I replaced my timing chain and tensioners on a 2002 jaguar xj sport about a year ago and now its time for a new project.

I have the engine heads off and they are in the shop being rebuilt. The pistons look great and the engine is definitely salvageable. I am also going to replace the timing chains and tensioners while I have it apart as well as the motor mounts. The car is immaculate inside and out. Just curious if I should replace anything else major while I have this apart.

I would change thermostat tower to aluminum and water pump if it has plastic impellers. When you get headgaskets get ones for a 04 4.2L engine. They are MLS and are better than the stock fiber ones.

should i replace the engine head bolts? someone told me they were torqued to yield. also should i replace the spark plugs?

If the head bolts are centre popped then yes, if not then they can be reused.

New plugs can't do any harm and should aid initial mapping when the engine is fired up after the rebuild.

Why are you changing the chains and tensioners again if you only did them a year ago?

Has this engine had a problem??

I would also address the ongoing problem with your car's ZF gearbox, they're a hand grenade item but preventative work and fitting of one part along with a fluid change should see the issue gone. Do a search for 'transgo' within this forum for all the info you need to save thousands of dollars on a reman trans

Hope this helps
SB

Hey thanks for the reply. This is a different jaguar, i have another jaguar, a jaguar xj8 sport that I replaced the timing chains and tensioners last year. I aquired another jaguar vandenplas that I am working on the engine heads. We knew right away that it had engine issues, we figured it slipped a cog in the timing because the car still ran when we got it. We took it apart and it had slipped a cog, and damaged one of the valves. It is still salvageable and we are having both the engine heads rebuilt right now. What signs should I look for this transmission failure that you are talking about??

If there's signs of failure it's already too late generally. Do a search and all will be revealed, the ZF transmission in both of your cars are fitted with the valve block leads to over-pressure breaking a snap ring and trashing the A drum. Old news on this forum and 1001 threads I'm afraid, but the nice thing is there's now a fix, see my post above for searching and further reading. If I where you I'd do both cars