Failure of Happy Time style 2-stroke Big End Connecting Rod Bearing

[Fabian]

Hi arceeguy

I've owned a lot of nice things, cars, motorbikes, radio controlled models ect.

The second most fun thing i've ever owned: a postie bike.

Without question, the most fun i've ever owned and had the pleasure of improving - a motorised bicycle.

Nothing has come close!

I've never enjoyed a toy (that doubles as transport) as much as my motorised bicycle.
Everything is a challenge; the art of motoring is just embedded in a motorised bicycle.
To maintain maximum speed, you need to be always looking ahead at the road terrain, for subtle changes in angle, picking the right gear ahead of time, having the right revs onboard,otherwise it's all over and you've just stuffed it up; having to change back into first gear for a slow climb till the road flattens out and you can pick another gear and start all over, trying to build speed.

With a car or motorbike, you just turn the key and go - it's so boring.
That's probably the best way to descibe it.

A motorised bicycle takes you back to the pioneering challenges posted by early mechanised transport - everything was a challenge (reliability wasn't guaranteed) and you needed mechanical knowledge and repair skills to fix problems along your journey.

When i travel from point "A" to "B", sometimes it's filled with challenging hill climbs, and gear change after gear change after gear change, my god, did i say gear changes; your arrival at destination brings on feelings of achievement, almost like climbing Mt Everest.

Nothing i've ever owned has given me so much satisfaction and a sense of adventure.
The ordinary road you travel on, effortlessly in a car, takes on a new sense technical challenges, never experienced by any other means of mechanised transport, particularly with a heavily loaded trailer.

Fabian

 

[arceeguy]

....With a car or motorbike, you just turn the key and go - it's so boring.
That's probably the best way to descibe it.....

With my motorized bike, it is pedal - pop the clutch and go. I have found it to be rock solid reliable because of proper installation and set up. Nobody wants to be wrenching on something when they just want to ride. I use my MB for short, in town trips less than 5 miles. I have a 110cc trail cub I use for longer trips. (goes 55mph, rides with local traffic - not the shoulder) And I just got a 500cc motorcycle for freeway use.

My point was that you are spending $900 to highly modify a piece that was meant to be the volkswagen of the motorized biking world. Why are you doing this? For more power and better reliability at those higher power levels. (Nitrous? not good for reliability!) Why not just get a used motorcycle, and you'll get the speed and reliability for less!


And what puzzles me is that you are keeping the stock carburetor, which (once again IMO) is probably the one part that you can upgrade and get a lot of performance benefit because of greater tuneability. Suzuki rods, nikasil plating, etc. and the stock carb with fixed pilot circuit. Does not compute!


If you want a good MB kit, I recommend you get a four stroke kit like an EZM or one of the Grubees and modify the HuaSheng four stroke to your hearts content. I like the 2 smoke happy times as-is. Sure they are crude little motorbikes - but that's part of the charm I suppose.

 

[Fabian]

The 4 stroke engines are not worth considering in an environment where legislation has effectively banned the use of motorised bicycles.
They are far too large to be used in a stealthy way - from a police perspective, a big engine must make more power than a little engine if the police officer doesn't have an understanding of the differences between 4-stroke vs 2-stroke.
The retailer in my area selling Chinese engine kits cannot understand why the 4-stroke kits refuse to sell.
Most of the people buying the 2-stroke kits have lost their car licence (myself included). I had to explain this simple fact to the retailer.

I only need about 25% more power, but a much broader torque band would be nice - this coming from the extra engine capacity of a big bore, stroker engine.
The standard carburettor allows enough power in standard configuration - i simply don't need more carburation or any more speed - i'm not modifing for extra speed but for reliability and a silky smooth engine.

The Nitrous setup is purely for the enjoyment of having nitrous on a bicycle, and the extra oomph for a few seriously steep hills - again, not for speed.
It will have it's own fuel injector together with nitrous injection so not relying on the carburettor suppling extra fuel - the standard carburettor works adequately for the application.

Computes perfectly.

I,ve had race bikes, high performance cars, fast road bikes but none of them come anywhere near the enjoyment of my motorised pushbike.

Fabian

 

[cpuaid]

i've pretty much given up on chinese frame mount 2-strokes. had similar problems as Fabian did with them. they are fun and a real bargain for the price but if you have to commute longer than 5 miles daily or face a lot of hills, they are going to break on you prematurely. i gave it a go on 5 different kits, even a Grubee, but they just aren't reliable enough for my needs. don't get me wrong, for short distance riding they are adequate. i bought them thinking they were reliable enough for my 25 mile daily commutes but have been disappointed so many times. i can't even count how many times i've had to disconnect my drive chain and peddle home. i still have my Grubee when i want to go meet up with other riders but its going to be my Staton or GEBE when i'm commuting to work.

 

[Fabian]

I have to agree with you cpuaid.

The Chinese 2-stroke engine kits are complete garbage and need major engineering work to make them reliable.
The simple fact that the primary drive gears are not lubricated in an oil bath is engineering stupidity at it's highest level.

Having said that, the only safe option for those people who have lost their licence and want a stealthy motorised pushbike is to go with an "in-frame" 2-stroke engine kit.
Standing from behind the bicycle, you can't even tell there is an engine in the frame - this is the only reason why it is so appealing.

My replacement engine is now starting to make big end bearing rattling sounds after just 1000 kilometers - the first engine lasted 700 kilometers.
Everyone who i've come accross with these 2-stroke engine kits has either had them seize from not running 20:1 or had the big end bearing fail.
Even the Chinese importer/distributor/retailer has admitted a lot of the kits are failing due to the big end bearing destroying itself.

Yes, these engines are complete garbage but they can be reengineered to work reasonably well - at a cost.
If you've lost your licence and need a stealthy engine package, the cost of reengineering becomes irrelevant.

Fabian

 

[arceeguy]

.......The Chinese 2-stroke engine kits are complete garbage and need major engineering work to make them reliable.
The simple fact that the primary drive gears are not lubricated in an oil bath is engineering stupidity at it's highest level......

Well, you're the one who is dumping several hundred dollars into one, not me!

FWIW, I have sold over a hundred kits and even fully assembled bikes. Haven't had one big end failure. (a couple of wrist pin bearing failures - riders admitted high revs might have contributed) Maybe the problem is isolated to an Australian supplier?

 

[Fabian]

Yes arceeguy,

I am dumping several hundred dollars into a 2-stroke Chinese engine but to do it only "once".

I can't believe that you have not had a big end failure.
Just looking at the big end design and the bearing used, and doing some maths on the forces acting on the needle rollers with a K16x21x10 - unreliability is built into the system.
The way to go is to replace the 16mm pin with an 18mm O.D. item; machining the connecting rod big end to 22mm and using a K18x22x10 bearing to lower the stresses acting on the needle rollers.

By offset line boring the crank halve pin bores to 18mm, stroke can be increased by 2mm and as part of the reassembly process, the crankshaft can be correctly balanced and trued for a vibration free engine.

Fabian

 

[arceeguy]

Yes arceeguy,

I am dumping several hundred dollars into a 2-stroke Chinese engine but to do it only "once".

OK, I get it now. If you doing this just to do it, that's cool. But you do have to admit that all these mods are impractical otherwise.

......I can't believe that you have not had a big end failure....

Not me, nor any reported failures from units sold. Sure I've had to warranty CDI units, and carbs that had floats that didn't - but no big end failures. And when people brought back seized engines from wrist pin failure, a quick look at the bottom of the piston and the burnt oil meant it had been run hard for a long time. In those cases, I provided parts for free but charged labor. When I asked if they were "racing around" people usually say "oh no, not me" - but when I show them the fried parts and ask how that possibly could have happened, they'll fess up.

I also instruct people to use a 32:1 ratio after the first tank at 20:1. No problems.

......Just looking at the big end design and the bearing used, and doing some maths on the forces acting on the needle rollers with a K16x21x10 - unreliability is built into the system......

I'm not a mechanical engineer. What exactly are the forces involved, and how much does a slightly larger bearing help?

I figure that the Chinese were using these engines by the millions before they started selling them outside of their domestic market, so the design, which is almost elegant in its simplicity, is sound. It has the same charm as the air cooled VW, and is quirky just like the air cooled VW.

 

[iron_monkey]

My replacement engine is now starting to make big end bearing rattling sounds after just 1000 kilometers - the first engine lasted 700 kilometers.
Everyone who i've come accross with these 2-stroke engine kits has either had them seize from not running 20:1 or had the big end bearing fail.
Even the Chinese importer/distributor/retailer has admitted a lot of the kits are failing due to the big end bearing destroying itself.

Judging by the fact you need 25% more power, you are probably wringing these engines near redline.

These chinese engines are reliable if you keep the rpm low and the oil mix reasonable (i run 30:1), but that means less power. Mine has done about 1000km - start and stop metro riding.

I only had trouble with the accessories; the CDI, small cog getting loose(when it was manual), and the centrifugal clutch.

I can't believe that you have not had a big end failure.
Just looking at the big end design and the bearing used, and doing some maths on the forces acting on the needle rollers with a K16x21x10 - unreliability is built into the system.

The forces cant be that big as these engines make stuff all power compared to a proper tuned 66cc 2 stroke with normal compression.

One thing that might break these engines is the lack of oil in the crankcase when new(can anyone confirm this?) and people riding them hard during this time. If so it would be beneficial to pour 2 stroke oil into the crankcase as these engines need splashing oil to be lubricated.

Given your situation, a 4 stroke is exactly meant for you. Not sure how it is so much less stealthy(perhaps remove the red covering). If the local police are going to nail you, they will.

 

[Turtle Tedd]

Happy time motors is what they is...mine running good after 400miles...cant make a Corvette out of a Kia