MTFCA Forum

I am going through my 1912 engine that was put together by the previous owner. He appears to have done a good job, but let's just say I am changing some things to suit my "preferences." Looking at the wrist pin setup in these Jahns pistons, I don't see a lubrication hole to catch oil from the splash system to lubricate the wrist pin. (Of course, I am hoping someone will tell me that there is a lubrication hole on the top sides of the wrist pin bosses.) Anyone familiar with Jahns pistons? I am not entirely sure of the age of this rebuild.

I need to get a smaller dental mirror to try and see the top of those bosses. If there is something that looks like a lubrication port, then I will be happy. If no lubrication port, I think there needs to be some. If it comes to that, I will take the pistons to my machine shop so they can do the holes and carefully do any deburring that needs doing. I suppose if worse comes to worse, I can fit new pistons but am hoping not to go that route.

Oh...and the wire through the bolt head, yeah, that will be changed to the proper cotter pin installation. There is already enough wire inside a Model T engine.

Drill both bosses with a countersink & centering drill. 1/8" hole with about a 3/16" countersink.
Be sure to hone the wrist pin holes for a drop out fit when turning the piston wrist pin vertical.
Also alow plenty of piston clearance. They tend to expand when hot. I like .0045-.005"

Remove the pistons, remove from rods, and just drill an 1/8" hole thru the pin boss on each side. You could use an egg beater drill, a battery powered drill or a CNC machining center and the piston won't know the difference. Deburr the pin bore with a small scraper and some fine abrasive cloth or sandpaper and put it back together. If ya gotta take it to a machine shop, have them check for proper pin clearance. Some of those pistons came from the factory with too tight pin fits. .0003-.0005" clearance would be about right.

Not sure you need the oil holes, but if it makes you feel better, by all means do it.

As far as the "correct" cotter pin comment- stay with the safety wire.

This is the only piston whose pin froze solid enough to seize the engine. I had to saw a chunk out of it to get the pin to move and remove from the rod. It had no oil hole. You can see how the pin bonded to the aluminum.
  I don't know if it is a version of the Jahns or not. I have used Jahns for years with no other problem.
Rich

It's well to be fussy about pistons and pin fit. FWIW, the original cast iron pistons and their bronze bushings were through-drilled for oil holes top and bottom of the pin bosses, so Ford also must've reckoned that it aids in oiling the pin.

Curiously (?) my Lizzie pulled up lame last spring with a frozen wrist pin in #4 (aluminum pistons, pin bosses through-drilled, not Jahn's). Reportedly this engine had some 20,000 miles on it at the time. You never know !

Cause ? Possibly "stuff" floating around in the system ? Wood band linings were at the point of failure when I got the car, leaving quite a log jam of splinters in the transmission cover screen through several oil changes. On tearing down, lining material failed on several of the turbo clutch plates, so you see, it isn't only lint from cotton band lining that can possibly cause mischief.

Scary stuff, drill the holes, do away with the wire and turn either the rods or the pistons as one or the other is in backwards, ie, the wrist pin lock bolt faces the camshaft and the split skirt faces away from the cam.