Technically you can remove the upper tensioners without removing the chains. However it involves removing the caps from one of the camshafts and lifting it slightly, specifically the camshaft not connected to the primary chain. Chains stretch over time so if you are replacing the tensioners might as well replace the chains too. I'd rather take care of it all and not worry about it for 100K then have to break back in earlier to replace the chains too.

 

Fixing stuff that isn’t broken and can’t cause serious damage is typical jag owner behavior. I’ve worked on Ford mod motors (same exact chain setup) that were running for thousands of miles on completely busted guides. Only replace the secondary tensioners and nothing else, it takes two hours start to finish. Leave the primary chain alone unless you can hear it slap or rattle on startup.

https://www.ebay.com/itm/173051386756

 

Remove the bearing caps from the exhaust cam and lift the cam to relax the chain. You can use two plastic tie wraps around the secondary timing chains to ensure they don't change timing.

Once the new tensioner is in place, refit the cam bearing caps in the correct order and torque them to specification, then remove the plastic tie wraps.

When refitting the cam covers, make sure to add some gasket sealant, about 10mm or so, to the areas on each head where the timing cover meets the cylinder head. DO NOT use gasket sealer anywhere else on the cam covers.

 

I doubt they were running well. Skip more than one tooth or give out under torque lash and you'll wish you replaced those parts. Replacement chain/tensioner kits are cheap compared to a rebuilt engine and I can't stand plastic in an engine. Anywhere I can get rid of it I'm onboard and I've pulled out primary chain tensioners cracked as bad as secondary ones, the oil pressure cylinder was useless. I get it, overdoing it. But these cars aren't some Lincoln LS I'm commuting in with coffee stains on the carpet, of course I'm going to baby them and be thorough. I want this thing to last as long as possible.

If your budget is tight or you are short on time I get it, just the secondary tensioner fix will last for a long while.

 

+1

The cam covers usually leak at the lower rear corner where the oil collects, I usually use a little RTV on the gasket in those corners and have never had repeat problems.