Marathon Jet Needs Engine?

Discussion in 'Jet Drives' started by Cody Symonds, Feb 2, 2024.

  1. Cody Symonds
    Joined: Feb 2024
    Posts: 4
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    Location: Claresholm, Alberta

    Cody Symonds New Member

    Hey guys I bought this Jet boat on a whim, it has a 309 American Turbine pump, and has headers for a 350.
    Bought the boat with no motor and no trailer. It’s a project boat would love suggestions on what motor to put in it.
    Boat is 19 feet long 84 inches wide. And it must have had two motors in it already.
     

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  2. Barry
    Joined: Mar 2002
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    Barry Senior Member

    I think that Marathon still builds in Edmonton.
    Otherwise try Outlaw in Red Deer.
    Otherwise, call Kem Equipment in Tualatin Oregon for a complete drop in motor. They marinize engines there.
    If it had a 350/5.7 engine in it, the impellor should be matched for that appropriate horsepower. Ie if you decide to go bigger hp, you will need a different impellor.
    The problem that I had with a 1979 21 foot Marathon BeaverJet, (460ci x 320 hp) was while the gunwales were 84, the chine was about 4 1/2 to 5 feet wide and with a full load,
    it was hard to get on step. Very narrow chine width.
    Very hard on fuel as back in the day, the impellor was an A cut.
    Also, Kem can sell you a plug and play instrument panel for their engines
     
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  3. C. Dog
    Joined: May 2022
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    Location: Coffs Harbour NSW Australia

    C. Dog Senior Member

    What's your budget and intended purpose? Are you able to afford a brand new dr0p-in or will it be 2nd hand?
     
  4. Tops
    Joined: Aug 2021
    Posts: 312
    Likes: 95, Points: 28
    Location: Minnesota

    Tops Senior Member

    Hi Cody,
    Do you have a(ny) picture(s) of the engine bay and jet pump?
     
  5. Cody Symonds
    Joined: Feb 2024
    Posts: 4
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    Location: Claresholm, Alberta

    Cody Symonds New Member

    And I have motor mounts, manifolds,
     

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  6. Barry
    Joined: Mar 2002
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    Barry Senior Member

    We have never installed an American turbine but I was under the impression that when Berkeley decided to get out of jets, that a group of ex Berkeley guys started AT and the pumps were close to the same.
    (though AT said that theirs was better)
    The only issue with the Berkeley or AT is that it takes a very small rock that can get into the grate to drop the thrust by half or more. Hence, most of the jet boat manufacturers use an easy clean intake and when
    rocks get lodged in the grate, you "stomped" on an assembly at the transom of the boat and every second grate would tilt down and hopefully drop rocks out


    I see that the pump impellor is marked AA. For the newer higher horsepower 5.7/350/5.4 you really should consider an impellor above the AA. if the Berkeley and AT designations are the same. American Turbine shows an Impellor to Horsepower chart that shows impellors above the AA. Best to give them a call before you decide on an engine.
    In addition you will need a flywheel adapter that bolts onto either the flywheel or Ring gear/flex plate and then a u-joint and spline assembly to bolt onto the adaptor.

    On the back of the bellhousing you will need a cone adaptor. This bolts to the bellhousing and reduces the larger size down to match the rubber ring that appears on the end of the pump. Maybe a ring that is 4 inches
    diameter, 3/16 inch thick. The cone clamps over top of the rubber bushing. Note, this gets the engine shaft and input shaft Co-axial. Ie the enter of each shaft intersects.
    But this does not mean Co-linear. Ie the axis are parallel. This is because the rubber bushing will allow a bit of angle to occure between the pump and engine

    When you are setting up the engine, you need to make a tool to ensure that the face of the bell housing is parallel to the perhaps the back end of the bowl on the pump.

    I cannot remember the length but this tool would be about 14 - 20 inches range.

    Take a 20 inch piece of 3/8 ready rod, and find a pipe that fits snug over the ready. put a nut on the ready rod and you can then lengthen the pipe ready rod outside length and merely move this tool between the
    two surfaces to ensure that they are parallel

    Summary
    1) Flywheel adaptor,
    2) Cone Adapter
    3) U joint with spline
    4) In essence an outside caliper

    I will see if I have any pictures of these

    When you get whatever engine that you have installed, fill it with fuel and a few buddies. Pull the engine cover. At the top of the pump is an inspection plate or a plate where you can remove
    with a couple of bolts to access the inlet side of the impellor. This allows you to clean our ski ropes, kelp, weeds and rocks that will not drop back out of the easy clean grate.
    If with your friends and gear you get water flooding into the boat from the inspection plate you will have to buy an extension that bolts to where the inspection plate mounted and provides maybe
    4 inches of additional height
    Try this in very shallow water in case you drop the inspection plate into the bilge and cannot stop water flowing through the inspection hole.
     
    Last edited: Feb 4, 2024
  7. Barry
    Joined: Mar 2002
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    Barry Senior Member

    bellhouseing adaptor.jpg Flywheel adaptor.jpg Short drive shaft.jpg IMG_3267.jpg

    Left to right
    Bellhousing adaptor, flywheel or flex plate adaptor, drive shaft and shopmade
    alignment tool, hand hole extension

    The alignment tool is made using a short piece of 1/2 inch pipe, weld on two 3/8 inch nuts, taper some ready rod
     

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  8. Cody Symonds
    Joined: Feb 2024
    Posts: 4
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    Location: Claresholm, Alberta

    Cody Symonds New Member

    Ok so I am trying gauge what motor is just right in this boat not a speedo not a dog just right Suggestion
     
  9. Barry
    Joined: Mar 2002
    Posts: 1,949
    Likes: 568, Points: 113, Legacy Rep: 158

    Barry Senior Member

    Attached is the AT horsepower to rpm curve for various types of impellors

    You need to know the condition of your impeller. Your cut is AA. If it is worn, it will act like an A or maybe even a B. Meaning the thrust for the rpm will diminish.
    If it is worn and you have to purchase a new impellor I would go with the 9.25 impellor which I am guessing is close to the same cut as the old Berekley A3 impellor. This is the impeller that
    gave us the best efficiency at our target 30 mph. With a fuel flow meter we would get almost 4 miles per Imperial Gallon. Medium load, 21 foot hull, 12 degree, chine width about 84 inches.
    Originally we used the 460 Ford or 454 GM which put out 320 Hp prox, naturally aspirated. The older 350's marinized put out 260 hp
    Then the EFI's came available and we could get the same hp out of the 350. Saved some weight.
    We used (I am pretty sure here) but cannot find a chart that says the Berkeley had an A3 impellor. I suspect this is the same impeller as a 9.25 or even a 9.5 but a call to AT would be worth it

    So if possible you would like to keep the engine rpm at around 3000 for normal cruise at 30 mph.

    So any engine that would put out between 300 - 320 hp would do the trick. The 5.3 litre from Kem seems more than adequate. Give them a call. See what they say.

    You can certainly find an older 350, but the cost to properly marinize and engine has quite a few hidden costs. Spark arrested starter motor, distributor and carb. Special marine fuel pump,
    water jacketed exhaust manifolds and risers. If you are running a jet in a sandy river you should go with a closed coolant system. Brass frost plugs? All these aftermarket can cost
    a mitt full of cash. All this stuff comes with a properly marinized engine. Additionally, many of the marinzed engines run roller rockers as well.
    If you go EFI, you need to specify that your engine has the fuel system that does not require an external fuel pump to get the fuel up the HP pump.

    Summary : Any engine producing 300 hp should be fine.
     

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  10. Cody Symonds
    Joined: Feb 2024
    Posts: 4
    Likes: 0, Points: 1
    Location: Claresholm, Alberta

    Cody Symonds New Member

    Thanks Barry
     
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