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piston to wall clearance

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I'm building a toyota 2RZ-FE, with an Arias Piston set PN A3720301 and had a machine shop oversize the bores 0.020 for the new pistons.

The piston to wall clearance calls for 0.005, and when I measured the bores I have 0.0055 to 0.0045 from the top towards the middle, and 0.003-0.002 clearance towards the bottom.

Is this cause for concern?

piston diameter: 3.755

It's always safer to stay on a loose side of clearance. If it has to be at least 0.005 I wouldn't expect to see anything less than that...

Thanks for the quick response. I guess I should reword the question. My concern is the taper in the bore.

The Piston to wall clearance should be the same all the way thru the bore, correct?

if it’s tighter on the bottom by 1-2thou, would that be a concern?

Yes, normally it's straight but sometimes you can find a bore tapering to the bottom a little bit if piston skirt doesn't reach that area. Otherwise it should be the same size everywhere...

Thanks again. I’ll try honing it out to size because the new pistons do pass the bottom of the bore about 10mm

The "machine shop" messed up - the bores should be straight and parallel, with the same skirt clearance at all points.

I would suspect they used a process that didn't actually rough-cut the bore first, with a rigid, fixed head - preferably indexed to the bores' actual centres, but used heavy/coarse hones to remove material that followed the original, worn bore - then compounded this by NOT removing the required material from the bottom of the bore, that was originally less worn.

You "might" get away with it, but I would suspect higher wear, potential power loss, and a good likely hood of seizure - espcially if driven hard when cold.

Thanks Gord, I had feeling those could be the potential problems after it was assembled and running. The piston seizing in the bore is my biggest worry. I spoke to the machine shop and they told me I could bring it back. The machinist said he’ll hone them out for me.

I decided to purchase a rigid hone to finish them off myself, rather than risk the shop going too big. Surprisingly it’s going well. I have 2 cylinders down to around 0.0005 of the final size from top to bottom. I’ll work the last two and switch to a finer grit to finish them off

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