Hi, as part of tracking a problem in the transmission of our 96 XJR i needed to remove the exhaust manifold. Damm, I can see exhaust leakage on the front manifold. Hang the expense, pull both off and have them machined. Hmm what is this rusty stuff on the alloy cylinder head? Ahh, its the core plug that is dispersing the green stuff into the atmosphere...very sneaky. Whipping the vernier guage from my back pocket I note it's 25mm or good old I inch.

So good people, information seems a little sparse on the ground. Are the three of them threaded or just knock in? Are there problems in replacement. I thought I would ask before I started the job...just for a change! I look forward to your thoughts.
Cheers from Brisvegas

 

The JEPC shows....

XJ Series (From (V)720125 up to (V) 812255)/ENGINE/CYLINDER HEAD, CYLINDER HEAD LESS VALVES 3.2/4.0 LITER.

"Cylinder Block Core Plug" (#2 on the illustration) as C168623.

No dimensions or other info is provided. I have never removed one so I can't help. I would imagine that they are simply 'swaged' into the holes.

bob