Motorized Bicycle Engine Kit Forum  


Go Back   Motorized Bicycle Engine Kit Forum > Motorized Bicycle > Motorized Bicycle General Discussion

Motorized Bicycle General Discussion All topics regarding bicycles with engines.

Thread Tools Display Modes
Old 10-14-2009, 08:01 AM
Fabian Fabian is offline
Join Date: Sep 2009
Location: Australia - Melbourne
Posts: 168
Default Chinese Bicycle Motor - Bearing Part Numbers

G'day all

I am in the process of rebuilding my Chinese 2-stroke 69cc Bicycle Motor as the bottom end needle roller bearing connecting the crankshaft pin has failed.
Amazingly and even though the connecting rod can move in the vertical plane by 2mm (clunk, clunk, crikey that's a lot of play when moved about on the crank pin), the needle rollers are somehow still captive in the needle roller cage and give the appearance of looking ok.
I don't understand how this is possible as the motor was rattling it's guts out and the small end needle roller bearing looks to be in perfect condition.
Upon disassembly, a metalic mud film was found to be covering the crankcase area, so something in significant quantity has removed itself from the bottom end bearing and pin.

Now that the motor has been stripped down, i want to replace all the bearings and seals, including connecting rod needle roller bearings with high quality items.
Does anyone know a reputable manufacturer and a listing of part numbers and dimension specifications for replacement bearings.
When the crankshaft is rebuilt, i want to get it balanced with the new piston for a super smooth and reliable engine.

I'll post hi-res photos of the rebuild process.

Maybe Normans input might be of some help here

Cheers Fabian

Last edited by Fabian; 10-14-2009 at 08:30 AM.
Reply With Quote
Old 10-14-2009, 05:13 PM
Junster's Avatar
Junster Junster is offline
Motorized Bicycle Elite Member
Join Date: Jun 2009
Location: Washington St.
Posts: 446
Default Re: Chinese Bicycle Motor - Bearing Part Numbers

Just a guess but I'm thinking the material came from the connecting rod itself.
Put something FUN between your legs..
Reply With Quote
Old 10-14-2009, 07:53 PM
wildemere wildemere is offline
Motorized Bicycle Elite Member
Join Date: Feb 2008
Location: Newcastle
Posts: 269
Default Re: Chinese Bicycle Motor - Bearing Part Numbers

Just get a new crank unless you have a 20t press and associated jigs to rebuild it.

I guess its the big end bearing cage which has disintegrated into your metallic mud.

The rollers are still present but the cage is gone.Unfortunately this bearing is hard to source and change.

Anyway, give Warren at ZBOX a call he may have a crank.

MBB Imports has the oil seals the other 4 bearings are stock items at CBC or other bearing suppliers. Get Japanese ones.

Stihl have a nice top-end bearing that fits these needle bearing motors. P.N 9512 003 23

Just remember these motors are junk, no retainers on bearings, no dowel pins anywhere.

So the end float on all critical parts is hit and miss, they sound and run different each time you start them.

Some run better than others, I find the older bushing motors run best. I have a 2 year old ZBOX that has done 100km a week sometimes. Others have grenaded in 2 months. Some pull 60 kmh with a 35t sprocket. others struggle to get over 45.

But I still like 'em. Just get 2 bikes and 3 or 4 motors and you cant go wrong.

I've commuted and relied on these stupid things for 2 years now. I tried the turd polishing for a while then realized it was pointless. Get a second bike then repairs happen when you want to do them.

At this time I have three bikes, the "champion shifter bike" (weekends only) as they are inherently unreliable, (3 chains and 2 freewheels) but it pulls 70+ kmh.

Then 2 single speeders for work and back.
Reply With Quote

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

All times are GMT -5. The time now is 08:58 PM.


Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2016, vBulletin Solutions, Inc.