Thread: Mercury Mark 40-H

  1. #1511
    Team Member R Austin's Avatar
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    So, if I understand correctly, I am half correct in that the 30H ran the same gear case as the A/B motors. Which would make the crank spline for the small drive shaft.
    If the engine I have, had been a 30H modified and they later decided to run the large foot, they had to modify the drive shaft or replace the crank.
    Modifing the shaft was probaby the first choice as the crank is padded and chamfered. They did not to go that path.
    Thanks, learn somthing new everday.

  2. #1512
    BoatRacingFacts VIP Aeroliner's Avatar
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    Hi,
    Although the case is the same the drive shafts are different in the A/B unit and the C unit. The A/B has a smaller 6 spline shaft and the C has a larger diameter and 10 splines on it. Although the C shaft and D shaft look similar the D is larger. The C and D crankshaft have different splines and the foot is not interchangeable. A D crankshaft could be installed in a C block and the a D foot could be used.

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    Administrator Ron Hill's Avatar
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    Default Long Skegs as We Called Them

    Quote Originally Posted by Aeroliner View Post
    Hi,
    Although the case is the same the drive shafts are different in the A/B unit and the C unit. The A/B has a smaller 6 spline shaft and the C has a larger diameter and 10 splines on it. Although the C shaft and D shaft look similar the D is larger. The C and D crankshaft have different splines and the foot is not interchangeable. A D crankshaft could be installed in a C block and the a D foot could be used.
    Seems to me, that the long skeg 20-H gearcase housing, to use it on a 30-H needed a larger needle bearing on the drivshaft.
    Last edited by Ron Hill; 12-18-2018 at 05:00 PM.

  4. #1514
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    The 30-H case became the 20-H replacement case after mercury ran out of the short castings. APBA published info on How to cut the Skeg to meet KG-4 requirements. Later Mercury made a shot case with the single water hole when they built the 25SS engines. Somewhere along the line Mercury lost the dies for the C and D cases so when the 10XS, 25XS and 44XS came out they had to go with a lost foam process for them. Also the skeg was swept back but the internals more or less were the same. Drive shaft lengths got shorter though.

  5. #1515
    Team Member MTECHMARINE's Avatar
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    Heres a powerhead service stand for the 2 shaft sizes - I believe that the Mark 30 was unique to that model alone. Ron - wasn't the difference in the driveshaft the top ball bearing rather than the needle by the pinion?

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  6. #1516
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    Correct. They went to a metric ball bearing. Different thickness also

  7. #1517
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    Default Mercury 40 cubic inch pistons

    I have been working with Wiseco on a Mercury 40 cubic inch piston. I am paying for new dies and will have them in Standard, plus .020 and .040 inches oversize. My initial run will be for 50 pistons. Next run I can add .015" and .030" oversize as well if folks want them. They will be to the latest Wiseco design, improved two ring configuration and there normal coatings. I am hoping that we can sell them for $130 with rings, pins and clips. Deposit has been sent so I expect to have them in hand in 6 to 8 weeks. Let me know if you would like some in that the first run will be 50 pistons or so. Pistons are impossible to find for the D Merc so I am hoping this will help with keeping the engine in service.

    Alan

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    Quote Originally Posted by Aeroliner View Post
    I have been working with Wiseco on a Mercury 40 cubic inch piston. I am paying for new dies and will have them in Standard, plus .020 and .040 inches oversize. -Alan
    Guys, this is a BIG DEAL!! I know several others have taken small bites of this project in the past, but van Weele's are really going to save alot of old Mercury engines with this investment! Lots of old racing engines and fishing engines, too, can be put back into service with these pistons!
    Thanks!

  9. #1519
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    20, 40, 60 cubic inch pistons are moving forward. The forging die has been paid for and now being manufactured. Expect it to be completed in 4 weeks. Next week Wiseco will assign the part numbers for the design and I will give them a deposit for the first run. With luck we should see pistons by mid summer. I had a special size 44 piston made to save a block. For special orders You have to order 12 pistons so we have a lot of options available now.

  10. #1520
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    Default Yamato 250 powerheads

    I have found a couple Yamato 250 powerheads that appear to be complete and in good condition. They roll over and are not stuck. Like to get an idea of the value of these. I would like to keep one for my collection and sell the other. Anyone with info I would like your comments.

    Alan
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