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Discussion Starter · #1 · (Edited)
Hi Guys,


I'm albinolynx from Hungary!
I hope not probleme the new topic...

I buyed used pocket bike ~80$. The Build date is: 2007
China Clone - called "YHXPB101"

I dismantled the bike. The frame, plastics not broked, damaged. Wheels, brakes are ok. I put the engine my desk. Spark is good.
Everything, except my pull starter... I read this engine has a very bad construction pull starter. Allways fall to pieces. Withal I have missed parts!
I want you to help me!

Here is some picture the starter:

pic 01 | pic 02 | pic 03 | pic 04

I now a missing part is a "coil spring" (retraction cord).
But the aluminium parts... Compression spring? Pressure washer?

I search wigh google, search in this forum - don't find exploded view over this unit.

Maybe this is a missing parts? -> missing parts

I hope can you helping me and understanding my not nearly english writes!
Thank You!

Ps.: If in the wrong place asked, please move the right place!
 

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There is a thin coil spring somewhere that keeps tension on the spool and the rope. there is a washer and bolt in the center. Parts must be hard to get there.
 

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Discussion Starter · #4 · (Edited)
Bigmotorsport.com looks a very good place. Unfortunately - not shipping to Hungary...

I found ebay the pull starter, but this ~20-30days shipping.
Now I'm trying start the engine with drill driver (with battery).

Thank You!
 

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Discussion Starter · #5 ·
Anybody have a 2D top view CAD drawing for this?

cylinder ports

I would like to know the ports:
- deep
- radius
- any dimensions

I can made this modifications with milling machine.


Thank You!
 

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Anybody have a 2D top view CAD drawing for this?

cylinder ports

I would like to know the ports:
- deep
- radius
- any dimensions

I can made this modifications with milling machine.


Thank You!
I grind in my boost ports by hand...I grind them between 5/16" wide all the way up to 1/2" wide,,,some go wider

I go pretty deep to the outter part of the cylinder within 1/8"..I mic my cylinder wall thickness so I know how far I can go

When I grind in the height I go 1/8 above the transfer ports and give the roof a 45 degree angle so the transfers dont interfere with the 3rd port feeding the cylinder or throw the fuel out of the tailpipe.....

Then I window the piston the same size in the same place as the boost port aswell as drill in 4 releif holes in the piston sides facing the stock transfer ports......







 

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Looks like you need to order a new cover and wait 20 or 30 days. Have to turn the engine pretty fast to get it to start, and you might break the head of the center crankshaft bolt off.
 

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Discussion Starter · #8 ·
That's my cylinder inside:

cylinder inside

The exhaust port:
exhaust port

The basic fuel canals (= transfer ports?) different's. I can do something modifying?



Here is a "mixed" pics (your & my):
inside & exhaust

I highlighted red are inside the cylinder. I think this is a simple "segments of circles" - as this sample:
sample "half" hole

(I force no the milling, but I have a milling machine and this cutting is very easy and clean can I make with the machine.)

Can you give a approximate dimensions of this "half" hole? Diameter, deep.
I try to understand what you tell me, but the language barriers... I hope you do not mind so!

Thank You!
 

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Discussion Starter · #9 ·
Yes, you right! I have idea resolving this problem. I make and show you.
(I ordered the new pull starter. I hope come fast.)
 

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That's my cylinder inside:

cylinder inside

The exhaust port:
exhaust port

The basic fuel canals (= transfer ports?) different's. I can do something modifying?



Here is a "mixed" pics (your & my):
inside & exhaust

I highlighted red are inside the cylinder. I think this is a simple "segments of circles" - as this sample:
sample "half" hole

(I force no the milling, but I have a milling machine and this cutting is very easy and clean can I make with the machine.)

Can you give a approximate dimensions of this "half" hole? Diameter, deep.
I try to understand what you tell me, but the language barriers... I hope you do not mind so!

Thank You!
Looks like you have an engine with a 40mm piston.....Itll still be pretty powerful and with the right mods scream pretty hard........

On the transfer ports[side ports] I widen them in the pockets and raise the height .025" without changing roof

Race porting the engine case and blueprinting flow by trimming head skirt for enhancing velocity



Theres a thread done by a very thorough member here who has built one in detail with numbers you may be able to follow if you have knowledge in a degree wheel................His name is Mexicano and the thread is called Race engine built.





 

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In your sample half hole it can be done at that depth but you can go 1/8" deeper to flow more fuel mix to the topend..........
 

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You could go 1/2" wide on the 3rd port you are adding, make 2 cuts down the bore. With the 40mm bore the cylinder is thicker than a 44mm bore so you can go deeper than the 44mm bore.
 

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Discussion Starter · #13 ·
I clean my engine and disassemled.



Here is the plan:
- surface refine on crank (lower curved part) ->crank surface (before)

- first milling 2 "half" hole (ports) in cylinder (wall thickness stay min. 2mm) -> cylinder + ports (before)

Here is the milling plan: milling plan

What mill use?
12mm endmill or 12mm radius mill (r=6)?


- turning off the cylinder head -> cylinder head (before)

Cylinder head (hope) after: cutted off cylinder head

- turning a new cylinder head (aluminium), center spark, better combustion chamber
- modifying the piston skirt (cut 2 window to skirt?)
- modifying the exhaust port

Some pictures:
clean engine
rasped molding surplusages, radius, chamfer making
my piston, looks fairly unused
piston head "grime" (black)

I hope my sketches is understandable. Thank You!
 

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Id put the two ports closer together and would also go .05mm higher on the boost ports than the transfer ports





Looking at the piston it looks like the old owner didnt ride it too gentle to break it in right,,,,

 

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Please tell me thats wide: dimension

What is the best?
Perpendicular or angled?

When they have their - i make the mod. :)

Thank You!
In dimension.....you want to leave enough meat for the ring splits...Just make sure the ring splits arent riding inside the boost ports and youll be ok......


On the perp or angled cut...its your call but I mostly go perp to keep the velocity and mass of boost consistent.........
 

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Discussion Starter · #17 ·
A made...

What is the maximum RPM this engines in factory version?
10.000 - 15.000RPM or lower?

I can using a 95 Octane gasoline. What is the best mixing ratio with oil?

Oil: full synthetic or half?
 

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A made...

What is the maximum RPM this engines in factory version?
10.000 - 15.000RPM or lower?

I can using a 95 Octane gasoline. What is the best mixing ratio with oil?

Oil: full synthetic or half?
8,500-12,000.

50:1 is a good mix for already broken-in engines,,,,if you put new rings go 32:1 for a tankful then go to 40:1 for a tankful then go 50:1......I use Maxxim927....Its synthetic and castor based........
 

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We just make the chamber smaller for more compression more horsepower. Some big bore kits have seperate cylinders and heads and a copper head gasket and in the head the compression piece is changable, 13:1, 15:1, 17:1, and there hemi head pieces with the spark plug in the center. Here are some engines I built.
 

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