Mr Plow

Does anyone know the thickness or could you please measure the minimum thickness of the piston crown on factory Mazda non-VVT 1.8 cast pistons.

Many thanks!

Mr Plow

Still after this if someone has a non-VVT 1.8 piston to hand. Many thanks for your help.

VertBert

I took some pictures of one of my pistons and some calipers. Let me know if any of the picture need clarification or if you need any other measurements, I can probably get them pretty quickly.

The last photo is a measurement from the top of the top piston ring to the top of the piston.

https://imgur.com/a/2ehP7zU?

Mr Plow

Many thanks VertBert. I still need an internal measurement from the bottom of the piston skirt to the underside of the crown at the center of the piston to calculate the crown thickness using the rest of your pictures. I've done this last measurement by sitting the piston upside down, using a flat edge like the side of a rule to create a flat horizontal plane across the bottom skirt of the piston and then using the internal caliper to measure the distance between the rule's horizontal plane (skirt bottom) and the underside of the crown.

Many thanks for your help on this.

VertBert

Let me know if this is what you're looking for.
https://imgur.com/a/9vXIaho
This is from the top of the skirt to the bottom of the inside of the piston dome. You'll need to subtract the thickness of the straightedge, which I've also included.

Mr Plow

Many thanks again VertBert!

I've run the sums:
Piston height: 2.401" measured
Top of piston to bottom of dome: 0.082" measured
External height = 2.319" calculated

Internal height from rule: 2.313" measured
Rule thickness: 0.047" measured
Internal height = 2.266" calculated

Crown thickness = 2.319"-2.266" = 0.053" or 1.35mm

This calculated crown thickness is far too low. I'd expect at least c.0195" / c.5mm if not more.

I think you may have measured from top of piston to the lowest part of the valve cut out instead of the dish height/depth on the second measurement. Lowest point of valve cut out is in a thicker part of the piston. I'm aiming for thickness at center point of the piston - not at valve cutout heights. Please measure the height difference between the height where 22 is stamped (top of piston) and where the A is stamped (depth of dish) if my assumption is correct as I think it will output a much more realistic number.

Many, many thanks for your time and effort. I promise to post an interesting piston thread of my musings once I have numbers.

VertBert

Here you go.
https://imgur.com/a/9vXIaho
Added one more picture from the top of the piston dome to the bottom of the skirt including the straightedge (~2.525"). From the inside of the piston dome to the top of the straightedge is ~2.315", giving a rough piston dome thickness of about .21". The fly cuts for the valves are rather deep (~.2" from top of dome to bottom of intake cut), but in the internal picture you can see how the casting has recessions for those; I would expect the piston thickness to be about the same the whole way around.

Mr Plow

Excellent work and very appreciated. I agree that the valve cut outs are significant but are covered by the form of the inner piston design in the cast shape as is normal.

At 0.21" / 5.3mm thick, the piston crown at the centre is roughly where I would expect for a cast N/A piston of this age/type. My VVT pistons measured in at c.5mm thick crown as well, I wanted to see if these had significantly more meat. This has been really helpful in my considerations as I'm currently looking at different piston options while trying to balance the cost of an overall build.

As said above, I really appreciate your time and help.