I am going to be doing my upper tensioners. The valve covers are notorious for leaking. Both of mine are seeping at 45k miles. Has anyone used form-a-gasket on the rubber valve cover gaskets to insure a better seal when putting the valve covers back on? If so, how did it work?
I'm guessing that, being rubber, adding form-a-gasket to them is probably a no-no......

 

If your current gaskets are leaking I would suggest that a new set is in order. You also cannot further tighten the covers down to reduce leaks. That will only crack the plastic covers. If the bolts are torqued to specs and it still leaks new gaskets are called for.The 'gaskets' are really more like 'O' rings and smearing with a little engine oil on clean head surfaces is all that is needed.

A dab of black RTV on the head to front cover joints is also advised. Unfortunately, your AJ26 engine cannot take advantage of the much less expensive FelPro gasket set made for the AJ27.

 

most of the time the gaskets are over torqued especially the lower rear bolts on both sides they are the hardest ones to get at and most people in their haste to get them done over torque them . i used permatex on the flat spots of the gaskets (the little square beads on each gasket) and those 2 lower rear bolt areas and it hasnt leaked yet for over a year .

 

btw use 1/4" drive socket with a long extension and a swivel for those two lower bolts and a couple of 3/8" extensions to use as a pry bar to move the heat sheilds away so you can get at them easier then just bend them back into shape with the extensions when finished. while at it may want to change the plugs while everythings open and clean out the breather tube. look up the directions on removing it as it breaks very easily {learned the hard way... expensive little devils }

 

Good Luck with your repair, btw you should read this entry as you should also replace the sparkplug well seals and center seals as well.
https://www.jaguarforums.com/forum/x...-plugs-135516/