Wanna know how many miles you got on your china girls before you had to rebuild?

Discussion in 'General Questions' started by nobullcraptalk, May 9, 2010.

  1. Just curious here.Wanna know who got the most miles on their 2 strokers before rebuilding.My personal best was 600 on my raw riding and gunning It hard.Please share your stories:grin5:

  2. Im at over 1,300miles on my 2-stroke and its running better than new and no rebuild now or probally ever.

    48cc Starfire gt-2 grubee dualstart(pullstart or peddal) dualclutch(manual and auto)
    from gasbike.net for $185 for kit. Its mounted on a Scwhinn del mar cruiser from walmart for $99.
  3. Glad you having great results cabinfever.That's more than my 3 ht's put together.Maybe I'll get a good one someday.
  4. Fabian

    Fabian Well-Known Member

    Ok, my story is a saga but the solution turned out to be a very simple one, though a frustrating one.
    In all cases, fuel/oil ratio was 20:1 using 98 octane unleaded and my location is, Kilsyth in Melbourne (Australia), for those who may want to know the approximate barometric pressure and humidity (at approx midday) of the area at the time of writing - 11th May, 2010.
    Humidity: 70%
    Barometric Pressure: 1024 hPa
    Temperature: 18 degrees celcius.
    Height above sea level: 100 meters.

    The story:

    1st engine: big end connecting rod bearing failed @ 700 Km (460 miles) - max engine speed, 3,500 rpm
    2nd engine: big end connecting rod bearing failed @ 700 Km (460 miles) - max engine speed, 3,500 rpm
    3rd engine: big end connecting rod bearing failed @ 800 Km (500 miles) - engine never revved over 3,000 rpm
    4th engine: big end connecting rod bearing failed @ 700 Km (460 miles) - back to using 3,500 rpm

    4th engine rebuilt with a replacement crankshaft (so technically a 5th engine) and at 350 Km (220 miles) the connecting rod bearing started to give the first signs (light rattles) of failing.

    Found out that the NT carburettors use the same main jet for the 48cc engine and the 69cc engine, on the shipments the shop was receiving.
    The retail outlet was having a shocking return rate with the larger engines; mostly failing from big end connecting rod bearing damage, yet the return rate on the 48cc engines was quite low.

    The solution was so simple - replace the main jet with a Dellorto No 84.
    Although a No 84 is not needed, i've fitted my bike with a shift kit and the engine runs at 100% duty cycle; the 84 jet has the motor running somewhat cooler.
    The engine ran best with a No 82 but a No 83, gave softer and smoother operation.
    With a No 84 and wide open throttle at 2,000 rpm, the carburettor is supplying too much fuel for the NGK BP8HS to maintain enough heat in the plug tip to prevent fuel fouling, but an NGK BP5HS plug may very well hold enough heat to cleanly burn the mixture under those low rpm conditions.

    It all came down to the 69cc engines running lean, with detonation pounding out the big end connecting rod bearing.
    The only modification to my engine is a ported intake tube and SickBikeParts high performance air filter for better flow, everything else is stock standard.

    There are so many reported stories that these China Girl engines run with much improved performance on the 69cc engines using drastically reduced jetting, in the range of No 72 or even smaller.
    I found exactly the opposite to be true.
    Some time ago i ordered a Dellorto SHA Clone and Billet Intake Tube from Rock Solid Engines and a Billet Cylinder Head (but the Billet Cylinder Head is another story in itself). It came fitted with a No 72 main jet and also had the standard No 79 main jet included in the package.
    For the life of me, i was never able to get the engine to run properly with the No 72 main jet fitted and strangely at the time, the engine ran better with the No 79.
    The results from my jetting experiments correlate with those of my SHA clone experience: the engine was under jetted with a No 79, worse still with a No 72 which had the engine running terribly hot, to the point where smoke would be rising from the cylinder head at slow bicycle speeds under wide open throttle, not to mention a pathetic level of power.

    All the obvious things were checked: carburettor and intake air leaks, plug leak, gasket leaks, but they came up perfect when spraying fluid around the component parts of the engine likely to cause leaks.

    I have no idea at all how others are making more power without pounding out the big end connecting rod bearing through low jetting numbers, as my experience has shown the opposite to be true.

    As things so stand, the 4th engine with a replacement crankshaft that's been partially damaged from 350 Km (220 miles) of detonation is now passing 3,000 Km (1,860 miles) using a No 84 main jet in the Nt carburettor - not bad for 100% duty cycle!
    Ok, 100% duty cycle might be stretching the truth just a little, but i'd be prepared to stand behind a figure of 90%.

    My choice of sparkplug heat range comes down to the load factors experienced by the engine.
    With the bike & trailer; shift kit combo and heavy haulage, the engine is always working her guts out; never any respite on a journey, of which some tend to be quite long (60 - 70 mile round trips) with a few painfully steep, 5 mile an hour hill climbs.

    Last edited: May 12, 2010
  5. Wow!!!!!Fabian that Is a saga of epic proportions.And I thought I was hardcore
  6. happycheapskate

    happycheapskate Active Member

    I have a 48cc Grubee "roundhead wingding" Skyhawk. I got about 600 miles on it, and it died tonight. The top ring split up, rammed into the port.
    I ran 32:1 all the time after break in, and ran it 90-100% WOT all the time.

    I just went to the 38tooth cog, and it was nice. The engine did some weird stalling earlier, and had a squeek on start up for a couple weeks, that i thought was a misadjusted clutch. I guess it was the ring scraping, till it finally blew.

    I didn't know what was happening with the stalling, so I put fresh gas in, cleaned the filter, greased the reduction gears, and took off. Ran hard!
    Then, when it crapped out at 30mph. I thought the chain fell off, and when I looked I was perplexed, till I tried to move it. Clunk, Clunk. Luckily only 1 mile from home.

    I don't think i'll ever go more than 50 miles from home again on a HT, because if it blows, I will have to pedal a 1x1 60lb beach cruiser all the way home.
  7. That's one reason I decided to go with a morini and pedal until I get enough paychecks from work to buy one or get a moped.And here In virginia It's hard to get parts unless you order them and wait one or 2 weeks.Which Is kinda hard considering I need a way to work till the parts come by.I ride 50 miles or even 100 on occasion and I am thankful you did not break down far from home.I broke down 35 miles from home once and let's say It was rough having to thumb a ride for 4 hours with a broken down bike
  8. happycheapskate

    happycheapskate Active Member

    Are you talking about the popular 100cc Italian moped engines that people are using as bicycle kits?
  9. AussieSteve

    AussieSteve Active Member

    Fabian, as I said elsewhere, all these engines appear to tune differently. Mine 4-strokes constantly with the standard 0.79mm jet and won't rev out, fouls plugs and smokes way too heavily. (At least I know that I have no air leaks.)
    Like you, I have a 66cc, port-matched and billet head. It runs at a nice temperature with no pinging whatsoever. In fact, unlike many stories I've heard, mine hardly even vibrates.The plug stays a nice clean light tan colour, not grey or white indicating a lean mix.
    It runs slightly warmer than with the stock head, but that's the billet head, not the mixture.
    From the day I bought mine, a little over 500km ago, it's never missed a beat or let me down in any way, except running out of petrol once. (11km walk home.)
    The only thing I'm doing differently to you is that I add octane booster to suit the head to avoid detonation.
    If I run larger than an 0.74mm jet, the engine 4-strokes and actually slows at WOT due to a rich mixture.
    I did plug chops at mid-throttle and WOT to fine-tune.

    I've been tuning 2-strokes on and off for 30 years and know how to recognise a lean mixture or over-hot engine. Not the case here - even in mid-Summer my engine runs at a good temperature.

    The biggest other difference between our situations is that you're about 90m higher. (I'd guess about 5-10m here in Nowra. I'm barely above the coastal wetlands.)
    EnFlaMed, (Andre in the Adelaide hills), went up to a 1.5mm jet to get his engine running well. Whatever it is, something is up to chance a bit and my guess is still an air leak somewhere that the big main jet compensates for, unless it is very slight differences in altitude making that much difference.
    Interesting to hear the various stories on this subject.

    By the way, which 'retail outlet' were you referring to?
    Last edited: May 12, 2010
  10. Fabian

    Fabian Well-Known Member

    The retail outlet is powercycle

    They've been reasonably good to me (and now they have the improved engines with crowded needle roller bearing for the connecting rod big end) but in the early period i just accepted these engines would be useless china junk and didn't bother with analysing the problem, so bought new replacement engines.

    After the 4th engine, i decided to disassemble and replace the crankshaft, mainly for mechanical curiosity.
    After my experiences with the Dellorto SHA Clone experience, i decided to play around with jet sizes and used the following combinations: No 78, 80, 82, 83, 84, 86 and No 90.

    The No 86 was way too rich and the engine was drowning with the No 90.

    I seriously doubt that 50 or so meters of elevation difference would have any significant impact on jetting size.

    Throughout the SHA Clone saga, i tested for air leaks and all was good; using identical checks when dialing in the jetting for the NT carburettor.

    Like i said, i have no idea how some people are making good power with a No 72 main jet.
    What needs to happen is a dyno day (all bikes on the same dyno) with sniffer pipe up the exhaust to see who is getting it right and who is getting it wrong and who is making the most power at 12.7:1 air/fuel ratio; listing jetting sizes attached to the power and torque numbers for individual bikes.

    This will, for once and for all, sort out the BS.

    I wouldn't mind that there's a psychological element going on to this whole debate: tell someone impressionable that their bike will be making more power with a particular jet and even if the bike makes less power, they'll convince themselves otherwise.
    It's a bit like the noisy exhaust system argument: "i've pulled the baffles out and my bike make 200% more power", but we all know it's a load of BS, particularly if they haven't rejetted to suit the reduced back pressure.

    Last edited: May 13, 2010
  11. when my muffler gasket blew out,my bike was atleast 50% faster at accelerating,im not sure if topspeed had changed.
  12. Ol Shakey

    Ol Shakey New Member

    Purchased two motors from Powercycle about 11 months ago, one for a mate that I stripped and matched gaskets ports and checked bearing fits. That motor is now close to 4000K,s without any problems.The other motor I used straight out of the box for my bike,wanted to see how it would perform compared with my mates engine, only lasted a few weeks before rings caught inlet port and stripped chrome from cylinder. This motor was a dog right from the start.Rebuilt motor with new cylinder, now has 3200K,s see Raceline full suspension bike in picture gallery

  13. fm2200

    fm2200 Member

    I have had my 80cc for almost two years, I expect that it will outlast my expectations. The reason I think my engine will last is I think of it as a toy engine and I treat it like a toy. I never run the rpm's high and I have a motorcycle if I want to get my adrenaline fix.
  14. Lazieboy

    Lazieboy Member


    150 miles 09 66cc grubee skyhawk Same thing happened to me. Top ring ended up in crank and locked her up. Happened in my yard and no doing 30....

    Attached Files:

  15. motorpsycho

    motorpsycho Active Member

    yeah bit the problem with a "dyno day" is that every carb. would be jetted different depending on what part of the world everyone is from. not every engine will run at it's optimal peak with a # 72 main jet.(for example) My stock n.t. carbs are jetted with #74 delorto jets, and they run very strong. (32 mph top speed, absolutly no 4 stroking, 41 tooth rear sprockets, 20" rear wheels, 20" frames, and i weigh 155 pounds.) both of my engines are from b.g.f. so they were cheap to buy.
    seriously, a dyno day? it would be interesting to see how much power people are actually putting to the ground on one of these.....altho it's probably not very much.
    Last edited: May 9, 2011
  16. Wheres my dog

    Wheres my dog Banned

    Now that is commitment with 4 rebuilt engines at hand
  17. ktjensen

    ktjensen New Member

    This discussion tells me a couple tips

    1) You engine might fail between 400 miles and 800 miles. Due to burnout, because the engine is not tuned right, or over stressing the engine.

    2) Should get the engined tuned for not too lean, not too hot, just right; by someone who knows two-stroke engines. Or just take your chances. And to not run the engine full power at all times.