Correct Crankshaft for 1956 RDE-18

[ADAM GIBB]

OLCAH,
The dimensions that I am most interested in would be on the top end. The distance from the bottom of the cam drive pin hole, to the top of the taper above the bearing surface. It is the carbon seal retaining setup that is not allowing me to seat the flywheel. I am away until Friday, but could post a picture when I get back.

I may be beating a dead horse here, but this has me stumped.

I came to the same conclusion as Frank with regard to all of the possible setups. The only think that was never done from the factory, was supplying the carbon seal on the top end of a 203655. Add the fact that they went back to the 302530 in later years, tells me that the difference must be in the top end. And following Franks logic, yes the 203655 would work anywhere the 302530 does, but not the other way around.

[olcah]

Should have the 203655 by next week, will get those dimensions.

[olcah]

1st pic is measurement from TOP of the cam drive pin hole to top of taper. 1.515 same on both crankshafts.
The top crankshaft was removed forcefully from a 53/54 Evinrude 25HP. cast into the top counterweight is 302??. Probably 302530. Etched into the flywheel taper of the NOS is a boxed M and number 203655. I’m thinking that the original castings differ between these crankshafts, maybe because of the supplier and so the machining drawings differed and so the crankshaft numbers differed but that the interfaces are the same and both crankshafts are completely interchangeable.

I did not find significant dimensional differences between the crankshafts in the top bearing/seal area. Maybe more experienced people could spot something. Only thing I noticed is the transition between the cam drive pin surface and the bearing surface where the seal rides is more gradual on the 203655 crankshaft. That would make the carbon seal easier to install on the NOS crankshaft but the 302530 crankshaft had a carbon seal on both ends when I removed it from the motor.

WRT the flywheel not seating maybe this would help. Last year I was unable to get the carbon seal onto its surface on the bottom of a big twin crankshaft. I just could not force it into place despite lube, etc and expected that I would soon break the carbon. Inside the carbon I had put a square ring instead of the originally provided o-ring. In the end I had to put a new o-ring in and the seal then slid into place with some difficulty. I don’t know why the seal would not go up with the square ring. I usually replace the o-ring with a square ring as recommended by the experienced people on the site. But somehow there was no way that seal would go into place with the square ring installed.

[frankr]

As I suspected, the new one has chrome plating on the bottom seal area. The M in a squared box is the OMC trademark.

BTW, Crankshafts were made in the Evinrude factory.

[olcah]

It appears that Frank has nailed the real difference!

[ADAM GIBB]

OLCAH
Can you please measure from the cam drive pin hole to the top of the short taper that is above the upper main bearing area on each crank.
Thanks.

[olcah]

Adam, Measurements are scaled with a Starrett steel rule having 0.020 in. increments.

302530: Scaled from bottom of hole to top (narrow end) of short taper. 0.330 Really hard to scale as start of taper is hard to determine. I could be out .030 easily.
Scaled from bottom of hole to bottom (wide end =start of bearing surface) of short taper. 0.400

203655 same locations
0.310 really hard to scale as start of taper is hard to determine. I could be out .030 easily.
0.440

Let me know if you need other dimensions.

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