Well, I looked up the impeller for your '59 35hp and it's the same. So the only critical difference might be the pump mounting holes. If that's the same on the 40hp as for your 35, I don't see any reason why the 40hp pump wouldn't fit.
The 40 hp one looks like it's the right one but not 100% sure ... The inside of mine has what looks like a broken edge in the impeller cup.. The one on eBay described as NOS.. Is the same as what I have .... The $187. One don't show the bottom side ... So now I'm questioning if mine is broke or just made that way.... I don't have a picture of my part . but it looks the same as this eBay part . But mine has sharp edges which look dangerous to the impeller...
DLB68 wrote: The 40 hp one looks like it's the right one but not 100% sure ... The inside of mine has what looks like a broken edge in the impeller cup.. The one on eBay described as NOS.. Is the same as what I have .... The $187. One don't show the bottom side ... So now I'm questioning if mine is broke or just made that way.... I don't have a picture of my part . but it looks the same as this eBay part . But mine has sharp edges which look dangerous to the impeller...
I wouldn't worry about that cutout, it's the way they are designed to work. Keep in mind that once the motor is at speed, the impeller blades curl up and act as a circulating pump; they barely "kiss" the sides of the pump.
At any rate, that new 40hp pump is purty cheep so not much to risk by picking that one up. OMC changed very little on these so I expect it'll probably work for your 35hp as well.
BTW you can smooth/sand out any rough edges that you think might catch a blade. Take a look at this eBay pump, the casting isn't exactly the cleanest you've ever seen, they tend to be a bit rough; but generally are machined properly where they need to be.
Many Thanks to the great responses. The cutout on the housing is obviously a manufacturing design , I will use a dremel and clean up the jagged edges on the one I have. The impeller that came out of it ,was missing 2 ends. The rest where ate up on the end and one was backwards. Upon installation I am sure...Please forgive me .. I was born into the Mercury blood line .. If it ain't a Merc.... It ain't right.... Was what I was told growing up... Now I am approaching 50 an Venturing into the unknown...
Spin the impeller into a lubricated pump body and it'll be easier to install. Then you just drop the pump right down so the drive key lines up with the slot in the impeller.
Use some Permatex No. 3 Aviation-Type gasket dressing, or the OMC equivalent, or Loctite 518 anaerobic sealer, on the pump's sealing surface. This will ensure good pumping action.
When you spin the impeller into the housing, remember that you're looking at it upside down, and you should turn the impeller CCW as it goes in the pump. This ensures that the blades will be rotating in the correct direction (clockwise) as the engine turns over. Lube the pump with a thin coating of Vaseline or marine bearing grease.
A little better on the price & readily available. #379775 is the complete kit. Everything you need in one kit. Find on eBay as low as $110. You can find these kits (& others) by dropping down below the parts look up page before you click on anything. All the books are there to click on. BRP, Sierra, Mercury, Arco, etc.
These books are for quick reference of fast moving parts. Assemblies that are competitive priced parts. Kits carry a higher mark up & therefore are discounted more to buyers on eBay & other sites. Hope that helps.