Evinrude 1956 7.5 powerhead

[james hobson]

I am wanting to rebuild the powerhead on my 7.5 what all needs to be done besides rings and seals I want to do a good job, where do you recommend buying parts, found some rings on eBay not sure if they great quality they are aftermarket any ideas would be greatly appreciated.

[fleetwin]

My first question is why do you want to rebuild the powerhead? Is it damaged or worn to the point of needing a complete rebuild, or are you just trying to make it as close to new as possible? Generally speaking, these engines never got enough hours on them to actually be worn out to the point of needing to be rebuilt. With that in mind, I don’t recommend rebuilding it unless you have confirmed it is damaged/worn and needs to be rebuilt.
Let’s just say it is damaged worn and needs to be rebuilt. My next question is what kind of physical shape is the rest of the engine in? Have you inspected/drained the gear lube? No sense rebuilding a powerhead on an engine with physical problems and a damaged gearcase. Was this motor used in fresh or salt water? I ask this only because trying to remove fasteners on a salt water engine can lead to more of a mess than is worth bothering with. Trying to drill out broken SS hardware is tough, and the powerhead castings may be eroded/damaged from years of salt water use.
OK, let’s just say this is a fresh water engine, in decent cosmetic condition, and the gear lube appears to be free from water, and needs to be rebuilt. The next step would be to pull the powerhead apart and inspect everything. These engines used plain bronze bushings for all the rotating surfaces. These surfaces can often be worn when folks mix gas/oil at ratios less then 16:1. No real way of repairing worn crank/rod rotating surfaces, those parts would need to be replaced. Is there any evidence that this powerhead has been apart before? If so, have a close look inside the crankcase for signs that the engine may have “thrown a rod” and been repaired. No sense rebuilding a powerhead where the inside of the crankcase has been damaged by rotating parts coming loose. Finding used replacement parts isn’t too tough, new parts can be had also, but tougher to find. You may want to find a service manual and parts book for this engine as a guide to rebuild procedures and to get part numbers.
How much money were you planning to spend? The dollars can add up quickly, in addition to parts for the powerhead, you will need new ignition components, carb rebuild kit, and water pump pieces. You will probably spend $200-300 on parts. I’m not a big fan of aftermarket parts in most cases, especially rings and gaskets.
So, let us know what you think, I encourage you to post pictures and ask more questions….
Don

[outbdnut2]

Run a compression test first if you haven’t already. If compression is low, check the head gasket. Like Don said, they seldom need rebuilding. If it’s not running good, most of the time it’s carb or ignition problems….or…you can have a brand new spark plug that’s bad.

Now if someone though they could mix gas/oil 100 to 1 because it said that on the can of oil, then you may have a parts motor.
Dave

[billw]

A 7 1/2 will tell you if it needs rebuilding, when there is a connecting rod sticking out the side of the crank case from running too lean an oil mixture. If, like has been said above, it has compression, I too, would leave the power head internals alone.

Long live American manufacturing!

[johng]

It seems to me 53′ – 58′ OMC 7 1/2 hp motors are more susceptible to bottom Rod Failure than their 5 1/2 hp cousins. The motor made just enough more power with that Aluminum Rod and no needle bearings that if the Impeller was failing or Insufficient Oil was used the result over time was excessive Heat on the Rod. Then a Crash. I blame the 50 : 1 oil mixture that came later as part of the problem.

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