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Connecting rod bearing failure analysis - Chinese Bicycle Engine

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Connecting rod bearing failure analysis - Chinese Bicycle Engine

Post by Fabian on Thu Jul 19 2012, 06:41



This post (and photos) relates to connecting rod bearing failure of 80cc Chinese Bicycle Engines, installed with a caged big-end needle roller bearing assembly.
I have no experience with the 50cc engines so i'm unable to comment on their reliability.

The newer crowded roller big-end connecting rod bearing assemblies are largely free of this problem and quite reliable.
These upgraded engines are the ones to purchase, as they have twice the load carrying capacity of the caged bearing assembly.
From my experience, all big end bearing failures were caused by detonation; induced by the standard CDI with it's incorrect (4-stroke) ignition curve. This continual stress hammers out caged roller bearings even if the engine is given a relatively easy life.
It must be said that excessive rpm for prolonged periods will produce a similar type of failure but the mechanism of the failure is completely different and not related to ignition induced detonation, which is outside of the users control.

The Jaguar CDI solves this issue with a correct 2-stroke ignition curve and has proven to be reliable for over 8,000 kilometers.
For a better understanding of why a 2-stroke requires a reduced ignition curve compared to a 4-stroke engine, this article will make it clear:

http://motorizedbikeforum.the-talk.net/t303-2-stroke-theory-excellent-atricle#471



Those wishing to experiment with upgrade options for the standard connecting rod, the following information may be of use:

Scroll down to Suzuki Connecting rods (3rd page from the bottom) and look for part number 03.3018
This connecting rod is for a Suzuki LT-80 which has the exact 85mm centre to centre dimensions of the original connecting rod, but it's 14mm in width, requiring it to be machined down 2mm on each side to 10mm: the width of a standard 80cc connecting rod, and also a 1mm tool steel sleeve needs to be press fitted to the big end to reduce the internal diameter from 23mm to the standard 21mm.

Replacement LT-80 connecting rod: http://www.pro-x.com/downloads/Technical.pdf



Another manufacturer of after market, high quality replacement connecting rods for the LT-80.

Replacement connecting rod: http://www.hotrodsproducts.com/ProductInfo.aspx?item_id=983



As the small end I.D. of the connecting rod is too large, it could be sleeved down from 16mm to 14mm if you want to use the original bearing and wrist pin "or" you could investigate this tempting idea:

Use a Suzuki LT80 Piston which is 50mm and over bore the 80cc cylinder to 50.8mm and have it electroplated back to the original LT-80 bore size - Engine capacity would go from 69cc up to 78.5cc

Piston: http://www.mfgsupply.com/673m05000.html






























































This photo shows the differences in design evolution of connecting rods installed in Chinese bicycle engines.
The rod on the far left is the most modern design and in step with a typical Japanese design.






Last edited by Fabian on Sat Aug 04 2012, 06:20; edited 15 times in total

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Re: Connecting rod bearing failure analysis - Chinese Bicycle Engine

Post by kavid2012 on Sat Jul 21 2012, 22:30

so if i use stock chinese CDI, my engine will break soon?
i have rode it about 1,000 miles and still ok.

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Re: Connecting rod bearing failure analysis - Chinese Bicycle Engine

Post by Fabian on Sun Jul 22 2012, 01:33

If your engine is fitted with a crowded needle roller bearing assembly, there's a much better chance the big end will survive the detonation caused by the stock Chinese CDI.

The best way to prevent such engine damage is to install a Jaguar CDI - it has an ignition curve designed for a 2-stroke engine.
It has worked so well on my engine that friends of mine have ordered their Jaguar kits.

If the kit didn't work, it would not be installed on my bike.
If the kit didn't stand the test of time, i wouldn't recommend it to other people.


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Re: Connecting rod bearing failure analysis - Chinese Bicycle Engine

Post by swiftyhernandez on Fri Nov 29 2013, 20:09

Fabian wrote:If your engine is fitted with a crowded needle roller bearing assembly, there's a much better chance the big end will survive the detonation caused by the stock Chinese CDI.

The best way to prevent such engine damage is to install a Jaguar CDI  - it has an ignition curve designed for a 2-stroke engine.
It has worked so well on my engine that friends of mine have ordered their Jaguar kits.

If the kit didn't work, it would not be installed on my bike.
If the kit didn't stand the test of time, i wouldn't recommend it to other people.

Please tell me more about the Jaguar CDI.
Where?
Who?
What?
How?

Thank you!!!
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Re: Connecting rod bearing failure analysis - Chinese Bicycle Engine

Post by Fabian on Sat Nov 30 2013, 19:17

The Jaguar CDI can be purchased from JN Motors

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Re: Connecting rod bearing failure analysis - Chinese Bicycle Engine

Post by elgallo on Tue Dec 31 2013, 09:11

Shifty you may want to look into this website also. http://www.dragonfly75.com/motorbike/index.html
And this one also
http://juicemotoparts.com
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Re: Connecting rod bearing failure analysis - Chinese Bicycle Engine

Post by James Cagney on Fri Apr 24 2015, 13:33

Fabian wrote:

This post (and photos) relates to connecting rod bearing failure of 80cc Chinese Bicycle Engines, installed with a caged big-end needle roller bearing assembly.
I have no experience with the 50cc engines so i'm unable to comment on their reliability.

The newer crowded roller big-end connecting rod bearing assemblies are largely free of this problem and quite reliable.
These upgraded engines are the ones to purchase, as they have twice the load carrying capacity of the caged bearing assembly.
From my experience, all big end bearing failures were caused by detonation; induced by the standard CDI with it's incorrect (4-stroke) ignition curve. This continual stress hammers out caged roller bearings even if the engine is given a relatively easy life.
It must be said that excessive rpm for prolonged periods will produce a similar type of failure but the mechanism of the failure is completely different and not related to ignition induced detonation, which is outside of the users control.

The Jaguar CDI solves this issue with a correct 2-stroke ignition curve and has proven to be reliable for over 8,000 kilometers.
For a better understanding of why a 2-stroke requires a reduced ignition curve compared to a 4-stroke engine, this article will make it clear:

http://motorizedbikeforum.the-talk.net/t303-2-stroke-theory-excellent-atricle#471



Those wishing to experiment with upgrade options for the standard connecting rod, the following information may be of use:

Scroll down to Suzuki Connecting rods (3rd page from the bottom) and look for part number 03.3018
This connecting rod is for a Suzuki LT-80 which has the exact 85mm centre to centre dimensions of the original connecting rod, but it's 14mm in width, requiring it to be machined down 2mm on each side to 10mm: the width of a standard 80cc connecting rod, and also a 1mm tool steel sleeve needs to be press fitted to the big end to reduce the internal diameter from 23mm to the standard 21mm.

Replacement LT-80 connecting rod:  http://www.pro-x.com/downloads/Technical.pdf



Another manufacturer of after market, high quality replacement connecting rods for the LT-80.

Replacement connecting rod:  http://www.hotrodsproducts.com/ProductInfo.aspx?item_id=983



As the small end I.D. of the connecting rod is too large, it could be sleeved down from 16mm to 14mm if you want to use the original bearing and wrist pin  "or"  you could investigate this tempting idea:

Use a Suzuki LT80 Piston which is 50mm and over bore the 80cc cylinder to 50.8mm and have it electroplated back to the original LT-80 bore size - Engine capacity would go from 69cc up to 78.5cc

Piston: http://www.mfgsupply.com/673m05000.html




In effort to reply,
The engine no less preforms well with exception to high RPM vibration that can only be resolved by using forged aluminum or titanium parts copied from the original engine parts of these none are yet offered from vendors.ZERO reply the the few known correct adjustments is troublesome alternatives are too few.















































This photo shows the differences in design evolution of connecting rods installed in Chinese bicycle engines.
The rod on the far left is the most modern design and in step with a typical Japanese design.




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Re: Connecting rod bearing failure analysis - Chinese Bicycle Engine

Post by James Cagney on Tue Nov 24 2015, 21:23

I've viewed some of the prices on replacement parts listed above and only due the 66 cc China doll as it's sometimes referred to as simply is not worth the expense. The failures of the internal assembly is due the mainly extreme RPM over fueling porting etc. You'll need a one piece crankshaft cut from a quality billet of steel or aluminum and a connecting rod with bearing that will attach in two halves by the way nearly anyone cat cut out of scrap with on a Dremel table if you want be cheapo 'bout it..Yeah you'll need to cut a window in the engine case to assemble the thing so forget it and spend some bucks on the other idea's Rolex make 2 stroke engine parts ?
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Re: Connecting rod bearing failure analysis - Chinese Bicycle Engine

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