Mathematical formula for balancing 69cc Chinese Bicycle motor

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The Suzuki connecting rod part number of FZ50 for the models 1979 and 1981 are both 12161-04001

The big end bearing part number for 1979 and 1981 are both: 09263-1501c or 09263-15016
This is because the print isn't very clear and i'm not sure if it's a c or a 6 on the end.

The Small end connecting rod part number for both 1979 and 1981 are: 09263-12003
 
Okies,

After splitting the crank on my 69cc Chinese Motorised Bicycle engine to replace the big end bearing (that always fails on these Chinese engines) with a high quality item,

I've not seen, or heard of many complaints of 'big bearing' failures.

I've seen lots of wrist pin bushings worn out. I've never had a roller bearing wrist pin, but have heard of a few failures.

The only bearing that has given any problems, on any of my kits, was a left side main crank bearing. This bearing was noisy, right out of the box, but I ran it several thousand miles. When I finally pulled the seal, some extra metal fell out.

clay,

great pics of your balancing & engine. I am not into extreme speed or power, but a smoother, vibration-free engine would sure be a plus.
Shame they don't engineer this in the factories!!
 
Scroll down to the "16" section - you'll find a K16x21x10

At least this is one company where the bearing can be sourced.

SrDavo, your comment is interesting
The retailer who is selling Chinese Bicycle Engines has had a large number of failures from the big end connecting rod bearings (including my first engine) and no failures from the small end bearing.
The other failures are from engine seizure due to incorrect oil ratio and plain mechanical failure.

I've spent the last two days with the importer/retailer and we have put together a large PDF doccument with photos attached of the big end failures.
It's been sent to the manufacturer in China, to fix their product.

Really interesting that you have only seen small end failures - surprising as the diameter of the small end bearing has significantly lower cage speed compared to the big end bearing.
If a bearing is going to fail, it's more likely to be the big end, come to think of it, my Kawasaki KX500 blew the big end bearing after a vicious over rev trying to hold the bike on the back wheel, going through the gears and maxing it out in top gear for too long on a long straight dirt road.
The small end didn't disintegrate, but it was replaced when the engine was rebuilt.

Fabian
 
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I've spent the last two days with the importer/retailer and we have put together a large PDF doccument with photos attached of the big end failures.
It's been sent to the manufacturer in China, to fix their product.
that's good news.... more improvements on the way. Do you mind telling us who the manufacturer is?

Really interesting that you have only seen small end failures - surprising as the diameter of the small end bearing has significantly lower cage speed compared to the big end bearing.
My daily rider... a 55cc grubee, (lots of miles) is on the 2nd wristpin bushing & is starting to 'tick tick tick'. It's about time to tear it down & have a look.
 
Gees, this is taking me back quite a few years now - a very long time indeed

In the early years of motorcycling my second bike was a Yamaha RZ250 with a set of modified carburettors and a set of race pipes.
It wasn't all that long before it blew the big end connecting rod bearing, after over rev chasing an early Suzuki GSXR 750.
Must have been about 115 miles an hour when it blew - certainly an intersting ride getting it to a stop.
After the thing was rebuilt with RZ350 cylinders, i left Melbourne and moved to Far North Queensland, a ride of some 3600 kilometers (2200 miles).
I loved that RZ250 with the 350cc engine capacity.
For a small engine, it really had some get-up and go.

Must have been up there for 2 years and i found a nice quiet straight road out the back of Cairns on the Atherton Tablelands.
I made another fatal engine mistake.
I maxed out the speed (loved it) speedo reading 220 kilometers (140 miles an hour) and it blew the big end connecting rod bearing
Made for another interesting stop from speed.
After the engine was rebuilt, someone told me that i should have used Yamaha TZ big end bearings as they were far more durable - if i only knew that before it was rebuilt, the first time.

From my experience, 2-strokes seem to have their achilles heel set in the big end bearing - they just don't tollerate over rev because of the limitation due to a needle roller bearing big end.

Fabian
 
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I have no idea which manufacturer the Chinese importer/retailer is using, i never even thought of asking.

The guy who prepared the PDF is Chinese and wrote the thing in Chinese.
He should know who the manufacturer is.

One thing is interesting to note - the early engine kits used a brass bushed small end and 8mm head studs, yet, when we checked a few of the motors from the current shipment, they all use 6mm head studs and a needle roller bearing small end.

Fabian
 
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It also looks like the ATALA RIZZATO Califfone uses a K16x21x10 big end connecting rod bearing - haven't been able to find an Illustrated Parts List to confirm this though.

It seems that all these 50cc 2-stroke mopeds use very similar crankshaft, connecting rod and bearing sizes compared to our Chinese Bicycle Engines.

Maybe someone can find out the dimensions of a Honda 50cc moped's connecting rod and small and big end bearing sizes.
Honda has some of the best engineered and most durable motorcycles.
If i could find a genuine Honda K16x21x10, i would buy it on the spot.

Fabian
 
Have you tried Timken bearings.com I tried to get the link posted,but won't work. They have a listing for 2 cycle small engine, outboard motor applications.
 
Hi Rich

That Suzuki part is not useable for our Chinese Bicycle Engines because the crankshaft pin is 16mm in diameter and the inner diameter of a K15x21x10 needle roller bearing is 15mm.

The only way it could be made to work is by having the working face that needle roller bearing rides on, offset ground to 15mm diameter.
This would have an added bonous of increasing the crankshaft stroke to 42mm from the standard 80cc engines 40mm.

Total capacity would go up from 69cc to 73cc with a boost in the compression ratio.
Fact is that we can get a K16x21x10 and it works with the standard engine parts.

Fabian
 
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