Johansson´s Pocketbike

[Johansson]

I move this up to a separate thread since I don´t want to be a thread-napper...

Now when my jetcart project is as good as finished I will start a more serious project. I will rebuild a medium sized truck turbocharger for ball bearings and make it into a diesel-fueled gas producer, which will be coupled to a power turbine as soon as it runs OK. The power turbine will run without a gearbox due to lack of space (and because I guess that I won´t be needing the extra power...) and will be linked to the rear wheel either by a chain or a belt.

I plan to build the engine directly into the frame of my pocketbike which was earlier powered by a 2hp 4-stroke engine, I guesstimate that the turbine will produce close to 10hp if the power turbine matches the GT. Scary...

I have begun to make some drawings of the bearing tunnel and have both the compressor and turbine housing, but the actual building will have to wait until I have bought a new compressor and turbine and had the shaft CNC-spun down to 12mm from 12.2mm in order to fit the bearings. The tunnel will have a integrated system to spray a mist of oil onto the bearings for cooling and lubrication powered by a small 12V pump.

My goal besides getting the darn thing running is to make the complete engine lighter than the 4-stroke engine with elektronics was, it will be a challenge but I have the funding and time to get it done.

Should I have the ball bearings outer races spring loaded in the shaft tunnel? I have been told that spring loading will increase bearing life since it eliminates axial stress when/if the metal expands due to heat.

//Anders

[paul skinner]

I move this up to a separate thread since I don´t want to be a thread-napper...

Now when my jetcart project is as good as finished I will start a more serious project. I will rebuild a medium sized truck turbocharger for ball bearings and make it into a diesel-fueled gas producer, which will be coupled to a power turbine as soon as it runs OK. The power turbine will run without a gearbox due to lack of space (and because I guess that I won´t be needing the extra power...) and will be linked to the rear wheel either by a chain or a belt.

I plan to build the engine directly into the frame of my pocketbike which was earlier powered by a 2hp 4-stroke engine, I guesstimate that the turbine will produce close to 10hp if the power turbine matches the GT. Scary...

I have begun to make some drawings of the bearing tunnel and have both the compressor and turbine housing, but the actual building will have to wait until I have bought a new compressor and turbine and had the shaft CNC-spun down to 12mm from 12.2mm in order to fit the bearings. The tunnel will have a integrated system to spray a mist of oil onto the bearings for cooling and lubrication powered by a small 12V pump.

My goal besides getting the darn thing running is to make the complete engine lighter than the 4-stroke engine with elektronics was, it will be a challenge but I have the funding and time to get it done.

Should I have the ball bearings outer races spring loaded in the shaft tunnel? I have been told that spring loading will increase bearing life since it eliminates axial stress when/if the metal expands due to heat.

//Anders

Is that a custom chassis, or did you just use a one off. It's really beautiful either way.

[Mike Everman]

Should I have the ball bearings outer races spring loaded in the shaft tunnel? I have been told that spring loading will increase bearing life since it eliminates axial stress when/if the metal expands due to heat.

//Anders

Spring preload does a few things that you want, reduces vibration, gets all of the balls in contact and part of the load equation, and as you say, either takes up the slop or relieves the load that thermal growth would create when everything gets hot.
Ideally, you'd get wave washers and spring the inner race of one of the bearings toward the other bearing. You also have to make sure that the sprung race has enough clearance and can still slide on the shaft when all is hot. That's not the easiest thing to verify, and may be cut-and-try.
Do you know if you have angular contact or radial bearings?

Angulars can be more thermally forgiving if set up right. It's not an obvious set up but I can sketch it for you if that's what you've got.

[Johansson]

Paul: The chassis is from a chinese pocketbike, CIG12A is the name if the bike. It is remarkable well built with hydraulic disc brakes and a sturdy frame, and if you consider that I payed 400 euros for the bike with a 4-stroke engine including shipping from China to Sweden it is real bargain.

Mike: The bearings are regular ball bearings. I can get cheramic hybrid bearings (~100 euro/bearing) in the same dimensions as the steel ones I use now, so when I get the engine running I will change to cheramic. I think that wave washers is the way to go, after some thinking and drawing I will post the Cad-drawing of the shaft tunnel here for your comments. This project must take its time so I get it right the first time since I will be sitting on a potential bomb while driving the bike... 8-0

//Anders

[racketmotorman]

Hi Anders
Nice bike , if you'd like some more info on possible freepower setups , have a look at how I did it on my kart at this link ,
http://www.nickhaddock.co.uk/jetgallery.htm
about 3/4 of the way down the page , heaps of pics and a vid , you should be able to get a lot more power than the original engine had .
Theres alo pics and vids of my full sized freepowered bike on the link .
Freepowered turbines are fun :-))
Cheers
John

[Johansson]

Hi Racket!

I can assure you that I´ve seen those pics, I had some plans to build a free-power turbine to the cart a while ago so I studied your projects to get some inspiration. Sadly enough the turbine that I plan to use for the free-power rotates the other way so if I had built it like you did I would probably have got the fastest reversing gocart known to mankind... *LOL*

Did you need any kind of cooling for the free-power turbine shaft?

//Anders

[racketmotorman]

Hi Anders
Theres some bleed air piped from the combustor to an air seal on the shaft behind the sprocket and air bled into and thru both bearings exiting onto the back of the freepower turbine to not only help cool it but mainly to keep hot gases from getting back to the bearings, theres two fittings at the end of the shaft tunnel near the sprocket, ones for air and the other is an oil bleed to lubricate the bearings with just a drip every couple of seconds .
The shaft I used for the freepower was a Cummins "W shaft", relatively thick shafting and the correct rotation to use with just chain redux drive, and the "motor" in its usual position, if I'd used a Garrett shaft , which has the opposite rotation direction I would have needed to put the freepower on the other side of the kart with greater mounting difficulties or used it with a single gear redux first to change rotation and then the chain if I wanted it mounted in the "correct" position .
The kart would have eventually had a larger freepower and all the gases going thru it with a gearbox , but sadly with nowhere to test it development stop at the early stage it did .
The kart has gone to a good home where it will be further developed into the "super kart" it has the potential to become :-))
All the best with your build.
Cheers
John

[Johansson]

The new turbine shaft and compressor wheel are now ordered, when I get them I will turn the old shaft down to aprox. 12mm on my lathe and use it as a guideline when I make the shaft tunnel.

More to come...

//Anders

[Johansson]

This picture gives a rough view of how the bike should look when it is finished, except for a fuel tank under the tail and such things. I have to buy a power turbine that rotates the other way, otherwise I have to rebuild the entire frame to make room for the chain drive on the other side of the bike and it would cause too much trouble.

I probably should wait until the gas producer is running so I can estimate how large the turbine has to be in order to give a moderate back pressure, if the turbine is to small I would have to bypass some of the exhaust gasses and lose power (=bad).

The combustor have to be quite short to fit under the tank cover, no more than 20 cm long. It can have a large diameter though because there is much clearance to the sides. I have decided to run it on kerosine with a propane starter, so the main question is how I should make the vapourization tubes. Would it be better to have lots of small tubes than a couple of big ones, and how should the top of the combustor be designed to produce recirculation? I know that it takes some trial-and-error but it would help to have some rough guidelines...

Does the front bearing leak enough air from the compressor to cool the bearings if I make a drain after the rear bearing? I will use the original shaft seal before the turbine so that no hot gasses reaches the rear bearing, and if there is a flow of bleed air running towards and through that bearing it should keep things cool(ish...). If that would work could I just spray a mist of oil before the front bearing and in that way lubricate both bearings?

//Anders

[Johansson]

The new turbine and compressor wheel have arrived! Now I can finally begin experimenting with the old shaft to find a good tunnel design.

Mike: It would help me a lot if you could make a quick sketch of the spring-loaded shaft tunnel that you were talking about, I don´t fully understand your explanation.

//Anders

[Johansson]

I have started to plan converting the shaft for ball bearings, but so far I haven´t found any useful information on the internet. Some micro turbines with a turbo turbine have had the original shaft spun down and threaded so a custom shaft can be attached with its rear bearing axially fixed, but that sounds way to risky for me. Does anyone know where to find more info on ball bearing turbochargers and such?

If it is possible then I would just spin the shaft down to 12mm and leave it as untouched as possible, just some minor modifications to get clearing to the rear bearings outer race and balls.

My idea is to fix the rear bearing with its inner race against the wide "oil seal" area just before the turbine and the outer race against the shaft tunnel, and then spring load the front bearings outer race with a wave washer and two spacers and make an aluminum spacer between the compressor wheel and the inner race. This picture I found on http://freespace.virgin.net/bigstuff.uk ... k/kj66.htm shows what I was thinking of.

A pipe with bleed air from the combustor and a small amount of oil enters the tunnel before the front bearing and a drain pipe is to be connected after the rear bearing so that the air and oil blows through both bearings and forms a rough heat seal for the rear one.

I may have to build a water jacket for the shaft tunnel in order to keep it from overheating since the bleed air probably won´t be enough to cool both the bearings and the tunnel, but that is a later problem.

//Anders

[mk]

Nice link.

Sadly I cannot provide any useful information to your questions. Despite reading Kamps' and Schreckling's books. They contain a couple of nice ideas, that already have been proven to work.

[Fricke]

[quote="Johansson"]If it is possible then I would just spin the shaft down to 12mm and leave it as untouched as possible, just some minor modifications to get clearing to the rear bearings outer race and balls.

I may have to build a water jacket for the shaft tunnel in order to keep it from overheating since the bleed air probably won´t be enough to cool both the bearings and the tunnel, but that is a later problem.[/quote]

Are You planning on to mount the flamholder between the comp- & turbine-wheels? Then the flamholder needs to be quite short. Turn down the shaft enough for holdning the bearings and place the flamholer behind the turbine, like the are doing on some realwold sized turbines (Have a look at the PAL-turbine, it was made in the mid -80´s (if i remember correctly)...

And you don´t need any waterjackeet around the shaft... the flame holder have a inner lining thet prevents the heat to spead to the shafttunnle...

Just my 50öres tankar...

Edited - Picture added...

[Johansson]

Hi Fricke!

Nope, the combustor will be a can-type just like the one on the gocart and will be located on top of the turbo where the fuel tank used to be, except that this one will be ligher and suffer several hours of testing so that I can modify it to keep the flame zone as short as possible. The one on the cart was sort of a lucky "drill ´n drive" combustor, not much testing there.

Yesterday I drove 700 km to bring my newly bought Honda SuperMagna home, so I won´t have any time to spend on the pocketbike this weekend. It may be wise not to rush things with this project and gather as much information as possible before I start building, the shaft alone cost me over 300$ so it would be stupid to modify it without knowing exactly how it should be done.

Until next time //Anders

[Fricke]

Aha... The usual type...

How is it going with the GO_Kart - have You sold it yet?