Building a reliable bike from a chinese 66cc

Discussion in '2-Stroke Engines' started by RFlash, May 13, 2012.

  1. RFlash

    RFlash New Member

    There is a lot of info dotted all around this forum, some relevant some not so. I would just like to bring together a lot of it for ease and convenience and to stimulate conversation on the matter with like minds.

    Anyway, this is my third chinese 66cc, first was stolen, second was built for a friend and now, building a third for myself once more. I have need for cheap transport, and frankly, I enjoy riding these bikes a lot. :likelots:

    My last one I made a lot of commonsense changes, added a better kill switch, replaced sparkplug with a high temp motorbike one, best oil available, new wiring etc.

    I am after the changes which are not too expensive (I am now a student) and generally lead to an improvement of the overall situation. I was always fixing thrown chains due to crappy runners etc, I know that has been rectified.

    I am considering the following:

    *Fill bike tubes as much as I can with spray foam filler for deadening
    *Cover inside of mounting brackets with thin rubber before mounting
    *Replace head studs and bolts with high tensile
    *Replace grip shift
    *Replace cables
    *Fit a metal tool box to a rack on the back with an alarm
    *Locate electronics in said tool box with keyswitch (or relay via alarm) (Alarm charged at night as bike is stored inside, 12-14v gel cel)
    *New carb (No idea which one)
    *Drill 2 holes in baffle

    Generally, aside from having to straighten spokes and fix thrown chains, I had a good biking experience so far, I am a girl, I do not have a workshop of any kind and I have limited tools, mostly cheap stuff, ie: no torque wrench. (Hence, I do not want to spend countless amounts on tools)
    I just want something that wont break down when I need it most, I know that most will just say upgrade to a Robin or such, but that isn't an option for me atm, I do look after my stuff and dont mind giving the bike a quick once over look and adjustment on the weekends.
    Sound good? :jester:

  2. Al.Fisherman

    Al.Fisherman Active Member

    A few more items to think about....
  3. Lunardog

    Lunardog Member

    Sounds like you have a solid plan in place. Ron knows 100 times more than I on this subject but I must say that the rubber placed between the mounts and the frame may not be the best idea but my engine vibrates so much with the rubber insulators I'd hate to ride one without. That being said maybe it will cause me issues down the road I dont know. One thing I can recommend highly if you have the ability, is to do the prep work on the engine beforehand. I'm referring to removing the head and the jug and clean and check the lower end for debris. Also a small round file and/or sandpaper to clean the edges of the ports etc for small pieces of casting that could break off and end up where they shouldnt. Take care to not scar the cylinder walls in doing so. I even went so far as to put a light coat of synthetic oil on the wrist pin and crank bearings just to coat them for break in. Good luck and spend some time reading here. Lots of great info from the experienced riders.
  4. RFlash

    RFlash New Member

    I run a wire directly to the engine for the kill switch as well (Prev bike was a non conductive alloy) so grounding is no issue, I do not want to minimise movement of course, will be using loctite on all threads.

    Oh, I will also be sanding all mating surfaces with fine grit sandpaper and using aircraft gasket sealant (that blue stuff) before bolting things together.
    Most of the issues I had was simply because pushbikes are not made for this purpose. (Accelerated wear etc.. Kept getting thrown chains for some reason, I was using high quality scooter chains too, the bike wasnt the best, the one I am motorising now is quality though, hopefully that limits the problems)

    Largely, I believe these engines aren't perfect but they certainly do the job and seem to last when looked after with an average level of care.

    Thanks for your replies :D
  5. HeadSmess

    HeadSmess Well-Known Member

    i like it when girls decide take the initiative :) being female is no excuse for being mechanically inept! anyone is capable if theyre willing. and why arent there any women driving at bathurst, huh? i hate these girls that whinge that they "cant drive manual"..theyre simply too lazy.

    then again my sister has a road train license, but never seemed to realise my pushy had 18 gears and i liked it left in low, not high, back in the day when she was borrowing it... i cant stand trying to downshift 18 gears on the first two metres of pedalling...

    so. rubber on mounts. dont do. while it sounds good in theory, practise proves otherwise. you cant get enough grip on the frame to hold the engine solidly whilst retaining any absorbing qualities, and, instead of reducing vibrations, by letting the engine do what it wants, it actually gets worse... excaberating chain throwing habits..

    a toolbox is a definite must! it should contain one of each screw/allendriver, every spanner you NEED (8, 10, 13, 15... depends on bikes really... some throw you 9mm or 11mm nuts...grrr.) pliers/sidecutters, a pump, spare cables and a patch kit. get a leather tool pouch thingy from the hardware so you can wrap everything up and stop it jangling away madly...

    scooter/moto chain can border on the clunky side, (415 or 420?) but works fine. dont use an o-ring chain if they try selling you one, and make sure theres clearance in the frame stays... i prefer using heavy duty freestyle bmx chain, its only issue is that it vibrates side to side at certain rpm... its very narrow, and only throws if too loose.

    while i first started installing the rear sprocket slowly and methodically, making sure it was fairly true, after 10 or so times i gave up and just bolted it as tight as possible with no ill effects.
    check the rubber supplied. if its an even thickness throughout, use it. if not, try a disc of plywood or something. youll never get the thing to run straight if the rubber looks like a rejected bit of car tyre with one side ground half away... ive had one 8mm one side, 2mm on the other. dodgy :) couldnt even fly straight when i threw it! there are two, so pick the best for the sprocket side of the spokes.

    an alarm...probably location specific. i thought melbourne was fairly easy going... apparently not. typical uni crowd i gather. what are you studying, btw?

    holes in baffle...oh. yeah. for once im not going to say anything about tuned pipes (i just did! :eek:!). if you can though,get a bit of 13mm steel pipe stuffed up its butt instead of the standard 10mm peashooter. im sure a friendly welder would do the work for free... takes all of 20 minutes. needed...a welder, a grinder and a really long 13mm drill bit... unless you skip a baffle or two :) or bash them out completely!

    the frame used is important. or, more to the point, the ACCSESORIES used are important. ally levers, brackets, etc. kiss plastic goodbye. get comfy handlebars. with good grips. the fat ones are the best. get some handlebar weights that are intended for motorbike handlebars and stick them in, they cut the vibrations drastically.( theres also neat lil bar end mirrors... fleabay :) )

    brakes should be alloy, not the cheap pressed steel things supplied on 90% of kmart cheapies. while ive never had one fail, that could be because i dont use them... :eek:

    proper 3 piece cranks, not the silly single piece things as used on huffy and similar.

    a cromoly frame is best, then hi tensile steel, then whatever. dont use aluminium frames!

    and some good pedals. nothing worse than a pedal up the shin because your foot slipped off...
    Last edited: May 14, 2012
  6. Big Red

    Big Red Active Member


    Throwing chains are usually due to poor chain to engine - sprocket alighnment. I run the cheapo chain that comes with the kit and have very few problems with it. If the chain is hitting the rear sprocket DEAD CENTER and tension is adjusted properly then it should run fine. Also use a good chain lube, and use it often.
    Big Red.
    P.S. Thanks for the votes on rep power, whoever you all were.
    Last edited: May 14, 2012
  7. Cavi Mike

    Cavi Mike Member

    No point in filling bike with spray foam or using thin rubber for mounts. It won't stop the vibration. It may lower the resonant frequency of the bike a bit but it just changes which RPM makes the bike vibrate.

    No need to replace the head studs. It's just a 2hp engine, not 20.

    Once again, no need. I'm probably the laziest person when it comes to maintenance, I rode my bike all winter in the salt and have never lubed my cables. They still work fine and haven't broken.

    Just make sure the mounting studs are threaded into the case properly and that's about it. Keep the revs down and don't push your luck with the 50:1 or 100:1 gas/oil mixes.
  8. Fabian

    Fabian Well-Known Member

    Have to agree with you Cavi: i've never broken a standard head stud on my previous 6 engines and including this current 2-stroke engine.
    On the dyno at Rock Solid Engines, the "stock standard" 66cc 2-stroke engines produces between 1.25 and 1.5 crankshaft horsepower, on a good day!

    The only way breakage can occur at such low levels of power is through over torquing, for looking at the maths, each stud is bearing a (max) load of 280 watts. That's a laughably low figure, even for 6mm head studs.

    I find it amusing to hear of all the rubberised anti-vibration techniques for these engines for the only real way to make any significant difference is to either add mass to the engine or add mass to the bicycle frame or if being particularly inventive, installing a balance shaft which just so happens to add mass to the engine as part of the process.

    Was it not Newton who mentioned something about every action having an equal and opposite reaction ;-)
  9. Lunardog

    Lunardog Member

    Well you gentlemen may be correct. I know only this. I have been riding motorcycles since I was a youngster and had probably 8 or 10 different models of road bikes over the years, some twins (v and inline) and some were in line four cylinder. Every one would put your hands to sleep 45 minutes into a long ride even with nice thick foam grips, all except one. The Harley I currently ride is an 01 and has no particular specialty upgrades on the suspension and is nearly stock. The difference between this bike and all the others is a rubber engine mount system.I have no disillusions of a 3/16 inch piece of rubber turning this vibrator on wheels into a Cadillac. I look at it this way, if you have a properly tightened and secure mount on the engine which allows no lateral movement and you can accomplish this with a rubber insulator layer between frame and engine, it may not help, but it cant hurt.
  10. Fabian

    Fabian Well-Known Member

    Lots of lead weight in the handlebar ends makes for a good mass damper.
    The rubber engine mount system will spread time over amplitude but the total vibrational energy remains the same.. It is also important to note that the weight of the bike vs the weight of the vibratory component (in this case the engine) is significantly heavier than the engine itself.

    In a motorised bicycle application the motorised engine kit weighs nearly as much as the bicycle; working harmoniously with Newtons 2nd and 3rd laws of motion.
    mosquito13 likes this.
  11. HeadSmess

    HeadSmess Well-Known Member

    look at the harleys engine mounts closely and note exactly where the frame holds the engine. it will be in more than two places, and those points shall be fairly wide, to stop any side to side motions. as with all motorbikes. the engine can only do circular gyrations on the same plane as the up and down, forwards and backwards.

    somehow buells mount their engines so they only go up and down.

    my hands dont go to sleep. im too busy braking, accelerating, changing gears or just plain stretching my hands occasionally for them to do so... and i dont have any bar weights yet. oops.

    now, a ht has these tiny little mounts, both on the underside, below the engines CofG, and the entire systems rigidity depends on the tightness of them.

    in other words, all it wants to do is flop over. there arent three mounting points. just two. add rubber and they will never grip the frame adequately. by the time its been tightened enough to hold still, the rubber is past its elastic limit. it no longer behaves like rubber, its compressed solid.

    and then, stick a marble in a can. shake it. hear it rattle? feel it rattle? now crush the can. shake it. marbles held tight, and you dont feel it shaking around anymore. anything other than solid metal between the mounts and the frame makes the engine behave just like a marble in an (uncrushed) can.

    having welded my mounts on from the 2nd build, all i can say is...welded mounts are best. solid, and they wont budge. theyre also the smoothest ride ive had. there is absolutely no give. its up to the frame to take out the buzz.

    and after riding mine and comparing, most people want me to weld theirs on too. and make a pipe...and tune it...and etc etc etc....grrrr :jester:
  12. Fabian

    Fabian Well-Known Member

    Your description sounds fairly logical
  13. Big Red

    Big Red Active Member


    HeadSmess is EXACTLY right. I know it don't SOUND right, but rubber mounting increases vibration. The rubber gives it room to move, even if it's just a very, very little bit. I tried rubber mounts when I started building MB's and soon found out, Rubber makes it worse. Solid mount is the only way to go. I do have some rubber on my personal bike though, It's on the U-bolts on my front mount. Thats just to help not scratch and dent the frame. The engine to frame connection, where the engine flat mount touches the frame, has no rubber.
    I used this mount, but not the rubber spacer that came with it.
    Big Red.

    Attached Files:

  14. RFlash

    RFlash New Member

    Thank you so very much, excellent ideas.

    My first bike was a kmart bike, oversize alloy frame and "falcon" accessories, it slips my mind what brand the frame was, but it handled it extremely well. Over a couple of years I replaced most of the accompanying hardware with shimano. Frankly, I am surprised at how well a $70 bike ran.. the wheels copped a beating, I also replaced those and adjusted them weekly with a spoke adjuster.

    I now have an Apollo, steel frame and shimano running gear, all in good nick. Welding the engine mounts is an excellent idea, I am already looking at having them machined and may well have those welded directly to the frame in a manner that the engine can still be replaced.

    I live in a relatively rough area, if something isn't nailed down it'll be stolen. I am studying in greenborough at this point but will be studying in the city shortly as well, there's alarms on dealextreme for around $50, cheap security and will raise attention if the bike is "messed with", and it will protect the tools as well. I kinda got sick of hauling around a lot of stuff with me and items such as the 2 stroke mixer bottle cannot be placed in my bag without making a mess, so leaving it on an alarmed bike is preferable. (I am studying Computer systems and Engineering)

    Thanks for your help :grin5:
  15. Lunardog

    Lunardog Member

    Id like to make one suggestion before you make a final decision. Being that your familiar with these engines you may have already considered this. I thought just a single sprocket and an engine would suffice for the riding I wanted to do. Over time I came to realize that I needed a slightly wider powerband. I.E. A little more low end torque for the hills in my area and being able to still hit around 25mph without having the engine at very high rpm's. There was no simple solution other than one. A shift kit. After reading from the experts here and doing the installation it was an excellent solution. The only reason I ramble on about this is, if you weld your mounts on you will be removing any chance to install a shift kit in the future. (unless you take a grinder and remove the welded mounts). The mount bracket for the kit needs to allow the engine to slide up and down the seat post for chain adjustment therefore cant be mounted in a permanent position. Anyhow, just food for thought before you commit to your build. Good luck and have fun.