3hp/4hp parts compatibility

[ltz82]

I have a Johnson 4HP 1976 with a thrown rod. I also a have a working powerhead from a 1968 Evinrude 3hp. I am wondering about putting the rods and crankshaft from the 3hp into the 4hp block any thoughts on this?

I looked at ********** and found they have different part numbers on the crankshaft/rods but they look identical. I'm wondering what the differences could be 4hp stronger? different stroke?

Anyone have any thoughts or experience on this?

Thanks in advance

Steve

 

[nwcove]

Re: 3hp/4hp parts compatibility

i would "guess" that at the very least the ds splines are different.

 

[F_R]

Re: 3hp/4hp parts compatibility

Well for one thing the 4hp crank is counterbalanced. Connecting rods are the same, 383459 for 4hp, 277301 superceded by 383459 for 3hp. But that doesn't necessarily mean that a 277301 can be used in place of a 383459. You can use the newer part in the old engine, but maybe not the other way around.

 

[ltz82]

Re: 3hp/4hp parts compatibility

Ok I see what you mean the ds splines for sure match that is one of the fist things I checked however the counterbalance issue is now very apparent after looking at both crankshafts. The difference there is rather significant. I was originally looking at flywheel mounting driveshaft and diameter of the shaft where it contacts the block. I guess the counterbalance issues scratches my plan of using this crank in the 4hp

I also see your point about the new rod being substituted for the old but not the old for the new.

Anyone have a 4hp crankshaft and rods for sale or trade? The 68 3hp power head seems to have good compression if anyone is in need of one.

 

[ltz82]

Re: 3hp/4hp parts compatibility

I suppose I could also just use the entire 3hp power head and then have a 3 with a 4hp cover

 

[hidef]

Re: 3hp/4hp parts compatibility

That would be the simpler and cheaper solution.