Aluminium half moon seals for V12

I am restoring Jaguar XJS 5.3 HE and I couldn’t convince myself to use genuine rubber half moon seals. After all the effort that is required to get to the seals and considering the high price of new updated cam cover gaskets I just couldn’t let this seals to leak oil again.
As you all know those original rubber half moon seals are doomed to leak sooner or later.
So I made aluminium half moon seals. I have made some extra if someone needs them. Just contact me if you need them

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Nice job indeed! I think I will print out your post and put it in my file of “Useful stuff to know.” For the future!

Ron Kelnhofer (who might have passed away?) used to sell something similar but it also had a groove for half a Viton o ring. I can attest they work great!


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I was also thinking about the groove for half o-ring, but evetualy decided to remove any rubber from that area completely and used anaerobic sealant to seal it in tappet block.

I am also rebuilding an HE for my 85 XJ12 VDP. I also tried contacting Ron K. but did not get a reply. I could certainly use 2 of your seals. I could also use 4 more for my other two XJ12’s (73 Sedan and 75 Coupe). If you have some to spare, let me know the cost and shipping charges. I can Paypal or send you a check. Thanks.

Hi John,
Thanks for your reply. Send me your email so I can Paypal you. My address is in Washington, DC and my email is Where in the UK are you?
Thanks, Rosendo

I originally designed the aluminum half moon seal with that groove for half an O-ring, but upon trying to install the first set in my own '83 I discovered that does NOT work. I omitted the O-ring groove from the design after that, although it didn’t really hurt anything because there’s still enough landing on either side of the groove to seal it up with Loctite 518.

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I like your solution!, I thought about doing that too, but I didn’t know what type of aluminum the head was made of, and was concerned about it still leaking (or worse) due the differences in expansion and contraction rates of the (possibly) dissimilar dissimilar types of aluminum. More often than than I care to admit, I think myself into a state of nothing gets accomplished. Ugh! This is one of those times. John!! Good For you!
I’d be interested in how the longevity works out for you…

I have Ron K half moons with O ring grove and his timing cover plug fitted to my 6 litre and there has never been a hint of any leakage


I tracked Ron K down last year or maybe two years ago to get some banjo bolts. He was no longer making the half-moon seals or bolts etc. But was selling off the products he had. I bought a set of everything he had available - - in case i need them again in the future. Like Baxtor, I have Ron K seals installed in my 6.0 litre and no leaks - - at least not there. Have an oil seep somewhere lower down though.
I think it is great to know John_John1 and others also manufacture .

Hi John,
I would like a pair of your aluminum half moon seals for my V12 project.
Please contact me at with a price and payment info.

Hi everyone,

Have just made a new lot of half-moon seals.
If anyone is interested, send me a message.


Hi John,

I would also like a pair please. Could you please quote me supply and postage to 3194 Australia.

Thanks and regards,

Hi Jonas,

Sounds good, could you please email me a private email address so we can sort details and PayPal.

Thanks and cheers,



Put me down for a set, please. My 6.0 has sat in the garage for years waiting for some TLC. This might kick start that. Thanks!

I would also like a set also possibly two can you pm with a price with postage to Phoenix Az 85021

Jonas, my two parts arrived safely today. Mighty fine! Thank you!

You’re welcome! Glad you like them :wink:

Just outta curiosity, how do you make these things? Do you machine a complete circle and then mill half of it away? Or do you somehow chuck up two blocks of aluminum in the lathe together and machine both halves at once?

If the latter, I think you could get away with using thinner blocks to start with, and leave flats on the bottom of the flanges (the top in the photo above). Wouldn’t hurt anything.

Hi Kirbert,

The height and circumference is very important here so I think that just “chucking two blocks together” will not work here :wink:
As you said I make a complete circle and then mill exactly half. I think it’s the proper way to do it. I use 0,05mm tolerance on height and circumference when machining them.
But I already have few design improvements for my next lot :slight_smile: also chain tensioner plug is on the way :wink: