How to Measure, Mic, a Piston
 

How to Measure, Mic, a Piston

Supertech PN# P4-MA835-N4

Factory supplied spec sheet.

https://www.miataturbo.net/attachmen...ine=1334796297

They ask for a bore spec 3.287/83.50 mm, This what is your recommend bore size.


Tools needed for the procedure, Outside micrometers 3-4 inch,
https://www.miataturbo.net/attachmen...ine=1334796297

But in a pinch, venire calipers will “Get you close” if just doing a quick check

https://www.miataturbo.net/attachmen...ine=1334796297

A machinist standard is handy to have, so you can zero your measuring tools.

https://www.miataturbo.net/attachmen...ine=1334796297

The points you want to measure 90* to the wrist pin centerline

https://www.miataturbo.net/attachmen...ine=1334796297
A view of the appox pot to measure from, with venire caliper.


https://www.miataturbo.net/attachmen...ine=1334796297
All 4 pistons in the box measured 3.2845

This is going to be Piston to Wall clearance, PTW, in theory. Your actual PTW will vary due to cylinder block finish.

The factory spec sheet says 3.287”/83.50 mm

The formula for converting mm to inches is

Mm x .03937 =Inches

83.50 x .03937 = 3.287395


Now to figure PTW (Theory)

3.287 – 3.2845 = .0025 PTW clearance


I am more accustomed to seeing .0035, but that is on a 85mm piston, and other brands of forged pistons.

That also be in part due to the “Phosphate dry lubricant”


From the super tech website
SURFACE FINISH:
Finally our "phosphate dry lubricant" coating is applied to protect the rings against "micro welding" and enhance lubrication on the skirt/cylinder area.
Piston Rings are manufactured in Japan with the latest technology for high performance applications.

Quality Control: Performed after every step of the manufacturing process in climate controlled environments to ensure reliability of dimensions.
http://supertechperformance.com/products.html?id=10

The tight .0025 clearance is mostly due to Supertech's 4032 alloy. It's got a higher silicone content than the standard 2618 that everyone else (Weisco, CP, etc) uses, which means the ultimate strength is a tiny bit lower (something like 5% IIRC) but the thermal expansion is quite a bit less. It allows for tighter wall clearances, less piston noise, and longer life.

Sav.. I understand that, But I am human, and humans do not like change. For most of machining life, I have set up PTW to the .0035 clearance.

I will adapt and use the tighter clearance.

When you been trained from day one that "loose lives"

It is ingraned in the thought prosses, It takes a bit to over come.

This has been mentioned before in some of your other threads; you need to enable the "Macro" mode on your camera.

The information you've been adding to our forum has been very helpful and I think everyone is very appreciative. In that sense it's hard to complain about your pictures, but there should be a simple switch somewhere on your camera that will help it focus for pictures like this.

Anyway, thanks again for all your knowledge dumping on this site.

The Macro/flower Icon would not come on when I took these pics.

With you cats so worried about the picture quality, maybe you should all pitch in and send him a camera.

Once again, thanks for the great read! +1 props.