New Inclined Briggs Motorbicycle concept

Discussion in 'Frame Mounted Engines' started by boogerballs, Sep 2, 2010.

  1. boogerballs

    boogerballs Member

    I've got a new idea for a motor bicycle. I want to take a small (2.5-3.5hp) Briggs and Stratton engine and mount it almost horizontal with the bottom of it mounted on the seat tube.

    I plan to have a belt drive with a belt-tensioning clutch. The engine will run to a jackshaft just behind the seat tube, then on to the sheave on the back wheel.

    I also plan to take off the air shrouding, trim down the fan blades on the flywheel, shorten the crankshaft at both ends, remove any excess aluminum air directional shrouds on the cylinder and reshape the cylinder as round as I can get it. This is to make it look less of a Briggs as possible.

    I took a look and as long as I keep the intake and exhaust to the top of the motor, I don't think I'll have a problem with excessive oil burn. Also, the little oil slinger will dip down into the new, tilted over bottom end and fling the oil just right. I'll probably have to drill and tap a new drain plug and filler plug and figure out some sort of dip stick to check the oil level.

    I'll have to use a small Tillotson type carb on a new intake manifold. I'm not sure quite yet what I want to do for the exhaust.

    I like the fact that this will get the bulk of the motor as far above the pedals yet still within the frame of the bike. I will use a Schwinn cruiser frame, there's more than enough room.

    So what to you guys think? I plan to get started soon.

    I'll try to upload an image of my plan soon.

    - boogerballs
    Last edited by a moderator: Dec 15, 2015

  2. Nuttsy

    Nuttsy Member

    If the only reason you're wanting to do this mounting method is pedal clearance, I get that. My concern would be the oil distribution. These are splash motors and in that orientation, I'd worry if that distribution was even and not starved on the upper (vertically speaking) side of the cyl. Then too the oil sump might not be 'ideal' in that attitude either. I'd compare it to trying to use a vertical shaft engine in a horizontal mount. Hope you've got it all figured.
    Plug fouling may be another problem.
    At any rate---good luck.
  3. boogerballs

    boogerballs Member

    I'll be doing everything I can to keep the lubrication as similar to a stock motor as possible and realize that this is not ideal for the motor. Also it's not just for pedal clearance but also for looks. A Briggs in it's normal stance looks like nothing else but a Briggs and Stratton. Since I'll be way over the 50cc limit here (illegal in my state), I want it to look like it's not a Briggs. As soon as I can I will try to get the engine running in this configuration and we'll see...
  4. Al.Fisherman

    Al.Fisherman Active Member

    If you rotate a B&S 4 stroke engine 90 degrees to it's intentional mounting, the engine will either burn up or throw oil all over the place. There is a oil sump and most rods have a splash tap on it.. Ummm need a customized intake manifold.
    Last edited: Sep 2, 2010
  5. boogerballs

    boogerballs Member

    I'm kinda hoping for the "throw oil all over the place" one. Since it's bottom edge will be mounted to the seat tube, the incline is not quite 90 degree, more like 75. And the customized intake manifold is already on the list.

    - boogerballs
  6. adb140275

    adb140275 Member

    its not gonna get enough lubrication to the top end.
  7. boogerballs

    boogerballs Member

    Why would you say that? It is still going to have the little oil slinger dip down into the oil sump and fling the oil around the crankcase, hitting the tappets and everything else exposed in the crankcase. Since that is the only oiling that happens (no oil pump) I don't see the real problem. The vertical shaft motor is already very similar.
  8. Wheres my dog

    Wheres my dog New Member

    Not a good idea cutting or trimming down the air shroud or blades....

    Can you say overheating?
  9. boogerballs

    boogerballs Member

    It's an aircooled motor mounted in a motorbike which won't be running in one spot for very long. The only reason that all those air shrouds were necessary is that the engine is normally revved to it's limits sitting in one spot or moving very slowly (lawnmower, pressure washer, rototiller). This application will be in a bike with airmoving all around it as it's merrily chugging along at 15-30mph. Cooled!
  10. Wheres my dog

    Wheres my dog New Member

    From all my experience....

    that airshroud and fan is there for a purpose just like on an air cooled vw!

    Not sure a passing by breeze is enough to keep it from overheating or seizing up!

    Just my two cents
  11. boogerballs

    boogerballs Member

    Do you have any experience removing the shrouds and eliminating the blades on the flywheel and running it on a motorbike? As a stationery motor?
  12. The Mechtician

    The Mechtician New Member

    I don't see a problem with tilting the engine, as long as the splash finger can still sling oil everything will be peachy. I'm guessing since you're removing the shroud and fan that you won't be retaining the governor, which means you'll have to find another way of limiting engine speed. Utility engines don't last long at high revs, especially the splash-lubed kind.

    As for removing or re-shaping the cooling fins on the cylinder, keep in mind that the more material you remove, the less dimensionally stable the cylinder will be. It'll still run and seem fine at first, but as soon as it heats up the cylinder will change shape, go out of round, burn more oil, lose some power and probably foul the plug. I would advise just turning off the top of the rough-cast aluminum fins (using a lathe) to square them off and make them look nice 'n shiny (see attached pic). Same goes for the cylinder head. If you don't have access to machine tools, take the parts down to your friendly neighborhood machine shop. I can't see it costing much more than about 50 bux.

    Keep us posted!

    Attached Files:

  13. boogerballs

    boogerballs Member

    The splash finger slings oil just great. I would have modified it so that it would but I didn't have to change it at all.
    Yes, no governor, but the way it is geared it probably revs to about 2500-3200 at around 30mph. That's as fast as I intend to go anyway.
    I made very minimal mods to the cooling fins mostly to expose the ones covered with castings and then to shape the square form to a more rounded shape. The head only got a couple of rounded corners, nothing too drastic.
    I'm attaching a few photos of my progress to date.


    Attached Files:

  14. The Mechtician

    The Mechtician New Member

    That is super cool! I've always had a soft spot for old school flathead industrial engines. I built a go-kart around a Honda 2.5hp pump motor that I dragged out of the dump when I was about 15, I'll never forget the horrible clattering exhaust note it had (the exhaust system was made from miscellaneous plumbing parts), it was music to my ears! Very nice installation, I'm glad it all worked out for you :D Those are some nice neat looking welds too btw, are they TIG welds?
  15. boogerballs

    boogerballs Member

    Yep, those are TIG welds. I've got a very experienced fabricator buddy who helps me with the welding and some fabrication ideas (pushes me in the right direction).
    Even though eventually this will have a clutch lever that will engage and disengage via belt tension, right now it is direct drive. Since it is belt drive, everthing happens kind of on a mellow basis as opposed to chain drive.
    This particular Briggs was one of the easiest starting motor I've ever seen. When it started up, with the gearing that it has, it just idled along at around 7-8mph with a wonderful pop-pop-pop exhaust note. On acceleration, it just sounds so great (music) since you never hear that minibike/centrifigal clutch revving, which is SO BRIGGS. The only time you hear it rev up and when it might possibly have that unmistakeable Briggs sound, you're moving along at around 30mph.
    I really like how this is turning out since I was getting very tired of that Chinese kit motor sound/vibration.
  16. The Mechtician

    The Mechtician New Member

    Awfully nice of your buddy to help you out with premium welding like that! I too have noticed that my chinese 66cc two smoke is really good at converting gasoline directly to noise, and the overall build quality never impressed me much to begin with. You've put a bug in my ear with your project! Keep up the good work! And buy your fabricator buddy a beer for me and tell him he does nice work :D
  17. professor

    professor Active Member

    Really nice job. And different too. How do you start it right now?
  18. boogerballs

    boogerballs Member

    The motor starts REAL EASY. I push start it since it is direct drive at this point. I will need to get longer belts or smaller pulleys moving forward to get the belt tensioning clutch working. In that case I will engage the belt tensioner and push start. Even with the gas turned off when I go to push the bike back to its home in the shed, it wants to start...
  19. SimpleSimon

    SimpleSimon Active Member

    If you incline the jug at 75 degrees, the flow of air between the fins is going to experience "stacking", which will reduce the flow rate sharply without the shrouds and the ventilation fan. Reduce the fin sizes, and you will be attempting to vent significantly increased amounts of heat per unit mass exposed to air flow, along with the reduced airflow. Most air cooled small engines are already engineered to minimize excess mass, so I would expect that the fin dimensions are already near their practical minimums as designed - designed to work with forced air cooling, at that.

    It may work, but I suspect you will burn the engine up quite quickly.