My 5hp Robin Build
- Thread starter midwestmayhem
- Start date
With what Sick Bike Parts(SBP) has to offer, pedalling w/their shift kit will be a simple, quick and inexpensive bolt-on.
Buy SBP crank arms, Jump-Stop, $20 freewheel and bolts, BB cartridge and 24-tooth sprocket. Drill your engine chainring sprocket to match the freewheel's bolt pattern. Install your pedals....and you're done!
No need for another jackshaft.
If you change to an 8t or 9t clutch along with the 24t bicycle chainring, you can reduce the size of your humongous!!! engine chainring.
I'm installing a 6hp Robin 170cc onto my project bike, so I NEED to know.....
How did your 5hp Robin engine run on your bike?
Did it break the tiny 5-speed bicycle chains?
How many teeth on the engine chainring and bicycle chainring?
How did the Robin engine like the gearing?
How fast is your bike now?
How was the bike in climbing hills?
Why are you changing to 212cc Predator? Is the 5hp Robin powerful?
Thanks for help.
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I am intrigued by your Robin-powered MB!
I may be wrong, but pictures of your chainrings lead me to believe that your engine is undergeared, even with that very large engine chainring. The correct gear ratios and SBP shift kit would allow you to pedal again.
Proper gearing would transform this MB into something with awesome stump-pulling low end AND high speed.
Let me guess what your gear ratio is:
If that's a 75-tooth engine chainring, initial gearing w/a 10t engine sprocket is 7.5:1.....
Your bicycle chainring looks to be 36t. Chained to a 28t first gear, ratio = .778:1.....
Gear ratio in 1st gear is 5.83:1, which is sluggish.
Gear ratio in 5th gear is 2.92:1.....unusable.
Since you're about to install a shift kit w/pedals, here's my suggestions:
Install SBP BB cartridge, BB adaptors, crank arms, $19.95 freewheel, chainring hardware and the $5.95 24-tooth bicycle chainring sprocket. Re-use your large engine chainring sprocket by redrilling(if necessary) to fit the SBP freewheel. If you do not need the bottom bracket adaptors, total cost would be $80.75.
For this amount, you would be able to pedal, ANNNND your bike would be much faster.
Using the 24t would lower(raise numerically) your gearing 50%, from 5.83:1 to 8.75:1.....
Your 5th gear would lower to 4.375, prolly usable for highway use.
JMO, ya just might not need that 212cc engine.
If you could raise gear ratio in 1st gear to 15:1, your MB would be a beast!
Awesome low gear with top speed of 37.2mph @ 3600rpm, or 56.7mph @ 5500rpm.
I may be wrong, but pictures of your chainrings lead me to believe that your engine is undergeared, even with that very large engine chainring. The correct gear ratios and SBP shift kit would allow you to pedal again.
Proper gearing would transform this MB into something with awesome stump-pulling low end AND high speed.
Let me guess what your gear ratio is:
If that's a 75-tooth engine chainring, initial gearing w/a 10t engine sprocket is 7.5:1.....
Your bicycle chainring looks to be 36t. Chained to a 28t first gear, ratio = .778:1.....
Gear ratio in 1st gear is 5.83:1, which is sluggish.
Gear ratio in 5th gear is 2.92:1.....unusable.
Since you're about to install a shift kit w/pedals, here's my suggestions:
Install SBP BB cartridge, BB adaptors, crank arms, $19.95 freewheel, chainring hardware and the $5.95 24-tooth bicycle chainring sprocket. Re-use your large engine chainring sprocket by redrilling(if necessary) to fit the SBP freewheel. If you do not need the bottom bracket adaptors, total cost would be $80.75.
For this amount, you would be able to pedal, ANNNND your bike would be much faster.
Using the 24t would lower(raise numerically) your gearing 50%, from 5.83:1 to 8.75:1.....
Your 5th gear would lower to 4.375, prolly usable for highway use.
JMO, ya just might not need that 212cc engine.
If you could raise gear ratio in 1st gear to 15:1, your MB would be a beast!
Awesome low gear with top speed of 37.2mph @ 3600rpm, or 56.7mph @ 5500rpm.
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Holy biscuits, I never thought so many people would be reading this and respond so soon 
I consider that a good thing though.
To recap the drive system, the clutch is a 10 tooth. It drives the big 72 tooth sprocket. Bolted onto that big sprocket is a 24 tooth spocket, which drives the 28 tooth sprocket on the rear wheel. For a final ratio of 8.4 in the lowest gear. The bike was FAST, at least in my opinion. I couldn'd do a road test, since it is not yet licensed, but I rode it around in the yard in the lowest gear. The centrifugal clutch didn't entirely engage to around 15mph, with plenty of throttle left to go.
To recap my re-design idea, I'm planning (so far anyway) to add a second jackshaft between the rear wheel and the seat post. The main reason for this is to get the motor centered in the frame (which it wasn't before) to help with balance. The second jackshaft will also make it easier to change gear ratios if I choose.
I had planned to run a sbp freewheel and sprockets, as mentioned. Didn't think of using a sbp bb cartidge, that might be worth a little more research to determine if the spacing would be enough. Originally planned on modifying some crank arms to fit a 5/8 keyed shaft and so forth. Sbp's cartridge, if it would work, would probably be easier.
As far as the motor change, a long story made short, I decided to put the robin back on the gokart so I can hopefully sell the gokart. Since I got a good deal on the preditor, and aftermarket parts are easier to get, I decided to put it on the bike. Though I doubt I will want to much more power than the pred already has stock.
I consider that a good thing though.To recap the drive system, the clutch is a 10 tooth. It drives the big 72 tooth sprocket. Bolted onto that big sprocket is a 24 tooth spocket, which drives the 28 tooth sprocket on the rear wheel. For a final ratio of 8.4 in the lowest gear. The bike was FAST, at least in my opinion. I couldn'd do a road test, since it is not yet licensed, but I rode it around in the yard in the lowest gear. The centrifugal clutch didn't entirely engage to around 15mph, with plenty of throttle left to go.
To recap my re-design idea, I'm planning (so far anyway) to add a second jackshaft between the rear wheel and the seat post. The main reason for this is to get the motor centered in the frame (which it wasn't before) to help with balance. The second jackshaft will also make it easier to change gear ratios if I choose.
I had planned to run a sbp freewheel and sprockets, as mentioned. Didn't think of using a sbp bb cartidge, that might be worth a little more research to determine if the spacing would be enough. Originally planned on modifying some crank arms to fit a 5/8 keyed shaft and so forth. Sbp's cartridge, if it would work, would probably be easier.
As far as the motor change, a long story made short, I decided to put the robin back on the gokart so I can hopefully sell the gokart. Since I got a good deal on the preditor, and aftermarket parts are easier to get, I decided to put it on the bike. Though I doubt I will want to much more power than the pred already has stock.
Excellent!
All you have to do is change the rear cassette to one that has 34t-32t-26t.....
If the cassette is too wide, just swap the 34t-32t-26t into your existing hub.
Your gear ratio will then be 10.2:1 in first gear, then 9:1 and 7.8:1.
Your bike will launch very well from a standstill and fly.
All you have to do is change the rear cassette to one that has 34t-32t-26t.....
If the cassette is too wide, just swap the 34t-32t-26t into your existing hub.
Your gear ratio will then be 10.2:1 in first gear, then 9:1 and 7.8:1.
Your bike will launch very well from a standstill and fly.
=======================================lol, that's ok wayne, I might need to spread rear forks sometime. This info will come in handy.
I already re-posted my question about sbp's shift kits on the 2 stroke part of this forum. It doesn't look like as many people visit that part of the forom, but I imagine someone who knows will run across it and answer it.
I had spread the left side of the rear drop out with a piece of aluminum stock with a hole drilled through it. I just let it flex about a quarter inch and it was OK. I rode it and no belt scrape or pulley either. It flexes back when I take the wheel out.
There was one thing you can check on my page 3 post #27 on how I needed to be able to have the brake shoe on my v-brakes reach the left side of the rear wheel rim.
Motor Bike DIY'er build to add side car maybe?
http://motorbicycling.com/showthread.php?t=29678&page=3
If I had thought of it earlier when I made the weld on bosses for the v-brake parts to attach to the tubes I would have made this rear left one reach over further to compensate. Too late, but extending the brake shoe round stock with threads made on the shoe round stock and put a coupler to attach to some more round stock that has threads so it worked out OK.
I put two roll pin tensioners through the two threaded areas so it is a onetime shoe. Made a second one today to have an extra one on hand.
MT
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=====================================Holy biscuits, I never thought so many people would be reading this and respond so soon
To recap the drive system, the clutch is a 10 tooth. It drives the big 72 tooth sprocket. Bolted onto that big sprocket is a 24 tooth spocket, which drives the 28 tooth sprocket on the rear wheel. For a final ratio of 8.4 in the lowest gear. The bike was FAST, at least in my opinion. I couldn'd do a road test, since it is not yet licensed, but I rode it around in the yard in the lowest gear. The centrifugal clutch didn't entirely engage to around 15mph, with plenty of throttle left to go.
To recap my re-design idea, I'm planning (so far anyway) to add a second jackshaft between the rear wheel and the seat post. The main reason for this is to get the motor centered in the frame (which it wasn't before) to help with balance. The second jackshaft will also make it easier to change gear ratios if I choose.
I had planned to run a sbp freewheel and sprockets, as mentioned. Didn't think of using a sbp bb cartidge, that might be worth a little more research to determine if the spacing would be enough. Originally planned on modifying some crank arms to fit a 5/8 keyed shaft and so forth. Sbp's cartridge, if it would work, would probably be easier.
As far as the motor change, a long story made short, I decided to put the robin back on the gokart so I can hopefully sell the gokart. Since I got a good deal on the preditor, and aftermarket parts are easier to get, I decided to put it on the bike. Though I doubt I will want to much more power than the pred already has stock.
MWM; You have gears that can be shifted, my lower power 3hp Briggs I have tried with centrifugal belt clutch where I have also 8:1 ratio and figured with the 26 inch wheel I would be going about 15mph when fully engaged clutch at 2200 rpm.
At 3500 rpm I'm fearful how fast it might go if it doesn't bogg down. I was trying to go slow as I forgot my helmet and just wanted to test it out going slow, it heated the clutch as it took time to get to the 2200 from the 1750 idle.
I understand 2000 to 2200 is the range of engagement. I am going to shoot for a 20:1 for dirt bike off roading. I have fixed ratio until I stop and move pulleys around but that is only for switching from parade speed 47:1 ratio 3.5 to 5.5mph to the faster OHV woods dirt bike riding and the double stacked jackshaft I am making it right now.
So I was wondering if you got your bike legal, as I am going to DMV when done to get OHV (not street ride-able)sticker, for your on street bike do you think 8:1 and the more powerful engine you would keep that gear ratio.
One day I thought if I have confidence in the bike as I try it at dirt bike speeds, see about time trials by officials at a desert location. Bonneville Salt Flats or where ever they have them.
I’m not saying you should do this, but that 212 is almost twice the displacement of my 3hp Briggs and probably gets twice the hp, you could haul #^&%$*!
MT
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I've been waiting till the bike is ridable and the way I want it to be before trying to get it licenced, just in case it takes me a while.
The clutch does get pretty hot, but not enough to start smoking or glowing. With the addition of the jackshaft I should be able to get ratios that are offroad worthy (or at least close to it) if I choose.
Anybody know much about sbp's 206mm bb? More specifically how far will it extend the crank arms away from the center of a bike? They appear to be offset towards the left side...
The clutch does get pretty hot, but not enough to start smoking or glowing. With the addition of the jackshaft I should be able to get ratios that are offroad worthy (or at least close to it) if I choose.
Anybody know much about sbp's 206mm bb? More specifically how far will it extend the crank arms away from the center of a bike? They appear to be offset towards the left side...
I measure 4 3/4" to the inside of the crank arm to center and they are not
offset so you have 9 1/2" total clearance.
Mid- my 2 cents on the predator. Put it on the go kart. Or test it out for vibration on the bike before parting with the Robin. The 212 vibrates wildly above fast idle. I am using one, but ended up isolating the engine completely with rubber isolators.
The vibes are not as much an issue on a go kart since the engine is more remote.
Also, the 212 is not the same as the Honda motor.
It is intentionally larger by HF to be non legal for gokart racing because HF's insurance underwriter was loosing a lot of money on warranty's via the gokart boys blowing them up and returning them for a new one.
I love the 212 (9hp with custom muff and intake) great torque and mileage too, but be forewarned about the vibes severe enough to cause vibration itch on your body after riding for a little while unless attended to. And this goes for the clone motors that karters use too. Big motors mean big vibration.
The vibes are not as much an issue on a go kart since the engine is more remote.
Also, the 212 is not the same as the Honda motor.
It is intentionally larger by HF to be non legal for gokart racing because HF's insurance underwriter was loosing a lot of money on warranty's via the gokart boys blowing them up and returning them for a new one.
I love the 212 (9hp with custom muff and intake) great torque and mileage too, but be forewarned about the vibes severe enough to cause vibration itch on your body after riding for a little while unless attended to. And this goes for the clone motors that karters use too. Big motors mean big vibration.
Using SBP's arms, I measure 3 1/4" to center, and 6 1/2" total clearance.
I am measuring this which comes in the 4 stroke shifter kit
and also using SBP arms.
Bottom Bracket Cartridge 206mm
I believe you, MBR.I am measuring this which comes in the 4 stroke shifter kit
and also using SBP arms.
Bottom Bracket Cartridge 206mm
I'm using SBP arms and the widest cartridge(unknown size) the local bike shop had. It works perfectly for my center-framed Tanaka 47R engine.
There has been a thread I saw here that someone took the cranks and made a double bend to have clearance. I think it was done not attached to crank as if it were the crank and the races bearing all could possibly dammaged as I saw a large pipe for leverage.
If you doing this with parts to replace, thats probably a more sound way. I will try one day and see if small MIG welder can do an extension to the crank. My needs negated the crank all together and I welded a plate over the pedal crank area to keep water out of the frame. Ofcourse this is not for street now, or atleast not motorized bicycle for street as no pedals. What does it take to get OK as motor cycle home built, probably not worth the effort.
MT
http://motorbicycling.com/showthread.php?t=32836&page=3
Thanks Wayne Z this is the one from 59Cruiser "Help - Crank Clearance Problem", but I suppose many have tried bending cranks, though kits to modify legnth don't have the "S" shape so some people may want it that way too. I sort of like that unique look of the "S".
If you doing this with parts to replace, thats probably a more sound way. I will try one day and see if small MIG welder can do an extension to the crank. My needs negated the crank all together and I welded a plate over the pedal crank area to keep water out of the frame. Ofcourse this is not for street now, or atleast not motorized bicycle for street as no pedals. What does it take to get OK as motor cycle home built, probably not worth the effort.
MT
http://motorbicycling.com/showthread.php?t=32836&page=3
Thanks Wayne Z this is the one from 59Cruiser "Help - Crank Clearance Problem", but I suppose many have tried bending cranks, though kits to modify legnth don't have the "S" shape so some people may want it that way too. I sort of like that unique look of the "S".
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That was prolly my thread on "cold bending' cranks. Search for the thread"cold bending cranks. I figured this out because I didn't want to scorch my chrome with a torch.
http://motorbicycling.com/showthread.php?t=35923
I bent them while installed. I used 2 bending forks with long pipe handles. 1 bar to do the bending and the other bar to counter the bending pressure. So no force was applied to the bearings or frame.
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Wayne Z thanks for adding in the reply that a counter force is used to allow the work while in the frame and protected the bearings!
I had found the other thread about heating and bending and the details on how 59Cruiser had some help do some of the work.
http://motorbicycling.com/showthread.php?t=32836&page=2
but the last page was page 3. A pictures shows the finished bike cranks bent.
I did not think too much of the cranks for pedaling being somewhat shorter throw as the bends take up some length, but that was mentioned to be minimal and it was OK for work to go ahead.
Ooooh I have to remember that about scorching chrome. If I can get the right colors I want and then fix them to stay on chrome if possible. Ay with all those colors I shall try that. Not mocking using cold bending, but you know twisted kind of Art project.
I remember looking at the chrome on 3 separate headers going to the 3 separate tail pipes having bluing on a two stroke Kawasaki 350 street bike from the 70’s.
I messed it up once when reaching down to grab a wrench and the poplin shell of my down jacket sleeve melted to one headers. I smelled plastic burning. I pulled my arm back and saw feathers pull out of my down jacket sleeve and stick to the melted shell for my jacket on the header. Winter in New York!
MT
I had found the other thread about heating and bending and the details on how 59Cruiser had some help do some of the work.
http://motorbicycling.com/showthread.php?t=32836&page=2
but the last page was page 3. A pictures shows the finished bike cranks bent.
I did not think too much of the cranks for pedaling being somewhat shorter throw as the bends take up some length, but that was mentioned to be minimal and it was OK for work to go ahead.
Ooooh I have to remember that about scorching chrome. If I can get the right colors I want and then fix them to stay on chrome if possible. Ay with all those colors I shall try that. Not mocking using cold bending, but you know twisted kind of Art project.
I remember looking at the chrome on 3 separate headers going to the 3 separate tail pipes having bluing on a two stroke Kawasaki 350 street bike from the 70’s.
I messed it up once when reaching down to grab a wrench and the poplin shell of my down jacket sleeve melted to one headers. I smelled plastic burning. I pulled my arm back and saw feathers pull out of my down jacket sleeve and stick to the melted shell for my jacket on the header. Winter in New York!
MT
hey everyone, it's been a while so I figured I make an update.
As far as the pedal crank goes, I think I'll try the idea of instaling a 5/8 keyed shaft like the ones used for jackshafts. While I still had access to a lathe, I made some adapters that fit tightly into the bike's bb and hold a 1 3/8 OD bearing. I'll try to get some pics latter. I have a 5/8 drill bit, so I'm going to try to drill out the square taper in the crank arms to 5/8, then cut a keyway. I'll have to use the bit on a piece of scrap first to see how well it will fit a 5/8 shaft. If everything works, I'll be able to offset the crank arms as much as is needed.
Does anyone here have experience with omb's weld-on bearing hangers?
http://ombwarehouse.com/Bearing-Hanger.html
I got some a couple days ago and they don't fit very well onto the bearings. The bearing will go in and fall back out on its own when tipped in the right direction. With all the bearing hangers I've ever used the bearing has to be tapped or pressed in, unlike these which fit so loosely that there's even a little slop between the bearing and the bearing hanger.
As far as the pedal crank goes, I think I'll try the idea of instaling a 5/8 keyed shaft like the ones used for jackshafts. While I still had access to a lathe, I made some adapters that fit tightly into the bike's bb and hold a 1 3/8 OD bearing. I'll try to get some pics latter. I have a 5/8 drill bit, so I'm going to try to drill out the square taper in the crank arms to 5/8, then cut a keyway. I'll have to use the bit on a piece of scrap first to see how well it will fit a 5/8 shaft. If everything works, I'll be able to offset the crank arms as much as is needed.
Does anyone here have experience with omb's weld-on bearing hangers?
http://ombwarehouse.com/Bearing-Hanger.html
I got some a couple days ago and they don't fit very well onto the bearings. The bearing will go in and fall back out on its own when tipped in the right direction. With all the bearing hangers I've ever used the bearing has to be tapped or pressed in, unlike these which fit so loosely that there's even a little slop between the bearing and the bearing hanger.
I like the bearing blocks from Mcmaster carr- they have set screws in them (locktite em).
Hey- are you still using the Robin engine?
The HF 212 is becoming quite popular, BUT very few parts are interchangeable to the old clone motors.
Hey- are you still using the Robin engine?
The HF 212 is becoming quite popular, BUT very few parts are interchangeable to the old clone motors.
Strangely I am just now building a bike using a 5/8 keyed shaft in the bottom bracket. I have cut the ends off a standard 3pc spindle to weld to the keyed shaft. Am just using the squared ends. Will still allow the bearings to slip down the shaft. The front chain ring is welded to a 5/8 sprocket I had laying around so it is keyed and adjustable. A standard lock collar will hold it all in position. Now I can easily make the pedals as wide as necessary.
ya, the bearing blocks are nice, but these bearing hangers still have me scratching my head. I e-mailed OMB two days ago and they still haven't got back to me. I'd call thier phone orders number, but they probably wouldn't like that
From what I herd, much of the internals of the 212 is different than the old clones. A whils back I did run across a site that sold aftermarket parts for the 212, the ones that couldn't be interchanged with the clones.
Just got off the phone with the guy at omb. Said that sometimes they will get a bad batch and that they are currently out of stock. I checked thier site and it looks like they still have them in stock. Something somewhere is goofed. Anyway he said that he'd send some new ones out as soon as they came in. This kinda sucks, I always felt that omb was a good place to go for parts, now I'm starting to wonder.
I'll try to keep you all updated...
I'll try to keep you all updated...