How Far To Machine Pistons

[Richie-Van-GTi 74 2 Cars]

Hoping some kind folk can advise, Im going to remove my pistons this week to have them machined down. Current situation is XU10J4R fitted with a PeterT stage 2 inlet cam and also an XUD9T crankshaft. In theory all was good however in practice the piston tops out against the head as soon as it was torqued to stage 1 setting. This was using a standard xu10 gasket rated at 1.4mm thick (genuine OE part). So I temporarily used 2 gaskets to resolve the issue. This set up allowed the reccomended advance on the inlet cam and stopped the pistons 'topping out'. I now want to have the pistons machined down which will mean needing to know how much to have taken off the top to run a single gasket and also how deep to have the pockets to run full cam advance. Pockets I can work out myself if I know about the piston tops. So advise on what/how to measure up and calculate. I dont have a plasti guage but do have DTI.

[renault 17 1]

I recently experienced similar Issued when i fitted a 1600cc crank to an mi16, However in the opposite direction, I was way down on compression and I had the block and liners machined. It was suggested at the time that perhaps I could have had the little ends of the rods bushed and moved. Perhaps moving the piston would be easier than having it all machined if the rods weren't made too weak.

[Sandy 191]

The simplest way Richie, would be to find TDC with the DTI, with the head off; then measure the prtrusion out of the block and simply get that machined off so they'll sit flush. Simple and good for squish.

[pugman211 0]

i was gonna say that, but didn't wanna sound stupid!

[Richie-Van-GTi 74 2 Cars]

I had thought to just go level with the block but was hoping I could maybe go for 0.5mm protrusion for that last little bit of extra squish?

[Sandy 191]

0.5mm is a bit brave really, I don't think you should risk it.

[Richie-Van-GTi 74 2 Cars]

OK, I really wasnt sure how brave I could be, I'll maybe play it safe then and go level then try and make up a little bit on the valve pockets by keeping them to an absolute minimum. What would you say was a safe tolerance for clearance on the valves? Ideally I'm looking for 2.7 lift at TDC, the valves are currently cut back 1mm into the head and given the gasket should give another 1.4 (but base it on 1mm for safety sake), could I get away with say a 1mm pocket? I think as standard they are 2.2mm