oversized pistons

[sam333]

Looking for .020 over pistons for my 1ZZ FE rebuild. Dont want to spend a fortune. The standard toyota pistons were $220 a set( they dont make oversized pistons).

Rock auto has oversized corolla pistons , but I dont know their quality.

I took my block to the machine shop a while ago, they cleaned, measured it and told me it had very little wear and a hone would do.

When I picked it up, they told me it was still within standard limits ( always ask for the numbers).

I orderd all my parts ( standard pistons/ rings), but when I was checking my ring end gap the clearances were large. I orderd a 3-4 mic and telescoping gauge. The bores were .0025 over the limit which gives me .0055 piston to bore clearence,( manual says .0026-.0035 (.0039 max) which is not good for a potential oil burner.

Thanks sam

[Milky]

did you just mic the bores? did you not drop a piston in and actually measure the piston to bore clearance?

i have never had a problem with rock auto's products.

[sam333]

Hey, milky

Yes, I measured the pistons( mic ) and the cylinder bores( with a telescoping gauge and mic) . No mistake the clearance is .0055.

The pistons are measured perpendicular to the pin bore, 25.6 mm down from the top edge of the piston, so there is no accurate way to measure them in the cylinder.

Even though its out of spec( for the corolla) most engines would be fine with that , but I dont want another oil burner.

I may give those rock pistons a try.

Thanks, sam

[sam333]

I took my block to a local machine shop and they are going to order .020 over pistons and then bore the block to fit.

They asked me if the engine came out of a "clown car", (they build mostly race engines there), I guess they took pity on me.

sam

[Milky]

Originally Posted by sam333

Hey, milky

Yes, I measured the pistons( mic ) and the cylinder bores( with a telescoping gauge and mic) . No mistake the clearance is .0055.

The pistons are measured perpendicular to the pin bore, 25.6 mm down from the top edge of the piston, so there is no accurate way to measure them in the cylinder.

Even though its out of spec( for the corolla) most engines would be fine with that , but I dont want another oil burner.

I may give those rock pistons a try.

Thanks, sam

the way your supposed to check the piston to bore clearances is with the piston installed and use a feeler gauge to measure the gap. using a mic and a telescoping bore gauge is not the right way to properly measure it. most of the time a telescoping bore gauge is used to check for cylinder out of round. i rarely use mine to check bore clearances like that.

still its not a bad idea to go to an oversized piston. this way you ensure a fresh cylinder wall and perfect clearances

[sam333]

On some pistons you can get away with using a feeler gauge IF the measurement is supposed to be taken at the bottom of the skirt( which I have seen).

The point of measurement is determined by the manufacturer of the piston and that depends on the piston design.

With the 1ZZ engine the piston measurements are taken at 25.6 mm down from the top edge of the piston and at a right angle to the pin bore( impossible to get an accurate measuremnt with a feeler gauge).

Measuring any other place could give you a tight or loose piston because of the different expanson rates on different areas of the piston and piston taper.

The accepted method is to use a mic and telescoping gauge or a mic and a bore gauge to take cylinder measurements.