OMC 40 hp Powerhead on 35 hp Midsection

[wbeaton]

Anyone know if a 40 hp OMC powerhead will fit on a 1958 Super Seahorse or Lark midsection? I’m building a couple 1958 superquiet outboards for my cabin cruiser and I’m curious if it will work. The extra 10 hp would be nice.

Wayne
Upper Canada Chapter

uccaomci.com

[chinewalker]

I don’t see why it wouldn’t. If they’re electric shift models, they may not have the shift stuff machined on the side of the block, but that’s easy enough to rectify.

[1946zephyr]

Yes it will work. I put a 1968 Lark X powerhead on a 1959 Johnson RDS-21B. Both motors will have to be the Super Quiet models though. You can’t use a Super Quiet style powerhead on an earlier style single wall Big Twin. The mounting surfaces are entirely different.

[frankr]

If I remember correctly, if the 40 has a hot water choke, it needs a hose fitting in the exhaust housing for the choke water out. Not sure if that can be put in the 35hp housing, or not. I’d have to look to refresh memory.

[wbeaton]

Thanks, everyone. I suspected it would work, but I didn’t know for sure. The 40 hp OMC’s are a little new for me. I didn’t realize some of them had hot water chokes. I’ll have to look at the parts catalogues to find out which ones to avoid. Fortunately, the 40’s are a dime a dozen around here.

Thanks again.

Wayne
Upper Canada Chapter

uccaomci.com

[frankr]

Hot water chokes were used on 40hp electric start models 1960 through 1963. Replaced with hot air choke in 1964-up

[chris-p]

Wayne, remember all those 40 hp Powerheads I couldn’t give away, and they were already at your house 😉

[wbeaton]

Chris, no one is more surprised than me. I’ve turned away dozens of superquiets – for free. I’m not even a fan of the 1958 Super Seahorse, but it’s the only superquiet I can tolerate. Quiet is more important to me than style when it comes to the new boat and these are about the quietest era correct motors there are.

Wayne
Upper Canada Chapter

uccaomci.com

[Casey Lynn]

Have installed a 1974 40hp workhorse style powerhead on one of my old 1957 midsections.
Had to grind a lip at the front where the lower bearing housing interfered. Also ground a lip in the lower bearing housing.
The driveshaft splines are different as well making it necessary to install the 40hp gearcase. I took the rear corners off the ventilation plate and copied the rounded profile of the 1957 gearcase so the changes would not be noticeable. Was a nice running "35" when I got done with it.
Powerhead is still sitting in the garage ready to install again if I want to.

[Mumbles]

So Pappy, I have a ’58 Big Twin here with a frozen powerhead and a later 40 could be adapted to it?

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