3 HP Briggs/Cranbrook Build

tnjeff

tnjeff

New Member
Finally going to attempt to build a bike (my first) with a 3 hp Briggs that used to power a go kart. I like the old bike look, so an American flathead just seems right. I know I'm going to learn alot on this one, so I'm approaching it as if it's a prototype, with the lessons learned to be applied on the second bike.

Cannonball's build (https://motorbicycling.com/threads/cannonball-builds-a-briggs-and-scrap-iron.60752/) really inspired me. My bike will not be street ridden, mainly used as a really cool pit bike. I had always thought the bottom bracket was a natural place to put the jackshaft, but really had no idea how to accomplish it. Thanks Cannonball! I also like the angle iron mount. Easy, and perfect for a prototype.

I'm going to try either a pz-19 carb or an nt carb on the motor. Need to figure out a manifold. The one thing that's on my mind now is whether I should remove the two stays under the main tube. It's a tight fit. I
could possibly angle the motor forward more, but would I run into oiling problems?
Here's a pic with the motor just sitting in the frame:

briggs.jpg


I guess it could be tilted forward more. What do you think? Tilt it forward or remove the stays?

As far as the angle iron mounts, it appears that on Cannonball's build holes were drilled in the frame tube and the mounts were bolted on. I plan to do that but, it seems like vibration might enlarge the holes over time. Or maybe not. Who knows how much time that might take if it happened at all.

Thanks,
Jeff
 
I've never done it, but since it's splash lube, you might only need to raise the oil level a touch to give it the same degree of splash. But that's the thoughts of a devout non expert.
 
That degree of angle will not hurt a B&S. They suffer a lot more in many applications.
Think about most rototillers.
 
That degree of angle will not hurt a B&S. They suffer a lot more in many applications.
Think about most rototillers.
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That's true. And I do like the way it looks.

Could weld in some tube sleeves to fit over the bolts, were it goes through the frame
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That's a good idea Curt. I need to space the brackets away from the frame tubes anyway. Thanks!
 
Probably better forward tilt than after due to the breather leaking oil. If I had known earlier would have not done mine backward tilt. In any case Briggs say 15 degree OK, also yes others here have tilted more and have been OK. If you remove any of those two extra tubes see if welding something in place of then elsewhere to keep strength up. I did a bit of gussets on my frame as I go on trails. My installing and removing engine is sort of a tricky business, but it just clears. The plug I changed out to a shorty with the same heat range. The insulater of high temp RTV I made for the high tension lead does not short through it to the frame, even though it is against the tube. Like to see pictures as it is coming together of the build your doing!
 
If you remove any of those two extra tubes see if welding something in place of then elsewhere to keep strength up.
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After seeing some of the replies I'm going to try and leave the tubes and just tilt it. I picked up some 1.25" angle stock (.125 thickness) this morning and played with it a few minutes. I can see right now I'm going to have to make a stand for the frame before I do anything else. Saw a couple made out of pvc on the webs that look cheap and adequate.

By far the biggest problem I'm facing this weekend is moving the drill press out of storage and into the bonus room. Not sure if Mama will go for that.
 
I see a lot of builders using angle iron for engine mounts and I can tell you from 30 years of building Briggs bikes that 1/8'' flat stock base and upper mount is totally adequate. Welded to the frame tubes. Much cleaner and never has one cracked or failed on me.

 
Way to go Dale, yes remember doing that about 55+ years ago, worked great. In fact most of the old car generator friction drive, with washing machine motors on we're done that way................Curt
 
curtisfox said:
Way to go Dale, yes remember doing that about 55+ years ago, worked great. In fact most of the old car generator friction drive, with washing machine motors on we're done that way................Curt
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That's cool, curt. I never got to do any of that as a kid, so I do it now.
 
msrfan said:
That's cool, curt. I never got to do any of that as a kid, so I do it now.
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Somewhere about mid 50's my brothers ( 3 years older ) friend had one of the old car generator friction drive. Got my first ride, boy did I get hooked. I think it was the next summer I got a Monark twin, road that day and night till a rod let lose, no parts. That is when I built the Briggs powered one, 11/2 hp. Road it every where for a couple years then traded it for model A Ford+$75 taboos. That was it till 8 years ago, had another ride, another hook............Curt
 
Yeah curt, kind of like race fever. You think it's all in your youth and then some one passes you on another motorized bicycle. Game on!.
 
Managed to get a stand built. Not optimal, but it makes it a little easier to work on.
stand1.jpg



Also tried to get some tools together. Since we moved, everything is out of place. Our old house had a basement, now I have a bonus room and a shed. I'll probably spend this week trying to get things organized.

shop.jpg


Just enough room to work. Guess I'll have to do some of the messy stuff outside. By the way, is the bolt that holds the clutch on left hand thread?
Thanks,
Jeff
 
That nice the engine already had threads in the shaft for the clutch.

Tell me about moving, just finding stuff even when I labeled boxes with fair description of contents is a $^&^.

Smart looking stand you built.

A center stand I got, I sometime have one or the other wheel on and weight down other end with lead dive weights so I can work on the bike with one or the other wheels removed.

It is just stable enough, but don't bump too hard or else.

MT
 
Looking at the crankcase wall of the engine does the engine crankshaft rotate counter clockwise?

If it does like my Briggs engine, then usual right hand threads would self tighten when the engine is running.

Threads on the other side by the flywheel I think would have left hand threads and similarly would self tighten as the engine turns too. The pawl clutch that goes on that side for the recoil starter I believe have the left hand threads.

https://en.wikipedia.org/wiki/Screw_thread
 
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