Rods for a 5" stroke engine

[JV Puleo]

Does anyone know the center-to-center measurements of the connecting rods for the 20's Buick or later Chrysler (or any other make for that matter) engines that had a 5" stroke? I am starting the rebuild of my 1910 Mitchell T engine. It measures 4 1/4 x 5 and the rods measure 10" from the center of the big end to the center of the wrist pin. One of my rods is bent but more importantly, I intend to make bronze shells that include the thrusts for the big end and babbit those rather than the rod itself. This requires a rod with a larger big end, which all engines in the 20's and later would have. I'm also making the pistons so I have some flexibility there. When I figure out what rod will likely work, I'll set about finding some.

[Owen_Dyneto]

By tape measure, center to center on a rod from a 3-3/16 x 5" Packard Eight is 11 inches.

[JV Puleo]

Thanks very much. This is what I need to know. Under ordinary circumstances that would be perfect... it may still be but I'll have to figure out the geometry. The Mitchell crankshaft is offset 1" from center which makes the rod pass very close to the left side... in fact, there are notches on the inside of the crankcase to accommodate it so I don't know if there is room for a rod 1" longer. I would really like to use something like Packard rods because the originals are, to put it plainly, pretty crude. Making the insert shells will be a lot easier if I have high quality rods to begin with.

[RU22]

It is easy....... build a simple cardboard model. Use 'Acorn' pins for pivot points..... This makes it fully adjustable, You can move it within a pair of lines on paper representing the bore. Use a 360 degree protractor as the crankshaft. You will see that the longer rod you get TDC=BDC .... They are never equal BDC is always longer.... When you get closest to equal that's the correct C-C

If you make pistons you can move the pin up in the piston. Make them 3 ring. Less drag less heat. Reduced oil temps! You can also reduce the skirt lenght since the long rod reduces skirt pressure

Have billet rods made that use a common bearing..... And make a smaller wrist pin..... smaller pin less weight less mass

About rings .... Thick rings doin seal as well as thin! Take a playing card set it on edge on the short side and lift one edge off the table ..... now the long side ...lift the same distance SEE MORE AIR

Now if we could only explain the stock markket so easy!

[Guest stude8]

Attached is a 1912 article about Mercer T head rods and crankshafts, don't know if it has anything that will assist your project but print it out and perhaps it has something of interest in it.

Stude8

[Rusty_OToole]

Maybe I am dumb but I don't see what con rods have to do with main bearing thrust faces. Why not machine the rods to take an insert bearing? No doubt you will have to grind the crank pins down anyway.

Friend of mine replaced the poured babbitt rod bearings in his Indian Four with home made inserts made of aluminum tube. He cut them to size then hand scraped for clearance. Worked great for 30 years or more.

[JV Puleo]

Not the main bearing thrusts... the rod bearing thrusts, which are babbit on these rods. When I make the bronze inserts I'll surface grind the thrust faces to get a perfect clearance for each journal, even if the original crank is slightly irregular. I'm not using modern inserts because I'd rather have the added thickness of poured babbit. Its a 3 main, 4 cylinder crank without counterweights and with the fairly small journals of most all brass cars. The rod journals are 1.650... I haven't measured the mains yet because the caps are still on. The babbit surface on modern inserts is extremely thin and the crank will flex more than any modern crank will, wearing through the very thin surface. It will also be a lot easier to pour the bearings in the inserts rather than the rods.

And, I've never poured babbit bearings before so I'd like to learn how.

[joe_padavano]

Does anyone know the center-to-center measurements of the connecting rods for the 20's Buick or later Chrysler (or any other make for that matter) engines that had a 5" stroke?

The length of the stroke is only ONE factor that determines the required length of the rod. You also need to account for the deck height of the block (the dimension from the crank centerline to the machined face that the head bolts to), the compression height of the piston (the dimension from the center of the piston pin to the top of the piston), and the factory piston top-to-deck clearance spec. The rod length is calculated by adding up the piston-to-deck clearance dimension, the piston compression height dimension, and half the stroke dimension, then subtracting that total from the block deck height dimension. Different manufacturers used different rod lengths in motors with the same stroke, so asking about a Buick or Chrysler rod length is irrelevant unless that's what you're working on.

[JV Puleo]

Thanks, I'm aware of all of that. This is a non-detachable head engine with pistons that already have an unusually high deck height, because the crank is offset 1". This makes it difficult or impossible to use a rod as long as would be conventional. The crankcase is already notched to allow the 10" center rods to move up. Longer rods would probably hit the side of the crankcase at the base of the jugs. But, since I'm making the pistons too, this can be dealt with. I don't want a shorter rod... that would make an awkward situation even more so.