Water cooled motobike

Local time
3:41 AM
Joined
Oct 13, 2019
Messages
32
Location
Big Island
Hey guys finishing up my 39cc chinese replica polini water cooled engine on a bicycle! Really wanted to do a water cooled bicycle project all my own, and now I am nearly complete with it. Grabbed this engine from aliexpress: https://www.aliexpress.com/item/225...00015065510190!sea&curPageLogUid=wLud4IZdfQtr



20210407_105635.jpg


A Translated version of engine specs:

Screenshot_20220808-202503-620_2.png


I have always wanted to build a water cooled motor bicycle, just thought it would be cool and one of a kind. After a year and a half of designing I have finally got a prototype 1:

\
bike 2022.jpg


It has a sickbikeparts.com hd jackshaft kit, 8t sprocket on the engine connecting to a 47t gear via a 25h chain. That is hooked through the jackshaft to a 10t sickbikeparts bmx sprocket hooked to a 44t bigger gear on the chainring. That is connected to a 36t sprocket connected to my rear derailleur then to my stock shimano 14-28t with a shimano tourney rear derailleur, the bicycle drive train being the stock one. Very sturdy and all the power is being transferred to the chains with the mounts I used. It has a 12v minimoto pump from italy that is powered by a 12v 5ah battery. The radiator is a minimoto one from gpi racing on ebay. The cooling system work great! no leaks. Fired up first time, using amisol saber at 30:1. alot of smoke but after a little carb tuning runs great! took it for a ride up the hill around the block, no speedometer but went maybe 10mph up a pretty steep hill, didnt sound like it was fully revving out. Once I got to a flat, It took off. Had to hit at least 25mph in 3 gear, had alot more potential. When I went to shift to 4th i overrevved and the chain fell off of the front chainring towards the inside, twisting aroung the bottom bracket and pulled on the derailleur. I was able to roll it home and get the chain back on in order, although after that I cannot get the bike to shift properly I think the derailleur is bent now. So now I gotta replace my drivetrain and want some suggestions. Should I go internal gear hub? Any suggestions of strong derailleur setups? Need something to handle all this power. Also, any regearing suggestions? Any help would be appreciated to get this thing to run optimal thanks
 

Attachments

  • 39cc info.jpg
    39cc info.jpg
    50 KB · Views: 52
Local time
3:41 AM
Joined
Oct 13, 2019
Messages
32
Location
Big Island
Shout out to #Chainlube and #Street Ryderz for helping me figure out the 47t sprocket, just need a little help getting it optimized. The 8t from the engine is connected with a shoe and clutch bell like a moped like auto clutch and puts a bit of stress on the drivetrain, I think I need softer springs to let it throw out at a lower rpm so I get power out of lower revs. Again any input is appreciated 👍
 

Urban Fatbiker

Well-Known Member
Local time
8:41 AM
Joined
Jan 30, 2019
Messages
257
Location
Nashville TN
I like it, but I have suggestions based on my experience with a shift kit.

1- add chain tensioner both sides. It’ll be nothing but grief unless you do.

2- modify bracket with half-moon clamshell brackets both sides of downtube, weld it in and replace u-clamp with standoffs.

3- add collars on both sides of sprockets to capture on shaft. This prevents loosened set screws from causing sprockets to walk off shaft.

4- trash those kit bearings and use PGN, or they’ll be crunchy in 200 miles.

5- drill dimples in shaft for sprocket set screws to lock them in place.

Do all of that, you won’t crunch chain in the engine, pop it off the crankset, walk off sprockets, twist bracket, and a loose sprocket set screw becomes routine maintenance instead of a shameful long walk.

See some of my posts with pics. I’m a greenhorn with the engine part, but I know what destroys hi-speed drive systems.
And I destroyed mine cause I wanted to ride, so yes BTDT, redid it second time like a pro instead of a shade tree ratchet driver.
 

Sidewinder Jerry

Well-Known Member
Local time
9:41 AM
Joined
Mar 14, 2011
Messages
3,520
Location
Rockwood, TN
First, I'd like to say welcome fellow brother shifter. What you most need is a tachometer/hour counter. Next, it appears your reduction range is off for your engine. What you currently have is 21.93:1 to 10.97:1. I'm going to assume you're using 26" tires.

With your current set up if it could pull the high gear you'd be doing over 63 mph at 9000 rpm. However, from your description, it sounds like the ratios are too high.

So I suggest changing the 36t chainring to a 30t chainring. If you changed nothing else this'll give you a reduction range of 26.32:1 to 13.16:1. Even then the reduction range is still too high.

What you need is my 4-speed 34-16 freewheel and the 30t chainring. Then the reduction range will be 31.96:1 to 15.04:1. It'll give you a speed of 46.3 mph at 9000 rpm in 4th gear. The 4-speed 34-16 freewheel will give you bigger jumps between the ratios and reduce the amount of lateral stress on the chain. With the chain lateral stress reduction, the correct ratio for a given terrain, and the strong tension in the Sram X4 it should stop the chain from coming off the chainring. You should also change the stock hub axle to a cro-molly one. You'll need to adjust the rear high on the derailleur so it doesn't shift past 4th gear.

Max speeds:
1) 21.8 mph
2) 26.4 mph
3) 30.9 mph
4) 46.3 mph

On the tach, if you can't hit 7000 rpm at WOT then shift to a lower gear. If you're going way over 9000 rpm at WOT then shift to a higher gear. The hour counter helps maintain a maintenance schedule. With this setup always take off in 1st gear. This'll save a lot of wear and tear on your clutch.

I use a Sram X4 rear derailleur and a Sram X3 shifter. My preferred bicycle chain is a Shimano HG71.

Thread '4 Speed Freewheel' https://motoredbikes.com/threads/4-speed-freewheel.58615/
 

Urban Fatbiker

Well-Known Member
Local time
8:41 AM
Joined
Jan 30, 2019
Messages
257
Location
Nashville TN
I didn't even look at gearing except to see lots of clearance for the input sprocket. Yeah, I concur!

I run a 21T to 9T, then 32 and 40 on crankset. Went with a 6-speed cluster, and dunped the 11T.

That range gets good pedal assist matching when I need it, course ya may not care but 48cc by itself won't climb all my hills around here.
Most, but not all.

Butt dyno says that'll get ya over 35mph at 7Krpm, but my butt needs a tach installed.
 

Sidewinder Jerry

Well-Known Member
Local time
9:41 AM
Joined
Mar 14, 2011
Messages
3,520
Location
Rockwood, TN
I didn't even look at gearing except to see lots of clearance for the input sprocket. Yeah, I concur!

I run a 21T to 9T, then 32 and 40 on crankset. Went with a 6-speed cluster, and dunped the 11T.

That range gets good pedal assist matching when I need it, course ya may not care but 48cc by itself won't climb all my hills around here.
Most, but not all.

Butt dyno says that'll get ya over 35mph at 7Krpm, but my butt needs a tach installed.
I'm going to assume this is what you're using and that you have a 10t on your engine; along with 26" tires. DNP 7 speed freewheel (32,24,21,18,15,13,11). Always take off in 1st gear.

(4.1×(21÷10)×(40÷9)×(32÷32))=38.27:1

(4.1×(21÷10)×(40÷9)×(13÷32))=15.55:1

(7,000×26×π)÷(1,056×4.1×(21
÷10)×(40÷9)×(13÷32))=34.8 mph.

If you changed the 40t to a 48t and started using the 11t for the high gear, you should be able to climb any paved hill without losing your top-end speed.

(4.1×(21÷10)×(48÷9)×(32÷32))=45.92:1

(4.1×(21÷10)×(48÷9)×(11÷32))=15.79:1

I know you like to off-road with this bike. You may want to consider Fabian's double chainring SBP shift kit. You would shift like this 1(1-4), 2(4-7) for 8 sequential non-redundant ratios. It'll also help lower the lateral stress on the bicycle chain.

 

2speedboi

Well-Known Member
Local time
6:41 AM
Joined
May 11, 2020
Messages
344
Very nice build!

I have been looking at the Zenoah 29cc water cooled engine for a water cooled friction drive! Might help in these crazy new high temps we are seeing.

Keep up on that sweet build!
 

Sidewinder Jerry

Well-Known Member
Local time
9:41 AM
Joined
Mar 14, 2011
Messages
3,520
Location
Rockwood, TN

Very nice build!

I have been looking at the Zenoah 29cc water cooled engine for a water cooled friction drive! Might help in these crazy new high temps we are seeing.

Keep up on that sweet build!
Unless you're a lite weight and a flat lander I'd build a shifter with an engine that small.
 
Top