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Thread: Announcing the Merc 888

  1. #31
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    Default Rod design

    Quote Originally Posted by R Austin View Post
    That's the setup on the rod. Obviously with a little more pin and a bearing in the rod link.

    The beast is just the standard ADI ignition with the primary coil feed connecting 2 standard coils in series. Not sure yet if that may be the problem with the ignition/fuel issue. I do not think it is but will not know for sure until I get it on the dyno.
    The standard Mercury rod throws offer precious little room for a master/link or blade/fork con rod setup. Top guided .450" thick rods fit between .535" counter-weight cheeks. It's attractive to use a larger pivot pin for the master/link, and it allows retention of crank pin needle bearings, but precious width must be consumed by some form of pin retention (possibly C- or E-rings).

    Because of the space limitation, I'm leaning toward separate .250" thick "knife blade" rods, eliminating the bearings in favor of more beef, even though offset loading will induce bending stress.

    All said, rod design is not yet determined. A few prototype designs will be built over the weekend.

    Thanks for your thoughts on the ignition as well. Good luck sorting out the Looper Beast!

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    Team Member daveswaves's Avatar
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    Dick, you may be better off firing the two coils in parallell rather than in series. The scr in the switch box is more than capable of providing current to the new lower resistance. Both in series is limiting your current flow to 1/2 of what the coil normally sees, that means smaller magnetic field and much smaller spark. Just a thought. Tim, the GM hei modules will work well, they use an inductive type trigger using reluctance. Assign some numbers to the main and secondary bank so we can think about firing order on both sides. Waste spark is one way to go, 4 coils sparking every 180 degrees. You could use a merc 4 cyl trigger and related linkage to fire the GM HEI module, just have to figure out how to sequence the modules. Normally the rotor looks after that for you. A standard GM 8 cyl hei with coil in cap would do everything for you, Good up to 10000 rpm, nicely matched. All you would have to do is adapt a merc pulley to the end of the distributor where the oil pump drive is, not too hard. The vehicle ones have a fairly chunky cap, Malory makes a narrower version that is pretty slick. I am willing to expand further as questions arise.

  3. #33
    Team Member R Austin's Avatar
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    Quote Originally Posted by daveswaves View Post
    Dick, you may be better off firing the two coils in parallell rather than in series. The scr in the switch box is more than capable of providing current to the new lower resistance. Both in series is limiting your current flow to 1/2 of what the coil normally sees, that means smaller magnetic field and much smaller spark. Just a thought. Tim, the GM hei modules will work well, they use an inductive type trigger using reluctance. Assign some numbers to the main and secondary bank so we can think about firing order on both sides. Waste spark is one way to go, 4 coils sparking every 180 degrees. You could use a merc 4 cyl trigger and related linkage to fire the GM HEI module, just have to figure out how to sequence the modules. Normally the rotor looks after that for you. A standard GM 8 cyl hei with coil in cap would do everything for you, Good up to 10000 rpm, nicely matched. All you would have to do is adapt a merc pulley to the end of the distributor where the oil pump drive is, not too hard. The vehicle ones have a fairly chunky cap, Malory makes a narrower version that is pretty slick. I am willing to expand further as questions arise.
    Dave you may be right. That has been my concern since the first test run as it acted like an ignition problem, fouled plugs or way to rich. The testing on the ignition indicated that in parallel that only the plug, coil, or condition with less resistance would fire. Could then the lower voltage from the coil in series be cured with conventional and smaller gaps be a solution.

    Tim
    Do you have a new email address. If yes email me so I can return on your email.

    Thanks.

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    Team Member daveswaves's Avatar
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    Quote Originally Posted by R Austin View Post
    Dave you may be right. That has been my concern since the first test run as it acted like an ignition problem, fouled plugs or way to rich. The testing on the ignition indicated that in parallel that only the plug, coil, or condition with less resistance would fire. Could then the lower voltage from the coil in series be cured with conventional and smaller gaps be a solution.



    Thanks.
    In theory, all of the coil(s) primaries should be the same resistance so should not favor one over the other, poor connections may be a problem. Agreed if the secondary resistances are different due to condition then you might loose a spark, smaller gaps might sort it out. Cant remember which coils you used on the looper beast. If was the stock merc coils with rubber jacket there are two things that could be messing you up. The ceramic core shoe tends to crack, causing weak spark, also, the other end of the coil wire is simply squished by the rubber to make contact with the mounting plate. Poor contact is the death of high voltage systems.

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    Quote Originally Posted by daveswaves View Post
    Dick, you may be better off firing the two coils in parallell rather than in series. The scr in the switch box is more than capable of providing current to the new lower resistance. Both in series is limiting your current flow to 1/2 of what the coil normally sees, that means smaller magnetic field and much smaller spark. Just a thought. Tim, the GM hei modules will work well, they use an inductive type trigger using reluctance. Assign some numbers to the main and secondary bank so we can think about firing order on both sides. Waste spark is one way to go, 4 coils sparking every 180 degrees. You could use a merc 4 cyl trigger and related linkage to fire the GM HEI module, just have to figure out how to sequence the modules. Normally the rotor looks after that for you. A standard GM 8 cyl hei with coil in cap would do everything for you, Good up to 10000 rpm, nicely matched. All you would have to do is adapt a merc pulley to the end of the distributor where the oil pump drive is, not too hard. The vehicle ones have a fairly chunky cap, Malory makes a narrower version that is pretty slick. I am willing to expand further as questions arise.
    Thanks Dave; here we go:

    The front bank is numbers 1-2-3-4, and the rear bank is 5-6-7-8 from top to bottom, respectively. The Mercury firing order is 1-3-2-4 (alternating pairs spaced 90 degrees apart). So, cylinders 1 and 6 fire, then 3 and 8, then 2 and 5, and finally 4 and 7.

    The issues are the same as Dick's Looper Beast. The need to fire two plugs, full power, simultaneously. http://www.superchevy.com/how-to/456...itions-basics/ explains where the twin (Siamese) coils designed for wasted spark systems fire one plug positive to negative and consumes 85% of the energy, while the wasted spark plug fires negative to positive and gets only 15% available energy, but fires fires only in a rarified atmosphere (not firing under compression). This solidifies the argument for twin indendent ignition systems. Your thoughts?

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    Something else to think about, coils have polarity, when you put them in series you should do it like batteries, +-+- etc/ If you are putting them in parallel then both positives should be joined and both negatives should be joined. If you mix up the polarity the coils will fight each other.

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    Nice project Tim,
    Well getting fuel and lube around might be a bit of an issue. One thing you might consider is to make a regular dry sump lube system with an oil pump. Reed block could stay in without the reeds and stops. The center main bearing carrier could be machined to allow the oil to drain down where it cam be pumped our. Exterior oil line to spray nozzle's should due the trick to keep the rotating system and the back side of the piston lubricated. For starting you can install a primer system to spray fuel into the intakes. With an electric pump this would be easy. This assumes that the carb will be in a pressure box.

    Good luck,
    Alan

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    Team Member GHMiller's Avatar
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    Tim, check out Electromotive Ignitions. I run a V8 HPV-1 model on my mod 44 merc and I ground one post on each of the four coils for my four cylinder set up. But for your eight cylinder setup it might just work. I power it with a 5ah trailer breakaway battery all weekend on one charge. (14vdc).
    Gardner Miller
    Lone Star Outboard Racing Association

    "Water is for racing. Asphalt is for the parking lot."
    Remember....Freedom isn't...."Free".......

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    Here is a feasible suggestion for rod design.....

    Just machine a gully through one rod end. Then narrow down the other rod end to fit and ride in between the other rod's gully or valley, whatever to call it. This way you will have complete circle end rods. You could also machine the space between the crank arms to make the crank pin longer to use two narrowed rods side by side. You will have to fill in and re-thread the rod bolt holes for something smaller and placed differently. It could work for a low output or medium performance set up.

  10. #40
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    ..."(On the EMD railroad locomptive engines) Now those are some BIG engines! Were they two strokes like the Detroit? "

    Yes, but they use a 4 poppet valve head with OHV for the exhaust. Make roughy 4,000 hp. at 900 rpm.


    Aircraft engines (like the Rolls Royce Merlin V-12) used the blade and fork design rods successfully (obviously!) They had the room for it on the journal, however. Gonna be a tough deal to make work reliably.

    Jeff
    "We live at the bottom of an ocean of air." - General Marvage Slatington

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