Briggs Slant-Single Rat

[boogerballs]

I’ve had a new idea for a motor bicycle. I wanted to take a small (2.5-3.5hp) Briggs and Stratton engine and mount it inclined. The bottom of the motor would mount on the seat tube.

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

In order for it NOT to look like a normal Briggs, I planned 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.

The intake and exhaust would be on top of the motor. Also, the little oil slinger will dip down into the new, tilted over bottom end and fling the oil just right. I figured I’d 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 use a small Tillotson carb on a new intake manifold. I wasn’t quite sure what I wanted to do for the exhaust.

Since I am using a Schwinn cruiser frame, there’s more than enough room.

So that was the plan.

- boogerballs

 

[Markm]

COOL!!!

 

[Beau]

Where does the oil pump go?

 

[boogerballs]

Oil pump? No it doesn't have one. The little splash finger on the connecting rod flings enough oil in the crankcase to lubricate everything.

- boogerballs

 

[murraymadman]

i would be surprised if the engine would survive this angle. :? when i was building the murray moto bike, i was going to run the briggs wmb at a slight angle and my buddy that has worked in small engines for 30plus years said no way. these motors have to run pretty much level. also, have you ever been mowing with your push mower on a steep incline and all the sudden it starts smoking from all of the oil going to the top end? not sure if that would happen here. would be great if the engine would function properly.

 

[Beau]

That's what I was thinking. The splasher only runs in a small section of the 'pan'.I wonder if it would slap the oil enough to make it splash up into the valves and cam shaft. I guess it never hurts to try. Parts are cheap.

I know vertical shaft motors don't do well when mounting them horizontal.

I do like the look of it at an angle though.

 

[boogerballs]

I guess I just like livin on the edge and testing out new ideas. I didn't really take that much material off the cooling fins. How long do you think it will last? The way that it is setup now, riding around town might get it to a max rev of 3200 rpm. At that engine speed, the engine is travelling through the air at around 30-35mph. At idle, it's going about 7-10mph. It's a little too hot to touch the motor after a 5 mile run at mostly 20-30mph but at idle it's just warm to the touch.

- boogerballs

 

[Beau]

Beautiful! :shock:

I would get a laser temp gauge. I believe the air provided by moving the bike is about the same or better than a fan would provide.

Awesome ride!

 

[MarksA-C]

I think that the angle is going to be too severe, but I've been proved wrong before.
Looks like a awesome bike!

 

[boogerballs]

The little splasher dips into the oil at its deepest part and flings it in the correct direction. I'm betting this engine lasts longer than most people think. I realize that not everyone agrees but I'm willing to take the risk. It is just such a sweet ride, it sounds cool, and it doesn't look at first glance like your typical Briggs installation. I'm happy.

- boogerballs

 

[K-dregg]

I think it looks really good! It looks a bit cleaner than the regular Briggs setups.. The way the exhaust flows with the carb and the general lines of the bike..
If it was my bike i would sand down the handlebars and fork to make it blend with the rest of the bike..

I know very little about these engines but i hope it keeps running!

 

[murraymadman]

:shock: that looks awesome!!! how many miles have you rode it? i would think that a 5mile or so ride would tell you if it is going to survive or not. really love your motormounts, super clean, and the intake is very nice. :wink:

 

[murraymadman]

how does your clutch set up work? close up pic?

 

[boogerballs]

Some of the parts on the bike are brand new and definitely need to have some treatment to make everything match. Whether that's paint or rust, I haven't decided yet.
I've ridden it about 15 miles so far, before the rain came. Next chance will be around Xmas. I'm already convinced that it will last...
The clutch set up will have a wheel mounted on bearings on an arm that will push on the rear belt just above the chainstay. There is already an arm there just hanging right now. I will either turn the wheel from wood or turn a skateboard wheel down. There will be a linkage that will go pretty much straight up from that arm to a bellcrank then forward to a lever on the side of the soon-to-be-built tank.

- boogerballs

 

[kcjim78]

Awesome build!! I think it will be just like a Timex, It’ll just keep on ticking! 8)

 

[Dowie Soetenga]

This is an awesome build. I had some of the same questions when building my flathead motor mounts. Can the motor be mounted on an angle? I opted not to be because I thought I would have problems with oil cooling, oil splashing differently, and or too much oil by the side valves. Looks awesome...and sounds like it's working great as well. GREAT BUILD!

 

[boogerballs]

Before I decided to do this I took the engine apart and saw what was going to happen. The splash finger hits the deepest part of the angled crankcase oil and it flings it up to the valve area. The oil drainage was modified for crankshaft lubrication and there is not enough oil to back up into the cylinder. I really don't know for sure how long it will last but I'm really not worried. We'll see. Now to finish the bike...

- boogerballs

 

[muddy]

Hows the Briggs going? I'm looking at doing the same thing, so your knowledge would be very useful. How did you modify the oil drainage?

 

[boogerballs]

I'm not riding it as much as I did when I first finished it. Probably becuase the winter rains in California were particularly frequent.
The little stock oil slinger was aimed just right to pick up oil from the angled sump. If you look at how the seals are lubricated for the camshaft and for the crank, you'll see that since they are lubricated by gravity fed oil, if you releive a bit of the metal at the top of each seal (once the engine is tilted) the lubrication will still work pretty good. It makes more sense when you look at it. I had to block off the normal filler neck and use the little drain plug for a filler since it is on top of the motor once tilted. I made a little dip stick for that hole so I could tell if it needed oil.
I had to make an intake manifold since the stock one wouldn't be at the correct angle. I used an old outboard motor carb and it seems to work pretty well. You just need to find something appropriate for the displacement from some other motor.
I've probably put about 300-350 miles on it and it runs very reliably. I would just make sure that it never overheated. I did releive a bunch of aluminum from the outside of the cycliner to expose as many fins as possible...
Good luck with your project. I'd like to hear how it goes.
Jeff

 

[cobrafreak]

Your engine angle is about identical to the normal running angle of a GX200 clone engine. As long as the oil dipper/slinger can submerge itself in the oil supply you are fine. I would be more worried about draining all the oil out during an oil change to rid the case of contaminants. Looks great.