Hi everyone.

Been doing some work on my ‘59 Thunderbird 430 and when I measured the pistons, somethings odd came out.
The piston size was slightly bigger (on the bottom of the skirt) then the manual said they should be. But not that big that it could be an oversize. Left the numbers in my garage (not located at my house), so the number will come later.
I’ve made a picture of the piston. On the lower side there is a 10 visible. Could that mean I have an .010 oversize? As far is I can find in my manual they only came in 0.003, 0.020, 0.030, 0.040 and 0.060.
They are original wedge shaped and fomoco is stamped in it.
My clearance is within the wear limit as the manual says.

There was no ridge from wear of the piston ring visible and on the lower part of the cylinder (where the piston doesn’t come) there was a nice and clean honing mark. Should someone had it rebuild in the past but with OEM or nos pistons??

Like to hear what you al think about it.

That is an original 4.300" piston. There have been a few comments here concerning rebuilding with the same pistons. Seems these things wear much less with the high gears Ford put in them.

Below are my measurements. They are all in millimetres, I hope you can understand them.
If not, let me know and I'll convert it all to inches.

Don't look to much on how well the chart is made... I'm a car guy, not a computer guy!

Thanks

Mine varied from 109.20mm to 109.21mm (photo from Piston Measurements I took).

I reused all of them without issues. Just need to CLEAN them very well and inspect for cracks.

Do your pistons show any scuff in the skirts? I think the manual mentions a optional oversize dim depending how the bore presented.