Finish on 20H Conversion LU

[Mark75H]

Lower units were short skeg unless you ordered a replacement housing in the basic C configuration with the long skeg.

Alan do you have some documentation of this or just hearsay? I did some research a few years back and determined that most of the last 1,000 serial numbered 20H's have a long skeg; only a few of the first 3,000 have the long skeg ... this appeared to be a pretty consistent pattern. The sense I get is that they ran out of short skegs at the same time they were making 30H lowers and switched production over to the short skeg rather than making more short skegs just for the 20's in 1956.

It is true that after 1956 any replacement 20H housings were long skeg.

Somewhere buried in the Merc service bulletins and APBA Propellor magazines there has to be documentation one way or the other of the change over date where you were allowed to retrofit the long skeg housing onto any 20H. That kind of stuff was and still is very strict in APBA.

[Aeroliner]

Hi Roger,
I bought a new 20-H in October 1955 and it still had the short foot. I bought two complete lower units for my B's in 1960 which were long skeg with 16:21 gears and came with instructions on how to cut them to the short skeg. If I remember correctly some time in 1956 they started using the long skeg. The three production years for 20-H were 1954, 1955 and 1956. The last 20-H's had a tower housing that looked like the 30-H with the single exhaust spout, very much like the 25SS unit. My old Mercury data shows that in the June 1957 the revision of the parts catalogue has both of the items shown. Hopes this helps a little Roger.

Alan

[Aeroliner]

Roger,
Here are a few units that are freshly refurbished. Note the black short skeg unit which is reshaped per the Mercury instructions. This allowed it to be used in class A with 1:1 gears. See the unit in the top row second from right which is a cut unit.
Alan

[A/B Speedliner]

While going thru our pile of rubble I found an original white fuel line still connected to the pump and the connector. The pump had all of the original fittings. I installed these parts on the 20H conversion so now the only thing missing is the white fuel hose the runs from the pump to the carb.

I am working on another conversion 20H that I hope to sell to help finance our other projects.

David

[Aeroliner]

David and I went to a garage sale this weekend and found an original cloud white conversion tower never used. We also got a few other things shown on the rack. Now we have a photo of what Mercury painted their last conversions. All early were as cast and late were white. Sam hope you like the photo.

Alan

[RogerH]

Damn!

You guys have all the luck AND great garage sales!! My wife doesn't come home with stuff like that!
Roger

[Aeroliner]

Roger,
A little training for your wife might help you with parts. Have to tell you though that if David's and my wife understood what we are doing we would be out of luck.

Alan

[Aeroliner]

Roger,
In the pile of things there was a brand new 20-H block and crankcase.

Alan

[X-racer]

Maybe we are getting a little confused... The "gold" painted lowerunits that we are now used to seeing on the MK20H engines are supposed to look like someone had an original (green & gold) MK20H engine and then, when the conversion kit came out, they converted it. That is where you get the gold painted powerhead, clamp brackets and lowerunit.
Another thing- the early lowerunit housings were sandcast and were finished in a polished appearance. These were on all the Q engines and had the bronze bushing tail cone. The later diecast units appeared to be natural diecast finish. They all had to meet the minimum dimensions at inspection. If yours was slightly undersized- you would paint it to make it pass! Over the years some of these lowerunits were painted many times and stripped almost as many times.
When I got my first MK20H, it was against my fathers wishes! He hated the sound of them and if I was going to get one to run on my AU, then I would have to buy it myself! I got the conversion parts from Buddy Tomlinson and actually ran one of my 1:1 A lowerunits until I could afford the gears....

As I recall, the MK-20H came out around the mid 50's (1954 if I'm not mistaken). My father was a Merc dealer at the time and I remember the lower units were painted gold like the rest of the motor and were definitely diecast with needle bearing tail cones. I think the "natural" die/sand cast lower units utilizing solid bronze bushings in the tail cones were used prior to 20H production possibly on the KG-4H or the KG-7H.

[Aeroliner]

Having bought a new 20-H in 1955 and still owning it I can tell you that the lower unit was gold and sand cast with the small holes for the water intake. Also having a KG-4H I know that the original engines had painted tower housings and lower units. I still have a brand new KG Q tower housing never used and it is painted silver as was the foot. The 20-H was the first engine to use the needle bearing in the tail cone while the older units had the solid cone with the brass bushings. When the short skeg became NLA the C foot was allowed for the B and C application. These were die cast with the single large water intake hole. It was permissable to cut the skeg to the short style and use it in class A. Today almost everyone polishes the lower unit. When I bought the B deep foot complete it always came black and when I bought cases sometimes they were in primer and other times in black.

Currently were are making a number of parts for the racing lower units. Look at our website aeroliner-boats.com.

Alan