Need trans for small diesel

Discussion in 'Diesel Engines' started by PAR, Nov 3, 2013.

  1. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I've found a used 5 HP, air cooled, electric start diesel with a 1" shaft. With some modifications, I'm fairly sure I can get 8 HP out of this puppy, with a new bore and typical hot rod tricks and it would be a great little engine in my 23' sailor.

    Now the butt kicker, a transmission for such a little engine. There are plenty of choices for bigger engines, but this thing is tiny. Any sources for a little FNR tranny. Anyone built the Glen-L home made tranny and do you think this will handle the torque of this little one lunger? It looks like an older Kohler and the reason I like it is it has a oil pump and pressurized lubrication, plus features seen on bigger engines.

    Don't say hijack a garden tractor trans, because they don't hold up and are usually easily broken. I'm at a lose, except for rigging up some belts on a rudimentary home made thing with pillow blocks, an idler and some wheels.
  2. Stumble
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    Stumble Senior Member

    What about a snowblower tranny? They run about 5hp, and deal with a lot of torqu I think.
  3. rasorinc
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    rasorinc Senior Member

    Would a Go/cart type tranny work out?
  4. PAR
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    PAR Yacht Designer/Builder

    Again most of these (snow blower, garden tractor, etc.) are wimpy belt or chain driven or worse pot metal and nylon gear units. Some are hydraulic pieces, though there's a good bit of lose with these. Most snow blowers are pretty simple, just an impeller really. The two stage, self propelled units usually have much bigger engines, than what I need.


    This is typical and I can make something like this that will be stouter, but I'd like to avoid that.


    A typical cheap (MTD) transmission, unfortunately, 90 degree direction change. I guess I could mount the engine transversely. This one is a 12 HP unit. It would need to be mounted rotated on it's side, which might cause thrust bearing and oiling issues too. In fact I've never seen a straight through garden tractor or snow blower tranny. I doubt these would last long in a boat, being asked to tolerate 80%+ output most of the time.

    Go carts usually are only forward and neural. Some of these look stout, with a few forward gears, which I don't need, but reverse is hard to find. These are all chain drive from the engine too.

    I have found this:


    and it has FNR, for about is $300 bucks. It's all steel and cast aluminum. It'll work, but for how long and it uses a $200 torque converter, though I could rig a dog clutch I'd think.
  5. rasorinc
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    rasorinc Senior Member

    Par, we have an old Sears mower we use to hall a trailer around the property ropeing and dragging logs around and just beating the hell out of this mower the last 3 years. No problems with the 5 speed tranny on the B and S engine
  6. michael pierzga
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    michael pierzga Senior Member

  7. BMcF
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    BMcF Senior Member

    We've had good luck using tooth-belts fro the "reduction gear" in many of our "small scale" projects, and have also had good luck with the 12V-operated lawn-mower drive clutches. Compact and designed to handle upwards of 35HP in some cases, they are pretty easy to mount on small engines because, of course, that's what they are designed for.

    For example, we mounted one of the electric clutches on an 18 HP Honda V-twin and then used tooth belts to drive two small waterjets.

    But you probably don't want something that requires the continuous 12V to operate.....

    Attached Files:

  8. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I've made a couple of transmission before and it's not a difficult proposition, but they where always plagued with issues, noise, heat, low hours before replacement parts were necessary. I have a relatively heavy small engine, considering it's output (nearly 80 pounds). A small light transmission would be idea, but only one that can tolerate continuous, hard use, which a boat trans must endure. Most garden tractor transmissions are lightly built and though they can tolerate dragging a mower deck and the wed fed operator around at 3,200 - 3,500 RPM, under relatively modest load, once you load one of these up with a prop, running at 80% of engine capacity, they don't last long.

    I know Glen-L sells plans for a home made FNR tranny, has anyone actually built one and did it survive? I have a dog clutch left over from the last rig I made, but not much else, though I have a stock of pillows I can use, I sure would like to find a unit similar to the Comet setup, but with a clutch or one that could take the dog clutch without tearing it apart, the first time I bang reverse at full speed.

    In other words, I've had no problem finding the weaknesses of garden tractor and home made trannies, within short order.
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    FAST FRED Senior Member

    No need for anything but a reduction gear , at idle the thrust will be so low the boat can be hand held .

    A set of sprockets and chain would allow a thrust bearing to take the push underway , maybe 100lbs if everything is perfect .

    Cheap and easy., and fine for hours on end of motoring.
  10. Landlubber
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    Landlubber Senior Member

    Can you just use a dog or cone clutch, we have and old engine here called a Blaxland (Blaxland Chapman Marine), I have a brand new one in my workshop that would be 50 years old if you wish to use it.
    Scroll down in this link to see the exact same clutch on the SXT Pup model for sale.
  11. pdwiley
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    pdwiley Senior Member

    Got the perfect g/box for you. Only 2 problems.

    First, it's sitting on the end of a Yanmar air cooled diesel already. The package was designed as an air cooled marine power plant.

    Second, it's in my workshop half a world away.

    I bought it thinking I might use it someday. 10 years later, I still have it (and 3 other marine diesels and a spare h/duty transmission - just in case).

  12. parkland
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    parkland Senior Member

  13. gonzo
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    gonzo Senior Member

    Does it need reduction or are you running it direct?
  14. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I think I've found one and yes I want reduction (1.5:1 - 2:1), which most of those listed offer, though I've seen very few with neutral and reverse.

  15. rxcomposite
    Joined: Jan 2005
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    rxcomposite Senior Member

    Have you tried Hurth/ZF marine gear? We used to get the small transmission from them for our small 8 to 20 single piston gas engine. It is more expensive than the gas engine we use though.

    Try searching also for small China made transmission. I have seen some in the small 12 to 20 Hp. range.
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