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

Discussion in 'General Questions' started by Fabian, Oct 26, 2009.

  1. Fabian

    Fabian Well-Known Member

    It's all fairly self explanatory

    The Chinese 2-stroke motorised bicycle engines that i have purchased from a Chinese distributor/retailer are all having similar problems with the big end connecting rod bearing failing in relatively short time.
    They initally thought it was the crankshaft bearings failing so ordered high quality bearings to be fitted for their subsequent shipments but the engine failures continued.

    When my first engine failed from a blown big end bearing and the second engine, now starting starting to make similar big end rattles, after being well looked after, had me develop a sense of frustration, to the point of wanting answers as to exactly which component of the bearing or it's construction is causing issues.

    It just looks like the cage and the needle rollers are made out of very low quality material.

    I've managed to find a supplier who can ship a high quality replacement K16x21x10 Needle Roller Bearing.
    Once i've received the bearing, i'll have the crankshaft, replacement connecting rod and bearing assembly and piston sent to a reputable Kart engine rebuilder to have the crankshaft lightened, balanced and trued to finally achieve the goal of a reliable and smooth running engine.


    Attached Files:

    Last edited: Oct 26, 2009

  2. Ol Shakey

    Ol Shakey New Member

    lightened crank

    Hi Fabian,I would not lighten crank to much as it serves as a flywheel in these engines,balance it certainly,this wil help with most fatige failures,My motor has had minor balancing,runs much better than standard,2500 k's and revs to 6500 no problems so far

  3. Fabian

    Fabian Well-Known Member

    Some Specifications for the Happy Time style 69cc connecting rod

    Attached Files:

  4. Fabian

    Fabian Well-Known Member

    I've come accross a Suzuki connecting rod that is very close to the 69cc connecting rod.

    Scroll down to Suzuki Connecting rods (page 252/253) and look for part number 03.3180
    It's 14mm wide, which works out very well for the small end, but the big end would have to be machined down 2mm on each side from 14mm to 10mm.
    The other obstacle to overcome is the 23mm big end diameter and 16mm small end diameter - a steel sleeve would need to be machined as a press fit for both the big end and small end to give the correct 21mm and 14mm for the original bearing sizes - can't see why this would be a major problem.

    I have no idea what model of Suzuki motorcycle this aftermarket connecting rod is used in replacement of the original Suzuki part.
    Still, it's a good option for a high quality item to replace the standard Chinese connecting rod.

  5. Fabian

    Fabian Well-Known Member

    Ok, been busy doing research.

    Looks like the Suzuki LT80 Connecting rod is perfect for the 69cc engine.
    It has the exact 85mm centre to centre dimensions of the original connecting rod (perfect) and with some basic modifications: big end diameter sleeved down to 21 or 20mm depending on what bearing you choose to use, and machining the width of the big end down to 10mm.
    The small end could be sleeved down from 16mm to 14mm if you want to use the original bearing "or" you could investigate this tempting idea:

    using the Suzuki LT80 Piston which is 50mm.

    This would require machining the original 47mm bore to 50.5mm and having the bore electroplated and honed to 50mm.
    I will have to do more reseach on the exact dimensions of the LT80 piston to see if the writpin to piston crown is similar.
    If it is similar, then you would not even need to sleeve the small end of the connecting rod and you would get the added bonus of having a beefier small end bearing.

    Engine capacity would go from 69cc up to 78.5cc :tt1:

    Connecting rod:


    Now that's an option, looking very much like Cherry Pie
    Last edited: Oct 30, 2009
  6. Fabian

    Fabian Well-Known Member

    There is also something else i'm looking at: stroking the crankshaft.

    Using an 18mm crank pin and line boring the crank pins holes in an offset manner, the stroke could be increased by 2mm.
    This could require a slightly shorter centre to centre connecting rod ength but that can be achieved by offset grinding the big end sleeve.

    Combine the extra 2mm stroke with a 50mm piston bore and engine capacity jumps to 82.5cc
  7. 210061741

    210061741 Guest

    Great work here.
    How much dough is this gonna take.

    I'm wondering what the real advantages of doing that would be.

    What is the overall impact to the system?
    More HP at the same RPM ?
    Where would the Optimum Torque end up at ?
    What would the max RPM be?
    Would the crank need balanced to match the piston?

    I seriously want to get to speed faster = higher torque
    I seriously want to go faster = Better Gearing / Jackshaft

    So if we can increase the effective Torque.
    And increase the RPM abilities.
    And make the motor last longer.
    I'm sure we would have what we're after.

    I spent the last week looking at high power high rpm motors.
    Honestly after it all I think the HT is a more usable soloution.

    I can't wait to see where you end up.
    I know how much work is involved in searching out these things.

    With great appreciation i will prolly follow you footsteps.
  8. Fabian

    Fabian Well-Known Member

    Hi Rich

    I am not looking for a huge amount of extra power; only need about an extra 25% to make the engine more usable. The nitrous kit will only be for overtaking purposes.
    My logic is to increase engine capacity for added low and midrage torque.
    I'll be using the original carburettor as this is an effective power restriction device because of it's low flow rate.

    Having said that, the extra engine capacity will allow the engine to draw in more air at lower rpms, adding torque at those rpm's.
    You won't have to rev the rings out of the engine to push the bike up hills.

    Yes, you would need to get the crank balanced as a larger and heavier piston is being substituted for the original.
    That doesn't worry me as i'm getting the crankshaft balanced and trued anyway.
    What i do need to investigate, is the minimum allowable wall level thickness before cutting into the cylinder ports.
    This will dictate what the maximum overbore can be.
    The Yamaha YZ80 Wiseco piston comes in 0.5 oversize increments, i.e 47.5, 48.5, 49.5, 50.5
    Im going to try for the maximum overbore and then have the cylinder impregnated with Nikasil for the hardest surface finish commonly available.

    Obviously cost is an issue, but i'm more interested in reliability and smoothness, as i don't want my frame to crack from stress related vibration problems.

    Just doing some numbers, the engine will cost somewhere between $700 and $900 when it's finished, including the cost of the engine and machining work and quality aftermarket parts.

    I'm prepared to pay for quality and reliability and usability.

    Last edited: Oct 31, 2009
  9. Fabian

    Fabian Well-Known Member

  10. arceeguy

    arceeguy Active Member

    Just my opinion, but I think that you'd be better off (and road legal in Australia) with a small motorcycle or scooter. You can buy a used postie bike (Honda CT-110) that would be super reliable and have better performance than any modified bicycle engine. I guess I am in the minority when I hop on my MB and putter around at 20mph. If I'm in a hurry, I hop on my motorcycle or get in a cage.

    FWIW, it seems like our suppliers here in the US have not had any problems with lower end bearing failure.
  11. Fabian

    Fabian Well-Known Member

    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.

    Last edited: Oct 31, 2009
  12. arceeguy

    arceeguy Active Member

    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.
  13. Fabian

    Fabian Well-Known Member

    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.

    Last edited: Oct 31, 2009
  14. cpuaid

    cpuaid Member

    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.
  15. Fabian

    Fabian Well-Known Member

    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.

  16. arceeguy

    arceeguy Active Member

    Well, you're the one who is dumping several hundred dollars into one, not me! :grin5:

    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?
  17. Fabian

    Fabian Well-Known Member

    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.

    Last edited: Oct 31, 2009
  18. arceeguy

    arceeguy Active Member

    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.

    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.

    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.
  19. iron_monkey

    iron_monkey Guest

    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.

    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.
    Last edited by a moderator: Oct 31, 2009
  20. Turtle Tedd

    Turtle Tedd Member

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