Rebuilding a 4 hp.

[Don Hansen]

I have a 1970 and a 1974 Evinrude 4 hp power head. Both power heads have bad cranks and the 1974 threw a rod putting a hole in the carb side block half. Not surprised at the 70 as it has many many hard hours on it. Have know idea why the 74 blew a rod because the motor has very few hours on it. The cross hatch can still be seen on the cylinder walls. What I would like to do is use the carb half of the 70 block and the cylinder half of the 74 to build a working power head. Both part numbers are the same so I was wondering if that would that work? Or should I look into having the damaged block welded. Also, I noticed on the 74 crank that the needle bearing is packed with grease while the bearing on the 70 does not. Did they come with grease from the factory and it's eventually washed out. I have the manual for the 70 and it doesn't say anything specific about lubing the needle bearing.


Don H

 

[JB]

Re: Rebuilding a 4 hp.

I do not know if the different crankcase halves are automatically compatible. Some 2 stroke crankcases are matched during assembly.

I do not remember ever assembling a rod to a crank with needles without grease to hold them during the assembly. It is quickly dissolved and washed away by fuel mix.

I wonder how the '74 managed to throw a rod and still have grease in the needles. Somebody must have screwed up big time, or do I misunderstand your post?

 

[nwcove]

Re: Rebuilding a 4 hp.

if the part #'s match, they should be ok. bearings packed with grease? odd? they would have come from the factory with a "preservative" for the powerhead, but that should have went away in the first 15 mins of running.

 

[Don Hansen]

Re: Rebuilding a 4 hp.

I don't know the history of the 1974 power head but as I said the cross hatch is still on the cylinder walls so it has very few hours on it. That might explain the grease in the bearing, seeing that the needles are not captive but need something to hold them in place during assembly. I talked to a guy who knows a lot about old Evinrude/Johnson motors. He said that the factory does not recommend mixing case halves because they are line bored as an assembly. I went to him to see if I could get the holes in the case welded. He said I could save money by using J. B. Weld and that he has used it a number of times on both outboards and chainsaws. Think I'm going to try that.

I looked up the cost of new parts and I could probably buy a use 4 hp for that amount or less. The thing is I've always liked to say "I built that myself".

Don H

 

[boobie]

Re: Rebuilding a 4 hp.

The guy that told you the halves were line bored was correct. Don't mix them. You could also try Marine-Tex. Good stuff.