Exhaust gaskets, valve cover gaskets and half moon questions

Good morning everyone, I went through the forums and got guidance there to most of my questions but i wanted to ask again just in case ‘things changed’ :wink:

The rear exhaust manifold of my 100,000 miles 1985 XJ6 has developed a crack and leaks, I sourced one on ebay and am now ready to tackle the swap.

Is there a particular brand/material I should get for the exhaust gaskets?
Do i change that one gasket only or both?
Do i ceramic coat the manifolds?
Ay particular tools/skills/procedure/technique/gotcha’s needed to remove the nuts?

I also noticed that my valve cover gaskets were leaking, mainly in the front, not much from the half moon.

Is the advocated fix still the no-gasket/black permatex combo?
Do i replace the half moons with jaguar ones or metal ones?

And now for additional points, I think my a/c compressor is on the out, i’ll know in a few days once the a/c gauges i ordered arrive. The system had been converted to 134 and one of those smaller and lightweight compressors used by the previous owner.

IF the compressor is faulty what do I replace it with taking into account the system’s requirements and the use of R 134?

Thank you so much!

Hi Francois,

You will need the sealing olive and the gasket. You may strip the large and break the small bolt that fix the heat shielding to the manifold.
I would buy two of each just in case. And if you want buy exhaust sealer but it is not needed to seal.

Buy a can of aluminum paint (like zinc spray) and spray it on the manifold. This is how they were for your year and it is cheap, easy and looks good.

All you need is patience and please do not overtighten the brass nuts that you might reach better if you attack some of them from below. It is all very tight in there but can be done.

For the valve cover seals cometic is recommended but paper works. Not a fan of sealant only. I never installed new half moon seals.

A thin (!!) coat of rtv is good but anything that gets squeezed inside can lead to a significant drop in oil pressure and is absolutely unnecessary. I had perfect results with a small amount of hylomar at the half moons and nothing else.

The copper washers seal well, but only if you hang them on a wire, heat them up until they just glow and allow them to cool down (or quench, it doesn’t matter for annealing copper) so they are soft again.

You will need something to scrape away the old gasket and may want to check valve clearances.


Is probably your best bet. Easier if it already fits but those don’t fail so often

As far as your a/c compressor is concerned I’d recommend you do NOT use one of those newer ‘modern’ lightweight compressors advertised on various auto parts websites. I bought one for my 1987 series 3 XJ6 and had it installed two years ago. Aside from the fact that R134A will never run as cold as R12, I noted that cooling was ‘sufficient’ as long as the car was being driven on the open road. If stuck in heavy traffic the a/c barely cools at all. On a recent visit to the a/c shop just several weeks ago, the owner, an honest man, said my compressor is ‘weak’, but did not predict its iminent demise. , in fact, the way it’s running is ‘normal’, it just cannot handle the demands of the series 3 XJ6. As I’ve learned the hard way, the newer ‘modern’ compressors brag to weigh half as much as the old ones, but the sales brochures do not tell you cooling capacity may be reduced by as much as half as well. When shopping for a new compressor, look for the ‘Harrison A6’ or equivalent. For now, I’m dealing with my situation by placing the gear level in neutral when stuck at a longer than usual red light, while revving the engine to 1200 RPM, whcih does make a noticeable difference.

That’s often the result of undercharging. Which in turn is the result of the myth that a system converted to R-134a is supposed to be undercharged.

I was instrumental in developing the no gasket/black permatex procedure for the V12. I’m not as familiar with the XK engine and find it interesting that apparently the same procedure is used on it. No surprise, I guess, since the gaskets and half moons are similar.

If it’s truly like the V12, this is the thinking: There are two different ways to seal it up. One is to use no gasket, permatex only, combined with a rubber half moon seal. The other is to use a gasket combined with a metal half moon seal. Both work well. What won’t work well is a gasket with a rubber half moon seal, because the rubber half moon seal does not provide a solid surface to compress a gasket against. The cam covers will eventually leak between the cover and the gasket directly above the rubber half moon seal.

I don’t even know if you can get metal half moon seals. Will the ones John_john6 makes for the V12 fit the XK engine as well?

Just out of curiosity: Why didn’t you just weld up the cracks in your original manifold?

Hi Kirbert, thank you for answering my questions over many years. I thought about welding the crack, yes but then the car is 36 years, i thought that if those nuts weren’t fighting me too much i d remove both manifolds, coat them and reinstall with new gaskets.

Are you advocating 'Hey if the gaskets dont leak, dont mess with them, just weld the crack and be done with it? "

are you talking about my existing copper washers, those used to fasten valve cover gaskets?

I’ll need to look at the brand they installed but i was not unhappy with it and the system was working fine until stupid me messed with it. I then paid an a/c place to evacuate the system and recharge it to the proper levels but functionality never came back.

Kirbert can you elaborate on that answer? if the sticker says system needed let’s say 4 ounces of old freon, what do you say system should be filled to with R134A? The shop put back exactly what the sticker said to put back in.

My clutch still comes on after a year of a/c not working right so assuming that compressor has LP protection, I want to believe my system is still tight

If they did not replace all the O rings in the system when the conversion was done you may be losing refrigerant.

No, I was suggesting you take the manifold out of the car, weld it up, clean up the mating faces, and bolt it back in.

That is not economical. The manifolds are cheap as chips, check flatness.

Yes, I was talking about the copper washers of the valve cover. Reusable but you need to anneal them.

oh ok so i still have to do the work then :wink: Well I already have the replacement manifold so, i’ll use it. Thanks!

The auto A/C world is so riddled with mythology that it’s amazing that anyone ever gets their A/C working right. One example: R-134a is less dense than R-12, so when you’re trying to put the same volume of refrigerant back in but you’re doing it by weight, that means you’ve got to be putting in less weight. Yet, somehow, the auto A/C world has concluded that means systems converted to R-134a are supposed to be undercharged. They are not, and performance will suffer when they are.

Those stickers often provide low values for some reason. I sometimes wonder if they were originally intended as starting values, put this much in and then check it and add a tad more as required.

It’s amazing how the myths reinforce one another. Another factoid is that you may not be able to rely upon a sight glass after converting to R-134a. That’s true, but the reason you may not be able to rely on the sight glass is that the oil used with R-134a may cloud it up so you can’t see through it. But this has evolved into a myth that bubbles are acceptable in a system converted to R-134a – in conjunction with the notion that it’s supposed to be undercharged. Nothing could be further from the truth. Bubbles are unacceptable in a liquid line regardless of the refrigerant involved.

And a third factoid: Pressures will run higher on the high side with R-134a. That’s true, and those pressures can get out of hand quickly unless one of two actions are taken: 1) either the airflow through the condenser is increased or the condenser itself is upgraded to keep it cool so the pressures don’t spike, or 2) a switch is installed in the circuit that will cycle the compressor off when those pressures climb too high. What must not be done is to limit or reduce the freon charge to keep the pressures down. That’s another myth, and it’s so egregious that IMHO any A/C tech who resorts to it should have his license yanked.

IMHO it’s likely enough that your system is undercharged that I’d suggest you pick up a can of R-134a and a charging hose and add a few ounces just to see what happens. If it doesn’t help, no real harm done – you can overcharge these systems by a half can or more with no ill effects. But I’m betting the system will suddenly start working a lot better.

Should I call the a/c shop to ask if they unercharged it? I remember him telling me after having taken a test drive he also noted when stopped at a long red light intersection cooling was not adequate. He pulled back into the service facility and hooked up his gauges. He said he was concerned low pressure side ran 55 to 60 which he considered high as it should only be 45. He then Noted if he revved the engine at 1300 pressure returned to 45 and cooling got better. What should I have him do now if anything? If I add R134A to the system perhaps it might run cooler but would this not increase the possibility of blowing a hose under congested slow moving traffic conditions?

So, one more question: Do you think it would be safe for me to add just a few ounces of R134A to the system, and should I consider having someone sit in the driver’s seat keeping RPM above 1100 while adding it? Thanks for your advice.

Yeah, like he’d admit that. He’ll claim he put in the specified amount, which he did. It’s just that the specified amount probably wasn’t adequate, and figuring out exactly what’s going on is beyond his pay grade.

I already said it would be. If you happen to have some gauges hooked up, and the high side pressures increase quickly as you add refrigerant, you’ll know it was undercharged before. Once sufficiently charged, pressure should only increase slowly as you add refrigerant.

Dunno why you would. You should, however, have a box fan in front of the radiator blowing air through the condenser. In the end, if you haven’t optimized airflow through that condenser or upgraded to a multi-row condenser, you’ll probably either blow a hose or vent a bunch of R-134a to atmosphere via a pressure relief valve somewhere.