Dark Blocks

[BJuby]

So curious, what's the story behind these. Are they special? Rare? Or are they just a different color due to casting? Just got two Mark 55s and one is an early model and appears to be a dark block. Just want to know what the deal is with these.

Thanks

[Gene East]

I don't really know the answer, however I do know Mercury used different alloys at times with more zinc to reduce corrosion. That could be an answer.

I can tell you the high zinc alloys could be a bear to weld at times.

[Krazy Karl]

There was a pretty extensive thread about this on John's Old Mercury Site. I don't remember the answer but it did have something to do with the alloy used. You could do a search to find it. It was very interesting and a lot of history brought up by some of the very knowledgeable members. I also have a 55H that has a black block but I also had/have a couple of fishing motors with dark blocks. Not real unusual.
kk

[Aeroliner]

Started working on Mercury engines in 1955 and owned a Mercury dealership for 35 years. In the early years Mercury used a high zinc allow for what they thought was needed to provide the required strength. The high strength allow was utilized to control the engine weight. This high zinc alloy was very prone to corrosion as anyone that worked on Merc's used in salt water. Growing up on Long Island I can point to lots of issues taking things apart. A benz-o-matic was nearly always needed to get a lower unit apart. Over time it became an extreame issue with the engines, so Mercury changed the casting allow to somthing closer to a marine grade of aluminum. To also protect the engine Mercury introduced the trim tab made out of zinc and added berried zincs other places. This in combination with the use of stainless fasteners greatly reduced the corrosion on their engines. So if you have a dark freshwater block it will be great but one used in salt water could be an issue when you look under the rear water jacket cover. I have seen cylinder heads completly corroded through.

Alan

[matt1us]

Black block was a slang term we used for the fishing version of the Mark 55h................using the fishing version of the Mark 55 was approved and soon became the 'block' of choice. Even with lower ports the 'black blocks' quickly obsoleted the 55h. Our best engine was being used as a anchor at a New England marina when we found it. We paid $25 dollars for it and it went on to win several titles in the day!..........i still remember my dad pulling it out of 10 feet of water on the end of a chain! Geesh, the things we did back then to find that 'killer' motor.

[BJuby]

How could an engine without the altered porting of the 55H powerhead perform better than it? No porting was done to these blocks whatsoever? Or were different modifications made.

[John Schubert T*A*R*T]

How could an engine without the altered porting of the 55H powerhead perform better than it? No porting was done to these blocks whatsoever? Or were different modifications made.

LOwer ports, more acceleration. The top runners all wanted the "black blocks". Also true for 30 c.i. blocks

[matt1us]

It was factory porting.............the 55h was percision machined at the Mercury race shop and they cut in 'high ports' for racing application. The 'fishing' motors were low ports for i guess idling and had no real percision as they were just for mass production. Hence the hunt for that 'killer' block was on!! Clark Maloof was my friend and mentor in New England and he would set up one crankshaft and have several blocks bored by Bob Thornton (fishing black blocks) and then put the same crank and pistons in each of those blocks and test them. Clark and Thornton could tell from the color of the sparks on the grinder which blocks would be best!! Clarks best Mark 55 threw off 'white sparks' while being bored and was his 'killer' engine for years on his DSH and of course Racer Allens DSR.........

[Ron Hill]

I'm not sure I'm buying the different metal theory as to why they were black.

The Mark 30-H was the first four cylinder race motor Mercury made that had a black block. My dad was pretty much of a nut when it came to cylinders and measurements. All the 1955-56 red Mercury 30-H's that I ever saw had black blocks. I found a Mark 30 powerhead in a junk pile at a Mercury dealer's once, one head was cracked and the crank was rusty as hell. But my dad "Shoe Shined" the crank and Slim welded the block and I ran that motor at the 1963 Nationals in Boston, and it was close to a gray clor.. We called this motor "The Whistler" as when it wound up getting on plane it "Whistled"...Ted Zohrski later told me my needles were skidding. Later, we had a Wizard block out of Nebraska we called "The Wizard" and it was close to aluminum color...Then we had the Nebraska Block that was also bleached out ... My three best C Motors in 1977, were a Wizard block, a Nebraska fishing block and a Black block. All three cc'd the same at had identical port measurements...plus or minus .002.

Because there was an anodizing shop was across the street from the Mercury Distributor...in Santa Ana, my dad talked to them about the "Black" blocks and he was told it was "HARD" anodizing. (Because all the port on the "H" blocks were black which: A. Led him to believe they were anodized after porting. B. When he ground on the black part, the aluminum was aluminum color. C. He figured someone would try and "port' there block and get it re anodized and he wanted to know how anodizing worked.

Fast forward to 1967, when a guy named Selfies buiilt a D Hydro but could not find a 55-H block, so everyone just told him go ahead and run a fishing block, but it will be slower than the "H" block. Well, about half way through the season, he started winning every race. Anyone at the 1967 Essex, Maryland Natioanls may have remembered about 9 restarts in DSH. Randy had been told his "Fishing" block would not pass inspection. This was a black block. He jumped the gun all nine times, but no one passed him!

Fishing blocks didn't get legalized in D Stock til after the 1972 Nationals, I think. It was around this time I got Gary Garbrecht to build some "D" gear cases, mid sections and .030 over A and C piston, and "D" pistons. Also, Gary built the 402 XS becasue of me, I bought 001 402 XS and picked it up at the factory.

Roy Miner told me the "GREEN" 55 block was the good block, so I bought two green blocks from Mark 55 fishing motors. One was "JUNK" . So, by the fall of 1974 at BAKERSFILED, I was testing my DSH May Craft with with my National Championship D Runabout , Mark 55 H block (black block) motor. It would run 74 MPH as i entered the turn, exited the turn at under 55 MPH on my Keller. But my Green block on and it went 75 MPH, same prop, but exited the turn at about 57 on the Keller and gaining speed fast.

At the Divisionals, May 1975, Jimmy Dawe had a black block 55 he'd bought from New York. When Jimmy pulled a port cover there were two colors (back and white aren't colors) black and white aluminum where the block had been machined. I'd say everyone on the beach said, "That motor has been "ported', so, my dad being the inspector made Jimmy pull the crank. My dad measured it on a pick nick table right out in the open in Indio. My dad said, "The block measures like stock blocks do. It is 100% legal." None of us had ever seen anything but "Black" ports and here was a black block with nice clean "WHITE" aluminum ports.

Well, the 1975 Dayton Nationals, I ran poorly with my green black motor and Ernie won with this New York black block. For 1976, I had my Dayton problems behind me and went to West Virginia planning on winning D Runabout. Well, I got a POOR 3rd, Racer Allen ran all of our asses off, he made it look easy. I watched D Hydro and Jack Neeley beat Clark on what I thought was a brain FART on Clark's part, but I decided right there to buy a Bezoats like Glasses had.

Clark and I went back pretty far....So, we were talking after D Hydro, he was in great spirits for just losing the Nationals, I on the other hand was in a "**** MOOD" for finishing a poor third. Clark said, "This motor is a 'PISSER', it is so fast. You've got to get a black block like this with the 89 serial number..."

So, that Christmas vacation, 1976, I headed out to find some black blocks. My first stop was at Apple Valley Marine. Dan Schwarzenbach had several 55 blocks and one 89 serial block. When I saw the heads in the 89 block it looked like a QUINCY. BUT THIS BLOCK WAS SALTED UP BEYOND REPAIR. From Apple Valley we went to Parker where I found one black black with 89 serial numbers. After going to Yuma, Blythe, Lake Mojave, and Lake Mead, I came home with five fresh water 89 serial number black blocks. (All in the truck of my wife's Monte Carlo).

As my dad looked at the five blocks, and we looked at the new 402 XS gearcase, we decide we could gain some sped for the 1977 Nationals. My goal with my new Bezoat, was to win SD Runabout and D Hydro Nationals with two different motors. We did discover that the 89 serial numbers had many more water out let holes than any four cylinder 55 block we'd ever seen.

Bunker Hill and I tested at San Diego, also ever other weekend all that spring, Bunker was just learning to drive an A Runabout. I was feeling pretty good as I'd picked up from 65 MPH in 1976, to 72 MPH and 1977. I knew Racer Allen was much fast than I was in West Virginia, but I was sure he wasn't seven MPH faster. My new BeZoat would run 76 MPH.

When we got to Bakerfield that August, 1977, my D Runabout tested at 70-71 on the course and my D Hydro tested with the same motor at 72 MPH. One of my motors had a high speed flutter, so I ran only one motor. But I qualified number one in D Runabout and D Hydro. I won D Runabout without falling out of the boat and I finshed second in D Hydro after falling out of the boat. A 1-2 in the D Classes wasn't too bad...That was third time I'd finished second in DSH to Clark Malloof.

Talking to Charlie one day, I asked, "Why were the 55E Higher compression and why did they have some many water holes?" Well, Carl felt, if you paid $24 for an electric starter, you shouldn't go slower than your neighbor, becasue you'd be carrying a battery. So, Carl wanted they guy who spent a few bucks more for an electric start motor to go faster. Now, the water deal, kept the engine cool or in fact cold. So cold then electriic start motor didn't idle for prunes. So, after the 89 series, the "HEATED" THE MOTORS UP.

AS FAR AS BLACK BLOCKS SPARKING WHE BEING BORED, when the boring bar came to the end of the sleeve and hit the hard anodized aluminum, it could spark.....also, you should stop the boring bar once you get to the end of the sleeve.

Mark 75 H stole my thunder, but the black block was hard anodized....and as far as higher compression motors, they all fit within the spec sheets. IF there were higher compression Mark 30's, they probably de tuned them becasue they blew gear cases like popcorn.

Finished

[Mark75H]

I have a block block 55H block. Charlie Strang says the black block experiment was just an anodization test to see if it would yield a stiffer block. No difference was detected, so they dropped it. The short run started all these wild rumors. There are no high compression 55's ... earliest 30's had higher compression, but people complained so it was reduced.

Doubters should contact Mr Strang

25E's DO have higher compression.