2 cylinder Merc racing motors Rockets, Hurricanes & "converted" 20H's

[Mark75H]

When boat racing restarted after World War II OMC did not resume production of the full race OMC "Midgets", Johnson KR's, SR's, Evinrude Speeditwins and OMC 4-60's. Racers and race promoters thought one of the solutions was to race unmodified production fishing motors. Several of the races faired very well without special racing motors; one race that drew a lot of entries and a lot of attention was the Hudson River Albany to NYC Marathon sponsored by Wm Randolph Hearst & his newspaper empire. Hearst was a big boat racing fan and put it on the front of the sport page right up there with Major League Baseball and Football. Imagine if that were the case these days ..... would be equal to Peter Jennings and Dan Rather running it 20 minutes into the evening news.

Every year in the late 1940's hundreds of boats entered the Hudson River Marathon. By 1948 some racers had figured out that a small light boat could run competitively with a heavier boat with a bigger motor. A bunch of them ran the new 20 cubic inch 10+hp Merc KF7s ..... one of the KF7's managed to place second over all behind just one 22 hp 30 cubic inch Evinrude....... litterally ahead of hundreds of much more powerful Evinrudes. Kiekhaefer made sure everyone heard about this.

If you are interested, subscribe to this thread ... there will be a lot more to come!

[Raceman]

We're interested, bring it on.

Thanks for posting this kind of stuff. I think it's interesting even to people who weren't around to see that stuff then.

[Trikki1010]

Sam,

Love my ole KG7H and Mark series motors

Ya got our attention

[Tom Foley]

Sam thanks for starting this thread , I will try to dig up some pics of a 73 merc 200 (20) that I built an adapter plate for and mated to an older "A" quicky lower . Still have homemade pipes I made in metal shop . Doubtfull of any performance gains , but an attention getter , very loud! Please post some pics of the 20- H affectionately known as the "toilet bowl " with the big exhaust bulge on the side . Thanks , Tom .

[Mark75H]

Please post some pics of the 20- H affectionately known as the "toilet bowl " with the big exhaust bulge on the side

OK, I'll get there in a few posts. I think there will be a better appreciation of the toilet bowl if everyone knows the evolution from the fishing motors and why Kiekhaefer made it.

[Mark75H]

We have set the stage with OMC out of racing and a new generation looking at "stock" racing. Formal rules were written up and the future of outboard racing looked both bright and simple: motors were available and easy to make run well, boats were available, home buildable and easy to drive, unlike the full racing hydroplanes driven by the guys with alcohol fueled pre-war OMC's.

Into this jumped 2 spoilers; Champion and Martin, each with a special racing motor with a special racing lower unit. These motors were full racing motors produced in quantity to satisfy the new rules. Carl Kiekhaefer had not planned on building special racing motors in hopes that his fishing motors could continue to dominate, but felt that his fishing motors were at a disadvantage. Specifically the new Martin and Champion had smaller diameter lower units with high prop shaft speed gearing (which allowed the use of smaller diameter props).

[Mark75H]

Here is an image of a good looking Hi-Speed 60 in Peter Hunn's "Beautiful Outboards" book (from the Devereau Books website).

[Mark75H]

The Hi-Speed 60 might not look like much to us now, but to Carl Kiekhaefer in 1949, it looked like the beginning of a war. Kiekheafer retaliated with this:

[Mark75H]

Within a few years Mercury came out with line of complete racing motors covering the popular A, B and D 15, 20 and 40 cubic inch classes........leaving M and C to other makes.

The M class that the Hi-Speed 60 fit in faltered and faded; HS 60's never really raced against any Mercs. Aluminum shortages caused by the Korean War choked down production of all brands of outboards in the early 1950's. As the shortages and restrictions eased Champion evolved as the competitor to Merc on the race course.

[Trikki1010]

Keep it coming

My first REAL hydro had the Hurricane 10 w/ the racing lower KG7.

Still in my friends garage waiting to rebuild the lower I blew. Got a new case, just have to spend the time.

Never to be compared to todays "arsenal"....lol

Thanks Sam

Trikki

[Laker]

THis is the best!
The martin silver streak and Chris craft commander along with the KG7 were the engines I lost allot of sleep over when I was starting to collect outboards.
THanks Sam!!

[Mark75H]

In 1954 Merc replaced the KG series motors with the Mark series. The 20 cubic inch Merc became the Mark20H.

The 20H had a bunch of improvements over the KG7H:


new crankshaft with dual row needle bearing center main bearing
a bigger carb, a one inch venturi Carter N
bigger reed cage including bigger openings all around
tighter crankcase
higher compression
forged flywheel
Phelon magneto
remote fuel tank

These changes kept the 20H on par with the Champion 6MR



In 1956 Merc updated the 20H with the deeper skeg single water inlet lower unit they were making for the new for 1956 Mark30H.
The 20H also got deeper clamps so it could be jacked up higher on the transom.

[Mark75H]

One problem popped up:

The new Champion Hot Rod 6NR racer

The new Hot Rod could out pull the 20H out of the turns and keep its lead down the straights. At first the Merc engineers were puzzled because the 20H always pulled more power than the Hot Rod did on their powerhead dyno. The answer showed itself when they built a propshaft dyno ..... the original 20H mid section seriously hurt the 20H's top end power. They decided to try redesigning the 20H mid section. A lot of things were tried, but none worked very well. In the end the decision was made to build a completely new mid section incorporating a separate tuned megaphone for each cylinder.

[Mark75H]

The end result is here:

[Mark75H]

A sharp eye might notice that these motors have Tillotson KA style carbs and not the original Carter N style.

Along with the exhaust conversion kit there was a second conversion kit to retrofit the Tillotson KA7A that was supplied on the 1959 version of the Mark55H (the Mark55H-1) to the 1956 and earlier Mk20H's.

A third conversion kit (to take advantage of a feature found on Hot Rods) was a 16:21 gear set to replace the 1:1 gears all the 20H's came with from the factory. The 16:21 gears give a 30% reduction in prop speed allowing a larger diameter (and area) prop to be used. The larger diameter/area props gave the 20H's equal accelleration to the Hot Rods coming out of turns.

A fourth thing was allowed as well: the 55H-1's came with a new style piston. This "flat topped" deflector piston was allowed as a replacement in the 20H's.