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Old 10-10-2021, 06:27 AM   #1
john charlton
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Default Piston question

Just watched the day old video on "You Tube" on fitting pistons to the block No mention was made to the alignment of the piston to the connecting rod . It looks like the pistons used were solId skirt so they could go any way around . O ver the years I have collected dozens of NOS and good used pistons both 3" bore and 3.7/8" and no solid skirt . My pistons have "FRONT" or" front" in Ford script . Made in England by "Hepolite" which could have an American parent company . The skirt is split from top to bottom at an angle with the the split on the left side of the engine when fitted . Just wondered if the split skirt is an English thing and in USA all pistons are solid skirt .Just wondered what the parts houses sell The video says the bore had 10 thou taper maybe solid skirt was chosen for this reason ,just thinking.
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Old 10-10-2021, 06:53 AM   #2
Bob Bidonde
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Default Re: Piston question

What follows is for USA production.

(1) The Ford Service Bulletin of January 1929, Page 312 indicates that a percentage of Model "A" engines were assembled with "Solid Skirt" pistons. So the initial standard production of engines had "Slotted Skirt" pistons. Further evidence appears in the Ford Model A Service Manual & Owners' Handbook, Figure 15 which shows a "Slotted Piston" on an X-beam connecting rod.
The "Solid Skirt" piston design was apparently a cost cutting idea that made piston installation into the cylinder block self-centering and with no need to use clearance gauges.

(2) Later in 1929, the Service Bulletin of April 1929 indicates that the A-6110-A2 "Strut Design" Piston was replaced by A-6110-A "Slotted Design." The Ford Parts Price List of July 1, 1931 lists the A-6110-A "Slotted Skirt" Piston for 1928 - 1931. Looking further down the evolutionary road, the A-6110-A became the B-6110-A "Slotted Skirt" Piston used through the end of 4-cylinder car & truck production in 1934. Also of interest, the "Slotted Piston" head has an arrow marked "Front." When properly installed with the arrow facing to the front of the engine, the slot in skirt faces the left side (driver's side) of the cylinder block.

The slot in a piston skirt enables the piston to be machined round instead of an oval shape. A solid skirt piston thermally expands differently along its wrist axis than it does normal to the pin axis because of the piston's material distribution. This makes it necessary to machine the solid skirt in a more costly oval. Now you know the rocket science of the slot!
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Old 10-10-2021, 11:35 AM   #3
Jim Brierley
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Default Re: Piston question

John, I think most, if not all, new replacement pistons are solid skirt. In general these require more piston-to-wall clearance than those with the full length split. Original Ford specs say "no more than .002" clearance", this can cause severe problems with modern pistons. I bore to .003" then hone another .0005" on stock rebuilds. For my street engines I bore to .004", then another .0005". On my Bonneville engine I have .009". Is it noisy? Not without a muffler, and at speed, I hear nothing but sweet music!
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Old 10-10-2021, 01:33 PM   #4
john charlton
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Default Re: Piston question

Thank you both for your replies . So as I understand it modern replacement pistons are unidirectional and can be fitted any way around I do remember reading somewhere that there is a "tongue" in some pistons in the inside of the piston skirt which indicates how it should be fitted to the connecting rod I have never seen this my pistons are uniform inside no "tongue" .This does explain why there was no mention of the "FRONT" marking in the "You Tube" video . After over 40 years in the hobby you can still learn new things !!!

John in Suffolk County England .
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Old 10-11-2021, 12:17 AM   #5
ursus
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Default Re: Piston question

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John, the "tongue" you mentioned is also described as a tongue depressor shaped thickened area on the inside wall of the piston. This should face the valve chamber or passenger side of the engine which is the major thrust side of the Model A engine.
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