Hello All –
I received all my bits and pieces back from the machinist some months ago and am now burning up some vacation time to build it back up. In utilizing Ray Livingston’s compression ratio calculator, I mentioned to him that I had to go negative with the piston-to-block deck clearance. That got his attention as he was quick to reply that the pistons normally stop below the top of the block when arriving at TDC. I’m really puzzled by this and am wondering if others have run in to this before? The pistons are new Mahle 0.020" oversize sold specific for the Jag 3.4L. I remember comparing them to the originals and they sure looked the same before discarding the latter in the scrap bin. As for the cylinder block: I know it hasn’t been shaved in the past other than my machinist’s light clean up as the letter markings for the original piston sizes are all still very legible and deep. As for the crank, my machinist said it had so little wear all he had to do was a light polish – so, nothing too involved there. The cylinder head had to have 0.016 shaved off the bottom as it had warped in the distant past .
So now I have pistons that protrude above the block and a head with chambers that are even closer to the block than they normally would be. What would be the calculation for purchasing a head gasket while still allowing for adequate valve clearance while still trying to maintain an 8:1 compression ratio? And at what point does a thicker head gasket make for an upper timing chain that won’t fit the sprockets? One of the local suppliers has an off-the-shelf Cometic at 0.074" available but I’m wondering if even that may not be enough. Ray suggested procuring shims and modeling clay followed by rotating the engine then checking clearances, but that’s putting me way out of my comfort zone here.
Here are my measurements so far:
*Cylinder head chambers: 99.3cc
*Piston dome: 17.1cc
*Piston-to-deck clearance: -0.045"
*Cylinder bore: 3.288"
Any thoughts going forward would be appreciated as my head is swimming in numbers and I’m also confused as to why the different compression ratio calculators found on the 'net can yield such different results.