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  1. #1
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    Merc Direct Charge

    I just ran into an ad for the new direct charge system on the mercs and the picture they show looks like all the fuel came out the hole in the side of the piston and then somehow gets to the combustion chamber. What is not at all clear is how the fuel gets to the combustion chamber once it leaves the hole in the piston and then how the exhaust gets out of the engine. The ad is dated 1969.
    Anyone ever mess with this system and can explain how it works.
    Again thanks in advance for any help.
    Last edited by ironlake2; 10-02-2009 at 04:27 PM.

  2. #2
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    Direct charge

    I thought direct charge was just a minor modification to a normal cross-flow design, but I may be mistaken.
    Markus' Performance Boating Links:
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  3. #3
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    That is a variation of the Direct Charge porting, in reality it was big marketing and small change

    The hole in the piston was called a "power port" and was actually a throw back design to the 1930's. OMC used it on some of their 1930's motors.

    If it was on this picture, it would just be an additional path of the blue arrows from inside the piston to the main line of blue arrows
    Attached Thumbnails Attached Thumbnails DIRECT_CHARGING_AD.e.jpg  

  4. #4
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    Direct Charging

    Yes, it is a variation of cross flow. The main intake ports were end milled rather than straight drilled, making for a bit larger intake area but still retaining a web in the center for piston ring support. The exhaust side is still drilled passages.
    The piston port consists of the hole in the piston, and an angled end milled slot in the cyliner liner that ends around the bottom of the intake ports mentioned above to add additional fuel/ air flow. You will see a nothch in the intake side of the piston on these engines to pick up that additional mixture.
    The high deflector piston channeled the fuel/air mixture up into the head that is basically contoured the same way, supposedly increases the turbulence and speed of the mixture for a more complete burn.
    Only thing I ever burned was the deflectors on the pistons - watch the timing and go big on the main jets!!
    There was a design that never got off the ground that used much lower exhaust ports, I think to retain the burn longer and not dump 30% of what you put in out the exhaust unburned. Dr. Blair from Belfast University gave us a talk one time 'way back in the day - I might even have the hand out material around yet on that one - will take a look.

  5. #5
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    Direct Charge

    The "Direct Charge" as Merc called it came out on the 1970 thru 1972 engines. The ported piston was added to the 1500 engines in 1973. The 4cyl
    800 engines used the same design piston baffle as the 6cyl.engines of the same years. The 4cyl. 850 engines added the ported pistons like the 1500.
    OMC was making a lot of noise about their "Loop-Charged" engine at
    about the same time as Merc started advertising the "Direct Charge" engines.
    Merc probably called it this as an advertising ploy against OMC. The Mercs
    were still cross-flow designs but with a new deflector design and milled instead of drilled ports.
    Run 'em rich on fuel, keep the RPMs up, burn good fuel & oil & watch your
    full-throttle timing.

  6. #6
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    The 800 was DC in '69. I always thought the '69 1250 was too, I could be wrong.
    http://books.google.com/books?id=wCk...age&q=&f=false
    Barry
    '06 Liberator Stealth, Merc 250XS
    '08 Checkmate Pulsare 2100 Long Deck, Merc 250XS
    '89 Viper (ordered from the factory), '73 Merc 1500SS
    '86 Lowe 14' aluminum 'dog swim platform', 9.8 Merc

  7. #7
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    Quote Originally Posted by bearclaw View Post
    The 800 was DC in '69. I always thought the '69 1250 was too, I could be wrong.
    http://books.google.com/books?id=wCk...age&q=&f=false

    I don't believe the 800 was Direct Charge in 1969 and the 1250 DEFINATELY WASN'T. The 1000 Super BP and 1250 Super BP were BOTH direct charge in '69, but to the best of my knowledge these were the only two DC powerheads prior to 1970.
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  8. #8
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    Quote Originally Posted by Raceman View Post
    I don't believe the 800 was Direct Charge in 1969 and the 1250 DEFINATELY WASN'T. The 1000 Super BP and 1250 Super BP were BOTH direct charge in '69, but to the best of my knowledge these were the only two DC powerheads prior to 1970.
    A page from the 1971 catalog (shown below) says "we put Direct Charge into our 80 hp two years ago".
    I distinctly remember this in the '69 model year, we didn't see at the time what made this so significant.

    If you look at the link in my post, It shows the article talking about the '69 800 with Direct Charge. I think it even said "DC" or "Direct Charge" on the lower cowl somewhere. Maybe I'll need to look for a picture...
    Attached Thumbnails Attached Thumbnails books_002.jpg   books3.jpg  
    Last edited by bearclaw; 10-10-2009 at 05:58 PM.
    Barry
    '06 Liberator Stealth, Merc 250XS
    '08 Checkmate Pulsare 2100 Long Deck, Merc 250XS
    '89 Viper (ordered from the factory), '73 Merc 1500SS
    '86 Lowe 14' aluminum 'dog swim platform', 9.8 Merc

  9. #9
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    Quote Originally Posted by Raceman View Post
    I don't believe the 800 was Direct Charge in 1969 and the 1250 DEFINATELY WASN'T. The 1000 Super BP and 1250 Super BP were BOTH direct charge in '69, but to the best of my knowledge these were the only two DC powerheads prior to 1970.
    Checked what piston used in the 1969 Merc800... guess what
    745-4879A2 this is the same piston as used in the later Merc1400, and now superceded to 774-9137A12 .

    Part # came from the Midas software...

    Got no problems with the rest of the Merc models in your post .

    Arne Kjetil
    My engines :
    Johnson V4m-10s 90 hp 1964,from the prosess.
    Mercury TII, next project
    True story ??:-)

  10. #10
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    There are a bunch of part numbers that will work fine in this motor and were super part numbers. The later pistons are all power ported even if the motor doesn't have the boost port. There are at least 3 different nominal diameter pistons that were used, 2 and 3 ring, high and low dome and I'm sure there were changes that generated a new part number that are less obvious.


    Quote Originally Posted by Droll View Post
    Checked what piston used in the 1969 Merc800... guess what
    745-4879A2 this is the same piston as used in the later Merc1400, and now superceded to 774-9137A12 .

    Part # came from the Midas software...

    Got no problems with the rest of the Merc models in your post .

    Arne Kjetil

  11. #11
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    Quote Originally Posted by Bruster View Post
    There are a bunch of part numbers that will work fine in this motor and were super part numbers.
    Point was the TYPE of piston , a crossflow piston would never be superceded to a direct charge piston...

    Quote Originally Posted by Raceman View Post
    I don't believe the 800 was Direct Charge in 1969
    The 1969 Merc 800 was a Direct Charge engine .


    Arne Kjetil
    My engines :
    Johnson V4m-10s 90 hp 1964,from the prosess.
    Mercury TII, next project
    True story ??:-)

  12. #12
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    Quote Originally Posted by Droll View Post
    The 1969 Merc 800 was a Direck Charge engine .

    Arne Kjetil
    That's just REALLY hard to believe. I can't figure the logic of WHY Merc would introduce a superior design in their lower end engine, leaving the 6 cyls in the old style when they had running racing versions of the 6 that were DC's. I'd like to see somebody post a picture of the starboard side of a '69 800 with the wraparound off.

    I'm gonna' pull my '69 Merc brochure first of the week and see if it makes any mention of it. (my old Merc buddy would know for sure, but he ain't answerin' the phone)
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  13. #13
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    Charlie Strang said Merc's development protocol was to develop on the 4 cylinder and expand to the 6's and twins as warranted

  14. #14
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    Quote Originally Posted by Raceman View Post
    That's just REALLY hard to believe. I can't figure the logic of WHY Merc would introduce a superior design in their lower end engine, leaving the 6 cyls in the old style when they had running racing versions of the 6 that were DC's.
    ...
    Nothing happens overnight. And they had every reason to do an 80. A slim, compact design that put out 80 hp. would look really good vs. OMC's barge motors of '68, and the Triumph of that era was only 55/60 hp. And the OMC's were notorious gas hogs. The market for a more efficient mid-range engine was huge.

    Ask your buddy.
    Barry
    '06 Liberator Stealth, Merc 250XS
    '08 Checkmate Pulsare 2100 Long Deck, Merc 250XS
    '89 Viper (ordered from the factory), '73 Merc 1500SS
    '86 Lowe 14' aluminum 'dog swim platform', 9.8 Merc

  15. #15
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    800 Merc pistons

    Bearclaw is correct on the 1969 800 pistons; the 800 with the direct-charge pistons did start at serial #2559001 for the 1969 year. The main point I was trying to make was that the 850 with ported pistons began in 1973 beginning with serial #3493913, the same year the 1500 came out.
    One thing to remember is the old Mercury parts books showed a lot of engines by serial number only. I have seen engines sold that had the current
    year on the bill of sale when they were actually produced to be sold as engines for the following year.

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