Project Polini


Local time
4:38 PM
May 2, 2008
Northern Suburbs, Adelaide, South Australia
Hey all, with the happy completion of my last motored bike, I have decided to kick off "project Polini"

I have mentioned it a couple of times before, but it has always been on the back burner.

This will be the motoredbike equivalent of a drag bike.

I had a stint a few years ago with pocket bikes (CAGs, etc.). Built a air cooled bike as far as you could go, and then stepped up to a watercooled 911 dreambike. In standard guise it was bloody quick. But me being me I couldnt leave it standard.

So I got from Italy a top end racing package. This was the head, cylinder, piston with rings, gaskets etc. Also got all the suggested upgrades to match, polini race exhaust. 19mm Dell ' Orto Carb (black version, factory set up for racing) , 2 shoe BZM race clutch, Polini carbon fibre reeds, etc..

Its a watercooled setup as I said as an air cooled motor cant put out the power of this thing without cooking itself.

To give you an idea, with the 3 port top end and everything stock these things put out 7.2hp. With the setup I have its rated to 13Hp+. On a pocketbike that means a top speed of in excess of 60mph, and brutal acceleration ( you have to lean all the way over the handlebars to take off unless you want to suddenly be on your back with a bike on top of you). Trust me that hurts, mine flipped me once, rather embarassing really.

So the pocketbikes are long gone, kids, curiosity and those things arent something I wanted to think about, but I kept the polini and its running gear.

This setup with Haggard's excellent rackmount conversion in my mind I had a excellent but truely scary idea.

And we all know what that is, but once its finished am I crazy enough to ride it?

Everything on the setup will be built with thick angle steel. I have a length of 40x40x5mm angleiron. All the bolts for the sprockets will be of M8 high tensile bolts. Motor mount bolts are M10.

Anyway, I have added some piccies so all can see what I have to play with.

Laying everything out, the rear rack will have to be about 18 inches long, so its gonna hang out the back a fair bit, but it should be okay.

I havent a clue as to what speed it is capable of, but its gonna be a lot more than I am comfortable with. But hey, I have the motor, what else would a mad motoredbike mechanic do???????????

I will keep you lot informed of its progress. Its not gonna be a overnight build, but I will add to this thread as I get to stages of the build.


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Wicked nice looking engine. I like how it has the rubberized engine mounts like a car has to absorb vibrations. It may look a little funny rackmounted with that tuned pipe sticking way out the back of your bike but you'll probably figure something out. My 2.2hp stock mitsu has a nice amount of power behind it I couldn't imagine 13hp! It'll be a great ride if the bicycle doesn't eat itself. Keep us informed I'd love to see this thing in action.
Well figured out today where everything will go. If it was a air cooled bike it would be a lot easier.

Got the sprockets figured out with their order and got it ready for the M8 hi tensile bolts.

I have the radiator rear mounted, I figured if it was front mounted it wouldnt get great air flow as it would be right behind my back. I also will mount it low as that will allow greater air flow through it.

Also I rear mounted the sprockets as I want the chains the furthest away from my body just in case. These things rev to 12,000 rpm ( 15,000 if I change the crankshaft ;) ), so I can live without the concern. I will fit guards where I can but its better to be safe than sorry.

It took me a good hour to mock up the arangement, but the attached picture shows the layout.

Long rack, but theres more than just a engine to mount and the exhaust is fairly long as well, so it will work.


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Are you going to do any further gear reduction to accommodate for the fact that a bicycle wheel is much larger than a pocket bike wheel?
Im gonna "suck it and see". See if it has a usable torque curve in the usable speed range, the output sprocket is a BMX front sprocket, so it can be changed, I will also run the chain down to the HT spoke setup, which can also be changed.

If the torque curve is usable, I will leave it as is, I mean we drive normally at less than half the top speed when we drive a car, so I can have the same luxury, hopefully.
/me pictures simon tucked into his handlebars with the engine screaming as he keeps up with cars on the state highways :)
Hows the ride?

My Polini clole will kick itself out of a vice at high throttle.
Is your bicycle rack sufficent to handle the forces .
I intend to use the mounting brackets and angle iron welded to the swing arm.
this project looks pretty exciting! a watercooled polini engine sounds amazing, u shud giv kawasaki999 a race, his top speed is 55! i wouldnt be surprised if with the right gearing you will get that.

Hey Simon, your layout picture helps me.

We have almost the same hardware. I just got started though.
I really can't wait to see yours and mine passing traffic!
I am not using a staton or anything, just a chain to the rear wheel using a hardly pedaling sproket that is designed for this purpose.It is about 8-10 inches across.There will be a tension pully on the chain. donno how many teeth that is. That size should accomidate for the higher revs from the engine and give more torque.
The engine will be mounted to a custom angle iron frame.
I want to see how you mount the water pump.
I have a raleigh bike computer already on the bike.
I can post results in km/h
Should be built in next month or so.
My Polini clole will kick itself out of a vice at high throttle.
Is your bicycle rack sufficent to handle the forces .

All metalwork will be/is 40mm x 40mm x 5mm steel. I hope its sufficient, if not then there is something seriously wrong.

Also I am gonna change the clutch to one that engauges a lot lower that normal, so the clutch cant kick too hard. Will mean clutch wear is something to be concerned about, but saves the bike becoming airborn at 8000rpm when the clutch engauges. The clutch can engauge and then it can hit the powerband, unlink both things happening at once.

We have almost the same hardware. I just got started though.
I really can't wait to see yours and mine passing traffic!
I am not using a staton or anything, just a chain to the rear wheel.

Dude, you do realise these things rev to 12,000 rpm + dont you. Direct drive would make me a lot nervious. It will need to be well geared down.

But yeah it will be able to pass traffic. Dont think I will rev it out more than once, bikes arent meant to be able to do that. But I know I will do a top speed run, once.