JE piston/valve clearance too large?
 

Just got spooked while checking my valve clearance after my top-end rebuild.

Heads are trimmed 3.0 SC, pistons are JE standard 9.5cr, my cams are stock CIS and my calculations show about 9.7 final compression ratio.

I am getting valve clearances of 6.25 to 11.5mm!!!!! I didn't expect this, and now I'm questioning myself. Do these pistons allow that much extra room for wild cams, or did I miss something important? Somebody please hold my hand and tell me it will be OK.

What is the dome volume? Lay out your CR calcs in detail.

J.E. puts enough pocket in their pistons to run racing cams.

That said, If you are still running CIS, you are limited in the cams that can be run.

With my new 98mm JE pistons, I settled on a deck height of 1.448mm, a combustion chamber of 87cc, piston dome 32.9cc per the included spec sheet or 31.6cc listed on box (I measured 31.5). With a stroke of 74.4, it comes out 9.41 to 9.63cr.

I was just surprised with 6 to 11mm valve/piston clearance. I don't know any way I could have inadvertently caused excessive clearances, so logic tells me that the pistons are designed that way. Agreed?

Since this project was initiated because of exhaust valve contact with my original stock pistons, I have been worried about how it would come out. Now maybe I can consider better cams, even though it is still for CIS. Any suggestions on what cams would work?

Thanks for the feedback.

There's a tech article on 964 cams in a 3.0. Worth looking into.