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post #1 of 22 (permalink) Old 3 Weeks Ago Thread Starter
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Hello there

Hey all. I bought a random pocket bike to fix up on a whim knowing nothing about it. Unbeknownst to me it was a Polini, which is like the ferarri of childrens' race bikes or something? Anyways, its cylinder head and piston are badly scored, and new ones look to be obscenely expensive. Now I'm trying to figure out what to do with it, any recommendations?
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post #2 of 22 (permalink) Old 3 Weeks Ago
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What's your budget???

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post #3 of 22 (permalink) Old 3 Weeks Ago
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Re: Hello there

Quote:
Originally Posted by Oranges0da View Post
Hey all. I bought a random pocket bike to fix up on a whim knowing nothing about it. Unbeknownst to me it was a Polini, which is like the ferarri of childrens' race bikes or something? Anyways, its cylinder head and piston are badly scored, and new ones look to be obscenely expensive. Now I'm trying to figure out what to do with it, any recommendations?
Welcome to the site...…...

Its more like a Corvette....I have a 1999 910 Carenna w/4.2 case that was $2000 brand new ...Phantoms,DM's and BZM's are much better but also much more expensive..

A very nice brand none-the-less...…….



It might be best to get the cylinder bored then chrome plated....

On this engine I bought a new blank sleeve and I mapped the old cylinder and cut the ports into the new one and went with a Wiseco piston with coated skirts.

BTW......This is a BZM engine too.....BZM's are around $5 grand



The sleeve was $155.00..The piston with pin bearing and rings was another $160.00 and to have theold sleeve removed and new one pressed-in after cutting in the ports was another $175.00...

All-in-all around $500.00 versing $1500.00 but this was also back in 05/06

Good Luck

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Last edited by CAM2; 3 Weeks Ago at 07:24 PM.
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post #4 of 22 (permalink) Old 2 Weeks Ago Thread Starter
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Re: Hello there

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Originally Posted by MrKitty View Post
What's your budget???
Honestly I wouldn't want to spend much more than $150-200 tops. Like, ballpark, how much is it worth in parts vs the value of a running bike?


I've never heard of chrome plating a cylinder. Makes sense, but the cylinder is deeply gouged. Not sure it's salvageable without a sleeve, which apparently costs more than a new cylinder and piston. I do have access to a machine shop with a CNC, but I'm pretty sure I wouldn't be able to DIY a boring/sleeving operation. Where would I go for an oversized piston? And any chance there are any knockoff parts that might work instead?
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post #5 of 22 (permalink) Old 2 Weeks Ago
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Quote:
Originally Posted by Oranges0da View Post
Quote:
Originally Posted by MrKitty View Post
What's your budget???
Honestly I wouldn't want to spend much more than $150-200 tops. Like, ballpark, how much is it worth in parts vs the value of a running bike?


I've never heard of chrome plating a cylinder. Makes sense, but the cylinder is deeply gouged. Not sure it's salvageable without a sleeve, which apparently costs more than a new cylinder and piston. I do have access to a machine shop with a CNC, but I'm pretty sure I wouldn't be able to DIY a boring/sleeving operation. Where would I go for an oversized piston? And any chance there are any knockoff parts that might work instead?
You can take it and throw it away 😢. It's not worth to repair that.
The biggest piston from Polini is 35,9mm as I know.
A new cylinder kit is about 260€ + shipping, with piston, pin, clips and ring(original Polini parts). It's a 5 port aircoold and yours looks like a 3 port.

Get your kick with 2 stroke mix
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post #6 of 22 (permalink) Old 2 Weeks Ago
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Unfortunately I don't see it happening with your budget those are extremely tight tolerance engine's and you definitely need a new cylinder piston and rings maybe a new crank

They go for about 1000$ running your looking at 600$ minimum to rebuild the one you have.

If it where me I would just box it up and save it for a later project and get a CAG for now you can get a CAG engine new complete for 65$ off ebay
https://www.ebay.com/itm/Blue-49cc-2...QAAOSwBG1cr~3t

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post #7 of 22 (permalink) Old 2 Weeks Ago
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You will only be in your budget with a used cylinder kit.

Get your kick with 2 stroke mix
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post #8 of 22 (permalink) Old 2 Weeks Ago
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Chrisi do you happen to have something that will work for him ?

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post #9 of 22 (permalink) Old 2 Weeks Ago
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Re: Hello there

Quote:
Originally Posted by Oranges0da View Post
Honestly I wouldn't want to spend much more than $150-200 tops. Like, ballpark, how much is it worth in parts vs the value of a running bike?


I've never heard of chrome plating a cylinder. Makes sense, but the cylinder is deeply gouged. Not sure it's salvageable without a sleeve, which apparently costs more than a new cylinder and piston. I do have access to a machine shop with a CNC, but I'm pretty sure I wouldn't be able to DIY a boring/sleeving operation. Where would I go for an oversized piston? And any chance there are any knockoff parts that might work instead?
Knockoff parts...…………...Nope...……Maybe if you buy a whole engine though.

Heres a Polini knockoff on ebay….Better act fast theres only 2 left...LOL

https://www.ebay.com/itm/MOTORE-MINI...-/130074866130

https://www.aliexpress.com/i/3284903...7094321fq2eC8t


Like I stated buying a sleeve mapping the old cylinder then transferring that map over to the new cylinder then dremelling them out perfectly then finding someone to remove the old sleeve and install the new sleeve was very involved and was a lot cheaper in 05/06 when I did it seings back then I was building 3500hp triple nitrous injected engines parttime for a pretty well known racer but was on hiatus pending a broken neck fixable through 3 major surgeries... ..LOL.

This is the place I got the sleeve from...…………

https://www.lasleeve.com/tech/tech-base

To overbore the cylinder

First you mic the skirt thickness to see how thick the material youre working with is...

Then you measure the damaged area and speculate how far the bore needs to go along with honing to clearance specs of the brand piston being used which is .0015" for Wiseco then buy a piston that size...The way it looks youll be increasing that engine a couple mm's larger easily making that sleeve awefully thin.

My BZM cylinder was super wiped out...The piston was so melted to death it was unrecognizable ....

Kind of like this piston on another catastrophic engine failure I had on another bike....LOL



When finding the right piston you need pin measurements,pin centerline to top of piston,ring width and ring groove heights aswell as overall piston height and size

Your best bet would be to find a new air-cooled or watercooled knockoff engine for under $500.00 if they can even be found anymore then buying that and slapping it in the frame...…



Apparently you can get one from Ali Express too but its a blata knockoff but with mods will fit..

https://www.aliexpress.com/i/2002808724.html

OR you can mod the frame to accept a 10hp KTM SX50 knockoff engine...……..

Theyre only $400.00...……….LOL

https://www.ebay.com/itm/Air-Cooled-...AAAOSwTPddGVyQ

Good Luck

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Last edited by CAM2; 2 Weeks Ago at 01:58 PM.
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post #10 of 22 (permalink) Old 2 Weeks Ago
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Chrisi do you happen to have something that will work for him ?
Yes I'll have a used polini cylinder but it's a watercooler, so he will need a waterpump, radiator and expansion bottle.

Also have a BZM air-cooled cylinder kit, but this has to be edited to fit on a Polini housing, when he has access to a cnc this should not be a problem.
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File Type: jpg 15804138659538581954762873606822_1580413882297.jpg (487.3 KB, 3 views)
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post #11 of 22 (permalink) Old 2 Weeks Ago
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That BiZeta cylinder would be really cool if he has to buy a pump radiator hoses overflow tank clutch Bell and housing and all that stuff he's going to be over budget really quickly.

It looks like that ring snaged really hard so I'm concerned about his crank/connecting rod bearing but if that's all good then he could put that BiZeta cylinder piston rings head on and it will bogie

Those China knock off water cooled engines and China knock off parts are trash not even worth fooling with in the end it will cost him more then if he fixes what he has...

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post #12 of 22 (permalink) Old 2 Weeks Ago
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Re: Hello there

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Originally Posted by MrKitty View Post

Those China knock off water cooled engines and China knock off parts are trash not even worth fooling with in the end it will cost him more then if he fixes what he has...
I guess you missed the part were he stated the BZM was AIRCOOLED and needed CNC work done on a watercooled bottomend to work...

Aint this you on a Chinese made rideable...……….?

Shouldn't you be riding a Blata quadard?

I like the caption you wrote about the gearing..To me it looks spot-on with an untuned bone stock engine and an adult rider thats way over the 80lb child rider its actually rated for...…Had it had a modified clutch and a rocket key the takeoff would've been a lot stronger…


Heres a pretty easy comparison video to go by....The pitch and revs match almost exactly until they really let them rip...…….


My real deal 1999 Blata 2.5 came with a Robin 2 stroke brushcutter engine and it costed me $999.00 in 1999....Whats your conscensus on that fact and also the fact that Blata used Polini engines way before they developed their own?...……..

Do you have first hand knowledge of this statement you made about Polini rep engines or are you just going by what others have said in threads which is 100% mainly about the C1/B1 Blata knockoffs which actually are the ones to suck as the steel internals for the waterpump rust-up easily and the seals suck to high heaven...…

On a Polini knockoff you can use a real deal waterpump which the OP should already have.……

What else can fail other than easy to replace inferior Chinese O-rings.....?....LOL

How hard is it to disassemble a brand new engine and tweak it to real deal polini specifications?..Oh wait you don't even know.....

When you look at the alternatives to actually riding the thing your suggestion to the OP would be to wait the time til theres either zero topends left to obtain as he's saving up and justifying spending thode saved-up funds needed to rebuild a bike that's 15+ years old already or actually finding a topend thats new non-used for less than a grand or get the rep engine that's 1/3 the price and if broken-in and treated right can last a pretty long time...

The other thing is the condition of his clutch,crank etc.....His problems could run between $1500 and $2000 especially if he needs a coil too...…..

He puts the running rep engine in his frame and has his fun then when he sells the bike he sells it with a running rep engine aswell as a rebuildable real deal engine that goes with it...…

He will get more money out of the bike than he will just trying to sell it as-is NON_RUNNING.

If the rep engine doesn't work out for him atleast hes out less than $400.00..

If he rebuilds the Polini wrong he will be out a lot more than that......


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Last edited by CAM2; 2 Weeks Ago at 10:28 PM.
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post #13 of 22 (permalink) Old 2 Weeks Ago
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No your right he should take his race engine out and replace it with a 60$ CAG engine

Honestly that's exactly what I would do since I don't have anybody to race anyway

I wouldn't waste my time with any of those reproduction fake Blata engines no one has ever came in here and said those engines are great I'm going to put that on my pocket bike cuz it's great quality.

Every one of those fake rep engines has overheating problems and eventually the carburetor will crack and fall off on top of a slew of other problems ( they sure don't have a very good track record do they)

So do what I would do take that race bike engine box it up put it in the shed write real race bike engine on the outside of the box get that Cagllari Daytona engine for 60$ fab up a mount with aluminum from a old truck bed tool box (use the braceing bars) pay a shop 96$ to weld it up you might need a chain and rear sprocket 12$

Yes fixing the real race engine is way way cooler 🙂 lol maybe just try and find a used CAG for 40 50$ and save that race bike project for when you have the cash to do it right it's so worth it those are supper awsome bikes I wish I had one...

PS if you do a complete BZM swap it's even cooler... EPR has one so awsome...
https://youtu.be/G1O_I6g0Q1I

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Last edited by MrKitty; 2 Weeks Ago at 11:42 AM.
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post #14 of 22 (permalink) Old 2 Weeks Ago Thread Starter
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Re: Hello there

Looks like there's some confusion here so just for clarification, the bike is air-cooled. Seems pretty clear there's no "cheap" way of getting it running without seriously cutting corners or replacing it with a different brand engine entirely. Would it help to make an assessment by inspecting the bottom end, and what would I need to do that?
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post #15 of 22 (permalink) Old 2 Weeks Ago
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Quote:
Originally Posted by Oranges0da View Post
Looks like there's some confusion here so just for clarification, the bike is air-cooled. Seems pretty clear there's no "cheap" way of getting it running without seriously cutting corners or replacing it with a different brand engine entirely. Would it help to make an assessment by inspecting the bottom end, and what would I need to do that?
I would dismantle the cylinder and the inlet in your place if you find no damage in the crankcase and the crankshaft rotates cleanly Buy and install a new original cylinder.

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post #16 of 22 (permalink) Old 2 Weeks Ago
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Check the spin it should spin nice and smooth without any grittynes then check the rod make sure there's no discoloration (blue is bad) and that the connecting rod has no up and down play in the big and small ends if that stuff is all good then you just need a cylinder piston and rings keep a lookout sometimes complete used engines come up for 350$ 400$ when you see one snag it

Check out that vid at 2:39 they show a air cooled on a dyno

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Last edited by MrKitty; 1 Week Ago at 10:27 PM.
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Re: Hello there

The $218 clone Polini is in Italy, will ship to the USA, yeah, for $100 plus or $325, then water pump, radiator, hoses etc. going to be more like $500 plus dollars. So, I assume its a 910. I just rebuilt my 4.2 40cc Polini air cooled engine for my 910 Carena this summer, it was not cheap. Flywheel $125, CS coil $88, $30 for a ring, new clutch arms $60, springs $15, $25 for gaskets, case bearings $30 seals $20 and on and on, my cyld and piston were good, I honed the cyld.
I have a W/C 39cc polini clone I went thru, has a real Polini clutch housing but you don't have a radiator & hoses, etc and its out of your budget. How much did you pay for the bike??
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Empty Pockets Racing: The difficult we do, the impossible takes longer.....

Last edited by EPR; 1 Week Ago at 12:50 PM.
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Re: Hello there

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Originally Posted by EPR View Post
The $218 clone Polini is in Italy, will ship to the USA, yeah, for $100 plus or $325, then water pump, radiator, hoses etc. going to be more like $500 plus dollars. So, I assume its a 910. I just rebuilt my 4.2 40cc Polini air cooled engine for my 910 Carena this summer, it was not cheap. Flywheel $225, CS coil $88, $30 for a ring, new clutch arms $60, springs $15, $25 for gaskets, case bearings $30 seals $20 and on and on, my cyld and piston were good, I honed the cyld.
I have a W/C 39cc polini clone I went thru, has a real Polini clutch housing but you don't have a radiator & hoses, etc and its out of your budget. How much did you pay for the bike??
Yeah my bad...so many members join and it seems most that join have problems that run in pairs or parallels as I call them.....


I forgot it was air-cooled yet I somehow lost track


Anyways heres an air-cooled engine...IDK if that's the actual price but after-all its real deal Polini too...

https://www.ebay.com/itm/Engine-Comp...-/283649823614

I still say the KTM knockoff would work out very well too...…..

Once the DIY motorized bike guys see the KTM50 knockoffs at this price they'll sell out very quick...That's Dax sells them for over $500.00....LOL

https://www.amazon.com/sthus-Cooled-.../dp/B07R33LY4R


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Last edited by CAM2; 1 Week Ago at 11:36 PM.
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The $218 clone Polini is in Italy, will ship to the USA, yeah, for $100 plus or $325, then water pump, radiator, hoses etc. going to be more like $500 plus dollars. So, I assume its a 910. I just rebuilt my 4.2 40cc Polini air cooled engine for my 910 Carena this summer, it was not cheap. Flywheel $225, CS coil $88, $30 for a ring, new clutch arms $60, springs $15, $25 for gaskets, case bearings $30 seals $20 and on and on, my cyld and piston were good, I honed the cyld.
I have a W/C 39cc polini clone I went thru, has a real Polini clutch housing but you don't have a radiator & hoses, etc and its out of your budget. How much did you pay for the bike??
Then you have the wrong dealer for your parts, EPR🙈

Get your kick with 2 stroke mix
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Re: Hello there

The flywheel was $125 dollars I miss quoted. Midsouthminimotos.com, and Stoney is where I got my parts. He is no longer around, to bad, great guy.
Yes, I got confused to, when people started talking about water cooled engines. Same engine cases, for A/C or W/C. My air cooled Polini engine I got off eBay $168, for long block, and had to buy the other parts listed above to complete. Think I have about $500 total.

Got to keep looking, you might find a deal on parts.
Look how well the PR200 Razor rocket body work fits the 910 Polini frame. I had to cut a hole for the gas tank cap to go thru. I have the OEM body.
If you look at the last photo you can see I turned the front forks around to make the wheel base more than 1" longer.
Attached Images
File Type: jpg Engine Polini AC 4.2 Rebuilt 1.jpg (507.5 KB, 6 views)
File Type: jpg Engine Polini AC 4.2 Rebuilt 2.jpg (510.2 KB, 6 views)
File Type: jpg Engine Polini AC 4.2 Rebuilt 3.jpg (490.1 KB, 6 views)
File Type: jpg Surfacing Polini Cyld and Head 1.jpg (509.6 KB, 6 views)
File Type: jpg Polini910 4.2 air cooled 40cc 2.jpg (481.0 KB, 6 views)

Empty Pockets Racing: The difficult we do, the impossible takes longer.....

Last edited by EPR; 1 Week Ago at 07:20 PM.
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