I have bought a 2005 4,2l sub assembly to put into my 1999 XJ8, the supplier has put in flat top pistons, but I have only seen this engine with slots for valves clearances, they say they are correct, can someone confirm this before I assemble and install, I have bought the 2005 heads and cams as well and believe the valve timing is higher than the 1999 cams, so I am totally confused.

 

EDITED

As far as I know the naturally aspirated pistons in the 4.0L are flat tops, the supercharged pistons are the dished ones to reduce the compression ratio, not for valve clearance.

I cannot find any pictures of a 4,2L N/A piston, only the 3.5L and the 4.2L Supercharged. Both of these are actually dished/shaped, not flat tops.

Also check the 4.0L to 4.2L swap thread at the top of this subforum regarding the camshafts, the VVT is different.

 

many thanks for your info; I based my idea of using the 4,2 on the same thread you mention and it sounded a good idea, but with little info on the 4,2 piston tops I am not sure I should use the sub I bought, but find a complete engine to fit.
I did find info on the VVT's the 4,0 has 30 deg advance and the 4,2 has up to 48 so valve clearance will be a problem, also the 4,2 has inverted tooth main chains which I would like to use.

 

The big question is, where did these guys get the pistons from?

There are no off-the-shelf aftermarket pistons for these engines.

And 4.0L pistons won't go in a 4.2L...

 

I have looked on the JTIS, and have found data on the pistons, the data given is that the 4.0 has relief for the valves, and shows a diagram, but on the 2004 (the highest year on JTIS) the piston is flat topped, also with a diagram!!!!!!!!!!!!!!!!!!!

As you suggest the pistons can only be P&A as I have found no supplier of a A/M version after hours of trawling on the internet.

I think I will put the heads on using an old gasket, and turn the engine over by hand allowing for the VVT lead on the timing, and see where that leads.