MTFCA Forum

What size replacement cast iron pistons were available from ford back in the day? I pulled these from my 27 TT engines while back and just got around to taking the rods off them when I noticed that they were oversized. My 3-4” micrometer is out of commission at the moment and I can’t tell if these are 0.025” or 0.0025” oversized. Someone educate me!

Brad

The would be .0025 OS. Which is one of the over sizes that was sold.

I have also seen.031. Go figure that one. Dan

Dan Hatch wrote: ↑

Wed Nov 25, 2020 11:17 am

I have also seen.031. Go figure that one. Dan

That one's easy - Bore the cylinder 1/32" OS and it gives you .0025" clearance between the cylinder wall and piston. For someone relying on "country smithy methods" where tools are in 32nds and 64ths, to fix a problemit makes surprisingly good sense.

Ford did not throw nothing out, if blocks where bored to big they waited and ran a bunch that way, I have found lifters smaller than stock, so I had to bore them out to except std. tappets, I found bores bored on an angle where something was under the deck when clamped down, decks of blocks off .015 from shavings also.

When I tore the engine down for the 21, still had stock standard pistons. However the valve stems were first over size 2 piece valves. My OP is it came from the factory that way.

Dan Hatch wrote: ↑

Wed Nov 25, 2020 11:17 am

I have also seen.031. Go figure that one. Dan

The junkyard replacement block that my Grandfather put in his 1927 coupe, was a 1922 numbered block. When my Dad and I pulled that engine in 1965, we found that only the block was 1922, When Granddad replaced the block, he evidently used the EE crank and other parts from the original 1927 block. The pistons removed from the 1922 block were Ford .031 o.s. cast iron pistons. I never have understood why, other than supplying a slightly o.s. piston for blocks which weren't professionally re-bored, why Ford didn't go .005, .010, .020,.030, .040, .060.

Regarding Ford Script .031” pistons:

Shortblocks rebuilt at Ford branch plants received those size pistons. Ford’s “in house” rebuilds are probably the major source of those pistons, but they likely were available as parts stock too.

The reasoning behind the .0025” and .005” pistons were that they could be installed at a certain wear point WITHOUT re-boring.

The 1921 parts book shows; 3-3/4", .0025, .03125 and .033. As Susanna said, this was in the days that many shops didn't tools like micrometers and were still using rulers.

I have been collecting good oversized cast iron pistons to use. Last year I got a good 1920s block is good condition that needed a lite overhaul. So last winter I just had to hone out the cylinder holes and use four 0.005 oversized pistons with 0.010 over sized rings (filed to fit) to get it back in shape. Of course I did tighten up the mains and the rods a little, put in new valves, and new crank and cam gears to boot. I still am looking for good oversized cat iron pistons to use, got any? I have found all sort of sizes. Even have a 0.031, and 0.033.

The question is for Ford sizes so will list those from a Canadian parts book/
Standard, .001, .002, 003, .003, .004, .005, .010, .015, .020, .025, .030, .033, .035, .040, .045
But rings was only, standard, ,005, .015, .025, .035, and .045

After market ones is another story