plenty to do. Headlining replacement is coming up once the fabric arrive and I get the last of the cables in for the reversing camera and media micro pc in the trunk. As my vehicle is an 03/93, I just missed out on the 1993 alarm and security upgrades so there are no connectors in the trunk for the security module unfortunately. Therefore I cannot interface an after market unit so I may just add an RF rolling code receiver for the central locking and scrap the IR system which is a fixed code which is not as secure anyway. Thank you for your input I will source to sealant when Lockdown is over. Many thanks for you valued input.

Regards from Rodoz

 

I’ve had a similar issue with the magnesium camcover on the AJ16 engine.

Only the OEM gasket works. There’s no aftermarket that fits. They’re all too big.

I have replaced the little rubber bolt gaskets, but they get squishy over time with oil.