Pistons

[tomcarman]

I discovered 8 of these and would like to positively ID them. From what I can surmise they are for a '38 to '42 Ford. The bore is 3.0625. Scrap?
Thanks, Tom

 

[Brian]

Strange combo...because the rods are for the 239 engine. The bigend of these rods is too big to fit down the 3 1/16 bore.

 

[tomcarman]

Strange combo...because the rods are for the 239 engine. The bigend of these rods is too big to fit down the 3 1/16 bore.

I remeasured across the top of the piston and came up with about 3 3/16" bore using a caliper. The actual measurement though admittedly crude falls between 3 1/8" and 3 3/16". Definitely not 3 1/6" or 3 1/8". Then with the caliper locked I measured the bottom of the connecting rod and it appears it will fit down the bore, but barely.

 

[cadillac512]

Measuring across the top ring land will give a slightly too-small number due to the reduced diameter there. Measuring the bottom of the skirt will be accurate within a few thousandths. Likely to be 3 3/16 I would bet.

 

[tomcarman]

Measuring across the top ring land will give a slightly too-small number due to the reduced diameter there. Measuring the bottom of the skirt will be accurate within a few thousandths. Likely to be 3 3/16 I would bet.

You would win the bet. I measured across the bottom of the skirt and it is
3 3/16" = 3.1875". In looking at Van Pelts a 3.1875" bore starts with a '39 Merc, but it's most likely in this case these pistons came out of anywhere between a '46 thru a '53 Ford. I have a block in the barn that these very well could be out of. I'll try and get to it after the holidays. Is there a way to measure the stroke with just the piston as shown?

 

[cadillac512]

Yes, the pin location relative to the top edge of the piston is less (by 1/8") for a 4" stroke engine but I don't have the numbers here right now. However, since the rods are "floating bearing" style and that was pre-Merc 255 production, the chances of the pistons being Merc 4" stroke type are slim.


- update: did a couple calcs and the Merc stroke piston will be approx 1.07" from the TOP of the wrist pin bore to the top outer edge of the piston. The Ford will be almost 1.20" Brain's a bit foggy this AM so hope I did that right!



Terry

 

[tomcarman]

Yes, the pin location relative to the top edge of the piston is less (by 1/8") for a 4" stroke engine but I don't have the numbers here right now. However, since the rods are "floating bearing" style and that was pre-Merc 255 production, the chances of the pistons being Merc 4" stroke type are slim.


- update: did a couple calcs and the Merc stroke piston will be approx 1.07" from the TOP of the wrist pin bore to the top outer edge of the piston. The Ford will be almost 1.20" Brain's a bit foggy this AM so hope I did that right!



Terry

Like this?

 

[cadillac512]

Yes, Sir....well done!

 

[Nailhead Jeff]

I usually junk 29A rods. 8BA cranks and rods are cheap and much better