‘Nice score on the Merc ! I’ll have to join that group so I can check out the progress ...
Very nice! ........ Smart move changing to a smaller and lighter engine.
Sam, I forgot JohnsOldMercurySite is behind a pay wall. Ned, I'm kind of excited about the motor... it will look right and still make good power, even excellent power for the weight. I really like the look of the 1950’s Mercury round top outboards, plus they were the only game in town at the time if you wanted something near the top end of the Wolverine's Cost Guard rated 50HP.
That said, it turns out 1950’s Mercury outboards north of 25HP are kind of rare out here in the deserts of Utah. After several months of checking the local classifieds, a 1958 Sunset Orange Mk55EL turned up!
Complete and in decent shape, the only real issue was the long shaft configuration, as the boat has a 16" transom. I went ahead a bought it, figuring I'd use spacer blocks on the transom for now.
I was getting ready to send it out for rebuild when a 1959 Mk55A unexpectedly turned up 150 miles from me (that's "local" for most western states).
I like the look of the round top housing better, but the white motor (while rated for the same 40hp) had the larger 44cid block. Turns out this block will still fit in the round top case (and vice versa) so I sent the 1959 44cid powerhead off to Wisconsin for a rebuild and a few upgrades.
Here are a few details from Chuck Petersen, the engine builder:
“In 1958, there were 2 Mercury choices to be had in the 35-45 hp. range. The 40cid AJ carb MK55 and the 44cid KA carb MK58. That expanded to 3 in 1959 with the MK35A, MK55A and MK58A. In reality these motors covered a 5 hp. range (40-45), but it allowed the number of product offerings to expand. This trend continued during the "white motor" era with 40 and 44 cid blocks eventually offered in 5 levels - M300, M350, M400, M450 & M500. (With the M500 producing 50hp from this same 44 cid block.)
The MK55A is a 1-year only hybrid detuned 44cid motor with small AJ50A (think MK55) carbs. The good news for a guy in 2020 looking for a performance 44 build includes the fact these restricted motors led fairly easy lives. All the internal parts are just the ticket for a performance build including the large-opening brass reed cages with labyrinth seal. The carb openings can be custom machined to flow better vs. a stock MK58. Guys learned this trick when the APBA made 40cid service blocks legal for D-Stock classes. The cases could be machined specifically for KA carb bodies vs. the much wider Carter specs. The exhaust ports receive a custom port modification designed to significantly increase performance.”
Original Carbs:
Upgraded Carbs:
Current state of the rebuild (everything machined and balanced, re assembly starting this week.)
